Department: Atmospheric Sciences ![[clear]](close-x.png "Remove this limiter")
25 matches in the database.
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1.
Amador, Nathan S.
Spatial and Temporal Characteristics of Supra-glacial Melt Lakes in west-central Greenland from Satellite Optical Remote Sensing.
Degree: MS, Atmospheric Sciences, 2009, Ohio State University
► Supra-glacial melt lakes form in the Greenland ice sheet ablation region in…
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▼ Supra-glacial melt lakes form in the Greenland ice sheet ablation region in response to surface melt. The Jakobshavn Ablation Region (JAR) in west – central Greenland (68.2 – 68.8°N) is an area with a high areal concentration of melt lakes, providing an ideal region to study melt lake development. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are acquired for the 2000 – 2008 melt seasons (days 150 – 274) to observe the spatial and temporal melt lake characteristics. Knowing that melt rates vary with elevation, JAR is divided into five elevation zones of 250 m intervals, between 585 – 1835 m above sea level. An empirically-derived depth function, based on MODIS optical reflectance, is applied to classified melt lake pixels at JAR, yielding depth, area and volume statistics. There is a strong correlation between melt lake area and volume quantities, regardless of elevation. Peak zonal fractional melt area, volume maxima and peak mean melt lake depth are reached at the mid-ablation zone (1035 – 1334 m). Melt intensity is determined from a Positive Degree Day (PDD) model. A correlation is found between melt lake area and volume anomalies and PDD anomalies that decrease with elevation. The melt season at the uppermost elevation (1585 – 1834 m) begins five weeks after the onset at the lowest elevation (585 – 834 m). The date of maximum area and volume also increase with time, with a difference of 50 - 60 days. Average melt season at JAR lasts 70 – 85 days below 1584 m and decreases to 30 days at the uppermost zone (1585 – 1834 m). To verify MODIS-derived lake area accuracy, three IKONOS 1 m resolution images are compared for a single lake, Lake Disco (67.23°N, 48.61°W). Uncertainty in MODIS estimates of area are 20±2%. Such differences confirm the difficulty of identifying depth values between 0 and ~2.5 m from the Box and Ski (2007) lake depth-retrieval classification. Shallow depths prevent the MODIS sensor’s coarse resolution from identifying lake perimeter in area estimation. Sixteen melt lakes are identified on an elevation-basis to describe melt lake behavior at JAR lakes individually. Melt lakes reappear in the same basin year after year and lakes that form more frequently are found at lower elevations, while lakes at higher elevations form less frequently. Overall, supra-glacial melt lakes in west-central Greenland show evidence of melt lake formation and evolution based on elevation and topography, as suggested by Lüthje et al. (2006) and McMillan et al. (2007). The highest rates of melt intensity occur at intermediate ablation zone elevations (835 – 1584 m), coinciding with larger area and volume quantities and a longer melt season duration. Anticipating continuing climate warming, it seems likely that the high ablation and lake formation in the mid-elevations (835 – 1584 m) will continue migrate towards the ice sheet interior.
Advisors/Committee Members: Box, Jason.
Subjects: Earth; Geography; Remote sensing
Keywords: Supra-glacial; Melt Lakes; Greenland; Cryosphere
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2.
Bathke, Deborah J.
Meteorological processes controlling the variability of net annual accumulation over the Greenland ice sheet.
Degree: PhD, Atmospheric Sciences, 2004, Ohio State University
► Climatic information available from the spatially extensive suite of firn and ice…
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▼ Climatic information available from the spatially extensive suite of firn and ice cores collected under the Program for Arctic and Regional Climate Assessment (PARCA), in conjunction with other data, provides an unparalleled opportunity to investigate accumulation changes over the Greenland ice sheet and to assess its ability to record and preserve a history of North Atlantic climate variability. The ice core derived accumulation histories demonstrate that the influence of glaciological noise on the climate signal is strongly influenced by the accumulation rate. Thus, it may be difficult to discern regionally representative climate signals from individual cores at lower accumulation sites on short time scales suggesting that either time or spatial averaging of the records is necessary. Individual rotated principal components analysis (RPCA) on the time series of net annual accumulation, the total concentration of insoluble dust particles, and the δ18O annual average and seasonal extrema reveal that cores located in different regions of the ice sheet do not vary consistently for the period of record in this study (1965-1996). Specifically, cores from southern Greenland vary in a manner different from those in the central west region. Thus, proxy climate histories drawn from a single core record are not necessarily representative of the entire ice sheet. Comparison of the scores associated with the central west and southern Greenland spatial patterns with atmospheric and oceanic data suggest that different processes may be responsible for delivery of precipitation to each region. Correlations of the North Atlantic Oscillation with the core data, combined with composites of mean sea level pressure and 500 hPA heights for accumulation extremes, suggest a negative relationship with the central west region during winter, spring, and summer. Conversely, the same analyses for the southern region suggest a positive relationship to the NAO during summer. Accumulation in the central west region is likely influenced by the NAO during winter and spring, as well as by associated changes in surface temperatures over Canada and sea surface temperatures in the Baffin Bay/Davis Strait. Alternatively, accumulation in southern Greenland is consistently associated with changes in the Pacific.
Advisors/Committee Members: Mosley-Thompson, Ellen S.
Subjects: Physics, Atmospheric Science
Keywords: Greenland; ice cores; NAO; proxy records
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3.
Davis, Michael A.
Cloud-Radiative Feedback and Ocean-Atmosphere Feedback In the Southeast Pacific Ocean Simulated by IPCC AR4 GCMs.
Degree: PhD, Atmospheric Sciences, 2011, Ohio State University
► Representation of clouds in global climate models (GCMs) offers a key source…
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▼ Representation of clouds in global climate models (GCMs) offers a key source of uncertainty in current climate projections. More specifically, low level cloud cover, such as marine stratocumulus (MSc), is often resolved with bias in these GCMs. MSc cloud layers are the vast “climate refrigerators” of the Tropics and subtropics, which they cool by reflecting sunlight back to space that could otherwise warm the ocean surface. This albedo effect is quite powerful as a theorized 4% increase in low level clouds could offset the warming of doubling CO2 in GCM projections. The formation of MSc favors the eastern subtropical oceans, and involves the interactions among many processes such as radiation, boundary layer turbulence, subtropical high, ocean upwelling, and cold currents, making it a highly coupled system that is difficult to model. No previous study has provided a comprehensive evaluation of MSc and the associated atmosphere and oceanic feedbacks in the GCMs, especially the model ensemble participating in the most recent Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) released in 2007, which often serves as the basis for climate change projection and policy. This study aims to provide the first systematic evaluation of the Peruvian MSc clouds located in the southeast Pacific (SEP) and the associated feedbacks in the 24 AR4 GCMs. Comparisons with long-term observational datasets are produced to assess the representation of mean state and climate feedbacks in the models. Three feedbacks are specifically discussed: the cloud-radiative feedback, the SST-upwelling feedback, and the SST-latent heat feedback. Horizontal plots are produced to assess spatial representation of atmospheric variables while cross spectrum analyses yield statistical and quantitative information on the robustness of the air-sea interactions and cloud-radiative feedback of the SEP region. Extension of the cloud-radiation feedback analysis into the whole Tropics is provided with additional cross-spectrum analyses. Most GCMs generate a persistent warm sea surface temperature (SST) bias of approximately 2 K capable of destabilizing the marine boundary layer. Since MSc evolve in regions associated with high lower-troposphere stability this destabilization process leads to the deterioration of the cloud deck. Almost all models simulate quite well the subtropical high and the weakening of trade winds associated with warm SST anomaly, which plays a key role in SST-upwelling feedback in SEP. Most models have significant difficulty in simulating the amount, location and land-sea contrast of stratocumulus clouds, which may stem from a deeper problem that they cannot reproduce the observed inverse relationship between stratocumulus clouds and SST. Six of the 24 GCMs cannot produce the albedo effect of stratocumulus clouds. Most models produce overly weak or even wrong sign of the SST-LHF feedback in SEP. A preliminary analysis of cloud-radiation feedback for the whole tropics reveals that almost all GCMs fail to capture the observed increase of cloud amount associated with tropical warming.
Advisors/Committee Members: Lin, Jialin.
Subjects: Atmospheric Sciences
Keywords: cloud, climate change, feedback, climate modeling, air-sea interactions
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4.
Decker, David T.
Remote Sensing of the Climate and Cryosphere of Nares Strait, Northwest Greenland.
Degree: MS, Atmospheric Sciences, 2010, Ohio State University
► A polynya is an area of open water or less thick ice…
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▼ A polynya is an area of open water or less thick ice compared to its surroundings that forms in polar regions during weather conditions that would normally produce thicker sea ice, and releases the most sensible and latent heat flux to the atmosphere. This thesis incorporates satellite imagery from optical, thermal, and microwave sensors to investigate the climate and cryosphere of the North Water polynya, the largest, reoccurring polynya in the Arctic. Ecologically, it is known to be of significance to marine animals, e.g. narwhals and beluga whales. The polynya normally results from the formation of an ice arch at the southern limit of Nares Strait that prevents multi-year Arctic sea ice drift through the strait. The ice arch usually collapses by early to mid-summer, thus ending the polynya. In a dramatic display of climate-cryosphere dynamics, the winter 2008-2009 sea ice arch consolidated, 500 km north of its normal position. Summer 2009, sea surface temperatures were 1.5 °C above normal in central Nares Strait. In June 2009, 25 km resolution passive microwave sea ice concentrations were 33% below normal. 12.5 km resolution passive microwave sea ice concentrations were 20% below the 2002-2009 average north of Smith Sound in southern Nares Strait, and 60% below normal in northern Baffin Bay. Optical satellite imagery are used to measure area and length changes of the Petermann and Humboldt glaciers that empty into Nares St., where area losses of 215.4 km2 and 175.2 km2, respectively, are observed since end of summer 2000; an area 4.5 times that of Manhattan Island, New York, USA (87.5 km2), ranking them among the top-area losses among Arctic glaciers. Polar MM5 simulations have been made for each season to calculate the net snow accumulation, melt water runoff, and surface mass balance for 2000-2009. Snow line detection data has been developed to approximate the equilibrium line altitude. Results at Humboldt glacier indicate a change in the snow line associated with decrease accumulation area and increase in melt water runoff. The fresh water from the glaciers mixes with the salinity of the ocean water in Nares Strait. Sea ice concentration, sea surface temperature, increase in melt season, increase in surface air temperatures, decrease of area in the north region of Humboldt glacier, and increase in snow line suggests that the summer of 2009 showed climate change signals different from other years in the 1979-2009 period.
Advisors/Committee Members: Box, Jason.
Subjects: Atmosphere; Oceanography; Remote sensing
Keywords: Climate; Cryosphere; Remote Sensing
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5.
Fairman, Jonathan George Jr.
Investigating Paleoclimatic Conditions in the Tropical Andes Using A 2-D Model of Glacial Mass Energy Balance and Ice Flow.
Degree: MS, Atmospheric Sciences, 2006, Ohio State University
► Glaciers in the tropical highlands are important and highly sensitive indicators of…
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▼ Glaciers in the tropical highlands are important and highly sensitive indicators of global climate change over different time scales. We apply a physically based, 2-D, glacier model to reconstruct steady-state glacier forms and mass distributions for a range of tropical climatic conditions in the Cordillera Blanca, Peru (8-10°S) and the Cordillera Real, Bolivia (16° S). The model is based on gridded digital elevation data, computes the effects of topography on the largest component of surface energy balance, shortwave solar insolation, calculates 2-D, in the horizontal-plane, distribution of snow accumulation using a surface mass and energy balance approach, and reconstructs resultant glacier shape with a 2-D flow model. We are able to reconstruct modern glacier extent to match satellite imagery using climate data from the separate regions including current observations at glacier elevations, and compute a modem equilibrium line at ~5000 m. We then apply the model in an inverse approach to infer sets of paleoclimate conditions for late Pleistocene moraine positions mapped in specific valleys with global positioning system positions and dated by radiocarbon dates on lake and peat sediments for locations in the Queshque Valley in the Cordillera Blanca and the Zongo-Milluni Valleys in the Cordillera Real. Our results show a range of climate situations possible for the existence of the delineated glaciers in the Queshque and Zongo-Milluni Valleys. For the Zongo Valley, we also find that 6.5 times more precipitation is needed to grow to the same dated moraine as the adjoining Milluni Valley with a -4.25 °C temperature change.
Advisors/Committee Members: Mark, Bryan G.
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6.
Fogt, Ryan Lee.
Investigation of the Southern Annular Mode and the El Nino - Southern Oscillation Interactions.
Degree: PhD, Atmospheric Sciences, 2007, Ohio State University
► The dominant mode of climate variability across the Southern Hemisphere is the…
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▼ The dominant mode of climate variability across the Southern Hemisphere is the Southern Hemisphere Annular Mode (SAM); however other modes associated with El Nino- Southern Oscillation (ENSO) variability also play a significant role. Notably, recent studies demonstrate significant correlation between ENSO and the SAM, primarily during austral summer in the 1980s and 1990s, and austral spring in the 1990s. The analysis presented here expands upon these studies to examine historical evidence of their coupling and the mechanisms that generate the shared variability. Using the methodology similar to previous studies, reconstructed indices of the SAM are calculated for each season and for the annual mean spanning nearly 150 years. Using these new SAM reconstructions, it was determined that the relationship between SAM and ENSO is quite variable in the historical record, and that periods similar to the 1990s when the two were strongly correlated in austral summer have occurred in the past. Using wavelet and spectral analyses, it was shown that the positive correlation between the SAM and ENSO is generated by interactions with 3-7 year periods. Stationary and transient eddies of heat and momentum are examined and reveal that during periods when the two climate modes are positively correlated, a band of E-P flux convergence during El Nino events (divergence during La Nina), associated with changes in the storm track and southern branch of the ENSO horseshoe pattern, extend from Indonesia to the high latitude south Pacific where the maximum teleconnection occurs. When the modes are positively correlated, the changes to the aforementioned storm track exist in a continuous fashion from the Rossby source region to the South Pacific where they interact with similar storm track anomalies forced by the SAM. The interaction of the storm tracks allows the tropical signal to penetrate deeper into the high southern latitudes and maintain a stronger anomaly, compared to periods when the two modes are anticorrelated and opposing storm track anomalies block the propagation of the tropical signal into the high latitudes.
Advisors/Committee Members: Bromwich, David H.
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7.
Fraza, Erik.
The Global 3-Dimensional Structure of the Pacific Decadal Oscillation.
Degree: MS, Atmospheric Sciences, 2010, Ohio State University
► The Pacific Decadal Oscillation (PDO) is a dominant mode of decadal variability…
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▼ The Pacific Decadal Oscillation (PDO) is a dominant mode of decadal variability in the global climate system. Decadal variability is important in terms of global warming projections as it can mix with human-induced climate change signals. Therefore, getting a better description and understanding of decadal variability can help to separate human-induced signals from natural variability. Most of the previous studies of PDO focused on its two-dimensional structure at the surface. This study examines the global three-dimensional structure of the PDO using 62 years (1948-2009) of the NCEP/NCAR reanalysis data. The warm phase of the PDO is characterized by tropospheric warming around the world, especially between 30°N and 90°S. There is high pressure anomaly throughout the troposphere in the tropics and midlatitudes, but low pressure anomaly in the two polar regions, leading to enhanced polar jet streams in both hemispheres. The Hadley circulation, Ferrel circulation and polar circulation are all intensified. The Walker circulation, on the other hand, is weakened. The wintertime polar vortex is intensified from the surface all the way up to 10mb in the northern hemisphere, but only up to 100mb in the southern hemisphere. Most of the previous studies of PDO focused on its extreme phases (i.e. the warm phase and cold phase), but not the transition phases in between. This study further examines the transition phases of the PDO using the 62 year dataset. The cold to warm transition phase of the PDO is characterized by a cold SST anomaly in the North Atlantic subtropics, which is associated with a significantly high SLP anomaly and weakened precipitation.
Advisors/Committee Members: Lin, Jialin.
Subjects: Atmosphere
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8.
Frederick, Meredith A.
Predicting the Predominant Winter Flight Category in Central Ohio Using ENSO Indices.
Degree: MS, Atmospheric Sciences, 2012, Ohio State University
► The links between El Niño/Southern Oscillation (ENSO) and precipitation, temperature, and extratropical…
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▼ The links between El Niño/Southern Oscillation (ENSO) and precipitation, temperature, and extratropical cyclone activity in the Ohio River Valley have been well-studied and documented. However, links with ENSO and flight category have hardly been examined. A flight category is a specific set of conditions defined by ceiling heights and visibility that governs aviation operations. There are three flight categories that are commonly used: Visual Flight Rules (VFR); Marginal Visual Flight Rules (MVFR); and Instrument Flight Rules (IFR). This study aims to see if those teleconnections between ENSO and various atmospheric effects extend northward into Central Ohio with enough strength to be able to be used to predict the predominant winter flight category for the region. This was accomplished by gathering 30 years of METAR data for the months of January, February, and March from three sites: The Ohio State University Airport (KOSU), Port Columbus International Airport (KCMH), and Tampa International Airport (KTPA) and comparing that data with various ENSO indices. The 30 years of METAR data were averaged for each year and month and compared with six commonly-used ENSO indices: Niño-1+2; Niño-3; Niño-3.4; Niño-4; MEI; and SOI. A regression analysis was used to gather p-values and slopes for each combination of site, month, flight category, and index. Few combinations resulted in overwhelmingly consistent results for the Central Ohio region, but a few possible relationships existed for MVFR and VFR conditions, especially when using the Niño-3 index. Data from KTPA correlated much more strongly with the various ENSO indices and month combinations, almost exclusively when looking at MVFR conditions. Niño-3 responded most closely with KTPA. The SOI also responded with KTPA, but only when looking at the three-month average dataset, not during individual months.
Advisors/Committee Members: Hobgood, Jay.
Subjects: Meteorology; Transportation; Transportation Planning
Keywords: Atmospheric Science; VFR; MVFR; IFR; Aviation; Flight Category; ENSO; Southern Oscillation; Ohio; Central Ohio; El Niño; Climatology; Forecasting; Flying
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9.
Hennon, Christopher C.
Investigating Probabilistic Forecasting of Tropical Cyclogenesis Over the North Atlantic Using Linear and Non-Linear Classifiers.
Degree: PhD, Atmospheric Sciences, 2003, Ohio State University
► Current numerical weather prediction models experience great difficulty in forecasting tropical cyclogenesis,…
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▼ Current numerical weather prediction models experience great difficulty in forecasting tropical cyclogenesis, primarily because of limitations of cloud parameterizations and observations. Forecasters have also struggled with the problem since they rely on the numerical models as an objective source of information. This research was performed with the aim of filling the void of objective guidance for tropical cyclogenesis. A new dataset of cloud clusters is created through the examination of infrared (IR) satellite imagery over the tropical Atlantic during the 1998-2001 hurricane seasons. Eight large-scale predictors of tropical cyclogenesis were then calculated from NCEP-NCAR Reanalysis dataset for each 6-hour interval of the cloud cluster life cycle extending back to 48 hours prior to genesis. Independent classifications were then performed on the entire dataset using both discriminant analysis (DA) and an artificial neural network (NN). The classifiers are fundamentally different from each other in that DA performs classifications based solely on linear trends in the predictors; the NN is potentially a more powerful classifier as it can find non-linear relationships in the data. The performance of each classifier was investigated through statistical scores and a series of case studies from the 1998-2001 Atlantic hurricane seasons. Tropical cyclogenesis is a rare event. Climatologically only about 15% of all cloud clusters develop into tropical depressions over the Atlantic Basin. The new cloud cluster database reflects that. 432 cloud clusters, of which 62 developed into tropical depressions, were tracked during the four seasons. Independent DA classifications show forecast skill over climatology. For the “prime” development season of August – October, the DA correctly forecast a higher percentage of clusters than climatology for all forecast periods. The most important predictors are latitude and the vertical shear structure. A comparison of DA forecasts with NN forecasts on the same dataset produced mixed results. The NN generally performed better with non-developing cloud clusters; however, there are indications that the NN suffers from over fitting to a greater degree than DA. An investigation of six case studies shows that both classifiers performed well in the majority of the cases. The DA appears to generalize much better than the NN in most cases. Danielle (1998) and a non-developing cluster (ND-6, 2000) brought to light several possible deficiencies in the statistical model. The large-scale predictors over-forecast genesis in a favorable shear environment, even if the thermodynamic environment is marginal. Also, the lack of any information on the convective structure of the cloud cluster will decrease forecast accuracy in some cases. Danielle (2000) developed explosively despite an unfavorable large-scale shear environment, perhaps due to mesoscale interactions that are not resolved in this model. Results suggest that this model has sufficient potential to be implemented as an objective forecast tool. Each predictor can easily be calculated from an analysis field that is routinely available to forecasters. The inclusion of mesoscale predictors, especially satellite derived temperature, moisture, and wind data, is thought to be an important next step for improvement of forecasts; especially since the current literature suggests that the important physical interactions for tropical cyclogenesis occur at the smaller scales.
Advisors/Committee Members: Hobgood, Jay S.
Keywords: tropical cyclogenesis; neural network; discriminant analysis; cloud cluster; statistical prediction; Atlantic Basin; cyclogenesis; tropical cyclone formation
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10.
Hennon, Paula Ann.
The role of the ocean in convective burst initiation: implications for tropical cyclone intensification.
Degree: PhD, Atmospheric Sciences, 2006, Ohio State University
► The upper ocean significantly influences tropical cyclone structure and intensity. These effects,…
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▼ The upper ocean significantly influences tropical cyclone structure and intensity. These effects, however, are not well understood mostly due to a lack of oceanic and atmospheric boundary layer observations within the inner-core region. This study relates ocean-atmosphere energy exchange processes to mid-to-upper tropospheric latent heating using mesoscale inner-core convective burst events. A global survey of convective burst events in tropical cyclones from the year 1999 – 2001 was constructed. This study shows that 80% of tropical cyclones have at least one convective burst event and that convective burst events usually occur during the intensification phase of the storm life cycle. Latent and sensible heat flux estimates and a measure of upper-ocean energy utilization were calculated for the inner-core (<.5° radius) and the near-core (.5° - 1° radius). This study found that tropical cyclones generally utilize only about 8% of the total enthalpy flux available from the ocean/atmosphere boundary layer. Storms with convective bursts utilize more energy from the ocean (11%) than storms with no convective burst (2%). Sea-air fluxes are greatly enhanced (doubled) during convective burst time periods. These along-track ocean-atmosphere analyses was compared to vertical profiles of atmospheric latent heating calculated using a combined active and passive TRMM PR and TMI retrieval algorithm. Results show strong positive space and time correlations between ocean-air fluxes and mid-upper tropospheric latent heating. Additionally, the 30 storms analyzed were categorized by the presence or absence of convective burst events during the storm lifecycle. Composite atmospheric latent heating profiles constructed for each group show a two-fold release in energy for the storms with convective burst events compared to storms with no convective burst event. Finally, seven case studies are presented which attempt to resolve the upscale energy cascade of the tropical cyclone with a convective burst event from the ocean through the troposphere. For these case studies, the TRMM vertical profiles of latent heating are compared with AMSU temperature anomalies in an attempt to link the enhanced tropospheric latent heat release with a developing inner-eye warm core anomaly.
Advisors/Committee Members: Hobgood, Jay S.
Keywords: hurricane; tropical cyclone intensification; theta-e; sea-air interaction; air-sea interaction; remotely-sensed flux; tropical cyclone boundary layer; ocean planetary boundary layer; hurricane heat content; TRMM latent heat; tropical cyclone latent heat r
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11.
Hung, Meng-Pai.
THE EVALUATION OF THE EAST GREENLAND SEA ODDEN ICE FEATURE USING THE COMMUNITY CLIMATE SYSTEM MODEL3.0 (CCSM3.0).
Degree: PhD, Atmospheric Sciences, 2009, Ohio State University
► The Odden event is a dominant mode of the Arctic sea ice…
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▼ The Odden event is a dominant mode of the Arctic sea ice variability, which is very important for the Arctic climate. The Odden sea ice feature extends northeastward from the Arctic pack ice of the east Greenland Sea during winter and spring, typically covering an area between 8°W and 5°E, and between 73° and 77°N. The key causes and forcing of Odden sea ice variability in the atmosphere and ocean is examined using the Community Sea Ice Model5.0 (CSIM5) within a Slab Ocean Model (SOM) called the M configuration of Community Climate System Model3.0 (CCSM3) provided by the National Center for Atmospheric Research (NCAR). A 26 year control run is made with the T62 NCEP/NCAR Reanalysis (NNR) atmospheric data from 1979 – 2004, and the simulated northern Atlantic sea ice is compared with that from the Hadley Center Sea ice and Sea Surface Temperature (HadISST) observational dataset in order to evaluate the model’s capabilities. The control run sea ice data were subjected to a rotated principal component analysis (RPCA) that revealed a component (#3) mode of variability that exhibited Odden-like variability similar to that obtained in observational data. To further investigate the single or multiple effects from the atmospheric and oceanic parameters associating with the Odden sea ice, 18 experiments are conducted with the NNR and a 1° x 1° Simple Ocean Data Assimilation (SODA) for the atmospheric and oceanic forcing, respectively. In one set of experiments the atmosphere and ocean model are run simultaneously in efforts to simulate the Odden while other experiments evaluate Odden forcing of individual atmospheric parameters with other parameter forcing being held in a non-Odden state. Model forcing data for Odden ice conditions are from 1997 (January – December) while those from 1994 are used as the forcing for non-Odden conditions, in keeping with observational studies. Results show that the model sea ice concentration (SIC) and ice thickness exhibit large variability in an area on the eastern end of the Odden region found in observational data. It does so particularly in response to air temperature and surface wind and ocean current forcing when the model output is averaged from February through April and May through July. The annual cycle of model parameter output shows that SIC peaks from March through May in experiments with full atmospheric forcing in the Odden and non-Odden years and where the ocean is held to climatological forcing. Parameters such as air temperature, overlying winds, longwave radiation, specific humidity and surface ocean currents make some of the larger contributions to SIC and ice thickness variations through the model year. At the time of peak model SIC and thickness (e.g., April, May) the wind forcing and that of surface currents appear to be larger than the SIC/thickness contribution by air temperature. In other words, the Odden mode in the model is mainly produced by dynamical effects of atmospheric winds and ocean currents.
Advisors/Committee Members: Rogers, Jeffery C.
Subjects: Earth; Environmental science; Geography
Keywords: Odden; Arctic; Greenland Sea; Nordic Seas; sea ice; sea ice variability; climate; model; NCAR; CCSM; PCA; RPCA; air temperature; wind driven effect; sea surface current
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12.
Jankot, Joshua Charles.
Synoptic Analysis of Large Snowstorms Affecting Boston, Massachusetts.
Degree: MS, Atmospheric Sciences, 2009, Ohio State University
► The synoptic conditions associated with the occurrence of snow storms in Southern…
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▼ The synoptic conditions associated with the occurrence of snow storms in Southern New England are examined. “Blockbuster” snowstorms, defined as those with 19.5-27.5 inches of snowfall accumulation at Boston are compared to “Major” snowstorms having 8.0-13.2 inches of snow accumulation. Gridded NCEP/NCAR Reanalyses model data are used to determine the snowstorm synoptic conditions at lower and upper levels of the troposphere at times before and during peak snow. Surface features analyzed include relative position of the surface cyclone, cyclone track and intensification, coastal frontogenesis, position of the anticyclone and cold air damming. The 850 hPa level depicts placement and intensity of the baroclinic zone and moisture content via specific humidity. The upper troposphere, via 850, 700, 500, and 250 hPa charts, depicts how the upper level trough, positive vorticity, vertical motions, and jet streaks evolve over time and to what role they enhance surface cyclogenesis. Seven cases of each storm type are found and composite averages of the weather data fields are created, sorted by time at 6 hourly intervals from 24 hours prior to, and 48 hours after, the onset of snow. The 7 Blockbuster storms developed more rapidly than Major storms due to more readily available upper level support. The upper-level trough was more amplified and located closer to the east coast prior to snow onset in these cases. Blockbuster events also had larger amounts of 500 hPa vorticity advection and 700 hPa vertical motion maxima over the exit region of the 250 hPa jet streak, further intensifying the divergence aloft and cyclone development. 850 hPa cold air advection was stronger initially over New England prior to snow onset in Blockbuster cases. Warm air advection also developed up the eastern seaboard more rapidly in Blockbuster cases providing an intense baroclinic zone for the surface cyclone to intensify and track northeast along. The greater initial temperature contrast along the coast also provides an explanation to why the surface cyclone developed sooner. Blockbuster storms became vertically stacked with the upper-level low up to the 500 hPa level at 18 hours after snow onset (T + 18). Major cases did not become vertically stacked to 500 hPa until T+30 hours. The vertically stacking of the cyclone southeast of New England in Blockbuster cases causes stalling and slowed eastward progression of the surface low, prolonging snow duration. The later development of a negatively tilted diffluent trough T+12 to T+30 hours in Major cases produces a steady northeastward track for these storms. The later development of upper-level divergence/difluence and slower developing 850 hPa baroclinic zone in Major cases resulted in their later development, having a more northward track hugging the coast. This causes some Major cases to include a changeover to rain and shorter snowfall duration.
Advisors/Committee Members: Rogers, Jeffrey.
Subjects: Earth
Keywords: blizzards, nor'easter, synoptic meteorology, cyclogenesis
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13.
Law, Kevin T.
A statistical model to forecast short-term Atlantic hurricane intensity.
Degree: PhD, Atmospheric Sciences, 2006, Ohio State University
► The accuracy of hurricane intensity forecasts has lagged the accuracy of hurricane…
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▼ The accuracy of hurricane intensity forecasts has lagged the accuracy of hurricane track forecasts thereby creating a need for improvement. Many models struggle capturing the rapid intensification period and identifying when it will occur which causes a large amount of error in the intensity forecasts. The method described in this paper uses a discriminant function analysis (DFA) to help identify how intense the tropical cyclone will become and also how close it is to the rapid intensification period. Identifying the proximity to the rapid intensification period is a key factor in improving the intensity forecasts. Based upon the intensity and its proximity to its rapid intensification period, as selected by the DFA, an appropriate regression model is applied to forecast the 24-hour and 6-hour pressure reduction and wind speed increase. Other statistical intensity models apply the same regression model throughout the entire lifecycle of the tropical cyclone. This model relies on the premise that factors which cause intensification affect the tropical cyclone differently throughout its life cycle. Therefore, by using the DFA, different stages in its life cycle are identified, which allows the regression model to use the most significant variables at the particular stage. They are shown to improve the intensity forecasts at the stages leading up to and during the rapid intensification, which happen to be the most difficult stages to predict. The forecasts were validated with 13 independent case studies and compared with the official National Hurricane Center (NHC) forecasts.
Advisors/Committee Members: Hobgood, Jay S.
Subjects: Physics, Atmospheric Science
Keywords: statistical model; atlantic hurricane intensity
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14.
Mauk, Rachel Grant.
Tropical Cyclone Formation in Environments with Cool SST and High Wind Shear over the Northeastern Atlantic Ocean (1975-2005).
Degree: MS, Atmospheric Sciences, 2010, Ohio State University
► This work analyzes the environment conditions in which tropical cyclones have formed…
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▼ This work analyzes the environment conditions in which tropical cyclones have formed during the months of October, November, and December in the northeastern Atlantic Ocean. The study period begins in 1975, the year of publication for the Hebert-Poteat and Dvorak techniques for satellite classification of tropical and subtropical systems, respectively. The northeastern Atlantic Ocean is defined as the portion of the Atlantic basin north of 20°N and east of 60°W. Purely subtropical storms were excluded from the study to focus on the conditions for tropical cyclone formation. Genesis was defined as the time in the official HURDAT record when the cyclone 1) had been classified as tropical, and 2) had maximum sustained winds of at least tropical storm force (greater than or equal to 34 kt). NCEP/NCAR Reanalysis data were used for atmospheric variables, and Reynolds SST and NOAA ERSST data were used for sea surface temperatures. Dynamic and thermodynamic parameters were analyzed to determine the environmental conditions during the period prior to genesis. Wind shear (magnitude and spatial orientation), vertical temperature profiles and stability indices were computed on 6-h intervals for the thirty hours prior to genesis. Synoptic geopotential height patterns were analyzed on 12-h intervals for the thirty-six hours prior to genesis. Seventeen of the twenty tropical cyclones in the study set had identifiable non-tropical precursors. These seventeen were subdivided into non-frontal baroclinic (NFB), frontal-weak (FW), and frontal-strong (FS) types based on the relative strength of the low- and mid-level vorticity maxima thirty hours prior to genesis. The three tropical cyclones with identifiable tropical precursors were observed to have the weakest 500 hPa vorticity maxima, consistent with the tropical wave structure. Sixteen of the seventeen storms from non-tropical precursors developed over sea surface temperatures less than 26.5°C. Local environmental wind shear varied widely among the twenty storms. Large ranges in magnitude and disparate spatial patterns were observed even among types. Wind shear was therefore determined to have secondary importance in the genesis environment. Geopotential height fields also had few discernable patterns within types. Thermodynamic variables showed distinct differences between NFT storms and the non-tropical types. Vertical temperature profiles for NFT systems were consistently warmer at all levels than the non-tropical systems. Thus storms originating from tropical precursors occurred in environments with larger convective available potential energy and higher equilibrium levels relative to those for non-tropical precursors. Static stabilities were lower for the NFT type relative to the baroclinic types when using 300 hPa as the upper level. This combination of cool sea surface temperature, moderate instability, and low equilibrium levels in the pre-genesis environments suggests that tropical cyclones from baroclinic precursors in this region are shallower than typical tropical cyclones, which would reduce the effects of high environmental shear.
Advisors/Committee Members: Hobgood, Jay.
Subjects: Atmosphere; Earth
Keywords: hurricane, tropical, cyclone, meteorology, atmospheric sciences, hybrid, subtropical, cyclogenesis
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15.
Melaragno, Scott Andrew.
The Global Three-Dimensional Structure for the Developmental Phase of ENSO.
Degree: MS, Atmospheric Sciences, 2010, Ohio State University
► An examination of NCEP reanalysis anomaly data for neutral El Niño-Southern Oscillation…
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▼ An examination of NCEP reanalysis anomaly data for neutral El Niño-Southern Oscillation (ENSO) phases is conducted in order to portray a three-dimensional view of the global teleconnections associated with this phenomenon. The neutral phase, which occurs when Niño 3.4 sea surface temperatures (SSTs) lack either warm or cold anomalies, precedes both warm and cold ENSO events. Few studies have examined the significance of these phases, usually grouping both warm-to-cold and cold-to-warm phases into one mean state, when in reality these transitional periods are far from neutral. Because of a lack of neutrality seen within NCEP reanalysis data from 1950-2007, the title of “developmental phase” will be given for apparent neutral events leading up to an extreme phase. During a developmental phase one year before a mature El Niño (December-January-February [-1]), warm SST anomalies bisecting the equator/date line and along 30°S within the eastern Pacific are seen. Increased SSTs also appear in the northern Pacific Ocean, southern Atlantic Ocean, Baffin Bay off the west coast of Greenland, Gulf of Mexico and the eastern Mediterranean Sea. Cold SST anomalies are seen predominantly throughout the Tropical Pacific. Enhanced precipitation and upward motion above warm SST anomalies occurs over the western Pacific, surrounding Indonesia and Papua New Guinea. Analysis of the zonal mean circulation provides a vertical representation of how the neutral phase affects the three latitudinal circulation cells, along with the horizontal Walker circulation. Symmetric cooling of the tropical troposphere and Northern Hemisphere (NH) midlatitudes can be seen during this phase, with a mid-level warm core above the equator. More vertical warming around the polar regions, especially in the Southern Hemisphere (SH) can be seen during the boreal winter one year before an El Niño. Combining these vertical and horizontal cross-sections shows a weakening and displacement of Hadley cells 20°N and S, with a strong westerly tropical jet positioned directly along the warm core in the mid-to-upper troposphere. Critical in the development and decay of ENSO events, the Walker Circulation appears to be deteriorating, a foretelling sign of an impending El Niño. Even in the polar regions, critical weakening of the polar vortex correlates with neutral conditions. The teleconnections seen during the neutral phases of ENSO provide new findings that help explain the complex dynamics associated with a coupled ocean-atmospheric system. The timescale of a developmental phase aids in predicting warm and cold events that are potentially one year away from fruition. With the completion of a three dimensional schematic and the corresponding teleconnections associated with a developmental episode, this study provides new methodology in forecasting extreme events throughout the entire ENSO cycle.
Advisors/Committee Members: Lin, Dr. Jialin.
Subjects: Atmosphere; Oceanography
Keywords: El Niño-Southern Oscillation; Teleconnections, Neutral Phase; Developmental Phase
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16.
Monaghan, Andrew J.
Recent variability and trends in antarctic snowfall accumulation and near-surface air temperature.
Degree: PhD, Atmospheric Sciences, 2007, Ohio State University
► A variety of methods are used to better understand how Antarctic snowfall…
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▼ A variety of methods are used to better understand how Antarctic snowfall and near-surface air temperature have been changing in the later decades of the 20th century. Polar MM5, a mesoscale atmospheric model optimized for use over polar ice sheets, is employed to simulate Antarctic snowfall for the past two decades. Averaged over the continent, the annual snowfall trends from Polar MM5 are not statistically different from zero, suggesting that recent Antarctic snowfall changes do not mitigate currently observed sea level rise. However, Antarctic snowfall does have strong seasonal and regional variability. Atmospheric model precipitation fields are blended with ice core accumulation records to reconstruct Antarctic snowfall with spatial and temporal continuity over 1955-2004. The resulting dataset is consistent with the results from the shorter, 1985-2001 Polar MM5 assessment, indicating that there has been no significant net change in Antarctic snowfall since the 1950s, and thus Antarctic snowfall is not mitigating observed global sea level rise as expected, despite recent warming of the overlying atmosphere. A new Antarctic near-surface air temperature dataset spanning 1960-2005 is constructed and compared with other observationally-based Antarctic near-surface air temperature datasets for the past ~45 years. The datasets indicate that no statistically significant near-surface air temperature trends have occurred annually or seasonally over Antarctica since 1960. The new snowfall and near-surface temperature records are used to assess five 20th century GCM ensembles run in support of the Intergovernmental Panel on Climate Change Fourth Assessment Report. It is found that the GCMs overestimate annual Antarctic near-surface temperature trends on average by a factor of 3 during the 20th century, and by more than 5 times during the latter half of the 20th century. The GCMs are able to accurately simulate the observed sensitivity of Antarctic snowfall to near-surface temperature of about +5-6 %/K, suggesting that if Antarctic near-surface temperature increases by about 2-3.5 K by the end of the 21st century as the GCMs predict, snowfall will increase by about 10-20%, having a negative impact on sea level of about -0.5 to -1.0 mm/y by 2100.
Advisors/Committee Members: Bromwich, David H.
Subjects: Physics, Atmospheric Science
Keywords: Antarctic snowfall; Antarctic precipitation; Antarctic temperature
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17.
Steinhoff, Daniel Frederick.
Cyclogenesis Near the Adélie Coast and Influence of the Low-level Wind Regime.
Degree: MS, Atmospheric Sciences, 2008, Ohio State University
► Cyclone activity in the Adélie Coast region is analyzed using three years…
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▼ Cyclone activity in the Adélie Coast region is analyzed using three years (2003-2005) of data from the Antarctic Mesoscale Prediction System (AMPS). "Type I" cyclone development occurs off-shore between 145°E-150°E on the leading edge of a dissipating cyclone to the west near 120°E, primarily as a result of barrier wind formation and favorable upper level support. "Type II" cyclone development occurs adjacent to the coast near 155°E. Type II development exhibits a barotropic structure, and leeside cyclogenesis is common, with near-surface cyclonic vorticity produced by interaction of katabatic winds with the ambient environment. In both categories of development, the low-level wind regime, especially the Adélie Land katabatic wind regime, is found to be a key component of cyclogenesis in the Adélie Coast region, contrary to inferences made in several earlier studies that effects are confined to mesoscale cyclone development.
Advisors/Committee Members: Bromwich, David.
Subjects: Atmosphere
Keywords: Antarctica, cyclones, mesoscale, katabatic winds, barrier winds
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18.
Steinhoff, Daniel Frederick.
Dynamics and Variability of Foehn Winds in the McMurdo Dry Valleys Antarctica.
Degree: PhD, Atmospheric Sciences, 2011, Ohio State University
► The McMurdo Dry Valleys (“MDVs”) are the largest ice-free region in Antarctica,…
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▼ The McMurdo Dry Valleys (“MDVs”) are the largest ice-free region in Antarctica, featuring perennially ice-covered lakes that are fed by ephemeral melt streams in the summer. The MDVs have been an NSF-funded Long-Term Ecological Research (LTER) site since 1993, and LTER research has shown that the hydrology and biology of the MDVs are extremely sensitive to small climatic fluctuations, especially during summer when temperatures episodically rise above freezing. However, the atmospheric processes that control MDVs summer climate, namely the westerly foehn and easterly sea-breeze regimes, are not well understood. The goals of this study are to (i) produce a coherent physical mechanism for the development and spatial extent of foehn winds in the MDVs, and (ii) determine aspects of large-scale climate variability responsible for intraseasonal and interannual differences in MDVs temperature. Polar WRF simulations are run for a prominent foehn case study at 500 m horizontal grid spacing to study the mesoscale components of foehn events, and 15 summers at 2 km horizontal grid spacing to analyze event and temporal variability. The Polar WRF simulations have been tailored for use in the MDVs through modifications to the input soil conditions, snow cover, land use, and sea ice. An objective foehn identification method is used to identify and categorize events, as well as validate the model against LTER AWS observations. The MDVs foehn mechanism consists of a gap wind through a topographic constriction south of the MDVs, forced by pressure differences on each side of the gap and typically set up by cyclonic flow over the Ross and Amundsen Seas. Significant mountain wave activity over the gap modulates the flow response over the MDVs themselves, and pressure-driven channeling drives foehn flow down-valley. During strongly forced events, mass accumulation east of the MDVs from flow around Ross Island is responsible for easterly intrusions, and not a thermally forced sea breeze as previously thought. A variety of ambient flow directions and associated synoptic-scale patterns can result in MDVs foehn, but adequate forcing is necessary to activate the foehn mechanism. The warmest foehn events are associated with amplified circulation patterns that are not associated with particular interannual modes of variability, but instead related to intraseasonal variability forced by the extratropical response to a stagnant MJO. Implications of the findings upon current MDVs paleoclimate theories on the existence of huge melt lakes at the LGM are also presented.
Advisors/Committee Members: Bromwich, David.
Subjects: Atmospheric Sciences; Meteorology
Keywords: McMurdo Dry Valleys; Foehn; Antarctica; Mountain Waves; Gap Flow; Polar WRF
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19.
Vogt, K. Brianne.
Spatial and temporal variability of United States cloud cover, 1893-1996.
Degree: MS, Atmospheric Sciences, 2007, Ohio State University
► Spatial and temporal variability of cloud cover across the conterminous United States…
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▼ Spatial and temporal variability of cloud cover across the conterminous United States from 1893-1996 is examined using statistical methods of principal component analysis (PCA), correlation, student t-test, and cospectrum analysis. PCA was performed on seasonal and annual cloud cover in order to determine locations of spatial nodes and temporal changes in cloud cover. The loadings of the PCA were plotted geographically and their time series scores were used for determining temporal trends. Correlations were performed between the cloud cover principal component scores and various teleconnection indices and sunshine data. The Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), Southern Oscillation Index (SOI), El Niño, and Arctic Oscillation (AO) have strong correlations with cloud cover. Cospectrum analysis was performed with sunshine and cloud cover data where correlations between the two were significantly robust.Cloud cover unrotated principal components (PCs) suggested relatively uniform variability across the country while the first rotated pattern (explaining the greatest variance) emphasized variance in the Midwest and northeast United States. Time series generally have large multi-decadal trends which reach a maximum in 1950s-1980s. These results counter those observed from a PCA of sunshine data where few significant trends are observed. Correlations between cloud scores and sunshine are highly negative between some PCs. Correlations to teleconnections are only large and pervasive for AMO. Cospectrum between cloud and sunshine PC scores suggest correlations are highly negative due to periodicities between 3-10 years. Correlations between AMO and cloud PC scores only occur due to similarity in trends between the two datasets.
Advisors/Committee Members: Rogers, Jeffrey C.
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20.
Walls, Kristin Ashley.
Synoptic Analysis of the Tornado and Derecho Climatology of Ohio from 1963-2002.
Degree: MS, Atmospheric Sciences, 2009, Ohio State University
► The synoptic conditions associated with significant tornadoes and derechoes in Ohio were…
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▼ The synoptic conditions associated with significant tornadoes and derechoes in Ohio were analyzed to help forecasters improve future predictions. Eleven significant tornado events and five derecho events from 1963 – 2002 were evaluated at the time closest to the event and composites made 6, 12, 18, and 24 hours prior along with 6 and 12 hours after the event to observe the changes that occurred. NCEP reanalysis data were gathered from the Climate Diagnostic Center. The variables used were air temperature, sea level pressure, geopotential height, specific humidity, omega, u-wind, v-wind, surface lifted index, and relative vorticity. The synoptic conditions of the significant tornado events were compared with the synoptic conditions of the derecho events to determine which variables played key roles in why each of these events occurred. The results found in this study for the tornado composite were very similar to previous research. During the time of the event for the tornado composite, the left exit region of a jet streak was located over the study area. The flow aloft was found to be from out of the southwest and the lifted index was negative. For the derecho composite, the lifted index was more negative than the tornado composite. One surprising find in this study was that no jet streak was present throughout the entire event for the derecho composite.
Advisors/Committee Members: Mark, Bryan.
Subjects: Atmosphere
Keywords: tornado, derecho, Ohio, severe weather
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21.
Wang, Sheng-Hung.
Large-scale moisture flux analysis for the United States.
Degree: PhD, Atmospheric Sciences, 2004, Ohio State University
► The seasonal and annual United States moisture budget (precipitation minus evaporation, P-E)…
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▼ The seasonal and annual United States moisture budget (precipitation minus evaporation, P-E) is calculated using monthly NCEP/NCAR reanalysis data. Statistical methodologies, primarily Rotated Principal Component Analysis (RPCA), are used to evaluate the variability in the moisture budget. RPCA was performed on monthly moisture budget data and each pattern identifies an individual region of the data domain exhibiting unique variability characteristics. Time series of the RPC patterns are correlated and compared to station precipitation records, and composites of atmospheric circulation fields are obtained during sets of years when extreme values of RPC scores occur. RPCA was performed on the annual mean values of total P-E in to examine the inter-annual and inter-decadal variability of the moisture budget changes. The seasonal RPCA analyses of P-E fields revealed patterns with similar characteristics. For example, the first principal component was centered over the continental interior, indicating high seasonal P-E variation in that area, while subsequent patterns are located near coastal areas including the Gulf of Mexico. The RPC scores were correlated to atmospheric and oceanic teleconnection indices and the links between the teleconnections and the P-E patterns were further evaluated. In winter, for example, the Pacific/North American teleconnection is best linked to continental interior moisture flux. The study indicates the possibility of detecting Great Plains low-level jet events in the NCEP/NCAR reanalysis by using spatial patterns of wind speed, locations of vertical maximum winds and the nocturnal characteristics of the low-level wind maximum. RPCA was performed on the monthly April-May-June P-E data in order to evaluate the low-level jet’s role in U.S. moisture flux. One RPC pattern in particular seems associated with low-level jet events in the central United States, having an association to drought and flood events in the Midwest and central United States.
Advisors/Committee Members: Rogers, Jeffery C.
Subjects: Physics, Atmospheric Science
Keywords: RPC1; NCEP/NCAR; MOISTURE; hPa; MOISTURE FLUX; teleconnection; moisture budget
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22.
Wei, Lijia.
Statistical Analysis of the Atmospheric Sulfate Hisotory Recorded in Greenland Ice cores.
Degree: PhD, Atmospheric Sciences, 2008, Ohio State University
► The Greenland Ice Sheet provides an excellent archive for the paleoclimatic and…
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▼ The Greenland Ice Sheet provides an excellent archive for the paleoclimatic and paleoenvironmental conditions, particularly for the Northern Hemisphere. The chemical analyses of five multi-century Greenland ice cores have yielded a high resolution volcanic aerosol history. This provides an improved estimate of the stratospheric sulfate burden, which is an important input for models assessing the climatic impacts of volcanic eruptions. Additionally, these cores made it possible to confirm the timing of the arrival of the ash and aerosols from Laki over Greenland, which is essential for dating ice cores from low accumulation region in Greenland.The spatial characteristics of the sulfate aerosol deposition associated with specific eruptions provide information about the transport processes and the mechanisms dominating local deposition. Examination of the sulfate deposited from the 1783-84 A.D. Laki and the 1815 A.D. Tambora eruptions reveals that precipitation over the southeastern regions in 1783 may have been suppressed. This also suggests that Laki aerosols were likely deposited primarily by dry deposition. In contrast, the Tambora sulfate is more spatially homogeneous, suggesting deposition primarily via wet processes. To quantify the impact of geographical factors on the deposition of volcanic sulfate over Greenland, a category explanatory variable analysis was conducted. The results indicate that the location of ice cores relative to the ice divide strongly affects EXS deposition, but the elevation of the core site is relatively unimportant. Since 1850, the EXS flux extracted from Greenland ice cores has increased primarily due to anthropogenic sulfur emissions. To quantify this impact as well as the accumulation effect, a linear mixed model was applied. The results indicate that for every Gg increase in the annual NH sulfur emissions, there is a 0.0013% increase in the annual non-volcanic sulfate flux. The impact of accumulation on sulfate deposition varies over Greenland, likely as a function of the dominant local depositional mechanisms. Additionally, as local sources as well as the depositional and post-depositional processes may affect the sulfate deposition on the ice sheet, it will be valuable to reconstruct the histories of other contributor and to closely examine the depositional processes.
Advisors/Committee Members: Mosley-Thompson, Ellen.
Subjects: Atmosphere
Keywords: sulfate aerosols, ice cores, Greenland
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23.
Wilson, Aaron Benjamin.
Enhancement of Polar WRF atmospheric and surface processes: An annual simulation.
Degree: MS, Atmospheric Sciences, 2010, Ohio State University
► In continuing the evaluation of Polar WRF 3.1.1, this high resolution mesoscale…
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▼ In continuing the evaluation of Polar WRF 3.1.1, this high resolution mesoscale model for regional scale studies is used to simulate Arctic conditions for the year December 2006 – November 2007. The goal is to examine key characteristics of weather patterns, comparing model output to documented reanalyses and observational data sets of surface and upper level observations. The domain mirrors that of the Arctic System Reanalysis (ASR), an assimilation of model results, field observations, and satellite observations of the Arctic being conducted partly by the Byrd Polar Research Center at The Ohio State University. Included in this area of study is the Arctic Basin, the river drainage areas of the subarctic, as well as the surrounding mid-latitudes in the Northern Hemisphere. This simulation takes advantage of previous polar modifications to mesoscale modeling, including updates to snow pack treatment, radiative transfer properties, and fractional sea ice implementation. A key development in this Polar WRF study is the extension of the seasonal progression of sea ice albedo to the entire domain. The boundary conditions are specified by the NCEP Global Forecast System (GFS) Final global gridded analysis archive (FNL); a 1deg x 1deg global grid updated every 6 hours. The simulations are performed in 48 hour increments initialized daily at 0000UTC, with the first 24 hours discarded for model spin-up. Overall, the results of the surface and upper air analysis are promising. Polar WRF predicted values of surface and sea level pressure are excellent, with good correlations between model and observations. In addition, Polar WRF 2 m temperature and 2m dewpoint show good skill and small biases. Likewise, the modeled upper air variables (temperature, geopotential height, and wind speed) outperform the surface analysis. In addition to the standard meteorological variable analysis, the hydrologic cycle is evaluated. Precipitation, when considering locations in open, flat areas away from high terrain is modeled well. Additionally, an investigation into the precipitation basins for Arctic rivers shows these areas have little bias when compared to observations. There are deficiencies identified with this current model configuration however. Most importantly, an evaluation of cloud fraction reveals that the summertime Arctic stratus clouds are severely under predicted, which leads to precipitation deficits in the Arctic as well as an amplified diurnal temperature cycle. While the modeled polar region suffers from too little precipitation, the mid-latitudes demonstrate a surplus owing largely to the convective parameterization. However, these limitations provide a benchmark from which to improve the model and guidance for further development for Polar WRF’s use as ASR’s primary model.
Advisors/Committee Members: Bromwich, David.
Subjects: Atmosphere
Keywords: Polar WRF; WRF; Arctic System Reanalysis; ASR
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24.
Yang, Lei.
Greenland ice sheet: surface climate variability and ice dynamics.
Degree: PhD, Atmospheric Sciences, 2007, Ohio State University
► The Polar Pennsylvania State University-National Center for Atmospheric Research Fifth Generation Mesoscale…
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▼ The Polar Pennsylvania State University-National Center for Atmospheric Research Fifth Generation Mesoscale Model (Polar MM5) regional climate model was run over the North Atlantic region for 1958 - 2006. Polar MM5 V0 (1958 - 2004) simulated surface mass balance and temperature are used to compare with observations and investigate the co-variability of surface climate variability and measured ice sheet changes. The correlation between ice sheet thickness change due to surface mass balance anomalies and due to ice dynamics became higher and statistically more significant from 1993 to 2005. The correlation varies with different based periods chosen for surface mass balance estimates, which suggests a threshold when glaciers start to accelerate. Longer term model temperature data was extracted from Polar MM5 V1, which is run over Greenland and surrounding areas for 1958 - 2006. Model temperature data are validated and calibrated using station observation records. With the longer term model assimilation available, melt index anomalies were calculated relative to the 1961-1990 base period. The co-variability of ice velocities and melt index anomalies are investigated for 3 largest outlet glaciers in Greenland. April-September Positive Degree Day, spring and summer temperature anomalies are found to be significantly correlated with ice velocities, which indicate a correspondence between surface melting and ice dynamics. Different responses of glacier speed to melt index anomalies after break-up also indicate an influence from bed geometry and other dynamic characteristics unique to each glacier. The small or even negative correlation after break-up at Kangerdlugssuaq Gl., and Helheim Gl. suggests that ice dynamics took control after melt triggered acceleration and retreat to re-adjust the glaciers toward an new equilibrium. The co-variability of glacier ice discharges and climate variability is also examined by using Polar MM5 V1 modeled summer temperature and April-September Positive Degree Day (PDD) anomalies. Ice discharges from south Greenland glaciers are found to be sensitive to temperature change. Based on sensitivities of ice discharge to melt index anomalies, time series of total ice discharge from 28 major glaciers since 1958 are modeled. The global sea level rise contribution from Greenland ice sheet during past 50 years is estimated be ~ 0.6 mm/yr in average.
Advisors/Committee Members: Box, Jason Eric.
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25.
Youderian, Bria Danielle.
Influence of the Atlantic Multidecadal and the Pacific Decadal Oscillations on Hemispheric Air Temperature and Cloud Cover.
Degree: MS, Atmospheric Sciences, 2009, Ohio State University
► The Atlantic Multidecadal Oscillation (AMO) and the Pacific (inter) Decadal Oscillation (PDO)…
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▼ The Atlantic Multidecadal Oscillation (AMO) and the Pacific (inter) Decadal Oscillation (PDO) are evaluated as potential controls on climate change in the Northern Hemisphere. Each sea surface temperature anomaly index is correlated with near-surface air temperature over land surfaces north of the equator from 1901–2002. Additionally, a combined PDO+AMO index is constructed and analyzed. Overall results indicate that the AMO and the PDO have impacts on air temperature. A positive relationship exists between near-surface air temperatures and the AMO with the land bordering the western Atlantic and parts of northern Africa. The PDO has a strong positive effect on temperatures over the Pacific coast of North America, Sudan, and the Philippines, and Japan is negatively influenced by the PDO. Strong positive correlations occur with the PDO+AMO in Africa, Spain, northern South America, the Caribbean, Mexico, Florida, and along the Pacific coast of North America. Cloud cover is dually assessed through correlations with temperature and ocean oscillation indices. The effects of cloud cover on temperature in the Northern Hemisphere vary spatially and seasonally with strong correlations noted throughout. Much of the Northern Hemisphere exhibits positive correlations with mean temperature in winter and negative correlations in summer. Cloud cover has positive influences on minimum temperature in the western Northern Hemisphere and negative influences on maximum temperature. When cloud cover and ocean indices are assessed, few locations are found to have significant correlations.
Advisors/Committee Members: Rogers, Dr. Jeffery C.
Subjects: Atmosphere
Keywords: Atlantic multidecadal oscillation; Pacific decadal oscillation
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