The Atlantic hurricane of May 1951 had several interesting characteristics. Chief among these were the high latitude and early season of its origin, the type of air mass in which it formed, its formation in a cold core low that extended high than the 200-mb level, and the loop in its path. There was not available enough observational data within and near the storm in order to make a detailed study sufficient to completely explain these phenomena. Some of the meteorological conditions observed shortly proceeding and during the existence of this storm were studied and are described here. Its formation and movement is analyzed and discussed in relation to various theories on the origin and movement of hurricanes. / Typescript. / "Submitted to the Graduate Council of Florida State University in partial fulfillment of the requirements for the degree of Master of Science." / "August, 1952." / Includes bibliographical references (leaves 15-16).

Understanding and predicting the inner-core structure and intensity change of tropical cyclones (TCs) remains one of the biggest challenges in tropical meteorology. This study addresses this challenge by investigating the formation, structure, and intensity changes resulting from localized strong updrafts in TCs known as convective bursts (CBs). The evolution of CBs are analyzed in high-resolution simulations of two hurricanes (Dean 2007 and Bill 2009) using the Weather Research and Forecasting (WRF) model. The simulations are able to capture the observed track and peak intensity of the TCs. With Dean, there is a slight lag between the simulated intensification and actual intensification, and the extreme rate of RI is not fully captured. However, the cycle of intensification, weakening, and re-intensification observed in both TCs is captured in the simulations, and appears to be due to a combination of internal dynamics and the surrounding environmental conditions. CBs are identified based on the 99th percentile of eyewall vertical velocity (over the layer from z = 6-12 km) in each simulation (8.4 m s-1 for Dean, 5.4 m s-1 for Bill). The highest density of CBs is found in the downshear-left quadrant, consistent with prior studies. The structure of the CBs is analyzed by comparing r-z composites of azimuths with CBs and azimuths without CBs, using composite figures and statistical comparisons. The CB composites show stronger radial inflow in the lowest 0-2 km, and stronger radial outflow from the eye to the eyewall in the 2-4 km layer. The CB composites also have stronger low-level vorticity than the non-CBs, potentially due to eyewall mesovortices. The analysis of individual CBs also confirms the importance of the eye-eyewall exchange in CB development, potentially by providing buoyancy, as parcel trajectories show that many parcels are flung outward from the eye and rapidly ascend in the CBs, with as much as 500 J/kg of CAPE along the parcel path. In addition, the location of radial convergence seems to play a key role in governing the radial location of CBs. Inner-core CBs seem to be associated with local convergence maxima in the eyewall, while CBs outside the radius of maximum winds (RMW) are associated with convergence maxima due to bands and/or secondary eyewalls. Analysis of intensity change in the simulations shows that there are more inner-core CBs during times when the TCs are intensifying, while weakening/steady times appear to be associated with more CBs outside the radius of maximum wind (RMW), consistent with observational studies and theoretical work. However, times when the TC has already been intensifying and continues to do so have more CBs than times when the TC has been weakening but then intensifies. This suggests that CB development may not always be predictive, but rather may sometimes occur as a result of ongoing intensification. On the other hand, rapid intensification (RI) in the simulations is found to be associated with an even higher density of CBs inside the RMW than slower intensification. Lag correlations between CBs and intensity are calculated to investigate the time of the intensity response to CB development. These calculations reveal a broad peak in correlation, with the CBs tending to lead pressure falls by 0-3 hours. These results confirm the notion that convective heating inside the RMW is favorable for intensification. The findings from this analysis show that eyewall CBs are driven by asymmetric dynamical processes in the inner-core region of TCs, both in and above the TC boundary layer. In addition, the relationship between CB development and intensity change is indeed positive, sometimes in a predictive sense, and at other times while intensity change is ongoing. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2016. / March 24, 2016. / Convection, Eye, Eyewall, Hurricane, Updraft, WRF / Includes bibliographical references. / Robert E. Hart, Professor Directing Dissertation; Irinel Chiorescu, University Representative; Mark Bourassa, Committee Member; Henry Fuelberg, Committee Member; Guosheng Liu, Committee Member; Robert Rogers, Committee Member.

The aim of these studies is to determine spatial climatological effects on hurricane intensification rates. Previous studies have noted that the skill in predict a hurricane's track has improved at a much greater rate than the skill to predict its intensity. There is even less research concerning hurricane intensification rates, let alone research done spatially and climatologically. Therefore, the research herein aims to understand what drives hurricane intensification rates. This is done by using spatial climatological analyses to determine the effects that intensity, sea surface temperatures (SSTs), ocean heat content (OHC), El Niño--Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Madden--Julian Oscillation (MJO), and the Pacific Decadal Oscillation (PDO) have on hurricane intensification rates. Using both equal-area hexagons and raster techniques, hurricane track data is plotted spatially. SST, ocean salinity, and OHC values are also represented on a spatial grid. Finally, climate variables are represented temporally as mean yearly values. A generalized linear model from a gamma family and a logarithmic link function, as well as a full probability model are used to determine the effects that the variables of interest have on hurricane intensification rates. It is found that intensity has a positive effect on hurricane intensification rates with an average increase of 0.024 ± 0.0032 m s⁻¹ in intensification for a 1 m s⁻¹ increase in intensity. SST is also found to have a positive effect on intensification rates with an average increase in hurricane intensification of 16% for a 1° C increase in mean SST. It is also found that decreased salinity may have a positive effect on hurricane intensification rates by inhibiting vertical mixing. In the North Atlantic basin, it is found that the NAO has a negative effect on intensification rates of ‒0.18 m s⁻¹ h⁻¹ per 1 SD, while ENSO and MJO do not have a statistically significant effect. In the Eastern North Pacific basin, it is found that both the NAO and ENSO have a positive effect on hurricane intensification rates, while the MJO and PDO do not have a statistically significant effect. Finally, in comparing the largest intensification rates during the most extreme NAO events in the North Atlantic basin, as well as the most extreme ENSO events in the Eastern North Pacific basin, it appears that rapid intensification (RI) may simply be normal intensification occurs over a longer time period. These studies confirm the previously held idea that warmer SSTs will lead to higher intensification rates. Along with this is the finding that the NAO has a negative effect on hurricane intensification rates in the North Atlantic basin. This was not something that was previously mentioned in the research. Finally, the idea that RI may not be due to small thermodynamic processes but instead normal intensification over a longer amount of time is an intriguing notion that deserves further analysis. / A Dissertation submitted to the Department of Geography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / March 15, 2016. / climatology, hurricane, hurricane climatology, intensification, rapid intensification, tropical cyclone / Includes bibliographical references. / James B. Elsner, Professor Directing Dissertation; Robert Hart, University Representative; Chris Uejio, Committee Member; Tingting Zhao, Committee Member.

The polar regions of the world constitute an important sector in the global energy balance. Among other effects responsible for the change in the sea-ice cover like ocean circulation and ice-albedo feedback, the cloud-radiation feedback also plays a vital role in modulation of the Arctic environment. However the annual cycle of the clouds is very poorly represented in current global circulation models. This study aimed to explore the atmospheric conditions in the Arctic on an unprecedented spatial coverage spanning 70°N to 80°N through the use of a merged data product, C3MData (derived from NASA's A-Train Series). The following three topics provide outline on how this dataset can be used to accomplish a detailed analysis of the Arctic environment and provide the modelling community with first information to update their models aimed at better forecasts. (1)The three properties of the Arctic climate system to be studied using the C3MData are sea-ice, clouds, and the atmospheric conditions. The first topic is to document the present states of the three properties and also their time evolutions or their seasonal cycles. (2)The second topic is aimed at the interactions or the feedbacks processes among the three properties. For example, the immediate alteration in the fluxes and the feedbacks arising from the change in the sea-ice cover is investigated. Seasonal and regional variations are also studied. (3)The third topics is aimed at the processes in native spatial resolution that drive or accompany with sea ice melting and sea ice growth. Using a composite approach based on a classification due to surface type, it is found that limitation of the water vapour influx from the surface due to change in phase at the surface featuring open oceans or marginal sea-ice cover to complete sea-ice cover is a major determinant in the modulation of the atmospheric moisture. The impact of the cloud-radiative effects in the Arctic is found to vary with sea-ice cover and seasonally. The effect of the marginal sea-ice cover becomes more and more pronounced in the winter. The seasonal variation of the dependence of the atmospheric moisture on the surface and the subsequent feedback effects is controlled by the atmospheric stability measured as a difference between the potential temperature at the surface and the 700hPa level. A regional analysis of the same suggests that most of the depiction of the variations observed is contributed from the North Atlantic region. / A Dissertation submitted to the Geophysical Fluid Dynamics Institute in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2016. / May 2, 2016. / C3MData, Cloud, Feedback, Interaction, Sea-Ice, Stabillity / Includes bibliographical references. / Ming Cai, Professor Directing Dissertation; Christopher Tam, University Representative; Allan Clarke, Committee Member; Guosheng Liu, Committee Member; Kevin Speer, Committee Member.

High frequency microwave instruments are increasingly used to observe ice clouds and snow. These instruments are significantly more sensitive than conventional precipitation radar. This is ideal for analyzing ice-bearing clouds, for ice particles are tenuously distributed and have effective densities that are far less than liquid water. However, at shorter wavelengths, the electromagnetic response of ice particles is no longer solely dependent on particle mass. The shape of the ice particles also plays a significant role. Thus, in order to understand the observations of high frequency microwave radars and radiometers, it is essential to model the scattering properties of snowflakes correctly. Several research groups have proposed detailed models of snow aggregation. These particle models are coupled with computer codes that determine the particles' electromagnetic properties. However, there is a discrepancy between the particle model outputs and the requirements of the electromagnetic models. Snowflakes have countless variations in structure, but we also know that physically similar snowflakes scatter light in much the same manner. Structurally exact electromagnetic models, such as the discrete dipole approximation (DDA), require a high degree of structural resolution. Such methods are slow, spending considerable time processing redundant (i.e. useless) information. Conversely, when using techniques that incorporate too little structural information, the resultant radiative properties are not physically realistic. Then, we ask the question, what features are most important in determining scattering? This dissertation develops a general technique that can quickly parameterize the important structural aspects that determine the scattering of many diverse snowflake morphologies. A Voronoi bounding neighbor algorithm is first employed to decompose aggregates into well-defined interior and surface regions. The sensitivity of scattering to interior randomization is then examined. The loss of interior structure is found to have a negligible impact on scattering cross sections, and backscatter is lowered by approximately five percent. This establishes that detailed knowledge of interior structure is not necessary when modeling scattering behavior, and it also provides support for using an effective medium approximation to describe the interiors of snow aggregates. The Voronoi diagram-based technique enables the almost trivial determination of the effective density of this medium. A bounding neighbor algorithm is then used to establish a greatly improved approximation of scattering by equivalent spheroids. This algorithm is then used to posit a Voronoi diagram-based definition of effective density approach, which is used in concert with the T-matrix method to determine single-scattering cross sections. The resulting backscatters are found to reasonably match those of the DDA over frequencies from 10.65 to 183.31 GHz and particle sizes from a few hundred micrometers to nine millimeters in length. Integrated error in backscatter versus DDA is found to be within 25% at 94 GHz. Errors in scattering cross-sections and asymmetry parameters are likewise small. The observed cross-sectional errors are much smaller than the differences observed among different particle models. This represents a significant improvement over established techniques, and it demonstrates that the radiative properties of dense aggregate snowflakes may be adequately represented by equal-mass homogeneous spheroids. The present results can be used to supplement retrieval algorithms used by CloudSat, EarthCARE, Galileo, GPM and SWACR radars. The ability to predict the full range of scattering properties is potentially also useful for other particle regimes where a compact particle approximation is applicable. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / March 21, 2017. / discrete dipole approximation, hydrometeors, microwave instruments, snow, T-matrix method, Voronoi diagrams / Includes bibliographical references. / Guosheng Liu, Professor Directing Dissertation; Max Gunzburger, University Representative; Jon Ahlquist, Committee Member; Robert Ellingson, Committee Member; Zhaohua Wu, Committee Member.

Thesis: M.S., Massachusetts Institute of Technology, Department of Meteorology, 1977 / Bibliography : leaves 125-126. / M.S. / M.S. Massachusetts Institute of Technology, Department of Meteorology

Includes bibliographical references (pages 139-143). / The central theme of this study concerns the use of classification schemes on weather modification experiments designed to investigate the possibility of increasing rainfall from individual cumuli or cumulus cloud systems. The principal objectives of these experiments are the evaluation of treatment effects and the identification of situations where seeding with artificial ice-nuclei is likely to have positive results. The classification of experimental units into categories that are associated with significantly different physical processes aids the evaluation process and the formulation of seeding strategies in the desired manner. As part of this study a classification scheme, which stratifies convective events on the basis of the synoptic situations which give rise to and maintain the convection, is formulated. In chapter seven and eight this scheme and another scheme presently being employed on a cumulus cloud weather modification experiment are examined statistically. Investigations show that the formulated scheme attains the objectives of classification to a greater degree. Certain attributes of the second scheme, permit the development of a classification procedure whereby the most effective stratification of experimental units can be accomplished.

In the presence of water vapor, photolysis of tropospheric ozone (O3) produces the hydroxyl radical (OH), which is a strong oxidant that directly and indirectly controls a host of greenhouse gases and air pollutants. When tropospheric O3 reaches the surface, its oxidative effects perturb plant transpiration and photosynthesis. Although these effects have been included in climate and air quality models, there are limited observational datasets to constrain key aspects of atmospheric photochemistry and O3 deposition on regional to global scales. This dissertation develops and uses two new datasets to better understand the ozone photochemistry and impacts. Photolysis, the breaking of chemical bonds by sunlight, is the engine for reactive atmospheric chemistry. It controls production of atmopsheric oxidants, especially O3 and OH, which then influence the lifetimes of other air pollutants and climate forcing agents. Global chemistry and climate models differ in their estimates of these photolysis rates and there have been datasets capable of discriminating among different models. Here, we integrate satellite-retrivals of clouds and aerosols into a photolysis code and produce a 3-D global photolysis dataset called Sat-J. We show that Sat-J is tightly correlated with in-situ measurements of pholysis rates from airborne chemistry campaigns, with errors (4-20%) mainly attributed to differences in nonuniform cloud sampling and time match differences. By comparing regional, not necessarily collocated, averages of aircraft data, SatJ, and a chemistry model (GEOS-Chem); we demonstrate that SatJ provides a representative climatology of photolysis rates across the globe and can serve as a benchmark for photochemistry models. Using surface micrometeorological fluxes and surface O3 monitoring networks, we also develop and evaluat a method to estimate O3 deposition and stomatal O3 uptake across networks of eddy covariance flux tower sites where O3 concentrations and O3 fluxes have not been measured. This method, called SynFlux, reproduces the variability in daily stomatal O3 uptake at sites with O3 flux measurements, with a modest bias (21% or less) attributed to gridded O3 concentrations. Across SynFlux sites, we highlight environmental factors controlling spatial patterns in O3 deposition and showed that previous O3 concentration-based metrics for plant damages did not correlate with SynFlux O3 uptake, which is a better predictor for plant damage than ambient concentration in air. SynFlux has dramatically expanded the the available data on surface O3 deposition, which can now be used for performing ecosystem impact studies across a species and climates in the US and Europe. Past controlled experiments involving single plant species have shown that O3 uptake can degrade water-use efficiency (WUE), which is the ratio of carbon uptake in photosynthesis (GPP) to water loss in plant transpiration (T). Using SynFlux sites, we can quantify this effect for whole ecosystems under natural environmental variability, which has not been previously studied. Across 74 SynFlux sites, we find a significant negative relationship (–0.02% per μmol m-2 d-1) between daily cumulative O3 uptake (CUO) and WUE anomalies, with the largest impacts occurring at forest sites. Past controlled studies of selected individual species also observed a similar O3 reduction of WUE over the growing season, indicating a consistent response to O3 across multiple species with an ecosystem. When we analyze the relationships between daily CUO and GPP or T anomalies, we also find that CUO degrades GPP and increases T over the growing season. We postulate that O3 degrades WUE through O3 non-stomatal biochemical factors, which result in a reduction of GPP or an increase in T. Our SynFlux results here provide climate models the ability to incorporate O3-dose response relationships between O3 uptake and ecosystem carbon and water vapor fluxes across ecosystems that have not previously been studied. For chapters 2-4, we have separate supplementary documents for each chapter. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / 2019 / November 4, 2019. / Global photolysis dataset, Ozone deposition dataset, Ozone dose-response relationships, Ozone uptake impacts on ecosystem water vapor and carbon fluxes, Sat-J, SynFlux / Includes bibliographical references. / Christopher D. Holmes, Professor Directing Dissertation; Thomas Miller, University Representative; Vasu Misra, Committee Member; Mark Bourassa, Committee Member.

A mathematical model was developed to predict water content profiles, evapotranspiration, water flow from or to the water table, root extraction and root water potential at the surface as functions of time under unsteady state conditions. The model was tested in the field at The Hullinger Farm near Vernal, Utah, in 1970 and 1971. Comparison of water content-depth profiles show excellent agreement at the end of a 9- day run in 1970 on oats seeded to alfalfa. In 1971 with alfalfa as the crop, the data show best agreement, between predicted and computed water content-depth profiles, 48 hours after any water addition. The poorest agreement for both crops was right after irrigation. The computed cumulative ET was 4.9 em which was 0.4 em less than actual (measured) ET, during the 9- day period in 1970. In 1971, the actual and measured ET were the same for the whole season. This agreement may be partially due to the "forcing" of the water removal by ET to be the same as measured. In 1970, the computed cumulative upward flow from the water table was 2.20 em which was 0.1 em greater than the actual for the 9-day period. In 1971, the cumulative upward water flow from the water table was 4.80 em which was 3.20 em greater than the calculated for the whole season of 116 days.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1983. / Microfiche copy available in Archives and Science. / Bibliography: leaves 208-212. / by Richard Craig Deininger. / Ph.D.