Atmospheric conditions during the dry season of the South American monsoon are instrumental in the initiation of convection during the wet season and are strongly correlated to SSTs within the Atlantic Warm Pool. Subsequently, accurate seasonal prediction of temperature and rainfall during the dry season has the potential to improve our understanding of and the predictability of these variables during future seasons. In this study, we review the fidelity of South American dry season (June-July-August) reforecasts from one global climate model (GCM), and one downscaled regional climate model (RCM). Additionally, we evaluate a second integration of the RCM that uses a bias correction method called anomaly nesting, which is designed to remove the bias of the GCM before the downscaling process is performed. The models are integrated for seven dry seasons (2001–2007), and each season consists of six ensemble members. For this study, we focus on two primary regions: the Amazon River Basin (ARB) and the subtropical region (ST). There are three objectives of this research. The first is to locate regions of model bias for two-meter air temperature and for precipitation within the ARB and the ST using NCEP Climate Forecast System Reanalysis (CFSR) as a comparison dataset. The second is to evaluate the predictability of above normal, normal, and below normal occurrences of the two variables using potential predictability ratios and calculations of the area under the relative operative characteristic (ROC) curve (AUC). Through this analysis we should be able to determine whether downscaling or anomaly nesting improve upon the skill of the GCM. Lastly we wish to evaluate how the three models depict land-atmosphere interactions during the dry season and compare their results with results from CFSR. The models produced the largest biases of both variables over elevated terrain and within the Intertropical Convergence Zone (ITCZ). However, neither of these locations significantly impacts the ARB or the ST. Signal-to-noise ratios show that the ARB exhibits more potential predictability than the ST and that temperature exhibits more potential predictability than precipitation. AUCs confirm that temperature is more skillfully predicted than precipitation and that the models exhibit more skill in the ARB than in the ST. AUCs show that the downscaled and the downscaled with anomaly nesting integrations display more skill than the GCM integration, particularly in the ARB. Lastly, we find conflicting results between the models and CFSR regarding how the land and the atmosphere interact during the dry season. However, a full moisture budget analysis is needed to completely resolve land-atmosphere feedbacks and that is beyond the scope of this study. / A Thesis submitted to the Department of Earth Ocean and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Masters of Science. / Spring Semester, 2011. / March 17, 2011. / RSM, CFS, Anomaly Nesting, Climate Model / Includes bibliographical references. / Vasubandhu Misra, Professor Directing Thesis; Henry Fuelberg, Committee Member; Philip Sura, Committee Member.

Anthropogenic pollution impacts many of the Earth's natural processes. Therefore, understanding the mechanisms that transport pollutants from the surface to the free atmosphere is important for understanding the chemical composition of the atmosphere. This study quantifies the vertical transport of lower tropospheric carbon monoxide (CO) by deep convection associated with mesoscale convective systems. Three squall line simulations (C1-C3) based on different environmental wind shear profiles are made using the 2-D Goddard Cumulus Ensemble, each providing post-convection CO profiles. Then, the Tropospheric Emission Spectrometer (TES) instrument's ability to resolve the convectively modified CO distribution is analyzed during one of the cases (C3) using a 'clear-sky' retrieval scheme. Results show that environmental wind shear not only impacts the structure of squall lines, but also their transport characteristics. The squall line simulation with the strongest low-level vertical wind shear is found to transport the greatest net mass of CO, with an amount of 13 421 metric tons in the low levels and 43 916 metric tons in the middle levels of the atmosphere. However, the storm with the weakest low-level vertical wind shear and weakest environmental winds aloft has a greater mass of CO transported by the updraft and the downdraft than either of the two other storms. The study finds that stronger environmental winds in the upper troposphere play an important role in the propagation speed of the squall line, which in turn impacts the horizontal distribution of convectively lofted CO. Results also show that TES has sufficient sensitivity to resolve convectively lofted CO, as long as the retrieval scene is cloud-free. TES swaths that are located downwind of squall lines are found to have the greatest chance of sensing convective transport because the impact of clouds on retrieval quality becomes less of an issue further from the squall line. / A Thesis submitted to the Department of Meteorology in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester, 2007. / July 5, 2007. / GCE, Cloud Venting, Meteorology, Squall Line, MCS, Mesoscale Convective System, Pollution Transport, Carbon Monoxide, CO, TES, Tropospheric Emission Spectrometer, Goddard Cumulus Ensemble / Includes bibliographical references. / Henry E. Fuelberg, Professor Directing Thesis; Guosheng Liu, Committee Member; Robert Hart, Committee Member.

The inter-annual variability of typhoon landfalls in China is investigated using historical and modern records. A north-to-south anti-correlation in yearly activity is confirmed from the historical records. When activity over Guangdong is high, it tends to be low over Fujian and vice versa. This spatial variation is identified in the modern record using a factor analysis model, which delineates the southern provinces of Guangdong, and Hainan from the northern provinces of Fujian, Taiwan, Zhejiang, Shanghai,Jiangsu, and Shandong. An index of annual activity representing the degree to which each year follows this pattern of activity is used to identify correlated climate variables. A useful model that includes sea level pressure differences between Mongolia and western China and SST over the midlatitude NW Pacific during the summer explains 27% of the inter-annual variability of the index. Physically, we suggest that a stronger than normal north to south pressure gradient increases the surface easterly wind flow over northern China, this coupled with lower SST over midlatitude NW Pacific, favors typhoons taking a more southerly track toward Hong Kong. / A Thesis submitted to the Department of Geography in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2004. / October 20, 2004. / Southern China, Typhoon Landfall, Variablity Historical Data / Includes bibliographical references. / James B. Elsner, Professor Directing Thesis; Thomas Jagger, Committee Member; J. Anthony Stallins, Committee Member.

The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze that is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning dominated the ARCTAS-A period and has been the focus of many ARCTAS related studies. This study determines the common pathways for anthropogenic emissions during ARCTAS-A. Trajectories are released each day from three historically significant regions of anthropogenic emissions (Asia, North America, and Europe). These fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectories then are examined to determine: Origins of emissions that reach the Arctic (defined as 70oN), pathways of the emissions reaching the Arctic, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. These results serve as regional "climatologies" for the ARCTAS-A period. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled by the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived "climatologies" and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2010. / September 30, 2010. / ARCTAS, Pollution, Anthropogenic, Emissions, Arctic, Arctic Haze, Transport, Trajectories / Includes bibliographical references. / Henry E. Fuelberg, Professor Directing Thesis; Guosheng Liu, Committee Member; Robert Hart, Committee Member.

African Easterly Waves (AEWs) are mesoscale synoptic features that form in West Africa and propagate westward. The relationship of AEWs to rainfall in the region has been examined in previous studies but no scientific consensus has been reached. This relationship, however, has been found to be complex and to involve numerous feedback mechanisms such as the African Easterly Jet (AEJ) fluctuations. Other mechanisms like latent heat release and the temperature gradient at the surface between the dry Sahara Desert and the moist maritime region along the Gulf of Guinea also play a role in the relationship between rainfall and AEWs. This study will investigate the relationship of AEWs to rainfall through objective analysis of the waves and an EOF analysis of daily rainfall over a prescribed region. Two classification schemes along with statistical techniques were used to investigate the spatiotemporal variability of the relationship between African Easterly Waves (AEWs) and the rainfall over West Africa. Two varying methods were used because of the highly subjective manner of tracking AEWs. This study was limited to four wet years (1958 –1961) and four dry years (1982-1985) during the summer months of June, July, August and September. The first technique was a new three-step method designed by Dr. A. Fink that makes use of 700mb and 850mb streamline plots and band-pass filtered meridional wind data. The second method uses the vertical structure of the band-pass filtered meridional wind to identify wave passage. The methods were compared and contrasted with one another, and both were shown to be adequate for tracking AEWs. However, for examining the relationship of rainfall with AEWs the second method appropriately named the Vertical Profile Method (VPM) was found to be preferable. Using the VPM the difference between wave characteristics and rainfall variability were examined on a daily timescale. This involved creating daily rainfall datasets for four different quadrants over the Sahel and relating any changes in rainfall activity to the AEWs as they both propagated across the quadrants. The differences in AEW and rainfall characteristics were examined by making comparisons within two distinct time-frame perspectives. The first perspective examined differences between wet and dry years and the second perspective examined differences between the 1st two months (June-July) and the last two months (August-September). For each category the strength of the waves, number of waves, location of the north and south regime, rainfall distribution and rainfall amounts were compared. During the wet years (1958 -1961) the number of waves that propagated across West Africa averaged 59 waves per year using the Vertical Profile Method (VPM) and 49 using the Andreas Fink Method (AFM). The number of AEWs tracked during the dry years (1982-1985) averaged about 63 with the VPM and 54 with the AFM. The difference in the average number of AEWs between the methods was probably a result of the limitations of each method. More waves in the dry years supports previous conclusions that stronger but less frequent AEWs occur in wet years and weaker but more frequent AEWs occur in the dry years. Tracking of the AEWs also allowed for the separation of the AEWs into two distinct wave regimes north and south of the African Easterly Jet (AEJ). Throughout all eight years the separation became apparent as the summer progressed with the separation reaching a maximum. This coincides with the fluctuations in AEJ intensity, which also has a maximum in the month of August. Rainfall within the tracked AEWs was found to be bimodal with the region of maximum northerly flow containing the most rainfall. This region is ahead of the trough and is typically associated with squall line convective activity. The maximum region was the same for both wet and dry years and also for the two month season comparison. An EOF analysis of daily rainfall was completed for 1958 (wet year) and 1983 (dry year) to determine if any relationship to AEWs could be identified in the rainfall time series. The resulting eigenvalues show the influence of topography along the Guinea coast with positive values: however, no discernable link to AEWs was present. The power spectrum of the first two principle components did identify a significant peak at the same period associated with AEWs. This power spectrum analysis demonstrated that rainfall is linked to AEWs, but a more detailed dynamical investigation is needed. / A Thesis Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Master of Science. / Spring Semester, 2006. / December 8, 2005. / Daily Rainfall, African Easterly Waves, EOF / Includes bibliographical references. / Sharon E. Nicholson, Professor Directing Thesis; T. N. Krishnamurti, Committee Member; Kwang-Yul Kim, Committee Member.

For many years tropical cyclone superensemble has shown remarkable skill in forecasting Atlantic tropical cyclone track and intensity. In this project tropical cyclone superensemble is applied to Eastern Pacific tropical cyclone forecasting for the 2004 Eastern Pacific tropical cyclone season. This task is completed by conducting a collection of model combination tests to discover which models perform best within the superensemble method. Then, the two main questions of this thesis are addressed: will a combined Eastern Pacific and Atlantic training set provide superior forecasts over just using an Eastern Pacific training set, and do intensity-specific training sets provide superior forecasts over just using all storms of varying intensities? In the context of the 2004 Eastern Pacific tropical cyclone season, the answer to both questions is yes. However, the ultimate findings are quite perplexing, as an Atlantic training set provides superior forecasts when compared to forecasts using an Eastern Pacific training set or a combined-basin training set. Furthermore, forecasts made using only hurricane training usually outperform forecasts made using combined-intensity training and tropical storm training. The rest of the project uses model bias comparisons and intensity-specific error calculations to try and determine why the results are as they are. / A Thesis submitted to the Department of Meteorology in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2005. / September 1, 2005. / Tropical Cyclone Forecasting, Hurricanes / Includes bibliographical references. / T. N. Krishnamurti, Professor Directing Thesis; Carol Anne Clayson, Committee Member; Peter S. Ray, Committee Member.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Bibliography: leaves 38-39. / M.S.

The objective of this research is to quantify the LAMP’s performance when forecasting for IFR conditions at specific major airports for forecast hours one, three, six, and twelve, and further determine how the LAMP performs seasonally at those specific airports and forecast hours. Two by two contingency tables were used to calculate the Probability of Detection (POD), False Alarm Ratio (FAR), Critical Success Index (CSI), Heidke Skill Score (HSS), and Bias score. The results show that the LAMP performs relatively better in the cool season compared to the warm season consistently at each chosen airport, and that the LAMP performs worse when forecasting for West Coast airports relative to inland airports.

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