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.

No description available.

No description available.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / Vita. / Bibliography: leaves 202-206. / Ph.D.

Weak-wind flow in the nocturnal boundary is one of the most poorly understood problems in the field of meteorology. The understanding of weak-wind flows is essential for the improvement of regulatory dispersion models which are currently rendered invalid under weak-wind conditions and stable stratification. Recently there have been increased efforts directed towards improving the understanding nocturnal boundary layer dynamics. The results of these studies have shown that nocturnal boundary layer flows are often dominated by intermittent turbulence and motions occurring on horizontal scales ranging from hundreds of meters to several kilometers and on time scales of 1 minute to 1 hour. We refer to these scales as sub-meso. This connection has led to the hypothesis that intermittent turbulence generation may be the result of sub-meso motions that are subject to external forcing originating in the deeper boundary layer. However, these processes have proven difficult to measure as traditional sensor networks have failed to provide the vertical and horizontal coverage necessary to observe the driving forces on these scales. This study sought to close this knowledge gap using SOund Detection And Ranging (SODAR). SODAR is a ground based acoustic remote sensing technology that is capable of measuring wind and turbulence at multiple heights in the boundary layer. Data were collected with a pair of SODAR systems with sequentially increasing separation distance at the Oregon State University Botany and Plant Pathology lab during the summer of 2010. The data have indicated that motion occurring on time scales of 2 minutes to 32 minutes are isolated to the lowest 50 meters of the nocturnal boundary layer. Surface-layer measurements were collected using a pair of sonic anemometers placed at heights of 1.5 and 7 meters above ground level. Comparisons of surface-layer measurements and deeper boundary layer measurements have shown that when the surface layer stratification is stable, processes within the surface layer are not likely to be influenced by external forcing from aloft. In contrast external forcing from the deeper boundary layer may still have an influence on weak, nocturnal surface flows when the surface layer is weakly stratified as is shown for the case of low-level jets. / Graduation date: 2013

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 97-106).

Certaines observations suggèrent une influence de la vallée du Saint-Laurent sur la distribution des averses à sa surface. D'autre part, depuis quelques années, les membres du "'Stormy Weather Group" ont enregistré sur films de 35-mm les échos apparaissant sur un écran de radar doté d'un indicateur panoramique à altitude constanto (IPAC). L'utilisation de ces films permet à l'auteur d'approfondir le sujet par l'identification des premiers échos et le tracé de leur trajectoire subséquente. Des dossiers, établis pour 76 premiers échos, relient ceux-ci à la surface et au profil du terrain. [...]