The recent elevated North Atlantic hurricane activity has generated considerable interests in the interaction between tropical cyclones (TCs) and climate change. The possible connection between TCs and the changing climate has been indicated by observational studies based on historical TC records; they indicate emerging trends in TC frequency and intensity in some TC basins, but the detection of trends has been hotly debated due to TC track data issues. Dynamical climate modeling has also been applied to the problem, but brings its own set of limitations owing to limited model resolution and uncertainties. The final goal of this study is to project the future changes of North Atlantic TC behavior with global warming for the next 50 years using the Nested Regional Climate Model (NRCM). Throughout the course of reaching this goal, various uncertainties and limitations in simulating TCs by the NRCM are identified and explored. First we examine the TC tracking algorithm to detect and track simulated TCs from model output. The criteria and thresholds used in the tracking algorithm control the simulated TC climatology, making it difficult to objectively assess the model's ability in simulating TC climatology. Existing tracking algorithms used by previous studies are surveyed and it is found that the criteria and thresholds are very diverse. Sensitivity of varying criteria and thresholds in TC tracking algorithm to simulated TC climatology is very high, especially with the intensity and duration thresholds. It is found that the commonly used criteria may not be strict enough to filter out intense extratropical systems and hybrid systems. We propose that a better distinction between TCs and other low-pressure systems can be achieved by adding the Cyclone Phase technique. Two sets of NRCM simulations are presented in this dissertation: One in the hindcasting mode, and the other with forcing from the Community Climate System Model (CCSM) to project into the future with global warming. Both of these simulations are assessed using the tracking algorithm with cyclone phase technique. The NRCM is run in a hindcasting mode for the global tropics in order to assess its ability to simulate the current observed TC climatology. It is found that the NRCM is capable of capturing the general spatial and temporal distributions of TCs, but tends to overproduce TCs particularly in the Northwest Pacific. The overpredction of TCs is associated with the overall convective tendency in the model added with an outstanding theory of wave energy accumulation leading to TC genesis. On the other hand, TC frequency in the tropical North Atlantic is under predicted due to the lack of moist African Easterly Waves. The importance of high-resolution is shown with the additional simulation with two-way nesting. The NRCM is then forced by the CCSM to project the future changes in North Atlantic TCs. An El Nino-like SST bias in the CCSM induced a high vertical wind shear in tropical North Atlantic, preventing TCs from forming in this region. A simple bias correction method is applied to remove this bias. The model projected an increase both in TC frequency and intensity owing to enhanced TC genesis in the main development region, where the model projects an increased favorability of large-scale environment for TC genesis. However, the model is not capable of explicitly simulating intense (Category 3-5) storms due to the limited model resolution. To extrapolate the prediction to intense storms, we propose a hybrid approach that combines the model results and a statistical modeling using extreme value theory. Specifically, the current observed TC intensity is statistically modeled with the General Pareto distribution, and the simulated intensity changes from the NRCM are applied to the statistical model to project the changes in intense storms. The results suggest that the occurrence of Category 5 storms may be increased by approximately 50% by 2055.

The spatial and temporal complexity of tropical cyclones (TCs) raises a number of scientific questions regarding their genesis, movement, intensification, and variability. In this dissertation, the principal goal is to determine the current state of predictability for each of these processes. To quantify the current extent of tropical cyclone predictability, we assess probabilistic forecasts from the most advanced global numerical weather prediction system to date, the ECMWF Variable Resolution Ensemble Prediction System (VarEPS). Using a new false alarm clustering technique to maximize the utility of the VarEPS, the ensemble system is shown to provide well-calibrated probabilistic forecasts for TC genesis through a lead-time of one week, and pregenesis track forecasts with similar skill compared to the VarEPS's postgenesis track forecasts. To quantify the predictability of TCs on intraseasonal time scales, forecasts from the ECMWF Monthly Forecast System (ECMFS) are examined for the North Atlantic Ocean. From this assessment, dynamically based forecasts from the ECMFS provide forecast skill exceeding climatology out to weeks three and four for portions of the southern Gulf of Mexico, western Caribbean and the Main Development Region. Forecast skill in these regions is traced to the model's ability to capture correctly the variability in deep-layer vertical wind shear, the relative frequency of easterly waves moving through these regions, and the intraseasonal modulation of the Madden-Julian Oscillation. On interannual time scales, the predictability of TCs is examined by considering their relationship with tropical Atlantic easterly waves. First, a set of easterly wave climatologies for the CFS-R, ERA-Interim, ERA-40, and NCEP/NCAR Reanalysis are developed using a new easterly wave-tracking algorithm. From the reanalysis-derived climatologies, a moderately positive and statistically significant relationship is seen with tropical Atlantic TCs. In relation to large-scale climate modes, the Atlantic Multidecadal Oscillation (AMO) and Atlantic Meridional Mode (AMM) exhibit the strongest positive covariability with Atlantic easterly wave frequency. Besides changes in the number of easterly waves, the intensification efficiency of easterly waves has also been evaluated. These findings offer a plausible physical explanation for the recent increase in the number of NATL TCs, as it has been concomitant with an increasing trend in both the number of tropical Atlantic easterly waves and intensification efficiency. The last component of this dissertation examines how the historical variability in U.S. landfalling TCs has impacted the annual TC tornado record. To reconcile the inhomogeneous, historical tornado record, two statistical tornado models, developed from a set of a priori predictors for TC tornado formation, are used to reconstruct the TC tornado climatology. While the synthetic TC tornado record reflects decadal scale variations in association with the AMO, a comparison of the current warm phase of the AMO with the previous warm phase period shows that the median number of tornadoes per Gulf TC landfall has significantly increased. This change likely reflects the increase in median TC size (by 35%) of Gulf landfalling TCs along with an increased frequency of large TCs at landfall.

Five statistical and dynamical tropical cyclone intensity guidance techniques available at the National Hurricane Center during the 2003 and 2004 Atlantic and Eastern North Pacific seasons were evaluated within three intensity phases: (I) formation; (II early intensification; and (III) decay. During the formation phase, the Decay Statistical Hurricane Intensity Prediction (DSHIPS) technique was the best technique in both basins. When the forecast errors during formation exceed +/- 10 kt, the statistical techniques tend to over-forecast and the dynamical models tend to under-forecast. Whereas DSHIPS was also the best technique in the Atlantic during the early intensification stage, the Geophysical Fluid Dynamics Laboratory model was the best in the Eastern North Pacific. All techniques under-forecast periods of rapid intensification and the peak intensity, and have an overall poor performance during decay-reintensification cycles in both basins. Whereas the DSHIPS was the best technique in the Atlantic during decay, none of the techniques excelled during the decay phase in the eastern North Pacific. All techniques tend to decay the tropical cyclones in both basins too slowly, except that the DSHIPS performed well (13 of 15) during rapid decay events in the Atlantic. Similar error characteristics had been found in the western North Pacific.

The Air Force Weather Agency (AFWA) version of the Advanced Research Weather Research and Forecasting (ARW) model with a moving 4-km nested grid is examined for 10 track and intensity predictions of six western North Pacific tropical cyclones during 2005. In three of the 10 integrations, the ARW vortex tracker algorithm based on the 500-mb height minimum failed to appropriately move the nest and thus lost track of the storm vortex. For the other seven cases, the ARW track forecasts are more skillful than the AFWA MM5 forecasts and (except at 12 h) the CLIPER-type forecasts. The ARW intensity forecasts were less skillful than the MM5 and CLIPER-type forecasts at all forecast intervals, and were severely degraded by a large negative bias at the initial time. The deficiency in these intensity forecasts is shown to be related to model spin-up (lasting 12-54 h) problems caused by the lack of a bogus vortex and a cold start initialization from the interpolation of the NCEP Global Forecast System (GFS) analysis to the 12- km and 4-km grids. Thus, a more appropriate initial vortex representation will be required to improve intensity forecasts.

This work deals with climatology of mediterranean cyclones. In first chapter short description of the Mediterranean area is given, second chapter depicts climate properties of Mediterranean focussed on air temperature, sea surface temperature and precipitations. Third chapter characterises Mediterranean cyclones, briefly brings some facts about their dividing and possibilities of their cyclogenesis in the Mediterranean area. In the last chapter the influence of cyclones at least partly originating in Mediterranean on the weather in the Czech Republic is studied.

Approved for public release; distribution is unlimited. / Large-scale circulations in the 15-25 day period over the western North Pacific during northern summer were determined using the leading modes of a Singular Value Decomposition of 850 hPa winds and outgoing longwave radiation. Composites were constructed to define the wave patterns' structural characteristics. Their evolution is characterized by alternating cyclonic and anticyclonic equatorial anomalies that are linked to anomalous convective activity. Mid-latitude perturbations appear to contribute to the growth of new equatorial disturbances. Variability within the cycle is examined relative to variations in the basic state vertical wind shear and zonal wind convergence or divergence in the region equator-10ðN, 140ðE-160ðE. For the 50 cases in a basic state with easterly vertical wind shear and convergence, westward-moving waves propagate farther northwestward, wavelength contraction is greater, their orientation changes from east-west to southwest-northeast, and waves appear to be coupled with a Southern Hemisphere mid-latitude wave train. For the zonal wind divergence set, wave activity occurs farther eastward, circulations maintain a longer wavelength and more zonal orientation, and linkage with the Southern Hemisphere mid-latitudes is minimal. A statistically-significant relationship exists between the 15-25 day wave phase and tropical cyclone activity. Formation frequency and preferred locations are modulated by the 15-25 day wave. / Lieutenant, United States Navy

The region of interest in this study is the ocean area to the north of the Western Australian coast; that is, the Timor Sea. It is the tropical cyclones (TC) that generate in this area that most often affect the people and industries located in this region of Western Australia. Accordingly, it is the case that there is a continuing need to improve our understanding of these systems using both observations and numerical models. After an introduction to the problems caused by TCs in the north of Western Australia, a description is made of the study area. A review of the various meteorological systems that can be identified in the tropics is provided. This is followed by a history of research on cyclogenesis. A detailed discussion is undertaken on the current state of knowledge of tropical cyclogenesis. This theoretical understanding subsequently is applied to three case studies. Following a description of the data used and the analysis techniques, the three case studies are presented. In each case study, a system, which later becomes a tropical cyclone, is analysed during the genesis period. The three case studies examined in this thesis are, case 1 (TC Tim, 1994), case 2 (TC Elaine, 1999) and case 3 (TC Isobel, 1996). In each case, the system was studied for at least 10 days prior to it being named. This approach was adopted to ensure that any potential development was not overlooked. A system is named when it reaches sufficient intensity for gale force winds to exist in all quadrants around the centre of that system. For each case, the environment in the vicinity of the location where the system was initially identified was studied until an evolving system was identified. Monitoring of the system continued until it was named. / Observations from the Geostationary Meteorological Satellite and the Defense Meteorological Satellite Program comprised the physical data set. In parallel with this data collection activity, meteorological products from a numerical model were catalogued over the same time interval. The thesis presents comparisons of the satellite products and the model output over the study period. In part, motivated by the outcomes of this comparison, it was determined to investigate further prospects for using the array of satellite-derived products that might be more appropriate for use as a forecasting support tool. Finally, as an example, a prototype index is proposed which has potential to demonstrate the degree of development of a system. In this work, for want of a name, this index is termed the Hamilton Index (HI). It uses meteorological products derived from the microwave DMSP series of satellites and provides a temporal sequence of values of the index that are applied to monitor the developing of the TC systems in the three case studies. The meteorological variables used in the index were selected because they were accepted indicators of tropical cyclogenesis identified in the research literature. When applied to the three case studies, the HI showed a significant improvement in sensitivity to the state of development of the systems, especially when compared to the computer model data examined for the case studies.

Thesis (M.S. in Meteorology)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Patrick A. Harr, Russell L. Elsberry. Includes bibliographical references (p. 117-118). Also available online.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010. / Committee Chair: Curry, Judith A.; Committee Member: Black, Robert X.; Committee Member: Deng, Yi. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 147 p.: ill. Includes abstract and vita. Advisor: David H. Bromwich, Dept. of Geography. Includes bibliographical references (p. 140-147).