The development of a heavy thunderstorm climatology in Saudi Arabia based on observations, analyses and numerical simulations
Ghulam, Ayman S.
PublisherUniversity of East Anglia
MetadataShow full item record
Abstract Thunderstorms can often result in direct threat to life and property when associated with heavy rain, hail, gusting wind and lightning. However, these events have received limited attention from a forecaster's and climatologist's point of view in Saudi Arabia. Meteorological research in Saudi Arabia has very limited; lack of data places severe restrictions on such work. The purpose of this research is to achieve a better understanding of thunderstorm formation in Saudi Arabia, advancing the understanding of the atmospheric processes that influence the initiation of storms and how they evolve over different types of terrain in Saudi Arabia; with the new datasets available now, this aim is possible. This study also aims to provide useful information on thunderstorm distribution and prediction to the local forecasters in Saudi Arabia to improve forecasting methods for all seasons. It was found that the study area presents many challenging meteorological problems. The synoptic climate has not previously been well documented and thereafter, it is poorly understood. Thus, this study provides, for the first time, a long term (44-year) synoptic climatology in Saudi Arabia based on ECMWF (ERA-40 reanalysis and operational) datasets. No thunderstorm climatology currently exists for Saudi Arabia; it is difficult to capture the high temporal/spatial variability of thunderstorms in Saudi Arabia due to lack of observation network coverage. Thus, this study has to include elements including satellite based data. By utilizing data from satellite-borne lightning detectors, is now possible to learn about thunderstorm distribution, especially in places where no enough surface stations such as Saudi Arabia. Reports of thunderstorms using surface observational data in Saudi Arabia are compared here with satellite based lightning data from the Lightning Imager Sensor (LIS) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite and with satellite based Outgoing Long-wave Radiation data, with strong agreement being found between them. Analysis of these data shows seasonal variability between various geographic regions. Although both frontal and air mass thunderstorms occur in Saudi Arabia spring months are characterized by particularly frequent thunderstorm activity in the kingdom. Furthermore, both LIS and OLR show, for the first time the distribution of lightning flashes over the central and southern Red Sea and over the Arabian Gulf where no observational stations. Thus, LIS and OLR can compensate the lack and fill in the gab of surface observations in Saudi Arabia. These results will help in flight route forecast in the future. The anomaly field on heavy thunderstorm days and on dry days was investigated to address the synoptic differences between dry and heavy thunderstorm days. The results highlighted the importance of number of key drives: surface disturbances, upper tropospheric mechanisms, sea breezes and instability due primarily to high insolation over the area. Severe thunderstorm occurrences in Saudi Arabia are associated with various types of weather systems, but synoptic typing in Saudi Arabia has not until now been carried out. Based on daily MSLP at 1200UTC, analyses of the synoptic situations accompanying heavy thunderstorms using, for the first time, a hybrid classification scheme combining subjective and objective methods showed that seven synoptic types are favourable for heavy thunderstorms formation. These patterns are: The Red Sea trough, the Red Sea trough combined with the Saudi low, the Middle East low, The Saudi low, the Mediterranean low, the Sudan trough combined with the Sahara low and the Indian monsoon trough. A comparison of subjective and objective classifications revealed that the classifications into these seven types match on more than half (52%) of the days, while 48% of the days were unclassified because of the subjectivity of manual classification. Local conditions determining spatial differentiation of thunderstorm occurrence in Saudi Arabia were also taken into consideration. Modelling work concerning meteorological issues is severely limited in Saudi Arabia. In this study the PSUINCAR MM5 model was adopted, for the first time, to simulate heavy thunderstorm events associated with rainfall (less than or equal to 10mm/day) to help simulate the synoptic and meso-scale environments conductive to heavy thunderstorm events in Saudi Arabia and understand their formation mechanisms. Three nested numerical experiments have been performed with grid resolutions of 135, 45, and 15 km. The spatial and temporal distribution of simulated heavy thunderstorms offered evidence linking to additional local effect factors such as terrain, high insolation leading to instability, low-level convergence zones, sea-land breezes and the interaction between flow and topography. Overall, this study presents information on the variability in thunderstorm occurrence in Saudi Arabia and pins-point favourable environmental and synoptic conditions, and the physical mechanisms of such phenomena in addition to numerical simulations of heavy thunderstorm events in Saudi Arabia.