The propagation of electromagnetic (EM) waves of frequencies above 100MHz is affected by the existence and properties of the atmospheric duct, i.e. a horizontal layer in the lower atmosphere in which radio signals propagate more efficiently. Atmospheric ducts can be found in many parts of the world ocean including the Arabian Gulf. Ambient winds blowing from different directions bring air masses of different properties into the area and hence have a significant impact on the formation and strength of the atmospheric duct. However, little information is available on the long-term and intra-annual variability of wind and its effect on the ducting phenomenon in the Arabian Gulf region. This study addresses this gap by characterising the local meteorology, with a special emphasis on its effect on electromagnetic wave propagation. This study uses a new methodology to measure the persistence of Shamal wind, by considering the number of days associated with the specific wind pattern in addition to commonly used parameters such as the wind speed. In this study, thirty years (1981-2010) of observations and NCEP/NCAR reanalysis data have been analyzed to identify a long-term trend and the intra-annual variability of various wind systems. Results clearly indicate that the Shamal (the northwesterly wind) is the most frequent meteorological feature over the region; therefore it has been investigated in greater detail. The Suhaili (southerly wind) is the second important wind which can occur any time of the year but it is less frequent than the Shamal. The Al-Nashi (cold and dry northeasterly wind) wind occurs only in December, January and February. The analysis shows that the wind strength and the frequency of Shamal days over the region have decreased over the last thirty years. Variations in the occurrence of summer and winter Shamal days were studied in relation to global atmospheric phenomena, and relationships have been established, synoptically and statistically between the frequency of Shamal days and large-scale atmospheric fluctuations. These links include atmospheric fluctuations over the Caspian Sea (a correlation coefficient of 0.66) and Siberia (0.69) in summer and Greenland (0.51) and Western Europe (0.65) in winter. The frequency of winter Shamal days during December, January and February are shown to be statistically related (a correlation coefficient of 0.41) to the North Atlantic Oscillation (NAO) and (0.49) the Arctic Oscillation (AO), as they influence the pathway of the westerly depression over the north Atlantic Ocean during the winter season. It is also shown that the decline in the number of Shamal days is linked to a decrease in the number of westerly depressions. The EM wave propagation has been examined using the Advanced Refraction Effects Prediction System (AREPS) model for different representative air masses. The radiosonde data from Abu Dhabi airport used in AREPS provided evidence of the general influence of each air mass. It was found that atmospheric ducting conditions and characteristics (height, thickness, and type) were variable in the lower part of the atmosphere (surface to 6000m) as a result of changing air masses. The influence of the Shamal conditions develop an elevated duct at approximately 850mb level. The Suhaili increases the thickness of the evaporation duct. In regards to the surface based and elevated duct, Suhaili and Al-Nashi provide standard atmospheric conditions. Land and sea breezes were mostly associated with the surface based duct and sometimes elevated the duct. Atmospheric ducting could extend the range of electromagnetic wave propagation above the usual range. Good knowledge of atmospheric duct characteristics enables the efficient assessment of the range of EM propagation, which is important for a number of practical applications, for example air traffic control and rescue operations. This could include the selection of the appropriate frequency and altitude of the electromagnetic wave device (e.g. radar and/or communication systems) operating with a frequency above 100MHz to be trapped in the duct to cover long distances.

The United Arab Emirates is a new country that has had little time to accumulate a scientific heritage. Meteorologically researched and documented weather material for forecasters is virtually non-existent and that available is fragmented and anecdotal. The thesis tackles this problem by identifying weather phenomena significant to aviation in the Emirates and particularly at Abu Dhabi International Airport (ADIA). Mechanisms responsible for their development are described and applicable forecasting rules and principles are derived. Surface and upper air observation data at ADIA from 1983 to 2002 were analysed to identify the weather phenomena, their associated weather systems and for statistical analyses. When relevant, observation data at Al Ain was also used. Post-processed numerical weather prediction Global Forecast Service Eta model data are used and when and where possible radar and satellite imagery. A secondary aim is to provide information of the general seasonal climate. This was achieved by means of a literature study of the dominating weather systems and the presentation of surface and upper air mean circulation charts. Fog is the most important weather phenomenon and serious disrupter of aviation at ADIA throughout the year. It does not occur during Shamal conditions, but fog can form well inland on the edge of the Empty Quarter at the Liwa Oasis when the Shamal wind becomes light. Contrary to local belief, fog is unlikely to occur on two, or more, consecutive nights. The Shamal can last for several days and disrupt helicopter flights to the oil rigs, while anabatic and katabatic effects often make it gustier and stronger inland at Al Ain than ADIA. While dust storms occur in strong southerly winds off the desert, the Shamal can bring dust from further afield from the north as can the previously unreported Nashi wind. The sea breeze can extend about 150 km inland to Al Ain and the Liwa Oasis. Thunderstorms associated with winter upper air troughs from the west, are the main producers of rain, while occasional thunderstorms off the Hajar Mountains in the east bring some rain in summer. Tropical depressions are a rare event. / Thesis (PhD)--University of Pretoria, 2010. / Geography, Geoinformatics and Meteorology / PhD / Unrestricted

Approved for public release; distribution in unlimited. / On day five of combat operations during Operation IRAQI FREEDOM, advances by coalition forces were nearly halted by a dust storm, initiated by the passage of a synoptically driven cold front. This storm impacted ground and air operations across the entire Area of Responsibility, and delayed an impending ground attack on the Iraqi capital. Military meteorologists were able to assist military planners in mitigating at least some of the effects of this storm. This thesis examines the synoptic conditions leading to the severe dust storm, evaluates the numerical weather prediction model performance in predicting the event, and reviews metrics pertaining to the overall impacts on the Operation IRAQI FREEDOM combined air campaign. In general, the numerical model guidance correctly predicted the location and onset of the dust storms on 25 March, 2003. As a result of this forecast guidance, mission planners were able to front load Air Tasking Orders with extra sorties prior to the onset of the dust storm, and were able to make changes to planned weapons loads, favoring GPS-guided munitions. / Captain, United States Air Force