Document Details
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Document Type |
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Thesis |
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Document Title |
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PREDICTABILITY OF EXTREME PRECIPITATION EVENTS AND THEIR RELATIONSHIP WITH LARGE-SCALE PHENOMENA DURING THE WET SEASON OVER THE KINGDOM OF SAUDI ARABIA القدرة على التنبؤ بحالات الهطول المتطرفة وعلاقتها بظواهر الأنظمة الحركية العالمية خلال الفصل الرطب على المملكة العربية السعودية |
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Subject |
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Faculty of Meteorology, Environment and Arid Land Agriculture |
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Document Language |
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Arabic |
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Abstract |
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An assessment of the Extreme Precipitation Events (EPEs) is important because of their potential impacts on the local livelihood, ecosystem, and water resources. In this Thesis, the EPEs during the wet season (Nov-Apr) over Saudi Arabia and their association with large-scale circulations particularly over the mid-latitude are analyzed. Moreover, an attempt is made to improve the EPEs predictability and forecast by using Saudi King Abdulaziz University Global Climate Model (Saudi-KAU GCM) simulations, Weather Research and Forecasting (WRF) Model simulations, and satellite imageries from Meteosat Second Generation (MSG).
The frequency, composite and correlation analyses are performed to evaluate the statistics of EPEs and their teleconnections using observed station and reanalysis datasets. The EPEs are defined by applying a non-parametric (95th percentile) approach using observed daily precipitation data for the period 1984-2016 obtained from 27 meteorological stations over Saudi Arabia. During the wet season, the frequency of the EPEs (≥25mm/day) is higher over northeastern, central and southwestern areas of Saudi Arabia. The composites and correlation analyses show that the EPEs over Saudi Arabia are associated with mid-latitude circumglobal wave train (CGT). The CGT modulates the upper-level trough over the Arabian Peninsula along with the surface anomalous low-pressure system that enhances moisture flux and convergence, favoring the occurrence of EPEs over the region. A lead-lag relationship between 500 hPa geopotential heights and the EPEs over Saudi Arabia shows that the mid-latitude CGT pattern becomes visible few days before the onset of EPEs and decays afterward. Simulations from Saudi-KAU GCM also confirm the presence of CGT in the mid-latitudes favoring the occurrence of EPEs over Saudi Arabia.
The EPEs over Saudi Arabia are also associated with El Niño Southern Oscillation (ENSO). During the warm (cold) ENSO phase the frequency of EPEs increases (decreases) over the country. It is also found that positive CGT phase is associated with warm ENSO (El Niño) phase while negative CGT phase is linked with cold ENSO (La Niña) phase. ENSO and CGT cause the upper atmospheric geopotential heights and wind anomalies which generate suitable conditions for the occurrence of EPEs over Saudi Arabia. Moreover, the El Niño (with CGT in positive phase) enhances the EPEs frequency whereas, in case of La Niña (with CGT in negative phase) the EPEs frequency is reduced over Saudi Arabia. Madden-Julian Oscillation (MJO) also impacts EPEs occurrence over Saudi Arabia as increased (decreased) frequency is observed during 1, 2, 7, 8 (3, 4, 5, 6) MJO phases.
To improve the forecast of the EPEs, selected extreme precipitation cases over different climatic regions of Saudi Arabia during the study period were simulated using the WRF model. It is found that forecast of the EPEs can significantly be improved by selecting the suitable cumulus schemes, within the WRF model. Moreover, cloud top temperature from MSG satellite imageries can serve as proxy to heavy rainfall which can improve the nowcasting of an upcoming extreme precipitation event. |
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Supervisor |
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Prof. Mansour Almazroui |
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Thesis Type |
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Doctorate Thesis |
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Publishing Year |
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1441 AH
2019 AD |
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Added Date |
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Thursday, December 5, 2019 |
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Researchers
| رانا محمد عاطف | Atif, Rana Mohammed | Researcher | Doctorate | |
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