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Document Type |
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Thesis |
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Document Title |
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PLANETARY BOUNDARY LAYER PARAMETERIZATION IN THE SAUDI-KAU GLOBAL CLIMATE MODEL AND ITS IMPACT ON CLIMATE PREDICTIONS تمثيل الطبقة الحدية في نموذج المناخ العالمي لجامعة الملك عبد العزيز-السعودي وتأثيره على التوقعات المناخية |
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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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A moist Planetary Boundary Layer (PBL), namely the University of Washington (UW) scheme is introduced into the Saudi King Abdulaziz University (Saudi-KAU) Atmospheric Global Climate Model (AGCM). The UW scheme estimates the turbulence due to cloud-topped closure, which is a novel development in the model. It maintains the low-level stratocumulus clouds near inversion layer realistically, which was overestimated in case of the default dry PBL scheme namely as Holtslag and Boville (HB) due to the missing cloud-topped turbulence closure. The UW scheme improves the modeled stratocumulus clouds in both winter and summer seasons with a significant impact in boreal summer season. The stronger heat and momentum diffusivity is noted in UW compared to that of HB run. The global rainfall bias is reduced about 18% during winter, and 22% in summer with UW compared to HB run, which is consistent with the reduction of surface fluxes biases and improved radiative balance. Significant reduction of summer precipitation bias is noted over Arabian Peninsula. The global temperature bias is reduced about 0.63 °C in UW compared to that of 0.8 °C in HB scheme during summer season, while not much difference is noted for boreal winter season. Further, the lower tropospheric moisture and temperature biases are reduced over most parts of the globe including tropics, which may have positive implications on seasonal to intraseasonal variability.
We also investigated the Arabian Peninsula summer (JJA) seasonal rainfall relationship with the El Niño Southern Oscillation (ENSO) phenomenon and found a negative (-0.43) correlation between them. This relationship is established through an atmospheric teleconnection which shows upper-level convergence anomalies over the southern Arabian Peninsula compensating the central-eastern Pacific upper-level divergence anomalies for the warm (El Niño) ENSO phase. The upper-level convergence over southern Arabian Peninsula leads to sinking motion, low-level divergence and consequently to reduced rainfall. The vice-versa happens for the cold (La Niña) ENSO phase. Predictability during the El Niño events is higher due to the stronger signal, and reduced noise compared to that of La Niña years. This shows that drought conditions are predictable for the Arabian Peninsula, which is important to manage the local water and agricultural resources. The ensemble simulation shows that this ENSO AP summer rainfall relationship is stronger with UW compared to that of HB run.
The Arabian Peninsula seasonal rainfall prediction skill is improved by 32% (43%) in summer (winter) with the UW compared to the HB run. Moreover, 200-hPa circulation anomalies over the Pacific and North American (PNA) region are more likely an observations with the UW as compared to the HB run, but there is not much difference in the predictability for two schemes. Furthermore, the Aqua simulations show a stronger tropical precipitation response with UW compared to that of HB scheme. A new PBL scheme “KAU” is proposed, which combines local, non-local, and cloud-topped turbulence closures and this scheme is a part of the latest release of the Saudi-KAU model. |
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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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1439 AH
2018 AD |
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Co-Supervisor |
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Prof. Ahmed Alamoudi |
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Added Date |
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Monday, January 15, 2018 |
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Researchers
| محمد عدنان عابد | Abid, Muhammad Adnan | Researcher | Doctorate | |
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