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İstanbul Teknik Üniversitesi (2011)

A Comperative Study Of Two Regional Mesoscale Models In Eastern Mediterranean Domain For A Historical Reference Period

Deniz Ural

Titre : A Comperative Study Of Two Regional Mesoscale Models In Eastern Mediterranean Domain For A Historical Reference Period

İki Orta Ölçekli Bölgesel Modelin Doğu Akdeniz Bölgesi Üzerinde Ve Tarihsel Referans Dönemde Karşılaştırmalı Olarak İncelenmesi

Auteur : Deniz Ural

Université de soutenance : İstanbul Teknik Üniversitesi

Grade : Master of Science (MS) 2011

Résumé
Global Climate Models are useful tools for predicting future climates. However their spatial and temporal resolutions are too coarse for regional climate studies. Therefore higher resolution regional climate models should be used to examine the regional climate changes. Eastern Mediterranean Region is a very interesting area for testing the performance of climate models due to its complex topography and variable climate conditions. In this study, NCAR ?s next generation non-hydrostatic mesoscale model, Advanced Research WRF (WRF-ARW) was used to analyze the regional climate of Turkey and its neighbourhood for the period of 1961-1990 and the results are compared with RegCM outputs and observations. A similar study had been performed successfully with hydrostatic ICTP-RegCM3 model that is based on MM5, the predecessor of WRF. WRF on the other hand, is superior to RegCM and MM5 in both physics, dynamics and numerics, but computationally more expensive accordingly. However, WRF is still underdevelopmentandrequiresmoreperformanceanalysesforitsvalidationinregional climate modelling. Therefore the result of this study is important for the validation of WRF in long term regional climate studies. The WRF Model was used to downscale NCEP-NCAR Reanalysis data over a domain that spans from 13 E - 55 E and 28 N - 51 N. The grid resolution is 27 km in both directions and there are 144 by 100 grid points in east-west and south-north directions respectively. In the vertical direction 35 levels are used and that happens to be the twice the vertical resolution of RegCM3 run. The time step is 60 seconds and the model outputs are saved every 3 hours. Physics and dynamics options are especially chosen for long term regional climate runs and GISST data is used as the additional SST input. In order to handle the steep topography of the domain, MODIS dataset with 30 arcsecond resolution and gravity wave drag (GWD) was used. Monthly means of the model outputs show that WRF is superior to RegCM over complex topography. WRF can simulate regional features better than RegCM. Generally, WRF has a negative bias in surface temperatures but it can solve the temperature distribution better than RegCM that has a positive temperature bias. Especially in Mediterranean shores the difference is very clear. Moreover GWD enabled WRF runs can solve the temperature field better over steep topography. Boundary conditions are also handled better in WRF than in RegCM. RegCM generates superfluous distributions in southern and eastern boundaries whereas such problems are not seen in WRF results. Statistical analyses have shown that WRF has a greater spatial correlation and smaller spatial variability than RegCM when compared against observations.

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