Pilch Kedzierski, Robin (2013) Comparison of extratropical cyclone characteristics from atmospheric global climate model simulations at different resolutions. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 94 pp.

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Abstract

Extratropical cyclones play a key role in weather and climate at mid and high latitudes. They are simulated with Atmospheric Global Climate Models (AGCMs) for weather forecasting and future climate projections. In order to determine how realistic the simulated extratropical cyclones are at different horizontal resolutions of an AGCM, this study compares the extratropical cyclone characteristics between the T31-42-63-106-159 resolutions of the ECHAM5 model (with prescribed SST and ice coverage) and the ERA-Interim reanalysis. The results show that cyclone characteristics are indeed very dependent on resolution in the ECHAM5 runs. Fewer cyclones are detected at lower resolutions, and the cyclone characteristics get more realistic at higher resolutions compared to the ERA-Interim reanalysis, but not in a constant way. The Atlantic Ocean is much more sensitive to resolution change than the Pacific, and the prescribed sea surface temperatures and ice coverage in the Atlantic do not force a similar NAO phase in the atmosphere in the ECHAM5 model runs compared to the predominant NAO phase captured in ERA-Interim (that happened in reality), which highly affects the cyclone spatial distribution and strength. Resolutions T106 and T159 have a realistic representation of extratropical cyclone properties in most cases, but they do not match that well with ERA-Interim when taking the most extreme cases.

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