Observing Systems Simulation Experiments on Abnormally High Surface Air Temperatures in the Tokyo Metropolitan Area Using WRF-VAR

Abstract

The impact of a foehn phenomenon on the generation of abnormally high surface air temperatures in the Tokyo metropolitan area was investigated through Observing Systems Simulation Experiments (OSSEs) by the use of the variational data assimilation system equipped on Weather Research and Forecasting model (WRF-VAR). First, an abnormally hot weather event on August 16, 2007 was simulated using the JMA’s operational meso-scale analysis data to produce “simulated observations”. Then, the vertical profiles of the simulated observations over several sites were assimilated into an initial field. Results of OSSEs demonstrated that northwesterly winds and high-temperature air associated with the foehn strongly affect the generation of the abnormally high surface air temperatures. Also, the results indicated that southerly sea breezes prevent the impact of the foehn from spreading to the southern part of the metropolitan area.