| dc.description.abstract | This study uses MM5 4DVAR to assimilate bogus vortex and satellite data to simulate Typhoon Kalmaegi (2008). There are three types of satellite data assimilated in the experiments. They are Special Sensor Microwave Imager (SSM/I) integrated water vapor (IWV), ocean wind speed (OWS) and Constellation Observing System for Meteorology Ionosphere & Climate (COSMIC) refractivity (REF) data. After applying bogus vortex data assimilation (BDA) based on 4DVAR, a cyclonic circulation with a warm core in the upper troposphere is produced. Moreover, moisture convergence near the typhoon center is induced and the location of the typhoon center is more accurate. Consequently, the simulated track and intensity of Kalmaegi (2008) were improved in these experiments with BDA.
Three group experiments are designed to study the impact of different observations. In the first group experiment, SSM/I IWV, OWS and COSMIC REF are assimilated into the Kalmaegi case individually. However, there is no significant impact on Kalmaegi simulation when applying satellite data only. In the second group experiment, only the bogus vortex data are assimilated. When assimilating the bogus vortex data, a great improvement on the track simulation is found, especially after 24 simulation hours. The third group experiment assimilates not only bogus vortex data but also different satellite data. The results indicate that the bogus vortex with REF data leads to an adjustment of the steering flow and successfully improves the simulated track. On the other hand, the assimilation of the bogus vortex with SSM/I OWS data can enhance the low-level wind, resulting in more latent heating. Therefore, it generates an environment more favorable for typhoon development. However, the simulation with assimilation of SSM/I IWV causes the correction of water vapor. In simulation of Typhoon Kalmaegi, such correction results in a more asymmetric structure of wind field and latent heat flux which appears to weaken the typhoon intensity.
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