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Abstract

The changes in the typhoon intensity are a very important process. In this study, we used satellite data to analyze the cloud structure of Typhoon Longwang. Results show that the changes in the high level cirrus pattern seemed to have a connection to the typhoon intensity. During the time period from 0600UTC to 1200UTC 30 September 2005, the high level cirrus clouds of Typhoon Longwang radiated from the inner core region. The cloud area that Typhoon Longwang covered grew larger, and the pattern changed from a asymmetric to symmetric distribution during 0000UTC to 1200UTC 30 September 2005. The best track from the Joint Typhoon Warning Center also showed that Typhoon Longwang’s intensity evidently decreased, but the speed did not change as much, and the radius of 17.2 m/s wind speeds increased during that period. According to the divergence and vorticity field of the reanalysis data from the European Center for Medium Range Weather Forecasting forecast model, it shows that the outflow and rotation of the high level clouds decreased from 0000UTC to 1200UTC 30 September, which may be a key reason in why Typhoon Longwang’s intensity decreased. A vertical structure with low level inward convergence and high level anticyclonic divergence were considered to be an important factor behind the pressure deepening, leading to the typhoon’s development. However, this study shows that the high level airflow of Typhoon Longwang radiated outward, resulting in its intensity to weaken. These results demonstrate that the cloud pattern observed by satellite images still serve as a valuable approach in determining the typhoon intensity.

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