Warm Core Structures in Organized Cloud Clusters Developing or Not Developing into Tropical Storms Observed by the Advanced Microwave Sounding Unit

Abstract

The temperature profiles of organized cloud clusters developing or not developing (nondeveloping) into tropical storms (TSs; maximum surface wind >34 kt) over the western North Pacific in 2004 were investigated using Advanced Microwave Sounding Unit (AMSU) observations in combination with the independently created early stage Dvorak analysis. Typical temperature profiles of the developing and nondeveloping cloud clusters were compared. From this comparison, positive upper-troposphere temperature anomalies were found in both cluster types; however, the spatial extent of the temperature anomalies for the developing cloud clusters was larger than those of the nondeveloping cloud clusters. Statistical analysis was performed on the temperature anomalies near the center of all clusters retrieved from AMSU observational data. Findings indicate that the area-average temperature anomalies increased along with the intensity of the clusters indicated by the Dvorak T-number classification. Using time series analysis of upper-level temperature anomalies associated with these cloud clusters, a definition of warm core structures showing the temperature anomaly greater than a threshold (WCT) was created. WCT exists when the area averaged temperature anomaly exceeds 0.9 K. Using this definition, almost 70% of the cloud clusters that had WCTs later became TSs, while 85% of those that did not have WCTs eventually dissipated without being classified as a TS. For the WCT clusters that developed into TSs, the lead time from the detection of their AMSU-based WCT to their classification as TSs was 27.7 h. These results indicate that there is a good possibility that the detection and forecasting of tropical cyclone formation, particularly those storms that later may become classified as TSs, will be improved using temperature anomalies derived from AMSU data.