CHARACTERISTICS OF ATLANTIC TROPICAL CYCLONES FROM OBSERVATIONS

Hurricanes are the greatest natural disasters facing coastal regions of the United States and progress in forecasting their track, intensity, and point of landfall is of great interest. We present results based on: (a) statistical analysis of tropical cyclones and their connection with variations in sea surface temperature (SST) in tropical Atlantic; (b) data analysis from recent field observations that provides new insight in hurricane formation and intensification.

The increase in Atlantic hurricane (AH) frequency and intensity may be linked to the trend of increasing global temperatures. Several studies have shown that the rise in global temperatures is correlated with upward trends in sea surface temperature (SST). Such trends have been documented in all ocean regions where hurricanes are formed. We present the AH characteristics by analyzing the statistics of long-term time series, illustrating the inter-annual and decadal variability. Hurricane trajectory data, peak wind speed and the “eye” or minimum pressure all display significant variability over the last century. Power spectrum density (PSD) analysis of time series of annual AH numbers shows periods of ~2-3 years and ~ 5 years. These periods are confirmed by PSDs of the annual SST anomaly, between 30 S and 30 N, and of the annual CAR Index (the SST anomaly in the Caribbean region). The analysis presented here suggests that part of AH inter-annual variability can be directly linked to SST variations in the same region.

During July, 2005, the National Aeronautics and Space Administration (NASA) conducted the Tropical Cloud Systems and Processes (TCSP) experiment from San Jose, Costa Rica. The purpose of TCSP was to investigate the genesis and intensification of tropical cyclones. Part of this program, one goal of the experiment is understanding of mechanisms and effects of ice nucleation in tropical cyclones. Such mechanisms are important in the detailed formulation of aerosol-cloud interactions in numerical models, used in research and forecast. We present results from models and observations concerning aerosol loading in tropical Atlantic region and possible impact on cloud systems associated with tropical cyclones.