Author(s):
Jongnam Choi* - Western Illinois University
Abstract:
Spatial patterns and temporal changes of apparent temperature were examined by hourly heat index values over the contiguous United States during a 45-year period (1961-2005). At lower threshold values for heat index, the normal daily frequency of maximum heat index shows no surprising spatial patterns. At higher threshold values of heat index, a distinct southwestern desert and south central Gulf coast pattern emerges for the normal daily frequency of heat index. Extreme heat index events in the southwest are driven by high surface temperature, while extreme heat index events in the south-central are driven by thermal and moisture advection from the Gulf of Mexico. Significant increasing trends were found at each threshold over most of the contiguous U.S. However, a decreasing trend is also found in the Pacific West Coast, the Intermontane West, and along the U.S/Canadian Border. This research also shows future trends in extreme heat index associated with increases in humidity and temperature in the lower troposphere.
