Investigating Trends in Lower Tropospheric Heat Content and Heat Waves over the Central USA Using Equivalent Temperature (1951-2011)

Author

Zachary Andrew Heern, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2013

Degree Name

Master of Science

Department

Geography and Environmental Resources

First Advisor

Schoof, Justin

Abstract

Equivalent temperature is an atmospheric variable that combines both dry static energy (associated with temperature) and moist static energy (associated with moisture). Changes in equivalent temperature therefore reflect changes in total surface energy content. This research is concerned with quantifying trends in equivalent temperature and its subcomponents at 8 National Weather Service (NWS) 1st Order stations in the central USA. Data quality control was conducted and time series and time-varying percentile trends of maximum and minimum equivalent temperature and its subcomponents were developed for each of the stations on the daily scale; along with a heat wave trend analysis. It was found that there is an overall positive trend in lower tropospheric heat content over the last 60 years--driven primarily by increases in low-level moisture. The largest changes in equivalent temperature occurred during spring and fall, with some of these trends as large as 5 deg. Celsius/50 years. Furthermore, it was found that there is an increase in the number of high humidity heat wave events and that these types of events are more frequent than low humidity events; which saw a slight decrease in frequency. Interestingly, one station (Nashville, TN) exhibited a slight negative trend in equivalent temperature maxima, which may be due to synoptic-scale influence such as the Great Plains low-level jet. The results demonstrate that equivalent temperature provides a different perspective than temperature for assessing regional climate change.