92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Sunday, 22 January 2012
The Effects of ENSO on Indiana Weather and Climate
Hall E (New Orleans Convention Center )
Gianna Hartman, Purdue University, West Lafayette, IN; and A. Pearson, R. T. Knutson, and D. Niyogi

The El Niņo-Southern Oscillation (ENSO) patterns have a remarkable link to global and regional weather and climate. ENSO is a natural oceanic feature associated with the mixing of the warmer and cooler water, changes in winds, and upwelling of waters. ENSO's signature is best monitored by changes in the Pacific Ocean sea surface temperatures (SSTs) and has three stages: El Niņo (warm phase), La Niņa (cold phase) and Neutral (or normal). An El Niņo event corresponds to warmer than normal sea surface temperatures, while a La Niņa event corresponds to cooler than normal temperatures. While ENSO events have global signatures that have been well documented for regions such as the southeast US, and southeast Asia, over the years the general perception and analysis from global studies has been that the effect of El Niņo/La Niņa events are found mostly in the coastal regions and are potentially negligible in the Midwestern United States. However, a spate of severe weather events, floods, and droughts in recent years may possibly be tied to the atmospheric conditions that accompany the different ENSO phases. This study sought to test the hypothesis that Indiana weather and climate do not have a detectable ENSO impact. Using retrospective climatological observations across Indiana over multiple decades (1950-2010), monthly temperature and precipitation data were clustered into ENSO phase years, following the NOAA Climate Prediction Center's (CPC) retrospective ENSO analysis. Taking the anomaly of the clustered data for El Niņo and La Niņa from Neutral, seasonal plots were generated to determine climatology for the weather variables of the three ENSO phases. Results showed that El Niņo years generally yielded cooler summers and variable winter conditions, while La Niņa years yielded warmer winter and summer conditions across Indiana. Results indicate that the hypothesis that Indiana weather does not have detectable ENSO impact could be rejected. Given this detectable difference from normal (Neutral phase), a freeze risk probability product was created for public dissemination through the Indiana State Climate Office. The freeze map delineates the probability of critical freeze thresholds across Indiana: freeze risk, 36⁰F; freezing, 32⁰F; and killing frost, 28⁰F. Additional data products are in development to make the climatic data usable by climate sensitive sectors.

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