Is There an Optimal ENSO Pattern That Enhances Large-Scale Atmospheric Processes Conducive to Tornado Outbreaks in the United States?

AbstractThe record-breaking U.S. tornado outbreaks in the spring of 2011 prompt the need to identify long-term climate signals that could potentially provide seasonal predictability for U.S. tornado outbreaks. This study uses both observations and model experiments to show that a positive phase TransNino may be one such climate signal. Among the top 10 extreme outbreak years during 1950–2010, seven years including the top three are identified with a strongly positive phase TransNino. The number of intense tornadoes in April–May is nearly doubled during the top 10 positive TransNino years from that during 10 neutral years. TransNino represents the evolution of tropical Pacific sea surface temperatures (SSTs) during the onset or decay phase of the El Nino–Southern Oscillation. A positive phase TransNino is characterized by colder than normal SSTs in the central tropical Pacific and warmer than normal SSTs in the eastern tropical Pacific. Modeling experiments suggest that warmer than normal SSTs in the easte...