ENSO and short duration extreme climate events in the U.S., 1850-2007

More than 250 U.S. Forts daily station observation time series are currently available from the NOAA Climate Database Modernization Program (CDMP). The lengths of these time series vary from 10 to more than 40 years during the 19th Century. Spatial coverage continues to improve as the CDMP progresses. There are now enough data to go beyond station-by-station analyses done earlier to examine the spatial patterns of response to a large scale climate forcing like ENSO. Many ENSO events are most noteworthy when punctuated by short term climate extremes, such as those that can only be discerned by using daily data. The main goal of this paper is to compare short term extremes evident during warm and cold ENSO events occurring during the 19th Century with those occurring during the late-20th Century, revealing spatial and temporal responses of U.S. surface climate to ENSO under quite different base climate regimes.

An innovative approach is used to define ENSO events in a manner compatible with the modern definition used by the World Meteorological Organization, but which is robust when sea surface temperatures are non-stationary. The statistics of daily and multiple-day temperature and precipitation extremes are examined by season for ENSO events given weak, moderate, and strong classifications. In addition, last freeze and first freeze timing are also compared, as well as other growing season parameters. This work demonstrates the value and utility of increased 19th Century daily data availability through the CDMP.