Decadal change of January and July persistence of monthly mean 500 hPa geopotential height anomalies

Abstract

The decadal variations of January and July persistence of monthly mean 500 hPa geopotential height (GHT) anomalies and associated persistence changes of sea surface temperature anomalies (SSTA) in the tropical oceans are investigated. January persistence of GHT anomalies in the most tropical regions exhibits a decadal change, with a sharp increase after the mid-1970s. This increase has been found to be closely associated with the enhanced persistence of SSTA in the equatorial central-eastern Pacific. July persistence of GHT anomalies in the most tropical regions and Asian regions shows significant decreasing trends between the 1950s and 1990s. The weakened effect of the ENSO on the Indian summer monsoon (ISM) circulation may be a possible reason why July persistence of GHT anomalies in the ISM region has been persistently decreased. The decreased persistence of SSTA in the tropical Indian Ocean, tropical North Pacific and tropical Atlantic possibly contributes to the decrease of July persistence of GHT anomalies in the tropical regions and Asian regions. Copyright 2008 by the American Geophysical Union.