This study investigates the occurrence of extreme precipitation events in California and a possible modulation by the MJO. Daily observed precipitation from gridded hourly station data (2.0º lat x 2.5º lon) from January 1958 to December 1996 is used to define extreme precipitation events. Anomalies (20-90 days) of 5-day averages of Outgoing Longwave Radiation (OLR) from January 1979 to December 1996 are used to identify tropical convective anomalies associated with the MJO. In addition, anomalies (20-90 days) of 5-day averages of zonal winds (U) at 200 hPa and 850 hPa derived from the NCEP/NCAR reanalysis from January 1958 to December 1996 are employed to characterize large-scale circulation anomalies related to the MJO.
Based on 5-day precipitation totals, three types of extreme events are defined: type I if the 5-day total precipitation exceeds 5% of the total annual precipitation, type II if the 5-day total precipitation exceeds 10% of the total annual precipitation and type III if the 5-day total precipitation exceeds 15% of the total annual precipitation. The results show that nearly twice as many extreme precipitation events of type I and II in central and southern California occur when tropical convective and circulation anomalies are large and associated with the MJO.
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