Occurrence of Extreme Precipitation Events in California and Relationships with the Madden–Julian Oscillation

Abstract

California receives most of the annual precipitation during the boreal winter season. Additionally, large spatial and temporal variations in the total rainfall amounts are observed. This study investigates the occurrence of extreme precipitation events in California and the modulation by the Madden–Julian oscillation (MJO). Three questions are investigated. 1) Are extreme precipitation events in California more likely to occur during active MJO than inactive periods? 2) In what phase of the MJO life cycle are extreme events more likely? 3) Are interannual variations in the frequency of extreme events in California related to interannual variations of the MJO? Daily totals derived from gridded hourly station data are used to define extreme precipitation events from January 1958 to December 1996. Outgoing longwave radiation from polar orbiting satellites (1979–96) and zonal component of the wind at 200 hPa and 850 hPa from the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis (1958–96) are used to describe the life cycle of the oscillation and its interannual variability. The results indicate that the frequency of extreme events are more common when tropical activity associated with the MJO is high, as opposed to periods of quiescent phases of the oscillation. Second, a slight preference for a higher number of events is observed when convective anomalies are located in the Indian Ocean. In this situation, low-level westerly and easterly wind anomalies are observed over the Indian and western Pacific Oceans, respectively. The analysis of the interannual variability in the amplitude of the MJO and the occurrence of extreme events over California indicates no direct and systematic relationships with the number of extreme events.