Signals of tropical processes as seen in Southern California precipitation

Precipitation in Southern California is the end result of processes occurring over a wide range of scales. Although topography has been acknowledged as playing a critical part in producing the variability of California climate, there is increasing interest in understanding the role of tropical processes on midlatitude precipitation. As of late, and in particular, the effect of intraseasonal processes, such as the Madden and Julian Oscillation, has been explored. By way of determining if signals of the MJO are present, Fourier techniques have been used to analyze long precipitation records in several areas of Southern California. In addition, a more direct investigation of the correlation between tropical processes and California rainfall has been made. This was accomplished by using a nineteen-year record of Outgoing Longwave Radiation (OLR) in the tropical Pacific as a cloud proxy, and a precipitation record of equal length. Analysis of these two time series indicated coherence in the spectral region characteristic of the MJO.