The MJO and Annual Rainfall in California

Several hydro-climate indices are used to characterize the strength and cycle of ENSO, to measure activity of the Madden-Julian Oscillation (MJO), which is the largest element of intra-seasonal (30 – 90 days) variability in the tropics, and to characterize several additional hydro-climate indices that reflect changes in pressure and height anomalies, circulation anomalies, and SSTs throughout the globe. Several of these indices, those related to ENSO and the MJO in particular, have been linked to variability in precipitation within the United States and hurricane genesis in the Atlantic Ocean.
The potential long-term (i.e. low-frequency) correlation between all indices and precipitation throughout the State of California was tested using the Hydro-FIT (HydroMetriks – Frequency Intensity Tool) software, which has the capability to identify links between nearly 40 different climate indices and various meteorological variables over a user-specified period, which is defined by a beginning month, duration, and lag time. The beginning month and duration, which are varied to optimize the correlation, specify the period of precipitation, while the lag time determines the beginning month for the period over which each climate index is averaged. “Long-window” correlation analysis, as opposed to conventional correlation analysis, uses longer durations of around 60 months, which was found to produce optimal results, and a longer lead time of 12, which facilitates the prediction of annual precipitation.
Initial results identifying correlations between long-term precipitation and low-frequency oscillations of hydro-climate indices for locations within California at a lead time of 12 months are shown in the figure above; indices and correlation levels are indicated by each symbol's shape and size, respectively. It is observed that the activity of the MJO has a dominating influence on 12-month precipitation throughout most of California with Pearson's correlation coefficients > 0.80 in many locations.

Leave a Reply