2.1 The Madden-Julian Oscillation and its influence on the predictability of precipitation

Thursday, 10 January 2013: 11:00 AM
Ballroom F (Austin Convention Center)
Charles Jones, University of California, Santa Barbara, CA; and L. Carvalho

The Madden–Julian Oscillation (MJO) has a significant role in weather and climate variability. The MJO significantly influences the occurrence of heavy precipitation around the globe. Since the MJO involves intense tropical convective heating anomalies, tropical–extratropical interactions are significant during its life cycle. Consequently, the MJO modulates the skill of weather forecasts in the medium and extended ranges especially the predictability of extreme precipitation. This presentation will begin with an overview of previous studies that examined the influence of the MJO on the occurrence and forecast skill of precipitation. As an example, the presentation will use a simple decision model to show that the value of deterministic forecasts of extreme precipitation over the contiguous United States is significantly higher when the MJO is active. Next, the presentation will discuss the predictability of precipitation over the United States during January 2005, a season marked by extreme precipitation over southern California. The Weather Research and Forecasting (WRF) model is used to investigate the predictability of extreme precipitation and the role of the MJO. The predictability experiments use two domains with 150 km and 50 km horizontal grid spacing and 35 vertical levels. The first domain (0-360, 60S-60N) is used to capture tropical intraseasonal variability associated with the MJO and teleconnection patterns to the mid-latitudes of North America; the nested domain (50 km) covers the contiguous United States. Predictability experiments are initialized during different phases of the MJO during January 2005. The presentation will discuss how different characteristics of the MJO modulate forecasts of extreme precipitation particularly over the western United States.
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