Impact of Madden–Julian Oscillation upon Winter Extreme Rainfall in Southern China: Observations and Predictability in CFSv2

Pengfei Ren,Hong-Li Ren

doi:10.3390/atmos8100192

Abstract

The impact of Madden–Julian oscillation (MJO) upon extreme rainfall in southern China was studied using the Real-time Multivariate MJO (RMM) index and daily precipitation data from high-resolution stations in China. The probability-distribution function (PDF) of November–March rainfall in southern China was found to be skewed toward larger (smaller) values in phases 2–3 (6–7) of MJO, during which the probability of extreme rainfall events increased (reduced) by 30–50% (20–40%) relative to all days in the same season. Physical analysis indicated that the favorable conditions for generating extreme rainfall are associated with southwesterly moisture convergence and vertical moisture advection over southern China, while the direct contributions from horizontal moisture advection are insignificant. Based on the above results, the model-based predictability for extreme rainfall in winter was examined using hindcasts from the Climate Forecast System version 2 (CFSv2) of NOAA. It is shown that the modulations of MJO on extreme rainfall are captured and forecasted well by CFSv2, despite the existence of a relatively small bias. This study suggests the feasibility of deriving probabilistic forecasts of extreme rainfall in southern China based on RMM indices.

Highlights

Extreme weather and climate events are typically responsible for the major environmental disasters in China
This study presented the statistical relationship between the Madden–Julian oscillation (MJO) and the probability and spatial distributions of extreme rainfall in southern China
The atmospheric circulation and moisture processes were analyzed to reveal the physical mechanism of the impacts related to the MJO

Summary

Introduction

Extreme weather and climate events are typically responsible for the major environmental disasters in China. These phenomena include droughts, flooding, typhoons, heat and cold waves and generally lead to catastrophic losses of property, agriculture, and human life. According to statistics [1], droughts, snow storms, cold waves, and dust storms occur frequently in northern China, whereas the southern portion of China is seriously affected by rain storms, typhoons, heat waves, and flooding. In early 2008, more than 100 million people were affected by the extreme cold, snow and frozen rain that occurred in southern China and more than 120 people died due to the disaster [3]. The largest threat to southern China is heavy rainfall, as this area is more vulnerable to flooding [2,3,4,5].

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