Characteristics and dynamics of the severe drought over southern China between January and May 2011

Abstract

Between January and May 2011, southern China suffered perhaps the most severe drought since 1954. This investigation was carried out based on OLR (Outgoing Long-wave Radiation) data derived from NOAA/AVHRR satellite observations, precipitation records at 753 meteorological stations in China and NCEP reanalysis data during 1990 and 2011. This was done by first calculating the January to May climate averages of all required atmospheric parameters during 1990 and 2011, and then calculating the January to May 2011 anomalies (the difference between the parameter value in January to May 2011 and its climate average), with the goal to understand the dynamic and thermal mechanisms behind the 2011 5 month drought. Results show that during the drought: (1) the large-scale circulations were abnormal with a strengthened Mongolian High, a weakened subtropical high and abnormal northerly winds prevailing over southern China and the South China Sea; (2) the air was drier due to the anomalous deep dry-cold air column at middle and lower levels over southern China (linked to the northerly wind from the Mongolian anticyclone and the northwesterly wind from the Yellow Sea cyclone); (3) the abnormal air temperature structure, i.e. warm at higher levels (due to the abnormal South Asian High) and cold at middle and lower levels (due to the anomalous deep dry-cold air column over southern China), and (4) a formation of an abnormal mesoscale circulation structure, with the cyclonic convergence at the mid-level low (due to the Yellow Sea cyclone), the anticyclonic divergence at the low-level small high (due to the Mongolian anticyclone) and the resulting abnormal vertical downward movement over southern China. All these factors contributed significantly to the January to May 2011 drought over southern China.