Characteristics and dynamics of the severe drought over southern C hina between J anuary and M ay 2011

Between J anuary and M ay 2011, southern C hina suffered perhaps the most severe drought since 1954. This investigation was carried out based on OLR ( O utgoing L ong‐wave R adiation) data derived from NOAA / AVHRR satellite observations, precipitation records at 753 meteorological stations in C hina and NCEP reanalysis data during 1990 and 2011. This was done by first calculating the J anuary to M ay climate averages of all required atmospheric parameters during 1990 and 2011, and then calculating the J anuary to M ay 2011 anomalies (the difference between the parameter value in J anuary to M ay 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 M ongolian H igh, a weakened subtropical high and abnormal northerly winds prevailing over southern C hina and the S outh C hina Sea; (2) the air was drier due to the anomalous deep dry‐cold air column at middle and lower levels over southern C hina (linked to the northerly wind from the Mongolian anticyclone and the northwesterly wind from the Y ellow S ea cyclone); (3) the abnormal air temperature structure, i.e. warm at higher levels (due to the abnormal S outh A sian H igh) and cold at middle and lower levels (due to the anomalous deep dry‐cold air column over southern C hina), and (4) a formation of an abnormal mesoscale circulation structure, with the cyclonic convergence at the mid‐level low (due to the Y ellow S ea cyclone), the anticyclonic divergence at the low‐level small high (due to the M ongolian anticyclone) and the resulting abnormal vertical downward movement over southern C hina. All these factors contributed significantly to the J anuary to M ay 2011 drought over southern C hina.