Correlation analysis of persistent heavy rainfall events in the vicinity of the Yangtze River valley and global outgoing longwave radiation in the preceding month |
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Authors: | Yanbing Tang Lu Zhao Kun Gao |
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Institution: | [1]Department of Earth Sciences, Zhejiang University, Hangzhou 310027 [2]Zhejiang Meteorological Observatory, Hangzhou 310017 |
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Abstract: | Based on the National Oceanic and Atmospheric Administration (NOAA) daily satellite dataset
of global outgoing longwave radiation (OLR) for the period of 1974--2004 and the NCEP-NCAR reanalysis
for 1971--2004, the linkage between persistent heavy rainfall (PHR) events in the vicinity of the Yangtze
River valley and global OLR leading up to those events (with 1- to 30-day lag) was investigated. The
results reveal that there is a significant connection between the initiation of PHR events over the
study area and anomalous convective activity over the tropical Indian Ocean, maritime continent, and
tropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the major
significantly anomalous convective centers have an apparent dipole structure, always with enhanced
convection in the west and suppressed convection in the east. This dipole structure continuously shifts
eastward with time during the 30-day lead period. The influence of the anomalous convective activity
over the tropical oceans on the initiation of PHR events over the study area is achieved via an interaction
between tropical and extratropical latitudes. More specifically, anomalous convective activity weakens
the Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening of
the Indian summer monsoon background state and the excitation and dispersion of Rossby wave activity
over Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result,
the condition of a phase-lock among major large scale circulation features favoring PHR events is
established over the study area. |
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Keywords: | persistent heavy rainfall events global outgoing longwave radiation the Yangtze River valley |
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