Date of this Version
JOURNAL OF CLIMA TE VOLUME 14 2469-2480
Summer rainfall in the central United States has singular interannual variations of a 3–6-yr period. Identifying the causes of these variations assures improvement in predictions of summer rainfall in the region.
A review of previous studies revealed a puzzling situation: the outstanding interannual variations of the summer rainfall in the central United States showed no persistent correlations with known influential interannual variations in the Northern Hemisphere and the El Nin ̃o–Southern Oscillation (ENSO). This study was undertaken to identify the cause of this situation and ultimately explain the causes of the observed interannual summer rainfall variations. Its results showed a teleconnection of the ENSO with the summer rainfall in the central United States. The intensity of which has varied over the last 125 years. The teleconnection was active in two epochs, 1871–1916 and 1948–78, and absent in the two epochs 1917–47 and 1979–present. This variation was associated with a multidecadal variation in both sea surface temperature and sea level pressure in the mid- and high-latitude North Pacific. In the epochs of active teleconnection, the circulation in the warm phase of ENSO favored a deformation field in the lower troposphere in the central United States causing wet summers and a reversed circulation in cold phase of ENSO yielding dry summers, a process that partially explains the interannual summer rainfall variations.
The result also showed that the variations of the teleconnection were ‘‘in phase’’ with the variation in the average surface temperature of the Northern Hemisphere. When the ‘‘abrupt warming’’ of the surface temperature developed in 1917–47 and the most recent two decades, the teleconnection broke down. Because of the limitation in data record length, this observed relationship and the persistence of the variation in the teleconnection need further investigations when additional data are available.