The interannual variability of summer upper-tropospheric temperature over East Asia

Abstract

By using 55-yr NCEP-NCARreanalysis data, two dominant interannual variabilitymodes of summer uppertropospheric (500-200 hPa) temperature over East Asia are identified. The first empirical orthogonal function (EOF1) mode in its positive sign features amonopole cooling anomaly, while the secondmode (EOF2) features ameridional dipolemode, with the positive (negative) center located south (north) of 35°8N. The EOF1 (EOF2) mode is associated with ENSO developing (decaying) summers. They are the result of dynamical teleconnections remotely induced by ENSOand local moist processes. During the El Niño developing summer, the Indian summer monsoon precipitation decreases and forces the Silk Road teleconnection pattern at 200 hPa, featuring an anomalous cyclone over the East Asian continent. Coupled with the anomalous northerly wind in easternChina at 850 hPa, rainfall over north (south) China is suppressed (enhanced). The anomalous cyclone in the upper troposphere, associated verticalmotion, and precipitation contribute to the heat and vorticity balance and maintain the monopole cooling. In the El Niño decaying summer, driven by the combined effects of a local SST anomaly and remote warm SST anomaly forcing from the Indian Ocean, precipitation is reduced over the western PacificOcean. Less latent heat is released and forces the Pacific-Japan teleconnection pattern along the EastAsian continent, inducing a tripolar rainfall anomaly overEastAsia. The tripolar precipitation and vertical motion anomalies and the zonal extended cyclonic anomaly in the upper troposphere provide the heating and momentum flux balance and maintain the temperature anomaly pattern during the ENSO decaying summer. © 2012 American Meteorological Society.