Systematic Variation in Wintertime Precipitation in East Asia by MJO-Induced Extratropical Vertical Motion

Abstract

The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden-Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974-2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3-4 mm day Ϫ1 , which corresponds to the climatological winter-mean value.Composite analysis with respect to the MJO suggests that the MJO-precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia uppertropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.

The Madden-Julian Oscillation and Extratropical Teleconnection over East Asia during the Northern Winter in IPCC AR4 Climate Models

“…Significant anomalous easterlies over the tropical Pacific, apparently the result of a Kelvin-Rossby wave response, merge with anomalous westerlies in the east of the enhanced MJO convection peak and turn into southwesterlies over South Asia. This circulation pattern is consistent with the results of Kim et al (2006) and Jeong et al (2008). Notably, a barotropic structure is established to the east of Japan over the western North Pacific, as indicated by the upper-level anomalous anticyclonic circulation (A2 in Fig.…”

“…The increase and decrease of the precipitation and convective activity over the wintertime East Asia associated with the MJO are roughly coincident with the enhancement and suppression of synoptic-scale transient activity at low-levels, respectively (e.g., Jeong et al 2008;He et al 2011). When the MJO convective signal is located in the Indian Ocean, the intensification of the upper-level anticyclonic circulation by the MJO as part of a wave train over Japan and the western North Pacific (as A2 in Fig.…”

“…Along with the upper-level circulation, the convective variability in the EANP region related to the MJO signal is influenced by the low-level circulation (e.g., Jeong et al 2008). Figure 6 shows the 850 hPa regressed circulation and moisture anomalies to the MJO indices at day 0 in OBS and the 16 models.…”

“…Significant circulation anomalies often cause climate anomalies in East Asia. Several studies have investigated the remote influences of the MJO on the weather in East Asia (e.g., Jeong et al 2008;Kim et al 2006;He et al 2011). These researchers demonstrated that the observed precipitation and convective activity increase considerably in the wintertime East Asia region when the center of convection associated with the MJO is located over the tropical Indian Ocean, while they decrease when the center is located over the western Pacific.…”

“…Kawamura et al (1996) showed that the MJO-related convective forcing excites a barotropic Rossby wave train extending to the central North Pacific that is approximately along the great circle. Jeong et al (2008) suggested that the relationship between the MJO phase and precipitation anomaly can be explained by the strong vertical motion anomalies that occur near the entrance region of the East Asian uppertropospheric jet and the moisture supply in the lower troposphere. He et al (2011) proposed a direct link between the MJO and East Asian precipitation through the local Hadley cell and a circulation anomaly with the equatorially trapped Rossby gyres forced by the MJO heating.…”