A new look at the midlatitude–MJO teleconnection in the northern hemisphere winter

Abstract

SUMMARYThe midlatitude to Madden-Julian (MJO) teleconnection in the northern hemisphere wintertime was investigated using twenty years of outgoing long-wave radiation and National Center for Atmospheric Research/National Centers for Environmental Prediction re-analysis data. It is revealed through empirical orthogonal functions and regression analyses that the tropical upper-level divergence (convergence) associated with enhanced (reduced) tropical convection has a subtropical counterpart of upper-level convergence (divergence). As the convective region of MJO moves eastward from the Indian Ocean to the western Pacific, the divergent circulation connecting the Tropics and subtropics moves eastward. From an analysis of vertical motion diagnosed by the generalized omega equation, it was revealed that the position of the subtropical Rossby gyres of the MJO with respect to the AsianPacific jet was the most important factor affecting the existence of the localized divergence (convergence) and associated lower-level vertical motion in the subtropics. As the subtropical Rossby gyres pass by the longitudinal position of the Asian-Pacific jet, vertical motion occurs to meet the balance required by quasi-geostrophic theory. Since this anomalous vertical motion is large enough to cause convection at that region, the diabatic heating process reinforces the vertical motion. Furthermore, other dynamical processes neglected in quasi-geostrophic theory are activated and contribute to the vertical motion balancing the diabatic heating. As a result of the vertical motion near the jet entrance region in the subtropics, the vorticity advection by vertical wind and the tilting of vorticity become important. Since these two terms are similar in shape and magnitude, they reinforce each other during the development phase of the midlatitude-MJO teleconnection. Combining these two terms, we define the baroclinic jet source (BJS). In order to evaluate the BJS as a source for the midlatitude-MJO teleconnection, a numerical experiment is carried out. The linear barotropic model is forced by only two terms, yet the model captured clearly the main feature of the midlatitude-MJO teleconnection.

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.…”

“…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.…”

The Impact of Trade Surges on the Madden-Julian Oscillation under Different ENSO Conditions

“…Consistent upper-level highs are also observed over the north Pacific especially north of 30°N in this study (not shown). The role of the Asian jet is noteworthy for the formation of the north Pacific highs (e.g., Kim et al 2006). A wave train along the jet excited by MJO-related divergence winds might be an important factor (Hsu 1996;Mori and Watanabe 2008).…”

“…Many previous studies showed that intraseasonal fluctuations of extratropical circulation accompany the eastward propagation of MJO convection (e.g., Knutson and Weickmann 1987) though its mechanism has not been clearly explained. A significant extratropical response over the north Pacific to the MJO convection over the Indian Ocean occurs in the boreal winter associated with the Asian jet (e.g., Hsu 1996; Kim et al 2006). With respect to forcing from the extratropics to the tropics, trade surges from an extratropical high over the north Pacific are observed at a time of active MJO convection over the Indian Ocean or maritime continent (e.g., Hsu et al 1990;Kiladis et al 1994).…”

Seasonal-to-Decadal Climate Forecasting

“…The Madden Julian oscillation (MJO), in the tropical West Pacific and Indian Oceans, is characterised by an eastward progression of atmospheric convection (Madden and Julian 1971). Studies suggest evidence of teleconnections between the MJO and variability in the extratropics in the Pacific basin (Kim et al 2006) and Atlantic (Cassou 2008) on monthly timescales. Seasonal predictability is also thought to arise from interactions between the troposphere and stratosphere, associated with the quasi-biennial oscillation (QBO) (Baldwin et al 2001) and sudden stratospheric warming (SSW) (Marshall and Scaife 2010) which can have an important influence on winter conditions, particularly over Europe ).…”