Tropical–Extratropical Interactions Associated with East Asian Cold Air Outbreaks. Part II: Intraseasonal Variation

Abstract

Intraseasonal variations of East Asian cold air outbreaks (CAOs) in relation to the tropical atmosphere during 34 winters (DJF) are investigated. This study is a continuation of Part I, which discussed the interannual variability of East Asian CAOs. Two types of quantitative East Asian CAOs, western and eastern CAOs, are examined. Their variations are identified by the zonal integration of equatorward flux of cold air mass (CAM) below 280 K at 45°N over 90°–135°E and 135°E–180°. A day-lagged regression analysis reveals that peaks of intraseasonal western and eastern CAO events are preconditioned by large-scale tropical convection anomalies resembling particular phases of the Madden–Julian oscillation (MJO). Western CAO events tend to occur when the convective phase of the MJO crosses over the Maritime Continent. In contrast, eastern CAO events are triggered by the MJO over the western Pacific. Observations of MJO-related atmospheric anomalies indicate the important roles of poleward Rossby wave trains in affecting extratropical East Asian CAOs. The barotropic Rossby waves develop negative geopotential height anomalies in midlatitude East Asia, which then induce a low-level equatorward cold airflow. Several experiments in an atmospheric model using prescribed MJO-like heating anomalies demonstrate that the Maritime Continent MJO and the western Pacific MJO clearly affect the equatorward CAM flux over the western and eastern CAO regions, respectively. Compared with the western CAO, the eastern CAO shows a more robust response to the MJO because of stronger wave activity during the western Pacific MJO.

Impact of cold surges on the Madden‐Julian oscillation propagation over the Maritime Continent

“…The MJO‐related heating may modulate the extratropical circulations including cold surges. Simple general circulation models have been widely used to identify the circulation responses to prescribed tropical heating forces (Matthews et al, ; He et al, ; Guo et al, ; Abdillah et al, ). To estimate the circulation responses to heating anomalies associated with MJO‐C, we perform a numerical experiment using a simple baroclinic model with prescribed heating that is a mimic of precipitation‐induced latent heating (Figure a), and the results are shown in Figure S3.…”

“…The MJO-related heating may modulate the extratropical circulations including cold surges. Simple general circulation models have been widely used to identify the circulation responses to prescribed tropical heating forces (Matthews et al, 2004;He et al, 2011;Guo et al, 2015;Abdillah et al, 2017). To estimate the circulation responses to heating anomalies associated with MJO-C, The values in brackets indicate SDs between cases, and asterisk denotes statistically significant departures from climatology at the 95% confidence levels.…”

Strong Linkage of El Niño–Southern Oscillation to the Polar Cold Air Mass in the Northern Hemisphere

“…In the extratropics, the SAT has also a good relationship with ENSO through the signature of PCAM anomalies (Figures 2a and 2e). Previous studies showed that the increase or decrease in the PCAM amount indicates cooling or warming of the SAT, respectively (Abdillah et al, 2017(Abdillah et al, , 2018KA15;Shoji et al, 2014). Here we will quantify the robustness of their relationship.…”

“…Previous studies reported that the distribution of the PCAM could be remotely controlled by variability in the tropics at both interannual (Abdillah et al, 2017;Kanno et al, 2017) and intraseasonal (Abdillah et al, 2018) time scales. The mechanisms appear to rely on the development of a poleward Rossby wave train excited by tropical convection anomalies (Hoskins & Karoly, 1981;Sardeshmukh & Hoskins, 1988;Trenberth et al, 1998).…”

“…The mechanisms appear to rely on the development of a poleward Rossby wave train excited by tropical convection anomalies (Hoskins & Karoly, 1981;Sardeshmukh & Hoskins, 1988;Trenberth et al, 1998). Circulation anomalies associated with the wave train affect PCAM streams and have implications on the changes in cold air outbreaks and PCAM distributions (Abdillah et al, 2017(Abdillah et al, , 2018. However, these previous studies are limited to regional PCAM patterns.…”