The Relation Between Sub-Monthly Retrograde Disturbances and East Asian Cold Surge

Abstract:

Cold-air outbreak is a major wintertime phenomenon in East Asia characterized by a rapid shift of the center of Siberian High southward, causing dramatic drops in temperature across the Asian continent. Understanding the mechanisms for the onset of cold surge has been a long-standing problem of theoretical and practical interests. Takaya and Nakamura conjectured that westward-moving high-pressure disturbances coming from the North Pacific may trigger the initial cold-air outbreak. This study examines this hypothesis, guided by a newly created catalog of retrograde-wave events. A recent analysis by the authors has shown that the retrograde disturbances are associated with a poleward extrusion of low potential vorticity air in Central Pacific, followed by the westward movement of a detached low PV (high pressure) vortex towards the Asian continent. Based on this insight, this work uses tracking of the low PV center to determine the timing of arrival of retrograde disturbances at the Asian continent. The timing of cold surge is determined by tracking the expansion of the high-pressure dome, and the sudden drop of temperature at its leading edge, across the Asian continent. The results from these analyses are synthesized to determine the causality between retrograde waves and cold surge. A case from the 1979-80 winter, associated with an extraordinarily strong retrograde-wave event, is found to exhibit the conjectured causal relation with retrograde disturbances as the precursor for cold surge. The detailed structure of atmospheric circulation for this case will be discussed. A further discussion will be presented on a systematic analysis through other major cases with an overlap between a retrograde-wave event and the onset of cold surge.