The Linkage between the Extreme Cold Air Outbreaks and Rossby Wave Breaking over East Asia

Abstract This study investigates the connection between Rossby wave breaking (RWB) and extreme East Asian cold air outbreaks (CAOs) from a diagnostic perspective. CAOs are quantified by the integral of equatorward cold air mass flux below the 280-K isentropic surface, and RWB is characterized by breaking extent, the ratio of breaking meridians to the meridional span within a region. Four key regions are identified based on cold air fluxes and RWB frequency. Results show that extreme western CAOs (WCAOs) are associated with significantly increased anticyclonic wave breaking (AWB) upstream (region 1) and cyclonic wave breaking (CWB) downstream (regions 3 and 4), while extreme eastern CAOs (ECAOs) are linked to increased upstream AWB in region 1 and reduced midstream CWB in region 3 prior to onset. Given the occurrence of RWB, these events also influence cold air flux strength and the occurrence of extreme CAOs, indicating a reciprocal relationship between CAO and RWB over specific regions. Composite analysis reveals three distinct synoptic evolution archetypes: extreme WCAOs coincide with upstream AWBs in region 1 and CWBs in region 3, while ECAOs are preceded either by AWBs in region 1 about 3 days prior or by CWBs in region 3 around 6 days earlier. It further shows that different extreme CAOs exhibit distinct wave evolution patterns: the inverted omega-shaped circulations associated with WCAOs originate from a localized wave train over central Russia, while those linked to ECAOs stem from a global wave train from southeastern North America to the North Pacific.