Large-Scale Midlatitude–Polar Flow Interactions Leading to Rapid Surface Ice Melt over Greenland and Sea Ice Volume Loss over the Arctic Ocean in June 2019

Flow amplification over the Northern Hemisphere contributed to rapid surface ice melting over Greenland and a large sea-ice volume loss over the Arctic Ocean in mid-June 2019. Surface ice melting over Greenland was driven by the formation of two adjacent strong upper-level blocking anticyclones. Southerly flow west of these twin blocking anticyclones transported warm, moist North Atlantic air poleward to the Arctic Ocean. Farther east, sea-ice volume loss over the Arctic Ocean accelerated after a large cutoff cyclone formed over northwestern Russia. Upper-level disturbances rotating around this cutoff cyclone triggered multiple interacting surface cyclones that consolidated into a single deep surface cyclone (< 976 hPa). Rapid sea-ice volume loss occurred where a poleward-directed flow of warm, moist air reached the Arctic Ocean on the eastern side of this deep surface cyclone. High winds from this surface cyclone likely triggered further sea-ice volume loss from wave action over the Arctic Ocean.

Flow amplification during early June 2019 occurred in response to an eastward surge of very warm air (potential temperature > 372 K) on the dynamic tropopause) off the Tibetan Plateau as the subtropical jet (STJ) extended toward the Dateline. Cyclonic wave breaking in the STJ exit region initiated downstream flow amplification that culminated in the formation of a deep trough over east-central North America. This deep trough then interacted with a remnant cutoff cyclone over the southeastern U.S. during 9–10 June 2019, facilitating the establishment of two corridors of poleward-directed tropical moisture surges during 10–12 June 2019, one directed toward Baffin Island and the other directed toward eastern Greenland. Both moisture corridors featured deep southerly flow west of two amplifying downstream ridges that became the aforementioned twin blocking anticyclones as the distance between them contracted. Continued downstream flow amplification enabled the formation of the cutoff cyclone over northwestern Russia and the associated surges of warm, moist air from interior Russia to the Arctic Ocean.