Date of Award

12-1-2021

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (xii, 73 pages) : color illustrations, color maps.

Dissertation/Thesis Chair

Lance F. Bosart

Keywords

Ice, Cyclones, Climatic changes, Heat, Atmospheric circulation

Subject Categories

Atmospheric Sciences

Abstract

Extratropical cyclones and/or short-wave disturbances can reinforce Greenland blocking through upper-level flow amplification and can increase poleward heat and moisture transport into the Arctic. Increased poleward heat and moisture transport into the Arctic may enhance Greenland ice melt during the spring, summer, and fall months. The need to better understand the underlying dynamical and diabatic processes that may contribute to Greenland ice melt motivates this thesis. The purpose of this thesis is to investigate: 1) the role of advective warming due to poleward heat and moisture transport into the Arctic in facilitating Greenland ice melt, 2) the role of adiabatic warming due to synoptic-scale descent associated with Greenland blocking in facilitating ice melt, and 3) the role of diabatic warming due to condensation and latent heating over Greenland in facilitating ice melt. Self-organizing maps (SOMs) are utilized to construct a synoptic climatology of Greenland ice-melt events during the April–October 1979–2019 time period. The SOMs identify three main types of synoptic-scale flow patterns during Greenland ice-melt events: 1) a blocking pattern over Greenland, 2) a positively tilted trough upstream of Greenland, and 3) a high-amplitude negatively tilted trough upstream of Greenland. During late July–early August 2019, 60% (i.e., ~984,000 km 2) of the Greenland ice sheet experienced melting, which is the largest ice melt event over Greenland since at least 2012. Ice melt over Greenland was associated with a blocking anticyclone over Scandinavia that subsequently shifted westward toward Greenland and permitted anomalously warm air of Saharan origin to reach Greenland. Upper-level flow amplification from eastern North America to western Europe resulted in ridge amplification over northwest Africa, which occurred in conjunction with the formation of an atmospheric river (AR) over the North Atlantic Ocean that was associated with a large poleward-directed moisture transport. Anomalously warm air of Saharan origin reached western Europe and Scandinavia, resulting in a record-breaking heat wave as the ridge over northwest Africa extended poleward and subsequently evolved into the blocking anticyclone over Scandinavia. The AR subsequently transitioned into a westward-directed moisture transport toward Greenland in conjunction with a westward shift of the blocking anticyclone over Scandinavia toward Greenland. Air parcel trajectories were computed to analyze the modifications of the air masses that contributed to the late July–early August 2019 ice-melt event and to identify their origins. Air parcels initialized in the AR over the North Atlantic Ocean at 1200 UTC 25 July 2019 first moved poleward in conjunction with the poleward extension of the ridge over northwest Africa toward Scandinavia and then moved westward toward Greenland in conjunction with the westward shift of the blocking anticyclone over Scandinavia toward Greenland. Moist ascending air parcels initialized in the AR over the North Atlantic Ocean experienced a median specific humidity decrease from ~8 g kg−1 to ~1 g kg−1 and a median potential temperature increase from ~298 K to ~315 K as these air parcels ascended from ~850 hPa to ~480 hPa during the 72-h period ending on 1200 UTC 28 July 2019. These respective changes in median specific humidity and median potential temperature are indicative of condensation and latent heat release over Greenland, such that the associated diabatic warming may have contributed to Greenland ice melt during this event.

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