Summertime midlatitude weather and climate extremes induced by moisture intrusions to the west of Greenland. (31st July 2019)

• Record Type: Journal Article
• Authors: Baggett, Cory; Lee, Sukyoung
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 145:Number 724(2019)
• Page Start: 3148
• Page End: 3160
• Publication Date: 2019-07-31
• Subjects: Arctic moisture intrusions -- climate -- dynamics -- extremes -- Geophysical Fluid Dynamics Laboratory experiments -- midlatitude -- observational data analysis -- polar -- Rossby wave train -- seasonal; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.3610
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract: The summer of 2010 was characterized by weather and climate extremes such as the western Russia heatwave and the Pakistan floods. A recent study found that summer was dominated by a particular 200 hPa geopotential height pattern featuring an anomalous Rossby wave train with ridges centred over Greenland, Europe and Russia. The daily frequency of this pattern has dramatically increased recently and closely resembles the mean‐state difference in 200 hPa geopotential height fields between 1998–2014 (P2) and 1979–1997 (P1). Because anomalous wave trains are often driven by localized diabatic heating, it is tested in this study whether the P2 minus P1 pattern is caused by diabatic heating anomalies near Greenland. While it is found that sea ice concentrations declined and sea‐surface temperatures rose over Baffin Bay to the west of Greenland during P2, surface latent heat fluxes actually increased downward, indicating that surface processes were likely not the source of diabatic heating. Rather, an increase in vertically integrated horizontal latent‐heat flux convergence over Baffin Bay was observed in P2, which led to the condensation of water vapour and latent heating. Thus, the mid‐tropospheric circulation established the diabatic heating. A set of initial‐value calculations with idealized heating over Baffin Bay show solutions that remarkably resemble the P2 minus P1 pattern and provide a plausible explanation as to why the pattern has been occurring more frequently. This study demonstrates that changes in the Arctic can arise from moisture transport from the midlatitudes, and, in turn, these changes can induce weather and climate extremes in distant midlatitude regions. Abstract : Recent summers in the Northern Hemisphere have been characterized by weather and climate extremes such as heat waves and floods. These extremes are associated with a frequently occurring Rossby wave train pattern that manifests itself downstream from Greenland. Both observational evidence and idealized model experiments reveal that the wave train is induced by a diabatic heat source over Baffin Bay associated with latent heat release from midlatitude moisture intrusions.