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Greenland's Influence on Cyclone Activity

LI, Lin
http://rave.ohiolink.edu/etdc/view?acc_num=osu1041624972

Abstract Details

2003, Doctor of Philosophy, Ohio State University, Geography.
The climatic significance of Greenland is determined by two main facts: the thermal forcing of its ice sheet and its topographic forcing near the middle of the North Atlantic storm track. The Greenland Ice Sheet boasts about 10 percent of the worlds freshwater and its melting contributes about 7 percent of the annual rise in global sea level. This study explores the connection between cyclone activity around Greenland and Rogers (1984) NAO monthly and seasonal indices. Serrezes (1995) storm tracking algorithm is optimized to track cyclones over Denmark Strait and along the west coast of Greenland using both the ECMWF Reanalysis mean sea level pressure field from 1979 to 1993 (ERA-15) and the ECMWF TOGA high resolution mean sea level pressure field from 1985 to 2000. It is found that cyclone activity along Denmark Strait is highly correlated with NAO indices, especially in winter. There are more cyclones passing Denmark Strait and more cyclogenesis in positive NAO months or seasons. These cyclones are more intense and their deepening rates are larger in comparison to those in negative NAO months or seasons. Along the west coast of Greenland, due to the different sources of cyclones from those passing Denmark Strait, cyclone activity does not show a high correlation with NAO indices. Cyclone activity is frequent along the southeast and west coasts and over northern Greenland. Cyclone activity along the southeast and west coasts of Greenland is associated with high precipitation, while over northern Greenland, cyclonic activity related precipitation is fairly small. Numerical simulations are carried out using Polar MM5 Version 2 (based on PSU /NCAR MM5 V3.4). Nudging toward gridded TOGA upper level wind and temperature fields is used to speed up 6 extended winter season simulations. The numerical simulations demonstrate that Polar MM5 V2 has good performance in simulating the surface weather features over the Ice Sheet. Generally, the precipitation over southern Greenland is negatively correlated to the seasonal NAO indices. There is less precipitation over western Greenland in positive NAO months than that in negative NAO months, while over eastern Greenland, there is more precipitation in positive NAO months than that in negative NAO months. Cases of cyclones crossing the Greenland Ice Sheet are examined with numerical simulations to determine the impact of the ice sheet cyclone formation. A cyclone can transverse the entire ice sheet and redevelop on the east coast due to the different movement rates of waves on the thermal and geopotential height fields that are caused by the high elevation of the ice sheet. At low levels, a low-level jet (LLJ) brings warm moist air from the southwest, and downslope northerly winds bring cold dry air from the ice sheet, increasing the baroclinic instability. Accompanying the cyclone evolution, tropopause folding or undulation is found. For a cyclone crossing the southern tip of Greenland, the surface wind shear formed by downslope easterly flow and by ambient westerly cyclonic flow causes a surface circulation to form, which later develops into a cyclone under upper level warm air advection downstream of tropopause folding. Frontal retardation and deformation by the southern part of the Greenland Ice Sheet, and a cold air outbreak boost the rapid cyclonic development. The impact of Greenland on the cyclonic activity is also investigated via a sensitivity study with Polar MM5 where the Greenland Ice Sheet is reduced to one tenth of its current elevation for a positive and negative NAO January. The monthly mean sea level pressure center with reduced Greenland both for positive and negative NAO months is located to the south of Iceland, whereas during the positive NAO month with current Greenland the center is located to the southeast of Greenland. This indicates that the chance of cyclogensis in the lee of southern reduced Greenland is greatly decreased. In part, this is due to altered cyclone paths that cross the reduced ice sheet with some frequency. Greatly amplified ridging over the reduced Greenland destroys the upper level jets. The reduced upper level wind speed may be explained by the disappearance of the channeling effect of the high elevation ice sheet. The sensitivity study also suggests that the reduced Greenland Ice Sheet could eliminate the North Atlantic Oscillation because the strength and position of the modeled Icelandic Low are similar for both positive and negative NAO months. This indicates that the NAO is related to the existence of the current Greenland Ice Sheet, and is not synonymous with the Arctic Oscillation (AO).
David Bromwich (Advisor)
Mineralogy
Greenland; cyclone activity; North Atlantic Oscillation (NAO); Arctic Oscillation (AO); numerical simulation; Polar MM5

Recommended Citations

Citations

  • LI, L. (2003). Greenland's Influence on Cyclone Activity [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1041624972

    APA Style (7th edition)

  • LI, Lin. Greenland's Influence on Cyclone Activity. 2003. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1041624972.

    MLA Style (8th edition)

  • LI, Lin. "Greenland's Influence on Cyclone Activity." Doctoral dissertation, Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1041624972

    Chicago Manual of Style (17th edition)

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© 2003, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.