Extratropical cyclones develop in regions of enhanced baroclinicity and progress along climatological storm tracks. Numerous studies have noted an influence of terrestrial snow cover on atmospheric baroclinicity. However, these studies have less typically examined the role that continental snow cover extent and changes anticipated with anthropogenic climate change have on cyclones’ intensities, trajectories, and precipitation characteristics. Here, we examined how projected future poleward shifts in North American snow extent influence extratropical cyclones. We imposed 10th, 50th, and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models to alter snow extent underlying 15 historical cold-season cyclones that tracked over the North American Great Plains and were faithfully reproduced in control model cases, providing a comprehensive set of model runs to evaluate hypotheses. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) were initialized at four days prior to cyclogenesis. Cyclone trajectories moved on average poleward (μ = 27 +/− σ = 17 km) in response to reduced snow extent while the maximum sea-level pressure deepened (μ = −0.48 +/− σ = 0.8 hPa) with greater snow removed. A significant linear correlation was observed between the area of snow removed and mean trajectory deviation (r2 = 0.23), especially in mid-winter (r2 = 0.59), as well as a similar relationship for maximum change in sea-level pressure (r2 = 0.17). Across all simulations, 82% of the perturbed simulation cyclones decreased in average central sea-level pressure (SLP) compared to the corresponding control simulation. Near-surface wind speed increased, as did precipitation, in 86% of cases with a preferred phase change from the solid to liquid state due to warming, although the trends did not correlate with the snow retreat magnitude. Our results, consistent with prior studies noting some role for the enhanced baroclinity of the snow line in modulating storm track and intensity, provide a benchmark to evaluate future snow cover retreat impacts on mid-latitude weather systems.
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The Impact of Storm Tracks on Warm-Season Precipitation in the Midwest: Contrasting the 1988 Drought and 1993 Flood
To assess the role of cyclone tracks in contributing to floods and droughts, we highlight the role of midlatitude cyclones played in the 1988 drought and the 1993 flood. Our results demonstrate that the 1988 drought featured a poleward-displaced cyclone track with a reduced role for cyclone-induced precipitation, especially in the spring of 1988. The 1993 flood featured a cyclone track from Mexico northeast to Missouri in the spring, while the summer featured two cyclone tracks: one in the southwestern US and the other across Canada linked to the right-entrance and left-exit regions of a strong 200 hPa Jetstream across the upper Midwest. Enhanced 850 hPa inflow from the Caribbean northeast to the Midwest with high precipitable water values occurred in conjunction with the right entrance portion of the 200 hPa Jetstream. Linking storm tracks and the 200 hPa Jetstream to a storm-rain index for the Midwest showed that these extreme events conformed to features of the general circulation normally associated with wet/dry episodes in the warm half of the year. Although El Niño did not play a role in the 1993 flood, the 1988 drought was associated with a poleward displacement of cyclone tracks in response to La Niña.
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- Award ID(s):
- 1355406
- NSF-PAR ID:
- 10023576
- Date Published:
- Journal Name:
- Advances in Meteorology
- Volume:
- 2016
- ISSN:
- 1687-9309
- Page Range / eLocation ID:
- 1 to 11
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1155/2016/6318460
