Date of Award

Spring 1-1-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric & Oceanic Sciences

First Advisor

Matthew Shupe

Second Advisor

Katja Freidrich

Abstract

The mass balance of interior Greenland is much less understood than the oft-studied melting coastal regions due to a dearth of observations. The ICECAPS project, which launched in the summer of 2010 at Summit, Greenland, offers a unique, ground-based opportunity to study precipitation in central Greenland where the mass balance is marginally positive. Combing the perspectives from a Precipitation Occurrence Sensor System (POSS), a Millimeter-wavelength Cloud Radar (MMCR), and an accumulation field, the annual cycle of precipitation at Summit is examined. The annual average snowfall measured by the POSS (MMCR) is 83.3 mm (88.8 mm) of liquid equivalent, with the seasonal cycle defined by a large peak in summer and a smaller one in late winter. Accumulation showed a similar seasonal pattern, though with damped variability and a one or two month time lag. Daily snowfall increases by a factor of 3 from June through October compared to the rest of the year, while accumulation only increases 18% during the same timeframe. This reduced variability is explained by the seasonally-varying nature of latent heat flux, compaction, and wind contributions. The ICECAPS remote sensors and the accumulation field measurements do not completely agree as far as total annual liquid equivalent. The deposition of snow by wind, among other factors, is suggested as a possible contributor to the discrepancy. To further examine the seasonal cycle, snowfall measurements by the POSS were linked to other local meteorological parameters, including wind direction, liquid water path (LWP), 2-m temperature, and precipitable water vapor (PWV). Snowfall rarely occurs and is typically very light if the wind does not have a southerly component, except in the summertime, for which moderate snowfall often coincides with all wind directions. Snowfall rate and occurrence are higher when PWV exceeds the current month’s mean PWV. The wind direction and moisture dependence are consistent with snowfall being linked to pulses of moist air that originate over nearby, ice-free ocean, a resource that becomes more readily available in summertime as the winter sea ice retreats. LWP is shown to have little relationship to snowfall, indicating that ice-phase precipitation processes are quite important for snowfall at Summit.

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