Date of Degree
Earth & Environmental Sciences
Cryosphere; Greenland; Ice Sheets; Mass Balance; Regional Models; Remote Sensing
In this dissertation, I present a series of studies that further our understanding of processes responsible for variations in the mass balance of the Greenland ice sheet, and assess our ability to model them. The Greenland ice sheet will likely contribute to sea level rise in a future warmer climate, and it is important to be able to predict future changes in sea level. I perform assessments of (1) spatiotemporal variations in Greenland ice sheet albedo, a key parameter that modulates the mass and energy balance at the ice sheet surface, and (2) spatiotemporal variations in Greenland ice sheet mass balance. Both studies make use of model results, and spaceborne remote sensing estimates, and one makes use of in situ measurements, to assess the observed quantities.
The first topic is addressed using satellite data, in situ observations, and results from the Modèle Atmosphéique Régionale (MAR), a regional climate model that simulates the ice sheet surface, and the atmosphere above. I find that MAR reproduces spatial variations in albedo captured by remote sensing and in situ observations, but overestimates albedo by up to 0.1 at low elevations, due to overestimated bare-ice albedo. This can significantly impact the simulated ice sheet surface mass balance. Declining trends in albedo over 2000-2012 are captured by MAR, satellite data, and in situ observations at low elevations. At high elevations, discrepancies between satellite data and in situ observations limit the ability to draw conclusions regarding albedo trends. Discrepancies between modeled and observed mean albedo and trends at low elevations may partially be accounted for by the presence of surface impurities, which are not accounted for by MAR. We also identify discrepancies between satellite albedo products in spatial variations in albedo north of 70°N, limiting our ability to draw conclusions for this region.
In the second portion of this work I compare MAR surface mass balance estimates combined with dynamic mass changes from the Ice Sheet System Model (ISSM) with satellite-derived estimates of mass change from the Gravity Recovery and Climate Experiment (GRACE). I find that the models underestimate mass loss at low elevations, and capture the timing of the GRACE seasonal cycle. There are discrepancies between the modeled and observed seasonal cycles at smaller spatial scales, suggesting the need for further study of mass balance processes not fully captured by ISSM or MAR. The studies collectively provide information that will allow for improvement of models used to simulate future changes in Greenland ice sheet mass.
I have also included a series of studies that I contributed to as part of my work for this dissertation. These include (1) a study investigating the processes responsible for trends in Greenland Ice Sheet albedo and predictions futurealbedo changes, (2) an investigation of processes responsible for record melting during the year 2012, and (3) a study of the role of surface lake drainage events in Greenland ice sheet motion.
Alexander, Patrick Michael, "Assessing Greenland Ice Sheet Albedo and Mass Balance Variability Using In-Situ Data, Spaceborne Observations and Regional Model Outputs" (2015). CUNY Academic Works.