Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

John J. Cassano

Second Advisor

David C. Noone

Third Advisor

Mark C. Serreze

Abstract

New estimates of the current energy budget of the north polar cap (the region north of 70N) are synthesized by combining data from new atmospheric reanalyses and satellite retrievals. For the period 2000-2005, monthly means from the Clouds and the Earth's Radiant Energy System (CERES) satellite data set are considered to provide the most reliable top-of-atmosphere (TOA) radiation budget. The remaining components of the energy budget, comprising of the energy storage, horizontal convergence of energy, and the net surface flux between the atmospheric and subsurface columns, are compiled using data from the Japanese 25-year Reanalysis Project (JRA) and the NCEP/NCAR Reanalysis (NRA). The annual cycles of energy budget components for the polar cap are fairly consistent between the JRA and NRA, but with some systematic differences. Estimates of the Arctic energy budget from WRF are compared with estimates from reanalyses and satellite observations. Apart from a few systematic shortcomings, WRF sufficiently captures the Arctic energy budget. The major deficiency, with differences from reanalyses and satellite observations as large as 40 W m-2 in summer months, is in the shortwave radiative fluxes at both the surface and top of the atmosphere, due to a specified constant sea ice albedo of 0.8, which is too high during the summer. Finally, the WRF model (version 3.2.0) is used to explore the sensitivity of the large-scale atmospheric circulation to prescribed changes in Arctic sea ice. Observed sea ice fractions and sea surface temperatures (SSTs) from 1996 and 2007, representing years of high and low sea ice extent, respectively, are used as WRF lower boundary conditions. This yields two 15-member ensembles that sample a large range of true climatic variability. Results of the simulations show both local and remote responses to the sea ice reduction. The local response is largest in October and November, dominated by increased turbulent heat fluxes resulting in a vertically deep heating and moistening of the Arctic atmosphere. Significant warming and moistening persists through November. This warmer and moister atmosphere is associated with an increase in cloud cover, affecting the surface and atmospheric energy budget. There is an enhancement of the hydrologic cycle, with increased evaporation in areas of sea ice loss paired with increased precipitation. Summertime changes in the hydrologic cycle reflect circulation responses to mid-latitude SSTs, highlighting the general sensitivity of the Arctic climate.

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