An Analysis of the Arctic Ocean Net Surface Heat Flux and Its Components From Atmospheric Reanalyses and Surface Observations

Helmberger, Meghan Nicole

Graduate Thesis Or Dissertation

An Analysis of the Arctic Ocean Net Surface Heat Flux and Its Components From Atmospheric Reanalyses and Surface Observations Public Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/sn00b065n

Abstract

As the Arctic Ocean loses its sea ice cover, one expects a larger ocean heat gain from the net surface flux throughout the spring and summer; meaning that there is more energy to transfer from the ocean to the atmosphere in the autumn and winter. Recent work has shown that increased oceanic heat content at the end of summer delays autumn ice growth, with implications for marine shipping and other economic activities. Depending on patterns of seasonal sea ice retreat and weather conditions, the spring-summer heat uptake and autumn-winter heat loss can be highly variable from year to year as well as across regions. The main goal of this work is the validation of reanalysis data, examination of net surface heat flux patterns, and estimation of an idealized net surface heat flux value. To date, there has been little research addressing net surface heat flux specifically.

Recognizing this gap, this dissertation systematically analyzes how net surface heat flux (April-August) varies over time. In order to evaluate this across the Arctic Ocean and the marginal seas, three reanalyses were used (CFSR, ERA5, and MERRA-2), acknowledging the scarcity of measurements across the region. Following the initial steps in the project, shortwave and longwave radiation values were examined from the three reanalayses. Four variable comparisons were undertaken showing differences between the reanalyses, exemplifying the areas of disagreement. A statistical analysis showed high correlations across the Arctic Ocean at the 95% confidence level for all variables between ERA5, CFSR, and MERRA-2.

Downwelling shortwave radiation that was collected on board the RV Araon in August 2018 from the Bering Strait and the Chukchi Sea showed that there is general agreement between all datasets and observations. Additionally, data from the SHEBA and MOSAIC expeditions were used to evaluate reanalysis accuracy, which allowed for the comparison of all radiation components used in calculating net surface heat flux. Since there are differences between the reanalyses, evaluating accuracy of individual components of the surface energy flux against observations was vital.

Comparisons of the net surface heat flux and ocean heat from from the reanalyses used in this study showed, as expected, positive trends in seasonal ocean heat gain from the net surface flux, but there was disagreement between values with large variability from year to year. Yet, over time, the net surface heat flux calculated from each reanalysis shows similar temporal patterns.

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