Local Atmospheric Response to an Open-Ocean Polynya in a High-Resolution Climate Model

TitleLocal Atmospheric Response to an Open-Ocean Polynya in a High-Resolution Climate Model
Publication TypeJournal Article
Year of Publication2017
AuthorsWeijer, Wilbert, Veneziani Milena, Stoessel Achim, Hecht Matthew W., Jeffery Nicole, Jonko Alexandra, Hodos Travis, and Wang Hailong
JournalJournal of Climate
Volume30
Number5
Pages1,629 - 1,641
Date Published03/2018
Abstract / Summary

In this paper we study the atmospheric response to an open-ocean polynya in the Southern Ocean by analyzing the results from an atmospheric and oceanic synoptic-scale resolving Community Earth System Model (CESM) simulation. While coarser-resolution versions of CESM generally do not produce open-ocean polynyas in the Southern Ocean, they do emerge and disappear on interannual timescales in the synoptic-scale simulation. This provides an ideal opportunity to study the polynya's impact on the overlying and surrounding atmosphere. This has been pursued here by investigating the seasonal cycle of differences of surface and air-column variables between polynya and non-polynya years. Our results indicate significant local impacts on turbulent heat fluxes, precipitation, cloud characteristics, and radiative fluxes. In particular, we find that clouds over polynyas are optically thicker and higher than clouds over sea ice during non-polynya years. Although the lower albedo of polynyas significantly increases the net shortwave absorption, the enhanced cloud brightness tempers this increase by almost 50%. Also, in this model, enhanced longwave radiation emitted from the warmer surface of polynyas is balanced by stronger downwelling fluxes from the thicker cloud deck. Impacts are found to be sensitive to the synoptic wind direction. Strongest regional impacts are found when northeasterly winds cross the polynya and interact with katabatic winds. Surface air pressure anomalies over the polynya are only found to be significant when cold, dry air masses strike over the polynya, i.e. in case of southerly winds.

URLhttps://journals.ametsoc.org/doi/full/10.1175/JCLI-D-16-0120.1
DOI10.1175/JCLI-D-16-0120.1
Journal: Journal of Climate
Year of Publication: 2017
Volume: 30
Number: 5
Pages: 1,629 - 1,641
Date Published: 03/2018

In this paper we study the atmospheric response to an open-ocean polynya in the Southern Ocean by analyzing the results from an atmospheric and oceanic synoptic-scale resolving Community Earth System Model (CESM) simulation. While coarser-resolution versions of CESM generally do not produce open-ocean polynyas in the Southern Ocean, they do emerge and disappear on interannual timescales in the synoptic-scale simulation. This provides an ideal opportunity to study the polynya's impact on the overlying and surrounding atmosphere. This has been pursued here by investigating the seasonal cycle of differences of surface and air-column variables between polynya and non-polynya years. Our results indicate significant local impacts on turbulent heat fluxes, precipitation, cloud characteristics, and radiative fluxes. In particular, we find that clouds over polynyas are optically thicker and higher than clouds over sea ice during non-polynya years. Although the lower albedo of polynyas significantly increases the net shortwave absorption, the enhanced cloud brightness tempers this increase by almost 50%. Also, in this model, enhanced longwave radiation emitted from the warmer surface of polynyas is balanced by stronger downwelling fluxes from the thicker cloud deck. Impacts are found to be sensitive to the synoptic wind direction. Strongest regional impacts are found when northeasterly winds cross the polynya and interact with katabatic winds. Surface air pressure anomalies over the polynya are only found to be significant when cold, dry air masses strike over the polynya, i.e. in case of southerly winds.

DOI: 10.1175/JCLI-D-16-0120.1
Citation:
Weijer, W, M Veneziani, A Stoessel, MW Hecht, N Jeffery, A Jonko, T Hodos, and H Wang.  2017.  "Local Atmospheric Response to an Open-Ocean Polynya in a High-Resolution Climate Model."  Journal of Climate 30(5): 1629 - 1641.  https://doi.org/10.1175/JCLI-D-16-0120.1.