Relationship Between Meridional Mass Circulation and Extreme Temperature Events in the Southern Hemisphere

• Other Authors: Yan, Ruikai (authoraut), Cai, Ming (professor directing thesis), Chagnon, Jeffrey M. (committee member), Liu, Guosheng (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department)
• Format: Text
• Language: English
• Published: Tallahassee, Florida: Florida State University 2016
• Subjects: Meteorology; Antarctic; Southern Ocean; Ross Sea; Scotia Sea; Weddell; Antarc*; Antarctica
• Online Access: https://diginole.lib.fsu.edu/islandora/object/fsu%3A360487/datastream/TN/view/Relationship%20Between%20Meridional%20Mass%20Circulation%20and%20Extreme%20Temperature%20Events%20in%20the%20Southern%20Hemisphere.jpg

This study explores extreme surface temperature events in Southern Hemisphere winter (June – August) from 1979 to 2011 and their relation with meridional mass circulation by using daily ERA-interim Re-Analysis data from European Center for Medium-Range Weather Forecasts (ECMWF). Meridional mass circulation indices are developed to quantitatively represent the warm air mass being transported into the polar region in the upper atmosphere and the cold air mass being transported out of the polar region in the lower atmosphere. Our results show that weaker poleward warm air mass transport aloft is associated with weaker cold air transport toward equator in the lower troposphere, resulting in cold air being confined in the polar regions. Similarly, stronger poleward warm air mass transport in the upper atmosphere is related to stronger cold air transport out of the polar regions, causing enormous cold air outbreaks in the mid-latitude regions. We find that regions to the south of 45S exhibit a robust relationship between surface air temperature anomalies and meridional mass circulation. Weaker circulation is associated with abnormally cold in Antarctica and abnormally warm in regions from 45S to 60S. Conversely, stronger circulation is related to anomalously warm in Antarctica and anomalously cold in the surrounding continental shelf, particularly over Weddell-Scotia Sea and north Ross Sea where are the two preferred routes for cold air coming out of Antarctica. On the other hand, temperature anomalies over the regions north of 45S are not sensitive to the meridional circulation variability. The fact that surface air temperature anomalies over the Southern Ocean rarely exceed 4C suggests that cold air coming out of Antarctic has limited impacts on the Southern Ocean due to its large thermal inertia. In summary, the meridional mass circulation indices provide a robust diagnostics for extreme cold events in 45S - 90S domain very well, but may not be adequate to describe all cold events over the vast mid-latitude regions ...