AGU Journal highlights -- Jan. 10, 2008

Though most human-generated aerosols reside in the Northern Hemisphere, a recent model study shows that in response to rising aerosol concentrations, the Southern Hemisphere’s ocean circulation, including retroflecting eddies and the entire subtropical gyre, intensifies and shifts poleward. Cai and Cowen seek to determine if these ocean responses also manifest in the Southern Hemisphere’s atmospheric circulation. Through analyzing data from two sets of 20th century simulations in a coupled ocean-atmosphere global climate model, the authors find that, as a result of the poleward shift in oceanic circulation, maximum sea surface temperatures, midlatitude storms, and the westerly jet shift southward. This shift in air circulation intensifies the trend of the Southern Annular Mode, a low-frequency pattern of atmospheric variability near Antarctica, causing a poleward shift and intensification in zonal wind and vertical velocities generated from the atmosphere-ocean interface to the middle of the troposphere. These atmospheric circulation responses, in turn, reinforce the ocean circulation changes. Thus, the authors suggest a contribution by human-generated aerosols to the observed trend of the Southern Annular Mode.

Title:

Impacts of increasing anthropogenic aerosols on the atmospheric circulation trends of the Southern Hemisphere: An air-sea positive feedback

Authors:

Wenju Cai and Tim Cowan: Marine and Atmospheric Research, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Aspendale, Victoria, Australia; also at Wealth from Oceans National Research Flagship, CSIRO, North Ride, New South Wales, Australia.

Source:

Geophysical Research Letters (GRL) paper 10.1029/2007GL031706, 2007; http://dx.doi.org/10.1029/2007GL031706

8. Effects of global change on Canada's Mackenzie River Delta

River delta regions along the Arctic coast are poorly understood ecosystems that are expected to change rapidly as the climate warms, sea levels rise, and seasonal river ice jams become less frequent. In northern Canada's Mackenzie River Delta, flood pulses driven by ice breakup control the degree to which river water moves off-channel to replenish nearby lakes, which only exist because of such river dynamics. Lesack and Marsh analyze more than 30 years of data on the Mackenzie Delta and find that the duration of river-to-lake connection has lengthened on average more than 30 days since the 1970s. Further, the duration of river-to-lake connection has shortened in the highest elevation lakes, likely owing to the declining effects of river-ice breakup. The authors conclude that not only are the higher elevation lakes at risk of drying up from declining water level peaks, but lower elevation lakes now contain more water than can be accounted for through sea level rise, suggesting that increasing storm surge intensity, permafrost melting, or backwater flow might play an unexpected role.

Title: