Which extratropical cyclones contribute most to the transport of moisture in the southern hemisphere?

• Published in: Journal of Geophysical Research: Atmospheres
• Main Authors: Sinclair, V. A., Dacre, H. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2019
• Subjects: Antarctic; The Antarctic; Antarc*; Antarctica
• Online Access: https://centaur.reading.ac.uk/82657/; https://centaur.reading.ac.uk/82657/1/Sinclair19.pdf

Predicted changes in Southern Hemisphere (SH) precipitation and Antarctic ice mass correspond to variations in the meridional moisture flux (MMF). Thirty‐five years of ERA‐Interim reanalysis data are combined with an extratropical cyclone (ETC) identification and tracking algorithm to investigate factors controlling SH MMF variability in the midlatitudes and near Antarctica. ETC characteristics which exert the strongest control on ETC MMF are determined thus identifying which ETCs contribute most to SH moisture transport. ETC poleward propagation speed exerts the strongest control on the ETC MMF across the Antarctic coastline. In SH winter, ETCs with the largest poleward propagation speeds transport 2.5 times more moisture than an average ETC. In the midlatitudes, ETC genesis latitude and poleward propagation speed have a similar influence on ETC MMF. Surprisingly, ETC maximum vorticity has little control on ETC MMF. Cyclone compositing is used to determine the reasons for these statistical relationships. ETCs generally exhibit a dipole of poleward and equatorward MMF downstream and upstream of the cyclone center, respectively. However, ETCs with the largest poleward propagation speeds resemble open frontal waves with strong poleward moisture transport downstream of the cyclone center only and thus result in the largest MMF. These results suggest that inhomogeneous trends and predicted changes in precipitation over Antarctica may be due to changes in cyclone track orientation, associated with changes to the large‐scale background flow, in addition to changes in cyclone number or intensity.