Which Extratropical Cyclones Contribute Most to the Transport of Moisture in the Southern Hemisphere?

Abstract

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.

Impact of climate change on the climatology of Vb cyclones

“…Using a radial cap around a cyclone centre to estimate cyclone related precipitation is a widely used approach, e.g. Hawcroft et al (2012), Zappa et al (2013b), Yettella and Kay (2017), Booth et al (2018) and Sinclair and Dacre (2019). Gradients that exceed (fall behind) one standard deviation, the 75th (25th) percentile or the 95th (5th) percentile of the distribution obtain a radius of 6.5 (5.5 ), 7 (5 ) or 7.5 (4.5 ).…”

Evaluating a Moist Isentropic Framework for Poleward Moisture Transport: Implications for Water Isotopes Over Antarctica

“…Pauluis et al (2010) espoused this choice, arguing that a moist isentropic representation can describe the trajectories of air masses with greater fidelity if the eddies responsible for transport are largely moist adiabatic. This is approximately the case in the extratropics, where much of the poleward moisture transport is accomplished through fast-moving episodic pulses (Fajber et al, 2018;Laliberté & Kushner, 2014;Messori & Czaja, 2013;Newman et al, 2012;Sinclair & Dacre, 2019). As a result, moist transport occurs on time scales faster than energy dissipation.…”

Atmospheric River Signatures in Radiosonde Profiles and Reanalyses at the Dronning Maud Land Coast, East Antarctica

“…The Antarctic continent is a highly complex and critically important component of the global climate system that remains poorly understood, especially due to data-sparse and remote regions with difficult human access. Precipitation over the Antarctic ice sheet is dependent on the poleward moisture transport (MT) from lower latitudes, which is mostly accomplished by exratropical cyclones reaching Antarctica (e.g., Bromwich et al, 1995;Tsukernik and Lynch, 2013;Sinclair and Dacre, 2019). Some of these extratropical cyclones [sometimes multiple cyclones, as demonstrated by Sodemann and Stohl (2013) for the Arctic] are asso-ciated with atmospheric rivers (ARs)-long, narrow and transient corridors of enhanced vertically integrated water vapor (IWV) and horizontal vapor transport (IVT) typically within the cyclones' warm conveyor belt, ahead of the cold front (Ralph et al, 2004;Cordeira et al, 2017).…”