Linking Sub‐Tropical Evaporation and Extreme Precipitation Over East Antarctica: An Atmospheric River Case Study

Abstract

We investigate an intense snowfall event between 15 and 18 February 2011 over the East Antarctic coastal region which contributed to roughly 24% of the annual snow accumulation. The event was previously associated with an atmospheric river, and here we use both Eulerian and Lagrangian analysis to gain an understanding of the processes contributing to the atmospheric river signature. The planetary-scale configuration during the event consisted of a persistent blocking situation resulting in a sustained meridional flow from the sub-tropics to the Antarctic ice sheet between 20 and 50°E. Within this configuration, synoptic-scale cyclogenesis contributed to slantwise ascent of moisture loaded air parcels toward Antarctica. Landfall of this cyclone's warm sector coincided with the onset of Antarctic precipitation. Subsequently, a secondary cyclone developed along a pre-existing baroclinic zone. The rapid intensification and propagation speed of this mesoscale cyclone alongside the warm, moist air mass resulted in strong moisture flux convergence ahead of the cyclone, providing additional poleward moisture transport. The poleward progression of warm moist air and a corresponding decrease of sea-surface temperatures implied downward surface sensible and latent heat fluxes throughout the region of intense poleward moisture, roughly between 40 and 60°S. Hence, moisture uptake via surface evaporation was suppressed between the sub-tropics and the polar continent, favoring long-range transport. Identification of the surface moisture uptake region by tracing changes in moisture in air parcels confirmed the limited uptake of moisture during the poleward transport in this case study, with the primary moisture source for Antarctic precipitation located in the sub-tropics.TERPSTRA ET AL.

Relationship Between Weather Regimes and Atmospheric Rivers in East Antarctica

“…The condensation releases latent heat fueling cyclogenesis via differential diabatic heat and acts to decrease the potential vorticity of the downstream ridge (Madonna et al, 2014;Terpstra et al, 2021;Woollings et al, 2018).…”

An Extreme High Temperature Event in Coastal East Antarctica Associated With an Atmospheric River and Record Summer Downslope Winds

“…Some high temperatures in the Antarctic coastal region have been linked to atmospheric rivers, which are narrow bands of warm, moist air originating in mid-or low-latitudes (Gorodetskaya et al, 2014;Wille et al, 2019). Typically, a ridge downstream of the river directs lower-latitude moisture flow toward the Antarctic (Terpstra et al, 2021). On average 12 atmospheric rivers occurred each year during 1979-2017 in the coastal region of West Antarctica, with these giving positive surface temperature anomalies of 4-5°C and extensive surface melt (Wille et al, 2019;Zou et al, 2021aZou et al, , 2021b.…”

Les rivières atmosphériques de l'Antarctique

“…Comprendre pourquoi des situations analogues, c'est-à-dire presque identiques, se voient associés ou non à des rivières atmosphériques reste un mystère. L'intensification de ces phénomènes pourrait provenir de la condensation se produisant avant l'événement au-dessus de mers froides (Terpstra et al, 2021). La libération de la chaleur latente facilite ainsi probablement la convection de l'air chaud en provenance des basses latitudes, mais rien n'est aujourd'hui clair sur ce point.…”