Synoptic review of a polar-low CAT event during ST25 flight

PAOLA RODRIGUEZ IMAZIO; NICOLAS RIBAVEN; ALEJANDRO GODOY

Workshop; SouthTRAC UTLS Chemistry and Transport workshop; 2020

A synoptic review of a Clear-Air Turbulence (CAT) event during ST25 flight was analysed usingERA5 reanalysis (ECMWF), GFS forecast model (NCEP), and measurements from a radiosondelaunched from Marambio station at 17:45 UTC. A strong and well-defined polar low was located atWest of the Antarctic Peninsula over the Bellingshausen Sea in the morning of 12 November. At thenorth of the polar low, a small and deep perturbation at 300 hPa level moved quickly towards thenorth-west of the Antarctic peninsula at 18 UTC, favouring a cold air advection at low levels overBellingshausen Sea and a stratospheric air intrusion between 450 hPa and 300 hPa levels near 62ºS-60°W. These conditions favoured a strong upper level frontogenesis, associated with a tropopausefolding in that region. Additionally, a strong jet streak greater than 100 knots at 300 hPa wasobserved at 60ºS, with horizontal and vertical wind shear. Strong temperature gradients and highThermal Front Parameter (TFP) were observed in the NWP model at 200-350hPa. Ellrod TurbulentIndex (1 and 2) and Brown Index indicate moderate to severe turbulence conditions between 300hPa and 250hPa. Radiosondes data from Marambio station show a sharp temperature inversionwith an amplitude of 4 K between 250hPa and 200hPa, for times close to the critical occurrence ofthe synoptic pattern. This situation is consistent with tropopause folding and exchange of tracergases, and it is expected to be confirmed and further investigated using high resolution data fromthe SOUTHTRAC campaign.