Contribution
Dynamics of a Puelche foehn event in the Andes
Beusch, Lea; Raveh-Rubin, Shira; Sprenger, Michael; Papritz, Lukas
Meteorologische Zeitschrift Vol. 27 No. 1 (2018), p. 67 - 80
39 références bibliographiques
publié: Jan 29, 2018
publication en ligne: Dec 1, 2017
manuscrit accepté: Aug 15, 2017
revision du manuscrit reçu: Aug 15, 2017
révision du manuscrit demandée: May 11, 2017
manuscrit reçu: Nov 24, 2016
Open Access (article peut être télechargé gratuitement)
Abstract
In this numerical modelling study, we investigate a Puelche foehn event (25–26 March 2014) in the southern Andes – a region with sparse observations. The synoptic environment as well as the mesoscale structure and the dynamics of the easterly wind are examined with European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and a simulation with the mesoscale non-hydrostatic limited-area weather prediction model COSMO with a grid spacing of 2.2 km.The large-scale synoptic situation leading to this Puelche event is characterized by a mid-tropospheric cut-off low above the mountain range, the formation of a coastal surface low, as well as high pressure extending over the southern Andes. Easterly winds extend throughout the entire troposphere, indicative of a deep foehn flow. In the free troposphere, the easterlies are geostrophically balanced and develop in association with increasing pressure to the south. In contrast, within the planetary boundary layer, the easterly winds occur predominantly due to an increasing cross-range large-scale pressure gradient with only a weak geostrophic component. Kinematic trajectories indicate that a significant part of the Puelche air mass originates from above an inversion on the upstream side of the Andes. Some air parcels, however, ascend on the upstream side to crest height as the boundary layer deepens during daytime and/or flow through gaps across the mountain range. Hence, this Puelche event shares characteristics of both a blocked and a non-blocked foehn type.
Mots-clefs
Puelche • Andes • foehn mechanisms • downslope flows • COSMO simulation • trajectories