Miltenberger, AK, Reynolds, S and Sprenger, M (2016) Revisiting the latent heating contribution to foehn warming - Lagrangian analysis of two foehn events over the Swiss Alps. Quarterly Journal of the Royal Meteorological Society, 142 (698 (Part A)). pp. 2194-2204. ISSN 0035-9009
Abstract
Foehn flows are typically associated with warm air temperatures. Though several theories for the so-called foehn air warming have been developed over the past century, no conclusion about the most important mechanism has been reached. The development of new methods to calculate accurate air-mass trajectories over complex topography has opened up a new perspective on this question. Air-mass-trajectories derived from wind-field data from COSMO model simulations with 20 s temporal resolution are used in this study to investigate the origin of the foehn air and the contribution of adiabatic and diabatic processes for two foehn events in the Swiss Alps, with a focus on the Rhine valley. The first foehn event investigated has no precipitation on the upstream side of the Alps. The majority of air parcels stem from upstream altitudes above 1.8 km and most of the foehn air warming is due to adiabatic descent (∼79%). In the second event investigated, significant upstream precipitation occurred. For this case, a significantly larger fraction of the foehn air parcels originate within the lowest 2 km of the upstream atmosphere (up to 70%). Adiabatic descent accounts for the largest part of the temperature change (∼70%), while moist diabatic processes explain about 60% of the potential temperature change. The vertical displacement across the Alpine range is correlated with the diabatic temperature change: parcels strongly heated by condensation, deposition and freezing are in general found at high altitudes above the foehn valley, while parcels affected by diabatic cooling through evaporation, sublimation and melting arrive closer to the valley floor. The high-resolution trajectories also indicate a much more complicated vertical and horizontal flow pattern than generally assumed, with several distinct air streams upstream of the mountain range and vertical ‘scrambling’ of air masses.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2016 Royal Meteorological Society. This is the peer reviewed version of the following article: Miltenberger, A. K., Reynolds, S. and Sprenger, M. (2016), Revisiting the latent heating contribution to foehn warming: Lagrangian analysis of two foehn events over the Swiss Alps. Quarterly Journal of the Royal Meteorological Society, 142: 2194–2204, which has been published in final form at http://dx.doi.org/10.1002/qj.2816. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. |
Keywords: | foehn flow; foehn air warming; trajectories |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst for Climate & Atmos Science (ICAS) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 16 May 2016 11:30 |
Last Modified: | 19 Apr 2017 03:45 |
Published Version: | http://dx.doi.org/10.1002/qj.2816 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/qj.2816 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:99697 |