Glaeser, G, Knippertz, P and Heinold, B (2012) Orographic Effects and Evaporative Cooling along a Subtropical Cold Front: The Case of the Spectacular Saharan Dust Outbreak of March 2004. Monthly Weather Review, 140 (8). 2520 - 2533. ISSN 0027-0644
Abstract
On 2 March 2004 a marked upper-level trough and an associated surface cold front penetrated into the Sahara. High winds along and behind this frontal system led to an extraordinary, large-scale, and long-lived dust out reak, accompanied by significant precipitation over parts of Algeria, Tunisia, and Libya. This paper uses sensitivity simulations with the limited-area model developed by the Consortium for Small-Scale Modeling (COSMO) together with analysis data and surface observations to test several hypotheses on the dynamics of this case proposedin previous work. It is demonstrated that air over central Algeria is cooled by evaporation of frontal precipitation, substantially enhancing winds at the leading edge of the cold front. This process is supported by very drylow-level air in the lee of the Atlas Mountains associated with a foehn situation. Flattening the mountain chain in a sensitivity experiment, however, has complex effects on the wind. While reduced evaporative cooling weakens the front, the elimination of the orographic blocking accelerates its penetration into the Sahara. The simulations also indicate high winds associated with a hydraulic jump at the southern slopes of the Tell Atlas. Feedingthe simulated winds into a dust emission parameterization reveals reduced emissions on the order of 20%-30% for suppressed latent heating and even more when effects of the increased precipitation on soil moisture are considered. In the experiment with the Atlas removed, effects of the overall increase in high winds are compensated by an increase in precipitation. The results suggest that a realistic representation of frontal precipitation is an important requisite to accurately model dust emission in such situations.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © Copyright [2012] American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org. |
Keywords: | Cold fronts; Cold pools; Dust or dust storms; Latent heating/cooling; Orographic effects; Regional models |
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) |
Depositing User: | Symplectic Publications |
Date Deposited: | 23 Oct 2013 09:05 |
Last Modified: | 30 Aug 2016 22:07 |
Published Version: | http://dx.doi.org/10.1175/MWR-D-11-00315.1 |
Status: | Published |
Publisher: | American Meteorological Society |
Identification Number: | 10.1175/MWR-D-11-00315.1 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:76591 |