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Lagrangian transport of water vapor and cloud water in the ECHAM4 GCM and its impact on the cold bias

Stenke, Andrea and Grewe, Volker and Ponater, Michael (2008) Lagrangian transport of water vapor and cloud water in the ECHAM4 GCM and its impact on the cold bias. Climate Dynamics, 31, pp. 491-506. DOI: 10.1007/s00382-007-0347-5.

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Official URL: http://www.springerlink.com/content/8211772057767131/fulltext.pdf

Abstract

The Lagrangian advection scheme ATTILA has been applied for the transport of water vapor and cloud water in the general circulation model (GCM) ECHAM4.L39(DLR) (E39) instead of the operational semi-Lagrangian transport scheme (SLT). ATTILA is a purely Lagrangian scheme that is numerically non-diffusive, while the operational semi-Lagrangian scheme exhibits a considerable numerical diffusion in the presence of sharp gradients. The model version E39/SLT significantly overestimates the water vapor mixing ratio in the extratropical lowermost stratosphere (wet bias) by a factor of 3–5 compared to HALOE observations. Compared to E39/SLT, E39/ATTILA shows substantially reduced water vapor mixing ratios in the extratropical lowermost stratosphere up to 70%, and a steeper meridional water vapor gradient in the subtropics which is in better agreement with observations. Furthermore, the temperature distribution as simulated with E39/SLT is characterized by a pronounced cold temperature bias in the extratropical lowermost stratosphere (cold bias) and in the polar stratosphere above 50 hPa in winter (cold pole). The improvements concerning the water vapor distribution in E39/ATTILA lead to a substantial reduction of the simulated cold bias by approximately 5–7 K which also results in a better representation of the modeled tropopause, especially in the extratropics. Sensitivity studies indicate that the warming of the extratropical lowermost stratosphere in E39/ATTILA is directly related to the reduced wet bias resulting in a less infrared radiative cooling. Additionally, the cold pole problem is also slightly reduced in E39/ATTILA by approximately 2–5 K.

Document Type:Article
Title:Lagrangian transport of water vapor and cloud water in the ECHAM4 GCM and its impact on the cold bias
Authors:
AuthorsInstitution or Email of Authors
Stenke, AndreaUNSPECIFIED
Grewe, VolkerUNSPECIFIED
Ponater, MichaelUNSPECIFIED
Date:2008
Journal or Publication Title:Climate Dynamics
Volume:31
DOI:10.1007/s00382-007-0347-5
Page Range:pp. 491-506
Status:Published
Keywords:Lagrangian advection scheme, numerical diffusion, wet bias, cold bias, extratropical lowermost stratosphere
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Dynamics
Deposited By: Dr.rer.nat. Andrea Stenke
Deposited On:18 Sep 2008
Last Modified:12 Dec 2013 20:28

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