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The Millennium water vapour drop in chemistry-climate model simulations

Brinkop, Sabine and Dameris, Martin and Jöckel, Patrick and Garny, Hella and Lossow, Stefan and Stiller, Gabriele (2016) The Millennium water vapour drop in chemistry-climate model simulations. Atmospheric Chemistry and Physics (ACP), pp. 8125-8140. Copernicus Publications. doi: 10.5194/acp-16-8125-2016. ISSN 1680-7316.

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Official URL: http://www.atmos-chem-phys.net/16/8125/2016/


This study investigates the abrupt and severe water vapour decline in the stratosphere beginning in year 2000 (the ``millennium water vapour drop'') and other similarly strong stratospheric water vapour reductions by means of various simulations with the state-of-the-art Chemistry-Climate Model (CCM) EMAC (ECHAM/MESSy Atmospheric Chemistry Model). The model simulations differ with respect to the prescribed sea surface temperatures (SSTs) and whether nudging is applied or not. The CCM EMAC is able to most-closely reproduce the signature and pattern of the water vapour drop in agreement with those derived from satellite observations, if the model is nudged. Model results confirm that this extraordinary water vapour decline is in particular obvious in the tropical lower stratosphere and is related to a large decrease in cold point temperature. The drop signal propagates under dilution to the higher stratosphere and to the poles via the Brewer-Dobson circulation (BDC). We found that the driving forces for this significant decline in water vapour mixing ratios are tropical sea surface temperature (SST) changes due to a coincidence with a preceding strong El Nino--Southern Oscillation event (1997/98) followed by a~strong La Nina event (1999/2000) and supported by the change of the westerly to the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) in 2000. Correct (observed) SSTs are important to trigger the strong decline in water vapour. There are indications, that at least partly, SSTs contribute to the long period of low water vapour values from 2001 to 2006. For this period, the specific dynamical state of the atmosphere (overall atmospheric large-scale wind and temperature distribution) is important as well, as it causes the observed persistent low cold point temperatures. These are induced by a period of increased upwelling, which, however, has no corresponding pronounced signature in SSTs anomalies in the tropics. Our free-running simulations do not capture the drop as observed, because a) the cold point temperature has a low bias and thus the water vapour variability is reduced and b) because they do not simulate the appropriate dynamical state. Large negative water vapour declines are also found in other years, and seem to be a~feature, which can be found after strong combined El Nino/La Nina events, if the QBO west phase during La Nina changes to the east phase.

Item URL in elib:https://elib.dlr.de/104656/
Document Type:Article
Title:The Millennium water vapour drop in chemistry-climate model simulations
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Lossow, Stefanstefan.lossow (at) kit.eduUNSPECIFIED
Stiller, Gabrielegabriele.stiller (at) kit.eduUNSPECIFIED
Date:6 July 2016
Journal or Publication Title:Atmospheric Chemistry and Physics (ACP)
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:Yes
DOI :10.5194/acp-16-8125-2016
Page Range:pp. 8125-8140
Publisher:Copernicus Publications
Keywords:stratospheric water vapour variability, tropopause
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Atmospheric and climate research
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Modelling
Deposited By: Brinkop, Dr. Sabine
Deposited On:17 Jun 2016 16:36
Last Modified:02 May 2019 13:59

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