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Overestimated acceleration of the advective Brewer-Dobson circulation due to stratospheric cooling

Eichinger, Roland and Sácha, Petr (2020) Overestimated acceleration of the advective Brewer-Dobson circulation due to stratospheric cooling. Quarterly Journal of the Royal Meteorological Society, pp. 1-15. Wiley. doi: 10.1002/qj.3876. ISSN 0035-9009.

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Official URL: https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.3876


Tropospheric warming and stratospheric cooling influence the vertical structure of the atmosphere. Numerous studies have analysed the thermal expansion of the troposphere, however, stratospheric cooling reverses the sign of this shift in the middle stratosphere, causing a downward shift in the upper stratosphere and mesosphere. This is a robust feature in transient climate model simulations, but its impact is commonly unappreciated. Here, we quantify the trend difference of the residual mean vertical velocity (w*), a proxy for diagnosing the advective Brewer-Dobson circulation (BDC) strength, which arises from implicit neglect of the shrinking distance between stratospheric pressure levels in the CCMI-1 (Chemistry-Climate Model Initiative part 1) data request. There, a log-pressure formula with constant scale height is recommended to compute w*. However, stratospheric cooling in transient climate simulations causes a reduction of the geometrical distance between pressure levels and thereby also the scale height significantly decreases over time. Using the general scale height definition for the transformation, the w* trends are therefore smaller. In both cases, the units are m·s-1, but in the latter case it is the constant measure of length geopotential metres and not log-pressure metres. We quantify that, due to the temperature dependence of log-pressure metres, past studies that based w* trend analyses on log-pressure w* overestimated the advective BDC acceleration by ~20%. This result is consistent among the CCMI-1 projections over the 1960-2100 period. We highlight that other diagnostics can also be affected by the neglect of the declining stratospheric pressure level distance. A detailed description of the diagnostics is necessary for consistent assessments of trends. Data processing tools should generally not include the constant scale height assumption if the data are used for trend analyses.

Item URL in elib:https://elib.dlr.de/136464/
Document Type:Article
Title:Overestimated acceleration of the advective Brewer-Dobson circulation due to stratospheric cooling
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Eichinger, RolandDLR, IPA und MIM, Univ. Münchenhttps://orcid.org/0000-0001-6872-5700
Sácha, PetrUniv. Prag, Tschechische RepublikUNSPECIFIED
Date:19 July 2020
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
Page Range:pp. 1-15
EditorsEmailEditor's ORCID iD
Gerber, E. P.New York Univ., New York, NY, USAUNSPECIFIED
Keywords:Stratosphere Brewer‐Dobson circulation global climate modelling vertical velocity CCMI scale height climate change coordinate system
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 - Middle Atmosphere, R - Atmospheric and climate research
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Modelling
Deposited By: Eichinger, Roland
Deposited On:07 Oct 2020 09:36
Last Modified:07 Oct 2020 09:36

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