Master Thesis by Karis Anneke Kürstein Glibbery – Niels Bohr Institute - University of Copenhagen

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Master Thesis by Karis Anneke Kürstein Glibbery

Verification of the longwave feedback in the climate model EC-Earth

Abstract

Radiative feedbacks are variables in the climate system that act to amplify or dampen a surface temperature response to an external radiative forcing. Knowledge on feedbacks is crucial in the determination of climate change after a forcing and the temperature response to increases in anthropogenic greenhouse gas emissions is of special current interest.
In this report, different time series of outgoing longwave radiation (OLR) and surface temperature are regressed to obtain the longwave feedback. The major task is to compare output data from the recently developed model EC-Earth, partially developed at the Danish Meteorological Institute, to observed data as a verification study on EC-Earth. Data from both the atmosphere-only and the fully coupled ocean-atmosphere model is used in the analysis and OLR data from NOAA, ERBE and ISCCP, measured from satellites, are used in the observed analysis together with surface temperatures from NCEP.
EC-Earth and observations yield similar feedback results with far most lying in the range of 1.41 Wm-2 K-1 to 1.71 Wm-2 K-1 . Similar results with different methods imply that the longwave radiative feedback is close to being a constant and is not dependent on the time scale in question. An attempt to quantify the longwave water vapor feedback using 'radiative kernels' and specific humidity data is made giving the result 1.65 Wm-2 K-1 for atmosphere-only EC-Earth which is close to results from previous studies.
A side project concludes that limiting the latitude range in the data changes the feedback result more or less from the result with a full spatial coverage. This is especially the case when only using data from the tropical region.
Supervisors: Eigil Kaas, Niels Bohr Institute, University of Cophenhagen and Shuting Yang, Danish Meteorological Institute