Detection of changing radiative forcing over the recent decades

Principal Investigator

Dr Shuting Yang and Dr B Machenhauer
Danish Meteorological Institute
Lyngbyvej 100
2100 Copenhagen
Denmark

shuting@dmi.dk or BM@dmi.dk

Project description

The EC-project DETECT will calculate temporal variations in AGCM estimates of systematic (i.e. long-term mean values of) initial temperature tendencies (SITTs) due to radiative forcings of the Earth climate system over the last four decades. The AGCM (atmospheric general circulation model) to be used is a new climate model version presently under development at DMI and MPI. It combines the very efficient dynamical core of the ECMWF Integrated Forecast System (the latest ARPEGE climate version) with the newest physical parameterization package (version 5) of the German climate model ECHAM, including its latest release of aerosol chemistry. The SITTs, due to different kinds of modeled processes, will be calculated during assimilation in the AGCM of data from:

• the new global reanalysis ERA-40, presently being made at ECMWF for the period 1957 to 2001, and
• For the same period analyses of observed emissions leading to aerosols.

The forcings to be analyzed separately are those related to

• observed antropogenic caused changes in well mixed greenhouse gases, ozone, tropospheric aerosols (e.g. sulfates and black carbon), and surface albedo (vegetation), as well as
• observed natural variations in solar irradiance and in stratospheric (volcanic) and tropospheric (i. e. desert dust) aerosols.

Also the forcing effects due to feedback variations in humidity, clouds and snow/ice coverage will be estimated.

During the assimilation we will also calculate a total energy budget, for different parts (sub volumes) of the Earth climate system, as a function of time. Using the discretization of the ERA40 assimilation model (TL159,L60) we will for each atmospheric sub volume monitor: observed (analyzed) monthly mean values of the total potential energy, P, and the kinetic energy, K, and for each land sub surface volumes considered we will monitor: observed monthly mean values of the internal energy, I. We will try to explain the resulting observed long term variations in the P and I values (which are proportional to temperature) during the four decades considered by variations in the different types of radiative forcings, SITTs, calculated during our AGCM assimilation. Thus, we try to explain the observed climate changes by the different kinds of model computed forcing. The reliability of these explanations will depend on how realistic the schemes of physical parameterization in the climate model are working. However, by computing the SITTs during an assimilation of observed data effects of model climate drifts are eliminated and the estimates are kept as realistic as possible. Another advantage is that also the errors in the SITTs can be calculated during the assimilation which will facilitate consideration of processes not included in the AGCM and give conservative estimates of errors in the model determined SITTs used in the explanation of heat budget variations. The resources applied for will be used to carry out the assimilation described above.

For more details, please also refer to the latest progress report.

Additional information

Project period 2001 - 2003.