Lennart Bengtsson, Max-Planck-Institute for Meteorology, Hamburg, Germany


Using atmospheric re-analyses for understanding the climate system.


Using analyzed weather maps to understand the general circulation of the Earth´s atmosphere started already in the early 1960. A complicating factor was the ongoing changes of the forecasting systems. The first efforts to produce an atmospheric data set for the global atmosphere with a unique data-assimilation system was done in 1979 covering a full year of daily observations from the global weather experiment in 1978. The work was undertaken by ECMWF and GFDL. It was increasingly realized by the scientific community that long series of consecutive daily weather analyses were useful for climate studies.  ECMWF and later NOAA started from 1986 to regularly producing re-analyses for different periods of time using the most advanced data-assimilation techniques available. Most work so far has been concentrated on the period after 1979 but daily data sets have been produced going back as far as to 1836.
Increasingly comprehensive re-analyses are becoming available including the recent ERA5 data set from ECMWF. In the talk I will present some recent results for the last 20 years using ERA5 comparing them with high-resolution climate change studies with emphasis on the Polar Regions. There are some inconsistencies in the data sets but they are generally reduced after 1999 suggesting impact from more consistent observations.
The studies so far highlight the difference between the two Polar Regions.  There is a clear increasing greenhouse signal at the North Polar Region while rather little at the South Polar Region. Polar  amplification is consequently not a general feature.
I am highly indebted to Matz Hedman for the technical work undertaken in connection to this study.

Some background references:

Bengtsson, L and J. Shukla, 1988: Integration of space and in situ observations to study global climate change.
Bull. Amer. Meteor. Soc. (1988) 69 (10): 1130–1143.<1130:IOSAIS>2.0.CO;2
Bengtsson, L.,  2013: The Changing Energy Balance of the Polar Regions in aWarmer
Climate.  J. Climate (2013) 26 (10): 31123129.


Tuesday September 29, 11:15


Remotely via Zoom - link will be distributed via MISU's seminar email announcement.