ORCESTRA: Half-time for the tropical cloud experiment

MPI-M researchers and their partner institutions are currently performing atmospheric measurements over the equatorial Atlantic with eight coordinated measurement campaigns. They want to find out what controls the structure of the tropical rain belt, how it will change in the future and what this means for weather patterns. A variety of state-of-the-art research platforms are being used for the measurements – from ships to satellites.

An international research team, including scientists from the Max Planck Institute for Meteorology (MPI-M), is currently conducting observations of the atmosphere in the tropical Atlantic in eight coordinated sub-campaigns. Among other things, a research vessel, research aircrafts and the EarthCARE satellite are being used. The two-month expedition started at the beginning of August in the African island state of Cape Verde. Now the scientists are heading over to the western side of the Atlantic, namely to Barbados, where they will continue their measurements until the end of September. Ground stations complete the observations at the two locations on land. In total, more than 200 scientists and technicians from almost 50 institutions are involved in the campaign.

Inside the tropical cloud band

Meteorologists are particularly interested in the tropical Atlantic because of the cloud band that determines the regional weather and which also influences the dynamics of the atmosphere globally: the Atlantic Intertropical Convergence Zone (ITCZ). The ITCZ is formed due to the intense solar radiation at the equator and encircles the entire Earth. It is known for heavy cloud formation and intense rainfall and distributes heat and moisture worldwide. However, researchers at the MPI-M, among others, have recently shown for the Atlantic that the ITCZ is not uniform but very complex with a rich internal structure. With the eight coordinated measurement campaigns in the international project “ORCESTRA” (Organized Convection and EarthCare Studies over the Tropical Atlantic), an international research team is now taking a close look at the inner life of the Atlantic ITCZ: How do the clouds in the tropical rain belt over the Atlantic organize themselves and how do these structures influence Earth’s climate? And vice versa: What does the current global warming mean for regional rainfall? “The MPI researchers are getting to the bottom of one of the big questions in atmospheric and climate research, namely: What controls the structure of the tropical rain belts and how do they respond to global warming?” says Prof. Bjorn Stevens, one of the scientific leaders of the project and director of the MPI-M.

Current climate models can only predict the changes in the ITCZ to a limited extent. It is therefore important to better understand the relevant processes. The ORCESTRA measurements are designed to provide key insights into this matter. The researchers are focusing primarily on mesoscale processes, i.e. those that take place on a horizontal length scale of a few to a few hundred kilometers and shape the overall picture of the ITCZ.

Scientific management by MPI-M

The MPI-M initiated ORCESTRA and is responsible for its scientific management. In the field, it is in charge of the “PERCUSION” aircraft/satellite campaign together with the German Aerospace Center (DLR) and other University research institutes supported by the Deutsche Forschungsgemeinschaft (German Research Foundation, DFG). MPI-M is also the scientific lead of the “BOW-TIE” ship campaign, which is co-led with researchers from the GEOMAR Helmholtz Centre for Ocean Research and employs the German research vessel (RV) Meteor, and the institute also contributes to many of the other sub-campaigns.

The individual campaigns are coordinated so that the concerted measurements from the different platforms complement each other. An important part of the project is the validation of the EarthCARE satellite of the European Space Agency ESA, which was developed together with the Japan Aerospace Exploration Agency JAXA. EarthCARE has been in orbit since the end of May 2024. For the validation, the HALO research aircraft operated by DLR will cross the ITCZ in sync with the satellite. “The measurements will help us to understand how to use global measurement systems like EarthCARE to study rainbelts, monsoons and tropical cyclones”, says Bjorn Stevens. Initial results also suggest that the vertical structure of the atmosphere in the region has some surprises in store. One immediate one, says Stevens, is the extent to which convection preferentially moistens the middle troposphere, near the zero-degree isotherm, something that strongly influences Earth’s energy balance, and hence how Earth responds to warming. Scientists will be busy analyzing the rich data set after the campaign, with many new insights to be expected.

Wissenschaftliche Ansprechpartner:

Prof. Dr. Bjorn Stevens, +49 40 41173-421, bjorn.stevens@mpimet.mpg.de

Media contacts:
Dr. Denise Müller-Dum, +49 40 41173- 387, denise.mueller-dum@mpimet.mpg.de
Michaela Born, +49 40 41173-154, michaela.born@mpimet.mpg.de

Weitere Informationen:

http://www.orcestra-campaign.org – ORCESTRA project website
http://www.mpimet.mpg.de/en/research/observations/orcestra – Information on ORCESTRA on the MPI-M website