ORCESTRA (Organized convection and EarthCare studies over the tropical atlantic)

During the summer 2024, several initiatives aiming at understanding the mesoscale organisation of tropical convection with field data and satellite observations will take place over the tropical ocean. This international initiative, named ORCESTRA, will include: the French airborne field campaign MAESTRO (Mesoscale organisation of tropical convection), the German airborne field campaign PERCUSSION (Persistent EarthCare underflight studies of the ITCZ and organized convection), the German ship cruise BOW-TIE (Beobachtung von Ozean und Wolken – Das Trans ITCZ Experiment) and the US initiative PICCOLO (Process investigation of clouds and convective organization over the tropical ocean).

The overarching objective of ORCESTRA is to better understand the physical mechanisms that organize tropical convection at the mesoscale, including the interaction of convective organization with tropical waves and air-sea interaction, and the impact of convective organization on climate and the Earth’s radiation budget and processes of tropical cyclogenesis. In addition to advancing understanding of tropical meteorology and atmospheric processes, ORCESTRA observations will to help calibrate and validate satellite remote sensing (especially EarthCARE) and a new generation of global ocean-eddy and storm-resolving climate models.

The ORCESTRA/MAESTRO field campaign

The ORCESTRA/MAESTRO campaign will take place from Aug 10 to Sept 10 2024 over the Atlantic ocean near Cape Verde, with research aircraft operating out of Sal (16o4’N, 22o6’W).

The SAFIRE ATR-42 aircraft will fly in the lower troposphere with a rich ensemble of in-situ and remote sensing instruments to characterize the interplay between coherent structures in the subcloud-layer, cloud properties near the cloud base level, the geometry of convective clouds and the horizontal and vertical distribution of water vapor and temperature in-between clouds. These observations will be completed by measurements from the HALO aircraft flying a large circle in the upper troposphere and dropping sondes intensively to characterize the dynamical and thermodynamical properties of the environment at the mesoscale (e.g. divergence and vertical motion), geostationary satellite measurements from which we will infer informations about clouds and vertical motions in the clear-sky atmosphere, and EarthCARE measurements of radiative fluxes, precipitation, clouds and vertical motion within clouds.

MAESTRO/ORCESTRA will build on experimental advances from the EUREC4A field campaign, and will develop new experimental techniques to provide unprecedented observations of the convective atmosphere. In particular, the ATR-42 will probe the atmosphere in multiple directions with a W-band pulsed Doppler cloud radar (RASTA) pointing up and down, a Doppler High Spectral Resolution Lidar (LNG) pointing up or down, a Doppler cloud radar (BASTA) pointing horizontally and, for the first time, a Raman lidar pointing horizontally (AWALI). These measurements will be completed by an ensemble of probes and sensors to measure temperature, humidity and winds at a fast rate and to characterize aerosols and cloud microphysics of liquid and ice clouds.

Most ATR flights will consist in a series of straight legs flown at different altitudes (near the surface, in the subcloud-layer, at cloud base and in the mid-troposphere around 6 km). The ATR is expected to fly twice a day, three days a week. Each ATR flight is expected to last 3-4 hours, including one hour during which it will fly in coordination with HALO. Some flights will be devoted to the calibration and validation of the European Space Agency (ESA) EarthCARE satellite, which is expected to be launched in Spring 2024. These flights will take place as close as possible to the satelite orbit.