How does rain develop? Will rain fall from a cloud, does it pass without rain, or even disolve? To help solve these question a team of five researchers led by Eberhard Bodenschatz, Director at the Max Planck Institute for Dynamics and Self-Organization (MPIDS), were conducting in cloud measurements in the mid-Atlantic. On their journey from Montevideo in Uruguay to Las Palmas on Gran Canaria on the German research vessel Maria S. Merian they took on board the Max Planck CloudKite, a newly developed balloon kite with measuring gondola. The details on how millions of micrometer-sized water droplets in a cloud grow into raindrops that are thousands of times larger still remains a matter of current research by physicists and meteorologists. The goal of the MPIDS researchers is to gain a better understanding of the microphysics and the role of turbulence in warm clouds. This is best studied at the equator, where shallow cumulus clouds occur basically every day.
At the start in the port of Montevideo in Uruguay the clouds were low. Nevertheless, the CloudKite team consisting of MPIDS Director Eberhard Bodenschatz, Marcel Schröder, Marcel Meyer, Oliver Schlenczek and Philipp Höhne boarded the research vessel Maria S. Merian full of expectations and anticipation. At 9 o'clock local time the ship's horn sounded - loud and low: the starting signal for the 3-week measuring campaign. With 20 scientists from seven different research institutes the Maria S. Merian was fully occupied.
First cloud measurements near the equator
The Max Planck CloudKite takes measurements from the ship in low clouds. It can climb up to two kilometers into the air. It consists of two balloon kites, an upper one with a volume of approx. 34 m3 and the main balloon with a volume of 250 m3. The MPIDS researchers had already met in Montevideo two days before the ship was due to leave to install the two balloons on the ship. Both were successfully filled with helium during the first three days on the ship. The first deployment showed that the balloon kites, are perfect to investigate cloud development and dynamics from a 100 meters above sea level all the way to 1.5km. This allows the researchers can carry out measurements from the cloud-base to the cloud top over long periods of time. The instruments on top of the Max Planck CloudKite measure insitu cloud properties at unprecedented accuracy.
Complete picture of droplet dynamics in cluster clouds
To obtain a complete picture of the droplet dynamics in cumulus clouds, the Max Planck Team carried out five measurement flights during the cruise. The cumulus clouds at the mid-Atlantic are especially important "Frist they are the most prevalent cloud on earth and contribute the most to the climate and second they are ideal to study rain initiation to the point where we can help improve weather forecast and calculations of the climate evolution ". From their experiments in the laboratory and also at the environmental research station Schneefernerhaus on the Zugspitze, the MPIDS researchers know that turbulence plays a dominant role in cloud development.
How uniform are clouds?
The two imaging instruments that are part of the Max Planck CloudKite help to understand when and how quickly the smallest drops become larger drops. Meteorologist Schlenczek adds: "Our holography instrument in the measuring gondola takes 75 pictures every second, which we can use to measure the position and size of the drops in a cylinder of cloudy air roughly 2.5cm in diameter and 25cm long. We also have a high-speed camera with which we can measure the speed of the drops. For this purpose, the cloud volume is illuminated with a light sheet made by a strong laser. From the displacement of the droplets from one image to the next we derive the speed of each drop." The researchers also need to know the meteorological background to understand the physical processes. To this end the Max Planck CloudKite gondola measures wind speed, humidity, temperature, and liquid water content at high resolution. Finally, the Max Planck researchers employed a fast inertial navigation system to be able to calculate which speeds are actually attributable to the wind and which result from the movements of the ship and the balloon.
Be able to better predict rainfall events
"Our just completed first campaign with the Max Planck CloudKite was a success. We have the first data analyzed and find important new insights " concludes Director Eberhard Bodenschatz. He is looking forward to the future campaign EUREC4A (Elucidating the Role of Cloud-Circulation Coupling in Climate), which will take place in January and February 2020 off Barbados. Together with three other Max Planck Institutes (for Meteorology, for Marine Microbiology and for Chemistry) and an international research team, they will study meteorology in a roughly 1 km2 area of the tropical North Atlantic for 6 weeks. The aim of EUREC4A is to increase our understanding of the interactions between clouds, convection and circulation and thus determine their influence on climate sensitivity. Starting from the Max Planck cloud observatory on Barbados, which has been in operation since 2010, measurements using the German research aircraft HALO and the French research aircraft SAFIRE and four ships are planned to get a comprehensive picture of the meteorological processes so important for our climate. The crew around Eberhard Bodenschatz will then work with their big Max Planck CloudKite on the Maria S. Merina and with the small one on the Meteor.