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Flight into Icy Clouds

The research aircraft Polar 5 will start its VerDI (Vertical Distribution of Ice in Arctic Clouds) campaign in the Arctic at the end of April with the NIXE-CAPS spectrometer on board. It will be used by Jülich scientists to examine the particles in “mixed-phase clouds” consisting of ice crystals and droplets of water.

“Unfortunately, we still know very little about mixedphase clouds. However, their properties are very important for climate models,” says Dr. Martina Krämer at IEK-7. This is because, on the one hand, clouds retain the thermal radiation of the earth within the atmosphere. On the other hand, they also reflect the incident radiation of the sun, thus cooling the earth. The intensity of these effects depends on the nature of the clouds; in mixed-phase clouds, the fraction of ice particles they contain is a decisive factor.
The goal of the VerDI campaign is to provide new information. Research flights coordinated by Universität Leipzig will take off from the Canadian town of Inuvik for a period of about one month. The spectrometer from Jülich will play an important role during these flights. “NIXECAPS is not only able to measure the size of the cloud particles, but can also be used to determine whether clouds are made up of water droplets or ice crystals,” says Krämer. This permits conclusions to be drawn on the fraction of ice particles in clouds.
NIXE-CAPS consists of two parts. A laser in the upper part measures the size of each cloud particle individually. Depending on its size, the light emitted by the laser is scattered to a different degree. “We are able to capture a size ranging from 0.6 to 50 micrometres,” says Krämer. The lower part of the spectrometer measures particles between 15 micrometres and one millimetre in size. Here, a laser beam hits cloud particles and produces shadows, the size and shape of which are determined by measuring diodes.

Krämer and her colleagues Armin Afchine and Jessica Meyer are also responsible for compiling weather forecasts for Inuvik. As the VerDI campaign is only entitled to fifty flight hours with the Polar 5 aircraft, the ability to respond to the weather is of great importance.

NIXE - CAPSAirborne spectrometer providing information on the size and number of cloud particles (drops and ice crystals) covering the size range of 0.6 - 900 µm in diameter.

Contact: Dr. Martina Krämer (