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Particle Backscatter and Relative Humidity in and around Cirrus Clouds Measured with a Lightweight Balloon Sonde

English title Particle Backscatter and Relative Humidity in and around Cirrus Clouds Measured with a Lightweight Balloon Sonde
Applicant Peter Thomas
Number 117987
Funding scheme Project funding (Div. I-III)
Research institution Institut für Atmosphäre und Klima ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Climatology. Atmospherical Chemistry, Aeronomy
Start/End 01.12.2007 - 28.02.2011
Approved amount 187'873.00
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Keywords (10)

supersaturation; optical backscatter; water budget; hydrology; dehydration / ice nucleation; atmospheric water vapor; balloon sounding; aerosol optical backscatter; stratospheric aerosol; frost point hygrometer

Lay Summary (English)

Lead
Lay summary
Dehydration mechanisms driven by the formation of visible and subvisible cirrus clouds determine the atmospheric water vapor budget and thus the chemical and radiative properties of the upper troposphere and the stratosphere. In contrast to previous understanding recent in situ observations have revealed high supersaturation with respect to ice of several 10 % occurring not only in clear air surrounding cirrus clouds but also inside the cirrus themselves, and apparently also in large interconnected regions where they cannot be explained easily in terms of local upwelling. It is not well understood how such supersaturations, if not caused by instrumental artifacts, can be maintained within clouds exposing large ice surface areas to the water vapor. Precise and frequent measurements of cirrus properties and relative humidity using independent instrumentation are required to obtain a better understanding of dehydration processes and of their influence on the global atmospheric radiation budget.

The main objective of this project will be to obtain new insights into these processes by performing measurements with an innovative, cost-efficient (max. 2000 CHF total) and lightweight (max. 2 kg total) radiosonde payload capable to measure simultaneously with high precision water vapor supersaturation and particle backscatter at two distinct wavelengths in and around cirrus clouds. This project aims at characterizing the sonde, calibrating it, employing it regularly (twice per month plus during intensive campaigns), and interpreting the obtained data. First test flight results with prototypes of the newly developed backscatter sonde prove it operational. Ultimate goal of the project is to characterize and understand cirrus nucleation and growth. In addition the sonde will provide particle size characterization from the boundary layer aerosol and clouds all the way up to the stratospheric aerosol layer irrespective of its volcanic loading.

We intend to make the newly developed backscatter sonde available to other researchers and monitoring services to eventually compile a cirrus cloud properties climatology, as this sonde will be an economically attractive asset when flying piggyback with other instruments on radiosondes, research balloons or aircraft.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
147127 BATTREX-CH: The Swiss contribution to the international BAlloonsonde Tropical TRopopause EXperiment 01.09.2014 Project funding (Div. I-III)
120175 Modelling Heterogeneous and Homogeneous Ice Nucleation and Growth at Cirrus Cloud Levels 01.03.2009 Project funding (Div. I-III)
159950 Investigation of midlatitude high clouds characteristics and processes 01.01.2016 Project funding (Div. I-III)

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