To develop and test radar based-algorithms to infer the
vertical profiles of cloud properties such as ice and liquid
water content. To study the properties of natural clouds, their
evolution and their characteristics.
An existing 94GHz radar will be upgraded to increase its
sensitivity to clouds and will then be deployed alongside two
existing 35 and 3 GHz radars at Chilbolton in the UK so that the
three radars, together with a 95GHz radiometer, can scan a common
volume of cloud.
The radar upgrade should take 10 months and will be followed by a
twelve month period of observations with the three radars and the
radiometer. Measurements will be made on both a statistical and
an event basis, and will encompass low level water clouds such as
stratocumulus, higher level cirrus clouds which are composed of
ice particles only, together with clouds of mixed phase.
Algorithms will be developed to infer cloud properties from the
radar measurements at the three wavelengths. The 3GHz
reflectivity is unaffected by attenuation or Mie scattering. The
increased attenuation at the higher frequencies will be used to
derive cloud liquid water content. For ice clouds the
attenuation at all three radar frequencies is negligible, but the
presence of larger ice particles results in Mie scattering and a
reduced radar reflectivity at the higher frequency, and this
reduction can be used to derive a mean size for the ice
In parallel with the establishment of algorithms to infer liquid
and ice water content, particle size, and the efficiency of cloud
detection by radar, studies will be carried out of cloud
evolution. Climate models are very sensitive to the assumed
terminal velocity of cirrus particles which affect the
persistence of ice clouds; direct radar measurements of these
velocities will aid parameterisation schemes.
Clouds represent one of the chief sources of uncertainty in
climate studies; small alterations to cloud parameterisation
schemes in general circulation models leading to very different
global distributions of clouds. The ultimate aim is for a
spaceborne cloud radar to provide vertically resolved global
cloud data, this first step is to provide ground based radar data
to improve and validate parameterisation schemes.
Funding SchemeCSC - Cost-sharing contracts
OX11 0QX Didcot,harwell,chilton
50013 Firenze Campi Bisenzio