  Clouds play a major role in Earth's energy budget and hydrological cycle.
Clouds dynamical structure and mixing with the ambient air have a large impact
on their vertical mass and energy fluxes and on precipitation. Most of the
cloud evolution and mixing occurs at scales smaller than presently observable
from geostationary orbit, which is less than 1 km. A satellite mission is
planned for bridging this gap, named "Cluster for Cloud evolution, ClImatE and
Lightning" (C3IEL). The mission is a collaboration between the Israeli (ISA)
and French (CNES) space agencies, which is presently at the end of its Phase A.
The planned mission will be constituted of a constellation of 2 to 3
nanosatellites in a sun synchronous early afternoon polar orbit, which will
take multi-stereoscopic images of the field of view during an overpass. C3IEL
will carry 3 instruments: (1) CLOUD visible imager at a spatial resolution of
20 m. The multi-stereoscopic reconstruction of the evolution of cloud envelops
at a resolution better than 100 m and velocity of few m/s will provide an
unprecedented information on the clouds dynamics and evolution. (2) WATER VAPOR
imagers at 3 wavebands with different vapor absorption will provide vertically
integrated water vapor around the cloud and possibly a 3-dimensional structure
of the vapor around the clouds due to their mixing and evaporation with the
ambient air. (3) Lightning Optical Imagers and Photometers (LOIP). The
lightning sensors will provide a link between cloud dynamics and
electrification at higher spatial resolution than previously available. C3IEL
will provide presently missing observational evidence for the role of clouds at
sub-km scale in redistributing the energy and water in the atmosphere, and of
the relation between storm vigor and frequency of lightning activity.
