Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing 1Johannes Gutenberg-University Mainz, Institute for Atmospheric Physics, Mainz, Germany
2Laboratory for Atmospheric and Space Physics (LASP), University of Colorado, Boulder, USA
3Laboratoire de Météorologie Physique (LAMP), Université Blaise Pascal, Aubière Cedex, France
4Alfred Wegener Institute for Polar and Marine Research (AWI), Potsdam, Germany
5Institute of Atmospheric Physics, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
*now at: Leipzig Institute for Meteorology (LIM), University of Leipzig, Germany
Received: 10 Jun 2009 – Published in Atmos. Chem. Phys. Discuss.: 23 Jun 2009 Abstract. The vertical distribution of ice crystals in Arctic boundary-layer
mixed-phase (ABM) clouds was investigated by airborne
remote-sensing and in situ measurements during the Arctic Study of
Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign
in March and April 2007. Information on the spectral absorption of
solar radiation by ice and liquid water cloud particles is derived
from airborne measurements of solar spectral radiation reflected
by these clouds. It is shown by calculation of the vertical
weighting function of the measurements that the observed
absorption of solar radiation is dominated by the upper cloud
layers (50% within 200 m from cloud top). This vertical
weighting function is shifted even closer to cloud top for
wavelengths where absorption by ice dominates. On this basis an
indicator of the vertical distribution of ice crystals in ABM
clouds is designed.
Revised: 04 Dec 2009 – Accepted: 04 Dec 2009 – Published: 15 Dec 2009
Applying in situ measured microphysical properties, the cloud-top
reflectivity was calculated by radiative transfer simulations and
compared to the measurements. It is found that ice crystals near
cloud top (mixed-phase cloud top layer) are necessary to reproduce
the measurements at wavelengths where absorption by ice dominates.
The observation of backscatter glories on the cloud top generally
indicating liquid water droplets does not contradict the
postulated presence of ice crystals. Radiative transfer
simulations reproduce the observed glories even if the cloud top
layer is of mixed-phase character.
Citation: Ehrlich, A., Wendisch, M., Bierwirth, E., Gayet, J.-F., Mioche, G., Lampert, A., and Mayer, B.: Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing, Atmos. Chem. Phys., 9, 9401-9416, doi:10.5194/acp-9-9401-2009, 2009.