The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia 1Centre for Australian and Weather and Climate Research, Melbourne, Australia
17 Aug 2011
2Laboratoire ATmosphere, Milieux, Observations Spatiales (LATMOS), Vélizy, France
3University of Reading, Reading, UK
4Monash Weather and Climate, School of Mathematical Sciences, Monash University, Clayton, Australia
5Australian Bureau of Meteorology Training Centre (BMTC), Melbourne, Australia
Received: 07 Jun 2010 – Published in Atmos. Chem. Phys. Discuss.: 25 Aug 2010 Abstract. The high complexity of cloud parameterizations now held in models puts more
pressure on observational studies to provide useful means to evaluate them.
One approach to the problem put forth in the modelling community is to
evaluate under what atmospheric conditions the parameterizations fail to
simulate the cloud properties and under what conditions they do a good job.
It is the ambition of this paper to characterize the variability of the
statistical properties of tropical ice clouds in different tropical
"regimes" recently identified in the literature to aid the development of
better process-oriented parameterizations in models. For this purpose, the
statistical properties of non-precipitating tropical ice clouds over Darwin,
Australia are characterized using ground-based radar-lidar observations from
the Atmospheric Radiation Measurement (ARM) Program. The ice cloud
properties analysed are the frequency of ice cloud occurrence, the
morphological properties (cloud top height and thickness), and the
microphysical and radiative properties (ice water content, visible
extinction, effective radius, and total concentration). The variability of
these tropical ice cloud properties is then studied as a function of the
large-scale cloud regimes derived from the International Satellite Cloud
Climatology Project (ISCCP), the amplitude and phase of the Madden-Julian
Oscillation (MJO), and the large-scale atmospheric regime as derived from a
long-term record of radiosonde observations over Darwin.
Revised: 27 Jul 2011 – Accepted: 08 Aug 2011 – Published: 17 Aug 2011
The vertical variability of ice cloud occurrence and microphysical
properties is largest in all regimes (1.5 order of magnitude for ice water
content and extinction, a factor 3 in effective radius, and three orders of
magnitude in concentration, typically). 98 % of ice clouds in our dataset
are characterized by either a small cloud fraction (smaller than 0.3) or a
very large cloud fraction (larger than 0.9). In the ice part of the
troposphere three distinct layers characterized by different
statistically-dominant microphysical processes are identified. The
variability of the ice cloud properties as a function of the large-scale
atmospheric regime, cloud regime, and MJO phase is large, producing mean
differences of up to a factor 8 in the frequency of ice cloud occurrence
between large-scale atmospheric regimes and mean differences of a factor 2
typically in all microphysical properties. Finally, the diurnal cycle of the
frequency of occurrence of ice clouds is also very different between regimes
and MJO phases, with diurnal amplitudes of the vertically-integrated
frequency of ice cloud occurrence ranging from as low as 0.2 (weak diurnal
amplitude) to values in excess of 2.0 (very large diurnal amplitude).
Modellers should now use these results to check if their model cloud
parameterizations are capable of translating a given atmospheric forcing
into the correct statistical ice cloud properties.
Citation: Protat, A., Delanoë, J., May, P. T., Haynes, J., Jakob, C., O'Connor, E., Pope, M., and Wheeler, M. C.: The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia, Atmos. Chem. Phys., 11, 8363-8384, doi:10.5194/acp-11-8363-2011, 2011.