1. Relationships inferred from AIRS-CALIPSO synergy
Upper Tropospheric Humidity and Cirrus Clouds: Relationships Inferred by Combined AIRS and CALIPSO Data, Evaluation of ECMWF Forecasts and Influence of Vertical Resolution on Ice Supersaturation N. Lamquin (1), C. J. Stubenrauch (1), K. Gierens (2), J. Pelon (3) (1) C.N.R.S./ I.P.S.L. Laboratoire de Météorologie Dynamique, Ecole Polytechnique, France (2) Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany (3) C.N.R.S./I.P.S.L. Service d’Aéronomie, Paris, France
qs integrated by steps of 1 hPa:
Relationships inferred from AIRS-CALIPSO synergy
Colocation: August 2006 – July 2007 Night, +60°/-60° latitude coverage
Lamquin, Stubenrauch and Pelon., JGR 2008
ps calculated by Sonntag’s formulae
(Sonntag, 1990):
q determined by means of the mixing
ratio in the AIRS layer:
q = w / (1+w)
RHice = q/qsat
AIRS (Atmospheric Infrared Sounder)
L2, version 5, NASA
Temperature and water vapor vertical profiles, quality flags…
(Susskind et al. 2003, 2006; Tobin et al. 2006)
RHice calculation in 50 to 100 hPa – thick pressure layers
CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation)
Data from NASA Langley Research Center Atmospheric Science Data Center
archived at ICARE and Climserv (IPSL)
High cloud top and base pressure: sub-visible cirrus, thin and thick cirrus
number of cloud layers, tropopause…
Estimation of highest cloud optical depth, colocations with retrieved AIRS cloud properties
Stubenrauch et al., JGR 2008
Midlatitudes
hPa
Distance of top
of highest cloud
to tropopause
Separation into two classes
of optical depth
Midlatitudes
hPa
Mean RHice remains < 100% even for clouds extending over the whole pressure layer (influence of vertical and horizontal humidity variability, supersaturation occuring over smaller vertical extents than cloud appear ?)
If significant, higher mean RHice for lowest optical depths at comparable geometrical thickness (more depletion of water vapor for largest optical depths)
Greater influence of geometrical thickness on mean RHice than optical depth ( % vs. 5 – 10 %)
Difficulties for detection of ice supersaturation
Tropics
hPa
Tropics
hPa
Multiple-scattering contribution increasing with optical depth
Evaluation of ECMWF (European Center for Medium-range Weather Forecasts)
forecasts with new ice supersaturation scheme
using AIRS and CALIPSO
Lamquin, Gierens, Stubenrauch, and Chatterjee, ACPD 2008
Comparison AIRS-CALIPSO,
LMD vs. L2 retrievals, high clouds.
From study in Stubenrauch et al. (JGR 2008)
Ice supersaturation in the upper troposphere is an explicit feature in the Integrated Forecast System, operational since Sept 13, 2006, was introduced by Tompkins et al. (2007), it adopts the supersaturated relative humidity (RH) threshold using empirical approximation of the results of Koop et al. (2000) given by Kärcher and Lohmann (2002), f(T).
It has produced some changes in the statistics of UTH and cloud fraction in the IFS (decrease in high-level cloud cover).
Small adjustments
for vertical griddings ←
Colocation:
Europe window
One year
Two resolutions of
ECMWF
forecasts →
Spin up phase for the model to reach constant ice supersaturation occurrence →
Good agreement between
ECMWF UTH and
CALIPSO high clouds
Comparisons between ECMWF forecasted UTH and AIRS UTH show a good agreement for clear (or mostly clear) scenes.
Cloudy scenes take into account a variability of RHi values found in AIRS subject to biases due to the vertical resolution, this has to be taken into account to evaluate the forecast of the nucleation of high clouds.
Influence of vertical resolution on
ice supersaturation occurrence
Confronting two resolutions in the ECMWF forecasts,
Comparison with radiosoundings
High cloud nucleation in the model resets RHi to 100% while AIRS sees a variability of situations.
Distributions consistent
with previous results
(first part of poster).
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