Name of proposer: 
Klaus Gierens

Institution:
Institut für Physik der Atmosphäre
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Oberpfaffenhofen
D-82234 Wessling, Germany

Contact:
phone: +49-8153-28-2541; fax: +49-8153-28-1841
email: klaus.gierens@dlr.de
www:   http://www.dlr.de/ipa/


Title of contribution:
"Ice supersaturation and cirrus clouds in the global tropopause region"

Main elements:
(a) Evaluation of global humidity and temperature data sets: e.g. MOZAIC,
	Satellite data;
(b) Evaluation of local humidity and temperature data sets:
	Radiosondes;
(c) Statistical interpretation of the data: distributions, extreme
	values, etc.;
(d) Physical interpretation of the data: Properties of processes that
	lead to the observed distributions;
(e) Change of the cloud physics of the ECMWF's forecast system in
	order to represent ice supersaturation in the model and to
	improve representation of cirrus microphysics.


Relationship to MoU Objectives:
This work contributes directly to objectives 2 (evaluation of data
sets, main elements a and b) and 5 (state of UTLS, relevant processes,
main elements c and d) of the MoU. Main element (e) will contribute to
objectives 2 (assimilation of data sets into models) and 6 (analysis
of anthropogenic impact) in a more indirect way through improvement of
the underlying model's cloud physics representation. Currently, these
models (and also many retrieval algorithms) use an upper cut-off of
relative humidity at ice saturation which is, however, in
contradiction to a growing volume of in-situ data and to the theory of
ice formation in the cold tropopause region. Element (e) aims to
abandon those cut-off values. However, the influence of this work will
probably only be felt after the end of Action 723.

Relationship to scientific program:
The contributions are mainly related to part C-3 "Understanding" of
the scientific program.

Deliverables:
Main elements (a) to (d) above will produce scientific papers. Main
element (e) will produce a new cloud physics module for the ECMWF
weather prediction system, which could also be incorporated in a
similar way in other NWP or GCM codes.


Indicative timetable:
Currently, elements (a) to (d) are topic of Peter Spichtinger's
doctoral thesis, which will probably be finished in spring 2004.  The
work in element (e) has just begun using a single column version of
the NWP code. I will go over to the 3D code in 2003. The new cloud
physics must be tested and validated before it can become
operational. This work will probably extend through the end of the
Action.

Manpower:
One doctoral student and the proposer himself will work on these subjects.

Assurance of availability of resources:
At the moment the work is funded through basic funding of DLR.

Foreseen collaboration:
Other participants, in particular those producing water vapour data
bases, and ECMWF.


Previous experience:

Gierens, K.M., U. Schumann, H.G.J. Smit, M. Helten, G. Zängl,
1997: Determination of humidity and temperature fluctuations based on
MOZAIC data and parametrization of persistent contrail coverage for
general circulation models. Ann. Geophys. 15, 1057-1066.

Gierens, K., U. Schumann, M. Helten, H.G.J. Smit, A. Marenco,
1999: A distribution law for relative humidity in the upper
troposphere and lower stratosphere derived from three years of MOZAIC
measurements. Ann. Geophys. 17, 1218-1226.

Gierens, K., P. Spichtinger, 2000: On the size distribution of
ice-supersaturated regions in the upper troposphere and lowermost
stratosphere. Ann. Geophys. 18, 499-504.

Gierens, K., U. Schumann, M. Helten, H. Smit, P.H. Wang, 2000:
Ice-supersaturated regions and sub visible cirrus in the northern
midlatitude upper troposphere. J. Geophys. Res. 105, 22743-22754.

Gierens, K., S. Brinkop, 2002: An exchange model for
ice-supersaturated regions. Theor. Appl. Climatol. 71, 129-140.

Spichtinger, P., K. Gierens, W. Read, 2002: The statistical
distribution law of relative humidity in the global tropopause
region. Meteorol. Z. 11, 83-88.

Ovarlez, J., J.-F. Gayet, K. Gierens, J. Ström, H. Ovarlez,
F. Auriol, R. Busen, U. Schumann, 2002: Water vapor measurements
inside cirrus clouds in northern and southern hemispheres during
INCA. Geophys. Res. Lett., 10.1029/2001GL014440.