Workshop on Cirrus Clouds and their Supersaturated Environment - Topics

Programme (tentative)

(I and II should be covered with talks, III should be discussion (plenary or
in working groups)

I. The Relation Between Cirrus Clouds and Their Environment

I.1 Physics and Meteorology 
    (observations, data analysis, theory, modelling studies)

Science questions:

Given Different kinds of cirrus and their environment:
	  convective vs. non-convective; 
	  visible, subvisible, UTTC;
	  cold (homogeneously formed) vs. warm (heterogeneously formed)

What do we know about the relation between cirrus clouds and 
* the humidity field in the upper troposphere?
* the dynamics, in particular the vertical motions?

How do these relations differ for different kinds of cirrus?

How are cirrus generation mechanisms related to the ambient humidity and
dynamics? How gets the air supersaturated in the diverse generation processes?

How can the different environments of the different kinds of cirrus be
characterised?  

How do properties of different kinds of cirrus correspond to their different
formation mechanisms and their different environments?

What is the life cycle of cirrus clouds and their parental airmasses?

Looking at global distribution of cirrus clouds and ice-supersaturated
regions: Is it possible to devise maps of dynamical properties that reflect
formation conditions for cirrus clouds?

How strong are the correlations between cirrus occurrence and weather
phenomena like fronts, jet streams, etc.?

Trend analyses of Cirrus and the UT humidity and temperature fields.


I.2 Representation of Cirrus and Ice-Supersaturation in NWP and Global
Circulation Models

Science questions:

How are cirrus clouds and their various formation mechanisms represented in
large scale models? 

What are the properties of the surroundings of cirrus clouds in the models?

What kind of future evolution of upper tropospheric humidity and cirrus
formation conditions do climate models predict?


II. Open Questions and Unsolved Problems

II.1 Physics and Meteorology

How does nature arrange for the exponential distribution of supersaturation,
or is it just an artefact?

How can the discrepancy between the coverage of ice supersaturated air masses
and the much larger coverage of cirrus be explained?

How can there be so much cirrus cloudiness when the probability to reach a
nucleation threshold of more than 30% supersaturation is so low?

How do cirrus clouds modify the humidity field in the UT?

How do cirrus clouds modify the (vertical) dynamics in their surroundings?

Trends of frequency of occurrence of ice supersaturation in the UT.


II.2 Large Scale Models

Which new developments are currently under way?

Where do we see fundamental and less fundamental need for improvements?

How sensitive are cirrus properties in the models to the assumptions regarding
their environment and to assumptions regarding their formation conditions?


III. Discussion of Possible Solutions, Research Strategies, and Future Work

III.1 Instruments, Observations, and Operational Needs

What can we learn from new IR satellite sensors, Lidars in space, Ground-based
Lidars (in particular Raman)? Can GPS occultation method furnish reliable
humidities for the UT?

Correction of operational Radiosondes to produce accurate humidity values in
the UT. How can this be achieved for all stations?

Operational aquisition of UT data from commercial aircraft, e.g. MOZAIC.

III.2 Modelling and Validation

New Modelling needs: Cloud resolving mesoscale simulations of cirrus fields
(i.e. ice-supersaturated regions with embedded cirrus clouds).

New parameterisations for large scale models.