Ice-supersaturation and cirrus clouds

Principal Investigator

Dr Klaus Gierens
Institut für Physik der Atmosphäre
DLR
Münchener Strasse 20
82234 Wessling/Obb.
Germany

klaus.gierens@dlr.de and peter.spichtinger@dlr.de

Other researchewr(s): Dr. Peter Spichtinger (ETHZ) and Dr Martina Kraemer (FZJ)

Project description

Since September 2006 the Integrated Forecast Model of ECMWF has ice supersaturation as an explicit feature (Tompkins et al., 2007), which led to improved representation of upper tropospheric cloudiness. The realisation of this new feature is a main result of this special project. In this project we have last year investigated the spin—up of ice supersaturation in the forecasts after the initialisation. Now we are interested in validating the supersaturation fields in more detail, by comparison with other data, in particular satellite data (currently AIRS), and we want to study where supersaturation occurs in various synoptic situations.

Ice supersaturated regions (ISSRs) are those regions in which aircraft condensation trails are persistent. The new feature of the IFS can therefore be exploited for contrail prediction and planning of environmentally friendly air traffic trajectories. There is currently ongoing work on that topic. For the purpose of contrail and contrail cirrus prediction we plan to set up a contrail plume model, which can track single contrails during their complete lifetime. Advection and contrail spreading will be simulated by the model, and the result will be compared with MSG derived satellite images, concatenated into movies. This allows both improved interpretation of satellite pictures, and tuning of the plume model. The meteorological background for the plume model should be IFS generated forecasts. This work is part of a new doctoral thesis at DLR.

This project will also continue with further work in the two doctoral theses which will be completed by the end of the year:

• Contrail-to-cirrus transition: investigation (i.e. numerical modelling) of the dispersion phase.
• Single-particle microphysics: Implementation of a radiation code; coupling to EuLag.

Cloud-resolving modelling of cirrus clouds using EULAG:

Clouds are still one of the least understood components of the climate system. As stated in the IPCC report (IPCC, 2007), cloud properties and their impact on the radiation budget in changing climate are insufficiently known. Especially, the impact of high clouds consisting purely of ice crystals, viz. cirrus clouds, is known poorly, although a net warming is typically assumed (Chen et al., 2000). However, recent studies of the radiative properties of mid latitude cirrus clouds indicate that under certain conditions the transition between warming (i.e., for dominating absorption of thermal radiation) and cooling (i.e., for dominating reflection of solar radiation) strongly depends on the ice crystal number concentration, whereas the ice water content determines mainly the magnitude of the warming or cooling (Fusina et al., 2007).

In order to obtain better insight into the life cycle of cirrus clouds and their potential formation regions (ISSR) we use the anelastic non-hydrostatic model EULAG together with a recently developed ice microphysics parameterisation (Spichtinger and Gierens, 2008a) allowing also the competition of arbitrary many different formation mechanisms, e.g. homogeneous freezing of solution droplets (Koop et al., 2000) vs. heterogeneous nucleation (Spichtinger and Gierens, 2008b). Within the framework of a Marie Curie Fellowship (IMDALCC, 07/2007-06/2009), the impact of mesoscale dynamics and aerosols on the life cycle of cirrus clouds is investigated. Here, we primarily focus on orographic waves but also on turbulence inside cirrus clouds, driven by breaking waves (Spichtinger and Smolarkiewicz, 2008). Additionally, the internal dynamics of cirrus clouds will be investigated during the next year. These studies will be continued further after the current Marie Curie Fellowship. In first simulations, the internal variations of cirrus clouds are investigated using idealized 2D setups. In a further step, within the framework of a PhD project, starting in 2009, 3D inhomogeneities of cirrus clouds will be simulated using idealized setups as well as meteorological analyses as initial conditions.

Numerical weather prediction will benefit from this work:

• Information about life cycle and internal structure of cirrus clouds might help to improve the existing parameterisations for ice microphysics in NWP models.
• Validation of the ice supersaturation fields.
• Possibility to offer contrail forecasts to aviation services.
• Representation of contrail cirrus.

References:

• Chen T., W. Rossow, Y.Zhang, 2000: Radiative effects of cloud-type variations. J. Climate, 13, 264-286.
• Fusina, F., P. Spichtinger, U. Lohmann, 2007: The impact of ice supersaturated regions and thin cirrus on radiation in the mid latitudes. J. Geophy. Res., 112, D24S14, doi:10.1029/2007JD008449.
• IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.
• Koop, T., B. Luo, A. Tsias, T. Peter, 2000: Water activity as the determinant for homogeneous ice nucleation in aqueous solutions. Nature 406, 611-614.
• Spichtinger, P. and K. Gierens, 2008a: Modelling Cirrus Clouds. Part 1: Model description and validation. Atmos. Chem. Phys. Diss., 8, 601-686.
• Spichtinger, P. and K. Gierens, 2008b: Modelling Cirrus Clouds. Part 2: Competition of different nucleation mechanisms. Atmos. Chem. Phys. Diss., accepted.
• Spichtinger, P. and P. K. Smolarkiewicz, 2008: Turbulence in cirrus clouds. 15th Conference on Clouds and Precipitation. Cancun, Mexico. 7-11 July 2008. (extended abstract)

For more details, please refer to the latest progress report.

Additional information

Project started in 2004.

Would accept support for 1 year only, if necessary