Influence of non-hydrostatic gravity waves on the stratospheric flow field above Scandinavia

Principal Investigator

Dr Andreas Dörnbrack
Institut für Physik der Atmosphäre
DLR Oberpfaffenhofen
82234 Wessling/Obb.
Germany

andreas.doernbrack@dlr.de

Other researchers: Piotr K. Smolarkiewicz, Christian Kuehnlein, Thomas Hamburger

Project description

Flow past orography excites internal gravity waves. Under favourable conditions these waves propagate up to stratospheric levels. The vertical displacements of air parcels by gravity waves influence the local temperature directly above and downwind of the mountain range. Especially in the winter months, these mesoscale temperature anomalies affect the formation of polar stratospheric clouds on the northern hemisphere. As documented in Carslaw et al.(1998), the subsequent heterogeneous chlorine activation reactions on particles of polar stratospheric clouds contribute significantly to the depletion of the Arctic stratospheric ozone layer. These mesoscale processes are currently underestimated in global weather prediction and climate models. It is the aim of our studies to support detailed information for an improved parameterization of these meso- and microscale processes (see Dörnbrack and Leutbecher, 2001).

In previous studies we studied stratospheric temperature anomalies by using mesoscale model simulations that resolve mountain waves with horizontal wavelengths greater than 50 km for the flow over Scandinavia (see References). Deviations of more than 10 K with respect to the synoptic-scale ECMWF analyses appear. The reason for this strong deviation are inertia gravity waves that seem to be poorly resolved by the coarse grid of T106 L31 analyses. Radiosonde soundings and lidar observations of polar stratospheric clouds indicate that the simulated mesoscale temperature structure did exist at a particular day in January 1997. For example, the record low temperature of -94.5 C measured at 26 km some 500 km downstream of the Scandinavian mountain range could be simulated successfully by the mesoscale model (Dörnbrack et al., 1999).

Other in situ observations of polar stratospheric clouds indicate that non-hydrostatic mountain waves can significantly influence the temperature directly above the mountain ridge (Wirth etal., 1999). These shorter wavelengths (8....20 km) cannot resolved by mesoscale models, therefore small-scale numerical models as the scheme of Smolarkiewicz will be used to model this part of the wave spectrum.

This special project consists of two work packages:

First, we want to analyse the ECMWF stratospheric temperature fields on the northern hemisphere. For this purpose, we use the analyses with the recently increased horizontal and vertical resolution. We want to find out if signatures of mountain waves in the analyses above Scandinavia exist. The next step is the investigation of their characteristics in terms of horizontal wavelengths, amplitude and meteorological conditions of appearance. Subsequently, this analyis will be expanded to other mountain ranges as the Ural, Novjia Semljia, Greenland etc.

The second part comprises the small-scale numerical simulations of the three-dimensional flow over the Scandinavian mountain range by means of the code EULAG by Piotr K Smolarkiewicz. This code allows a much more realistic resolution of the Scandinavian topography. Here, the influence of shorter, non-hydrostatic mountain waves will be studied and compared with independent observations of European and international field campaigns.

References

Carslaw, K. S., Wirth, M., Tsias, A., Luo, B. P., Dörnbrack, A., Leutbecher, M., Volkert, H., Renger, W., Bacmeister, J. T., Reimer, E. and Peter, T. 1998. Increased stratospheric ozone depletion due to mountain-induced atmospheric waves, Nature, 391, 675-678.

Carslaw, K. S., Wirth, M., Tsias, A., Luo, B. P., Dörnbrack, A., Leutbecher, M., Volkert, H., Renger, W., Bacmeister, J. T. and Peter, T. 1998. Particle microphysics and chemistry in remotely observed mountain polar stratospheric clouds, J. Geophys. Res., 103, 5785-5796.

Dörnbrack, A., M. Leutbecher and H. Volkert and M. Wirth, 1998: Mesoscale forecasts of stratospheric mountain waves, Meteorol. Appl., 5, 117-126.

Dörnbrack, A., Leutbecher, M., Kivi, R. and Kyrö, E., 1999: Mountain wave induced record low stratospheric temperatures above Northern via. Tellus, 51A, 951--963.

Dörnbrack, A. and Leutbecher, M., 2001: Relevance of mountain wave cooling for the formation of polar stratospheric clouds over Scandinavia. Towards a climatology of mountain wave cooling, J. Geophys. Res., 106, 1583--1593.

Dörnbrack, A., Leutbecher, M., Reichardt, J., Behrendt, A., Müller, K. P., and Baumgarten, G., 2001: Relevance of mountain wave cooling for the formation of polar stratospheric clouds over Scandinavia. Mesoscale dynamics and observations for January 1997, J. Geophys. Res., 106, 1569--1581.

Kivi, R. Kyrö, E., Dörnbrack, A. and T. Birner, 2001: Observations of vertically thick polar stratospheric clouds and record low temperature in the Arctic vortex, Geophys. Res. Letters, 28, 3661-3664.

Voigt, C., Tsias, A., Dörnbrack, A., Meilinger, S., Luo, B., Schreiner, J., Larsen, N., Mauersberger, K., and Peter, T., 2000: Non-equilibrium compositions of liquid polar stratospheric clouds in gravity waves, Geophys. Res. Lett., 27, 3873-3876.

Wirth, M., A. Tsias, A. Dörnbrack, V. Weiss, K. S. Carslaw, M. Leutbecher, W. Renger, H. Volkert, and T. Peter, 1999: Model guided Lagrangian observation and simulation of mountain polar stratospheric clouds, J. Geophys. Res., 104, 23971-23981.

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

Additional information

Project started in 2000.

Would not accept support for 1 year only.