INFLUENCE OF NON-HYDROSTATIC GRAVITY WAVES ON THE
STRATOSPHERIC FLOW FIELD ABOVE SCANDINAVIA
Special Project Report 2002/03
Andreas Dörnbrack, DLR Oberpfaffenhofen
Mesoscale Forecast and Hindcast Simulations for Scandinavia
As in the years before, we have supported European field activities in the Arctic by
providing mesoscale forecasts of the stratosphere above Scandinavia. In the framework
of VINTERSOL (http://www.ozone-sec.ch.cam.ac.uk/VINTERSOL), we participated in
the European-American campaign EUPLEX/SOLVE2 (http://www.nilu.no/euplex and
http://cloud1.arc.nasa.gov/solveII/index.html).
During the intense observational period (mid January till mid February 2003), the Arctic
stratosphere warmed up quickly due to a major warming event. Therefore, the originally
planned flights to explore mountain wave induced PSCs (see last report) were largely
replaced by flights scanning the state of the broken polar vortex. As additional products
we placed synoptic-scale analyses and forecasts of the northern hemispheric
stratosphere on our webpage (http://www.pa.op.dlr.de/arctic). Furthermore, ECMWF
analyses and forecasts were used by the Forschungszentrum Jülich for their CLAMS
model simulations.
Either as first author or as coauthor I contributed to a number of published papers
directly related to the special project (most of them from the SOLVE/THESEO 2000
campaign in 1999/2000, see references)
Idealized numerical simulations with EULAG
This last year, we have investigated inertia-gravity wave dynamics in the variety of
"extreme-environment'' scenarios. Historically, theoretical studies addressing orographic
flows and inertia-gravity waves have assumed relatively simple environments (viz.,
balanced background flows) together with heavily idealized initial and boundary
conditions. Related numerical studies typically adopt a similar strategy. In effect, the
numerical research models and the relevant expertise are well tuned for idealized flows,
but often become inadequate as the complexity of the problem increases. However, high
confidence in the accuracy of numerical tools is essential for interpreting simulations of
natural flows in atmospheres and oceans. In order to address his issue, several distinct
numerical projects have been conducted with the anelastic model EULAG. In particular,
we have studied formation of fine-scale rolls often observed in simulations of
orographic flows with directional shear. In as much as these rolls appear a realistic
finite-amplitude aspect of the flow, they turn out merely a manifestation of esoteric
truncation errors, absent in simpler environments. Adopting a fully implicit secondorder-accurate integrals for the buoyancy terms in the governing equations remedies the
problem.
Dynamic grid adaptation is an alternate avenue for increasing the models' efficacy (i.e.
accuracy versus efficiency). This has been pursued  and documented successful in
tracing targeted flow features and dynamically adjusting to prescribed undulations of
model boundaries  in the context of traveling stratospheric inertia-gravity wave
packets.
For extending the expertise of atmospheric models on extreme environments, we have
found physical scenarios of oceanic flows especially useful. One project, set in the
context of breaking of internal solitary waves in coastal flows, has expanded our
expertise on simulating nonlinear interactions (of internal inertia-gravity waves) with
larger scale tides and complex lateral boundaries. A direct numerical simulation of the
laboratory experiment on the separation of the western-boundary current, advanced the
massively-parallel version of EULAG on simulating flows with high-frequency
restoring forces (here, large beta effect) in presence of very steep orography (here, 45
degree slopes) and complex inlet-outlet lateral boundaries.
Mountain wave above the Andes and CRISTA observations
During the second CRISTA mission in August 1994, large amplitude gravity wave were
detected over the Andes. Mesoscale simulations forced by ECMWF analyses were
performed to compare the observed amplitude and phase of the mountain waves.
Especially, above the southern tip of South America the agreement was very good. The
results are published in a paper by Preusse et al (2002).
Gravity wave activity over South America on a pressure surface of 30 hPa. The vertical wavelength
measured by CRISTA and the viewing direction of the instrument are shown in Panel (a). The wavelength
information is significant only for waves with amplitudes,  1.5 K. The wave amplitudes are shown in
Panel (b) together with the phase of the waves, which is indicated by the direction of the arrows. An
upward pointing arrow indicates 0° and increasing phase is indicated by counter clockwise rotation. Panel
(c) shows the temperature field at 30 hPa as simulated by MM5 and Panel (d) shows MM5 results using a
nested grid to increase the horizontal resolution. Only the run with enhanced resolution exhibit
pronounced wave structures at the red dots, which give the location of the three strong amplitude profiles
visible in Panel (b).
References
Bevilacqua, R.M, Fromm, M.D., Alfred, J.M., Hornstein, J.S., Nedoluha, G.E., et al.:
Observations and Analysis of Polar Stratospheric Clouds Detected by POAM III during the
1999/2000 Northern Hemispheric Winter. Journal of Geophysical Research, 107, D 20
(10.1029/2001JD000477), (2002), S. SOL 24-1-SOL 24-17,
Dörnbrack, A., Birner, T., Fix, A., Flentje, H., Meister, A., et al.: Evidence for Inertia Gravity
Waves Forming Polar Stratospheric Clouds over Scandinavia. Journal of Geophysical Research,
107, D20 (10.1029/2001JD000452), (2002), S. SOL 30-1-SOL 30-18,
Flentje, H., Dörnbrack, A., Fix, A., Meister, A., Schmid, H., et al.: Denitrification inside the
Stratospheric Vortex in the Winter 1999/2000 by Sedimention of large Nitric Acid Trihydrate
Particles. Journal of Geophysical Research, 107, D16 (10.1029/2001JD001015), (2002), S.
AAC 11-1-AAC 11-15,
Hertzog, A., Vial, F., Dörnbrack, A., Eckermann, S.D., Knudsen, B.M., et al.: In-Situ
Observations of Gravity Waves and Comparisons with Numerical Simulations during the
SOLVE/THESEO 2000 Campaign. Journal of Geophysical Research, 107, D20
(10.1029/2001JD001025), (2002), S. SOL 35-1-SOL 35-11,
Larsen, N., Hoyer Svendsen, S., Knudsen, B.M., Voigt, C., Weisser, C., et al.: Microphysical
Mesoscale Simulations of Polar Stratospheric Cloud Formation Constrained by in situ
Measurements of Chemical and Optical Cloud Properties. Journal of Geophysical Research,
107, D20 (10.1029/2001JD000999), (2002), S. SOL 44-1-SOL 44-10,
Preusse, P., Dörnbrack, A., Eckermann, S.D., Riese, M. ., Schaeler, B. ., et al.: Space-based
Measurements of Stratospheric Mountain Waves by CRISTA. 1. Sensitivity, Analysis Method
and a Case Study. Journal of Geophysical Research, 107, D23 (10.1029/2001JD000699),
(2002), S. CRI 6-1-CRI 6-23,
Schiller, C., Bauer, R., Cairo, F., Deshler, T., Dörnbrack, A., et al.: Deydration in the Arctic
Stratosphere during the SOLVE/THESEO-2000 Campaigns. Journal of Geophysical Research,
107, D20 (10.1029/2001JD000463), (2002), S. SOL 36-1-SOL 36-9,