INFLUENCE OF NON-HYDROSTATIC GRAVITY WAVES ON THE
STRATOSPHERIC FLOW FIELD ABOVE SCANDINAVIA
Special Project Report 2003/04
Andreas Dörnbrack, DLR Oberpfaffenhofen
Further Hindcasts and Analysis of Observation of Polar Stratospheric Clouds
above Scandinavia
During the recent year, the data analysis of the results of the most recent Arctic field campaign
EUPLEX/SOLVE2 (http://www.nilu.no/euplex) started. I contributed again by providing
meteorological data for the interpretation of the observations (see references). Furthermore,
several studies have been performed which are devoted to the mesoscale influence of the
Scandinavian mountain range on the formation of PSCs (Reichardt etal, 2004) and on the
chlorine activation on mountain-wave induced PSC particles above Scandinavia. This effect
could be proven for the first time on mesoscale PSCs based on GOME observations (Kühl etal.,
2004).
Participation at the ATReC 2003
The DLR Falcon participated in the Atlantic THORPEX Regional Campaign (ATReC) which
was conducted from October to December 2003 under the lead of EUCOS with participation of
NOAA, NCAR, UCAR, NASA, NRL, DLR, and Environment Canada. During that time the
Figure 1: Vertical profiles of the horizontal wind speed (m/s) along the flight track . Wind
profiles are derived from averaging over four scanner revolutions (bottom). ECMWF
operational T511/L60 analyses interpolated in time and space onto the flight legs are shown in
the top panel.
DLR research aircraft Falcon was based in Keflavik, Iceland. The goal of the DLR participation
was to deliver targeted dropsonde and wind lidar observations. Together with colleagues from
our Lidar group we are analyzing the data and plan to publish a case study about the
observations of the Greenland tip jet. Figure 1 presents the airborne lidar observations of the
horizontal wind speed averaged over four scanner revolutions from a flight in the lee of
Greenland under strong westerly flow. Missing data points are kept black. These missing values
are either due to the extinction of the laser pulse in clouds, or to very clear air without
backscattering aerosols. The lidar observations reveal three dominant wind systems in the lee of
Greenland:
(1) after a segment of weak south/southwesterly winds in the first part of the flight, a wind
maximum with a dominant westerly component is seen between profile #15 and #20;
strongest winds of up to 30m/s were measured at ~1000 m MSL; above this maximum the
wind speed decreases with height. The whole jet extends up to ~ 4000 m altitude; the same
wind system has been sampled between profiles #52 and #65 on the way back to Iceland;
however, the horizontal wind speed is weaker and the jet spreads over a wider horizontal
range
(2) the Greenland tip jet itself could only be sampled by a couple of profiles around profile #32;
unfortunately, cloud streets of cumulus with cloud tops between 2000 and 3000 m altitude
blocked the laser beam; however, maximum wind speeds close to the surface of ~40 m/s
could be sampled
(3) between the two jet regions, the lidar observations reveal a region of variable wind speeds;
we loosely refer to this region as turbulent wake. It extends from profile #20 to #30 on the
southbound and from profile #35 to #50 on the northbound leg. Below ~2500 m altitude the
wind speed ranges from 15 to 25 m/s. The wind is strongest in a few narrow (~40 km wide)
bands. Above this wake region, there exist a pronounced wind minimum between 2500 and
3500 m (profiles #21...23 and #45..55). Most remarkable, there is a jet with a maximum
wind speed of ~30 m/s sitting on the top of wake region; the dominating wind direction in
this area is west although exceptions occur in the turbulent wake.
The ECMWF T511/L60 operational analyses interpolated onto the flight path reproduce the
observed wind structure rather well. However, there are significant differences (up to 12 m/s) of
the observed and analyzed wind. For instance, the jet on top of the wake region is about 10 m/s
weaker in the analysis and also the wind minima at about 3 km MSL are not reproduced by the
ECMWF analysis which does not resolve the complex wake structure of Greenland.
Analysis of Water Vapor Observations above the Northern Atlantic
The access to the ECMWF operational analyses via my special project has also been used to
study the “Water vapor heterogeneity related to stratospheric intrusions over the northern
Atlantic revealed by airborne water vapor lidar” (Flentje et al. 2004). Airborne differential
absorption lidar (DIAL) measurements of tropospheric water vapor and aerosol/clouds were
performed along extended flight sections across the northern and middle Atlantic on 13-15 May
and 16-18 June 2002. Owing to intense dynamical activity over the Atlantic complex
atmospheric structures such as upper tropospheric/lower stratospheric intrusions to the lower
troposphere were observed. Those intrusions with H2O mixing ratios well below 50 ppm are a
frequent phenomenon rather than rare exceptions. They occur on the anticyclonic side of the
polar jet and do mostly but not always correspond to PV anomalies in ECMWF analyses. The
observed features cover a large range of scales from synoptic wave disturbances to mesoscale
fronts, gravity waves and convective cells further to turbulent entrainment and flow processes at
the small end of the cascade. Correspondingly huge is the dynamical range of the associated
water vapor mixing ratios, covering more than 3 orders of magnitude thereby exhibiting very
large gradients - typical scales of the intrusions are 1 km vertically and few 100 km
horizontally. ECMWF-based 3-D trajectories and simulations with the MM5 mesoscale model
are mostly capable to reproduce and explain the ongoing dynamical processes.
Figure 2 illustrates the synoptic situation based on tropopause maps (see also current maps on
http://www.pa.op.dlr.de/arctic) and Fig. 3 the lidar observations.
Figure 2: Potential temperature (K, left) and horizontal wind speed (m/s, right) on the ynamical
tropopause (defined as 2 PVU surface; 1PVU = 10-6 m2s-1Kkg-1) at the marked days valid at
0000 UTC. ECMWF T511L60 operational analyses. The Longitude given in °E corresponds to
°W+360°.
Figure. 3: Water vapor mixing ratio (mg/kg; upper panel)) and aerosol backscatter ratio at 1064
nm (middle panel) along the westbound transfer flights from Germany to Oklahoma (USA) on
13 – 15 May 2002. The black lines mark the height of the dynamical tropopause (2 PVU
surface) based on operational T511L60 ECMWF analyses. Their valid times are 14 May 00
UTC for the segments east of 60°W and 15 May 06 UTC for the segments west of 60°W. Lower
Panel: corresponding DLR Falcon flight legs. Note, that the vertical scale is strongly
exaggerated due to the tremendous horizontal scale compression; typical “steep” intrusions
actually have aspect ratios (vertical to horizontal scale) of about 1/50.
Meteorological Forecasts for the ASTAR 2004 Campaign
The Arctic Study of Tropospheric Aerosols, Clouds and Radiation Campaign 2004 took place in
Spitsbergen from May to June 2004. Meteorological forecasts of the basic meteorological fields
plus detailed fields describing the cloud structure above the observational region haven been
provided under http://astar2004.awi-potsdam.de or, just to give an example of the layout via
http://www.pa.op.dlr.de/arctic/astar/fc_040608.html. The main objective of this campagin was
certainly the characterization of the Arctic aerosol particles, however, due to interesting flow
situations also interesting meteorological studies can be expected.
References
Flentje. H, A. Dörnbrack, G. Ehret, A. Fix, C. Kiemle, G. Poberaj, and M. Wirth, Water vapor
heterogeneity related to stratospheric intrusions over the northern Atlantic revealed by airborne
water vapor lidar, submitted to JGR 2004.
Kühl, S., A. Dörnbrack, W. Wilms-Grabe, B.-M. Sinnhuber, U. Platt, and T. Wagner,
Observational evidence of rapid chlorine activation by stratospheric mountain waves above
Northern Scandinavia, submitted to JGR 2004.
Lowe, D., MacKenzie, A. R:, Schlager, H., Voigt, C., Dörnbrack, A., and M. J. Mahoney,
Composition of, and heterogeneous chemical reactions on, liquid particles in a lee-wave polar
stratospheric cloud, Submitted to ACPD, 2004.
Reichardt, J., A. Dörnbrack, S. Reichardt, P. Yang, and T. J. McGee, Mountain wave PSC
dynamics and microphysics from ground-based lidar measurements and meteorological
modeling, ACPD, 3, 5831-5873, 2003.
Deshler, T., N. Larsen. C. Weisser, J. Schreiner, K. Mauersberger, F. Cairo, A. Adriani, G. Di
Donfrancesco, J. Ovarlez, H. Ovarlez, U. Blum, K. H. Fricke, and A. Dörnbrack, Large nitric
acid particles at the top of an Arctic stratospheric cloud. JGR 108(D16), 4517,
doi:10.1029/2003JD003479, 2003.
Schreiner, J., C. Voigt, C. Weisser, A. Kohlmann, K. Mauersberger, T. Deshler, C. Kröger, J.
Rosen, N. Kjome, N. Larsen, F. Cairo, A. Adriani, G. Di Donfrancesco, J. Ovarlez, H. Ovarlez,
and A. Dörnbrack, Chemical, microphysical, and optical properties of polar stratospheric
clouds. JGR 108(D5), 8313, doi:10.1029/2001JD000825, 2003.