A HALO aircraft mission to explore gravity waves in the polar night jet
Mission status: Scheduled.
Persons in Charge
Bernd Kaifler (DLR-IPA)
Contact point at DLR-FX for this mission:
HALO Deployment Base
September – December 2026
Atmospheric gravity waves (GWs) play an important role in the dynamical coupling of the atmosphere. They propagate horizontally and vertically over vast distances and transport energy and momentum. The dissipation of this momentum in the mesosphere drives the global residual circulation which connects both hemispheres and causes drastic effects on the thermal structure of the atmosphere. As internal GWs are mainly generated in the troposphere, wave generation, propagation and dissipation represent the dominant mechanism which couples the atmosphere from below to above. However, the atmosphere is also coupled from above to below by means of GWs. Since GWs modify the background flow through wave dissipation and momentum deposition, they influence the propagation of planetary scale waves, thereby affecting the circulation in the troposphere.
Understanding and quantifying these coupling processes is essential for improving both climate models and numerical weather prediction models. However, the details of the involved processes are not yet understood, and parameterizations of GWs used in models yield inadequate results so far and are subject to tuning. For example, state-of-the-art general circulation models (GCMs) show that, in particular, GW drag is missing in a latitude belt near 60°S (e.g. McLandress et al., 2012). The missing drag contributes to the so-called cold pole bias observed in climate chemistry models. Many ideas and suggestions have been put forward to explain its existence. Proposed generation mechanisms for the missing GWs include fronts and jets in the troposphere, orography from big obstacles (mountain ranges) to small islands in the ocean, secondary wave generation by the multitude of primary waves excited in the troposphere, and stratospheric sources. The latter are least explored due to inherent difficulties in observing the dynamic state of the atmosphere at stratospheric altitudes. Satellite-based instruments have a comparatively low spatial resolution and, most importantly, lack the necessary temporal coverage to detect and track the formation of individual gravity wave packets. On the other hand, ground-based instrumentation is non-existent at southern latitudes near 60°S and very sparse in the northern hemisphere. Only very recently have airborne high-resolution remote sensing instruments for the middle atmosphere become available. During the DEEPWAVE field campaign, stratospheric and mesospheric GWs were observed over and in the vicinity of New Zealand. Only one single flight at high latitudes (to 63°S) was undertaken during DEEPWAVE (Fritts et al., 2016). More observations of gravity waves in the middle atmosphere at high latitudes are needed in order to solve the puzzle of the missing GW drag which is an important step forward in improving GCMs.
1. An unexplored stratospheric GW source exists at locations of the polar night jet (PNJ) which are characterized by significant deviations from a balanced state, more exactly, at positions where the balanced state changes temporally.
2. These meridionally and zonally distributed sources contribute to the generation of a GW belt near the edge of the polar vortex and, eventually, to the missing GW drag in current GCMs.
3. The PNJ acts as converging lens and waveguide for GWs: orographic and non-orographic GWs are refracted into the polar jet and are able to propagate over vast distances within the jet.
4. These refracted GWs interact with locally generated GWs, and enhance the depth of the GW belt and increase the GW drag.
The primary objective of the proposed WAVEGUIDE mission is to test the hypotheses listed in the previous section. In particular, the mission addresses following scientific questions and tasks:
(1) Sources of non-orographic internal GWs in the vicinity of the PNJ
- Which local conditions relative to the PNJ are necessary to excite GWs effectively?
- validate theoretical and numerical predictions about potential source regions in terms of horizontal/vertical extent, direction of GW emission, temporal coherence, spectral distribution, wave capturing
(2) Propagation of internal GWs in the PNJ and secondary sources
- focusing of GWs into the PNJ: which horizontal dimensions do wave packets achieve? Role of
individual wave packets versus “background noise”? Intermittency in space and time and the
relative contributions to momentum deposition in the mesosphere.
- breaking of GWs and secondary sources in the upper stratosphere and mesosphere
downward propagating waves
- properties of other waveguides (inversion layers in the mesosphere)
Secondary objectives include observations of small-scale (secondary) GWs (horizontal wavelength < 5 km) and estimation of associated momentum fluxes in the stratosphere.
Long duration, high altitude flights are conducted to measure the vertical distribution of GWs in the northern hemispheric GW belt as function of longitude and latitude over the North Atlantic and underneath the PNJ and along north-south sections from mid latitudes to the Arctic. The synergy of downward-looking sensors (e.g. GLORIA 1 ) and upward-looking remote sensing instruments (ALIMA 2 , AMTM 3 ) is exploited to resolve the different tropospheric versus stratospheric sources of GWs and to investigate the vertical propagation of GWs. Momentum fluxes are derived from in-situ measurements (BAHAMAS) and dropsondes are used to characterize the wind field in tropospheric sources. Data from ground-based radars and lidars in Kühlungsborn (Germany), Kiruna (Sweden) and Andenes (Norway) are utilized to investigate the changing wave propagation conditions when the edge of the PNJ passes over these stations. The temporal evolution is separated from spatial changes in the structure of the PNJ by conducting lateral transects as well as overpasses with HALO over the ground-based instruments.
- German Aerospace Center, Institute of Atmospheric Physics (DLR-IPA)
- Forschungszentrum Jülich
- Karlsruhe Institute of Technology
Scientific instruments and payload configuration
List of scientific instruments for the mission:
|ALIMA||Iron resonance lidar||Name||Institution|
Cabin and exterior configuration of HALO for the mission
HALO flights for this mission
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Press releases, media etc