SOUTHTRAC-GW: An Airborne Field Campaign to Explore Gravity Wave Dynamics at the World’s Strongest Hotspot

Rapp, Markus; Kaifler, Bernd; Dörnbrack, Andreas; Gisinger, Sonja; Mixa, Tyler; Reichert, Robert; Kaifler, Natalie; Knobloch, Stefanie; Eckert, Ramona; Wildmann, Norman; Giez, Andreas; Krasauskas, Lukas; Preusse, Peter; Geldenhuys, Markus; Riese, Martin; Woiwode, Wolfgang; Friedl-Vallon, Felix; Sinnhuber, Björn-Martin; Torre, A. de la; Alexander, P.; Hormaechea, José Luis; Janches, Diego; Garhammer, Markus; Chau, Jorge L.; Conte, J. Federico; Hoor, Peter; Engel, Andreas

doi:10.1175/bams-d-20-0034.1

Cited by 56 publications

(104 citation statements)

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“…The correlation of enhanced gravity wave activity in the middle atmosphere to the wind speeds was evident early on (Preusse et al, 2003). From the Southern Andes and the Antarctic Peninsula waves propagate to about 60 • S into the Drake passage, a mechanism which was further studied by a dedicated air plane campaign (Rapp et al, 2020). For gravity wave activity far off land, however, the main sources remained unclear.…”

Section: Introductionmentioning

confidence: 99%

Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis ﬁelds around the Southern Polar Night Jet

Strube¹,

Preusse²,

Ern³

et al. 2021

Preprint

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Abstract. In the southern winter polar stratosphere the distribution of gravity wave momentum flux in many state-of-the-art climate simulations is inconsistent with long-time satellite and superpressure balloon observations around 60° S. Recent studies hint that a lateral shift between prominent gravity wave sources in the tropospheric mid-latitudes and the location where gravity wave activity is present in the stratosphere causes at least parts of the discrepancy. This lateral shift cannot be represented by the column-based gravity wave drag parametrisations used in most general circulation models. However, recent high-resolution analysis and re-analysis products of the ECMWF-IFS show good agreement to observations and allow for a detailed investigation of resolved gravity waves, their sources and propagation paths. In this paper, we identify resolved gravity waves in the ECMWF-IFS analyses for a case of high gravity wave activity in the lower stratosphere using small-volume sinusoidal fits to characterise these gravity waves. The 3D wave vector together with perturbation amplitudes, wave frequency and a fully described background atmosphere are then used to initialise the GROGRAT gravity wave ray-tracer and follow the gravity waves backwards from the stratosphere. Finally, we check for indication of source processes on the path of each ray and thus quantitatively attribute gravity waves to sources that are represented within the model. We find that stratospheric gravity waves are indeed subject to far (> 1000 km) lateral displacement from their sources, taking place already at low altitudes (

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Section: Introductionmentioning

confidence: 99%

Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis ﬁelds around the Southern Polar Night Jet

Strube¹,

Preusse²,

Ern³

et al. 2021

Preprint

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“…ERA5 assimilates and uses decades of earth system observations to constrain model forecast and variability, and does so using a high-resolution forecast model. Thus, ERA5 provides a bridge between (sparse and spectrally limited) GW observations from satellites and field campaigns (Alexander et al, 2008;Ern et al, 2018;Fritts et al, 2016;Grubišić et al, 2008;Hertzog et al, 2008;Rapp et al, 2020;Wu & Eckermann, 2008) and unconstrained high-resolution models (e.g., Sato et al, 2012;Polichtchouk et al, 2018), which can potentially resolve mesoscale GWs.…”

mentioning

confidence: 99%

Importance of Gravity Wave Forcing for Springtime Southern Polar Vortex Breakdown as Revealed by ERA5

Gupta

Birner

Dörnbrack

et al. 2021

Geophysical Research Letters

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Planetary waves (PW) and gravity waves (GW) are the key drivers of middle atmospheric circulation and variability by transporting momentum from the surface to stratospheric and mesospheric altitudes. In the stratosphere, PWs predominantly drive the wintertime circulation by mixing potential vorticity in the winter middle and high latitudes (Haynes et al., 1991;Holton et al., 1995). In the mesosphere, however, GWs are the main driver of the pole-to-pole global circulation (Becker, 2012;Holton, 1982;Plumb, 2002).GWs are ubiquitous in the stratosphere (Fritts & Alexander, 2003) and have been shown to play an important role in the southern springtime polar vortex breakdown (de la Cámara et al., 2016; McLandress et al., 2012). Here, the breakdown is defined as the westerly-to-easterly transition of zonal winds at 60°S and 10 hPa in the Austral spring. PWs and GWs, in concert with radiative adjustment, govern the dynamical evolution of the stratospheric circulation during the breakdown period (de la Cámara et al., 2016). Additionally, PWs and GWs are coupled and interact with each other (Holton, 1984).Comprehensive climate models do not adequately resolve the GW spectrum relevant for the stratospheric circulation. Most of the GW forcing in models is approximately represented by Orographic (O-) and Non-Orographic (NO-) Gravity Wave Drag (GWD) parameterizations (

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“…This reflects the nonphysical nature of single column parameterisation schemes currently in use for GWs (e.g. Kim et al, 2003;Sato et al, 2012;Ribstein and Achatz, 2016;Amemiya and Sato, 2016;Krisch et al, 2017;Plougonven et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event

Geldenhuys

Preusse²,

Krisch

et al. 2021

Atmos. Chem. Phys.

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Abstract. To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography. We observe GWs along a transect through Greenland where the GW packet covers ≈ 1/3 of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13 km of altitude with a horizontal wavelength of 330 km, a vertical wavelength of 2 km and a large temperature amplitude of 4.5 K. Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72 m s−1) the GW packet has a slow vertical group velocity of 0.05–0.2 m s−1. This causes the GW packet to propagate long distances while spreading over a large area and remaining constrained to a narrow vertical layer. A plausible source is not only orography, but also out-of-balance winds in a jet exit region and wind shear. To identify the GW source, 3D GLORIA observations are combined with a gravity wave ray tracer, ERA5 reanalysis and high-resolution numerical experiments. In a numerical experiment with a smoothed orography, GW activity is quite weak, indicating that the GWs in the realistic orography experiment are due to orography. However, analysis shows that these GWs are not mountain waves. A favourable area for spontaneous GW emission is identified in the jet by the cross-stream ageostrophic wind, which indicates when the flow is out of geostrophic balance. Backwards ray-tracing experiments trace into the jet and regions where the Coriolis and the pressure gradient forces are out of balance. The difference between the full and a smooth-orography experiment is investigated to reveal the missing connection between orography and the out-of-balance jet. We find that this is flow over a broad area of elevated terrain which causes compression of air above Greenland. The orography modifies the wind flow over large horizontal and vertical scales, resulting in out-of-balance geostrophic components. The out-of-balance jet then excites GWs in order to bring the flow back into balance. This is the first observational evidence of GW generation by such an orography–jet mechanism.

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SOUTHTRAC-GW: An Airborne Field Campaign to Explore Gravity Wave Dynamics at the World’s Strongest Hotspot

Abstract: Capsule summaryThe SOUTHTRAC-GW airborne mission explored the dynamics of gravity waves in the region of the Southern Andes and Antarctic Peninsula during the extraordinary southern hemisphere SSW of September 2019.

Cited by 56 publications

References 102 publications

Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis ﬁelds around the Southern Polar Night Jet

Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis ﬁelds around the Southern Polar Night Jet

Importance of Gravity Wave Forcing for Springtime Southern Polar Vortex Breakdown as Revealed by ERA5

Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event

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