Gravity wave excitation during the coastal transition of an extreme katabatic flow in Antarctica

Vignon, Étienne; Picard, Ghislain; Durán‐Alarcón, Claudio; Alexander, Simon; Gallée, Hubert; Berne, Alexis

doi:10.5194/egusphere-egu2020-3043

Cited by 11 publications

(17 citation statements)

References 15 publications

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“…For this case Fr decreased from 5.2 to 2.7 during the intervals between P0 and P4, indicating that, although the jet momentum was considerably reduced, the flow remained supercritical or "shooting" (Ball, 1956;Renfrew, 2004) for the entire transect, with no katabatic (also known as "hydraulic") jump (e.g., Vignon et al, 2020), as would occur if Fr became unity anywhere. Gravity waves traveled at speeds c kat slower than the wind speed within the jet and thus were not able to efficiently dissipate momentum and adjust the mass upstream in this situation, allowing the katabatic wind air parcels to travel several tens of kilometers over the ocean.…”

Section: Scale Analysismentioning

confidence: 87%

Inside Katabatic Winds Over the Terra Nova Bay Polynya: 2. Dynamic and Thermodynamic Analyses

Guest

2021

JGR Atmospheres

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Antarctic coastal polynyas (ACPs) occur where air is funneled into valleys and ejected horizontally over adjacent ocean regions, pushing any newly formed sea ice away from the coast. During cold seasons, the exposure of the relatively warm ocean surfaces to the sometimes hurricane-force winds causes great amounts of enthalpy (sensible and latent heat energy) to be lost from the surface of the polynyas, resulting in sea ice formation (e.g., Gordon & Comiso, 1988;Z. Zhang et al., 2015), and brine rejection (Mathiot et al., 2012) which can lead to the creation of deep ocean water masses that circulate throughout the world ocean (Orsi & Wiederwohl, 2009;Rusciano et al., 2013). Although the surface areas of ACPs are relatively small (e.g., Bromwich & Kurtz, 1984), their potential impacts on regional and global climate are significant due to the large amounts of sea ice and dense water that are created within them (Fusco et al., 2009;Gordon, 2001) and the injection of heat and moisture into the atmosphere (Renfrew, 2002).Due to their small size, ACPs are not resolvable by the general circulation models (GCMs) that are used to understand and predict future climate change. Therefore, to quantify the potential impacts of ACPs on global climate and regional ice production, their enthalpy loss and related effects must be simulated using sub-grid scale parameterizations. Typically, these parameterizations of surface fluxes are based on bulk

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Section: Scale Analysismentioning

confidence: 87%

Inside Katabatic Winds Over the Terra Nova Bay Polynya: 2. Dynamic and Thermodynamic Analyses

Guest

2021

JGR Atmospheres

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“…The model has been run with a downscaling method where a 27‐km resolution parent domain contains a 9‐km resolution domain which itself contains a 102 × 102 km 2 nest at a 3‐km resolution (see Figure 1). Note that achieving a 3‐km resolution is needed to correctly capture the dynamics of Antarctic katabatic winds and in particular their coastal transition (Vignon et al., 2020; Vignon, Traullé, et al., 2019). All WRF domains have been built with the same polar stereographic projection and they are centered over Mawson station.…”

Section: Meteorological Setting Observations and Simulationsmentioning

confidence: 99%

Challenging and Improving the Simulation of Mid‐Level Mixed‐Phase Clouds Over the High‐Latitude Southern Ocean

et al. 2021

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Climate models exhibit major radiative biases over the Southern Ocean owing to a poor representation of mixed‐phase clouds. This study uses the remote‐sensing dataset from the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) campaign to assess the ability of the Weather Research and Forecasting (WRF) model to reproduce frontal clouds off Antarctica. It focuses on the modeling of thin mid‐level supercooled liquid water layers which precipitate ice. The standard version of WRF produces almost fully glaciated clouds and cannot reproduce cloud top turbulence. Our work demonstrates the importance of adapting the ice nucleation parameterization to the pristine austral atmosphere to reproduce the supercooled liquid layers. Once simulated, droplets significantly impact the cloud radiative effect by increasing downwelling longwave fluxes and decreasing downwelling shortwave fluxes at the surface. The net radiative effect is a warming of snow and ice covered surfaces and a cooling of the ocean. Despite improvements in our simulations, the local turbulent circulation related to cloud‐top radiative cooling is not properly reproduced, advocating for the need to develop a parameterization for top‐down convection to capture the turbulence‐microphysics interplay at cloud top.

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“…Conversely, Dumont D'Urville is located on Petrel Island and approximately 5 km from the main ice sheet. It is subject to strong katabatic winds, which flow from the Antarctic interior, which can also generate gravity waves (Vignon et al, 2020). It is also expected, from previous studies (Moffat‐Griffin et al, 2011, 2013), that those stations close to the Drake Passage will see greater levels of gravity wave activity as this is where the main gravity wave “hotspot” is located.…”

Section: Radiosonde Datamentioning

confidence: 99%

Radiosonde Observations of a Wintertime Meridional Convergence of Gravity Waves Around 60°S in the Lower Stratosphere

Moffat‐Griffin

Colwell

Hindley

et al. 2020

Geophysical Research Letters

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Satellite observations show that there is a wintertime hotspot of gravity wave activity, located mainly over the ocean, around 60°S in the stratosphere. However, the sources of the gravity waves making up this hotspot are varied and complex and remain unclear. Here we use radiosonde observations from 11 Antarctic stations and selected small islands close to 60°S to examine the horizontal directional pseudo-momentum flux and energy density distributions of upward propagating gravity waves in the lower stratosphere. This paper shows, for the first time, that short vertical wavelength gravity waves in the lower stratosphere clearly propagate meridionally toward 60°S during the winter months. This result supports previous studies that show that this belt of gravity wave activity over the ocean is contributed to by wave sources outside 60°S. Plain Language Summary Atmospheric gravity waves are buoyancy waves, where the restoring force is gravity, which can have horizontal wavelengths from a few tens to hundreds of kilometers. They can be generated by a variety of sources including wind flow over mountains and storms. Over the Drake Passage and out to the east around 60°S, a large hotspot of gravity waves has been observed in the wintertime stratosphere using satellite observations. The sources for this gravity wave hotspot are unclear as it mainly located over the open ocean. In this paper radiosonde observations are used to examine, for the first time, the directional variation in short vertical wavelength gravity waves close to 60°S in the lower stratosphere. It is found that during the winter months there is a meridional convergence of gravity waves toward 60°S, implying that the gravity wave sources of the hotspot are in fact be outside this region.

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Gravity wave excitation during the coastal transition of an extreme katabatic flow in Antarctica

Cited by 11 publications

References 15 publications

Inside Katabatic Winds Over the Terra Nova Bay Polynya: 2. Dynamic and Thermodynamic Analyses

Inside Katabatic Winds Over the Terra Nova Bay Polynya: 2. Dynamic and Thermodynamic Analyses

Challenging and Improving the Simulation of Mid‐Level Mixed‐Phase Clouds Over the High‐Latitude Southern Ocean

Radiosonde Observations of a Wintertime Meridional Convergence of Gravity Waves Around 60°S in the Lower Stratosphere

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