Turbulent Transport in the Gray Zone: A Large Eddy Model Intercomparison Study of the CONSTRAIN Cold Air Outbreak Case

Roode, Stephan R. de; Frederikse, Thomas; Siebesma, A. Pier; Ackerman, A. S.; Chylik, Jan; Field, Paul R.; Fricke, Jens; Gryschka, Micha; Hill, Adrian A.; Honnert, Rachel; Krueger, Steven K.; Lac, Christine; Lesage, Andrew T.; Tomassini, Lorenzo

doi:10.1029/2018ms001443

Cited by 32 publications

(41 citation statements)

References 76 publications

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“…Salesky et al (2017) realized a set of simulations with different stability conditions, from neutral to highly convective. An intercomparison of several LES studies performed on a CAO case was made by de Roode et al (2019) to improve the current parametrization schemes used in weather prediction models.…”

Section: Introductionmentioning

confidence: 99%

Organized Turbulence in a Cold-Air Outbreak: Evaluating a Large-Eddy Simulation with Respect to Airborne Measurements

Brilouet

Durand

Canut

et al. 2020

Boundary-Layer Meteorol

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Cold-air outbreaks (CAO) lead to intense air-sea interactions, the appropriate representation of which are fundamental for climate modelling and numerical weather forecasting. We analyze a CAO event with low-level wind speeds of approximately 25 m s −1 observed in the north-western Mediterranean Sea. The marine atmospheric boundary layer (MABL) was sampled with an aircraft equipped for turbulence measurements, revealing the organization of the MABL flow in coherent structures oriented along the mean wind direction, which was then simulated in two steps. First, a one-dimensional simulation enabled the determination of the forcing terms (particularly horizontal advection) required to adequately reproduce the vertical structure of the MABL flow. These terms were computed from a limited-area forecast model in operation during the entire field campaign. Then, a large-eddy simulation (LES) was performed during the well-established phase of the CAO event. The LES output is validated with respect to airborne data, not only with respect to the mean wind-speed and thermodynamic profiles, but also the turbulence statistics and coherent structures. The validated LES results enable description of the turbulent field as well as the coherent structures. The main discrepancy is a considerable underestimation of the simulated evaporation (computed with a parametrization of the turbulent surface fluxes), and hence of the moisture fluctuations throughout the boundary layer. Several possible explanations may explain this underestimation. The structure of the boundary layer is nonetheless well reproduced by the LES model, including the organized structures and their characteristic scales, such as the structure wavelength, orientation, and aspect ratio, which closely agree with observations. A conditional-sampling analysis enables determination of the contribution of the coherent structures to the vertical exchange. Although they occupy a limited fractional area, organized structures are the primary contributors to the turbulent exchange.

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Section: Introductionmentioning

confidence: 99%

Organized Turbulence in a Cold-Air Outbreak: Evaluating a Large-Eddy Simulation with Respect to Airborne Measurements

Brilouet

Durand

Canut

et al. 2020

Boundary-Layer Meteorol

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“…Biases in surface fluxes over the MIZ can be substantial and extend hundreds of kilometers downstream (e.g., Bourassa et al 2013). Such biases are caused by poor representation of surface exchange (e.g., unrepresentative drag coefficients; see Elvidge et al 2016;Renfrew et al 2019) or inadequate atmospheric boundary layer parameterizations (e.g., Renfrew et al 2009;Boutle et al 2014;de Roode et al 2019). Consequently, even though the broadscale meteorology can be reasonably well simulated, the associated air-sea interaction can be difficult to capture accurately, particularly during CAOs over the MIZ.…”

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confidence: 99%

The Iceland Greenland Seas Project

Renfrew

Pickart

Våge

et al. 2019

Bulletin of the American Meteorological Society

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The Iceland Greenland Seas Project (IGP) is a coordinated atmosphere–ocean research program investigating climate processes in the source region of the densest waters of the Atlantic meridional overturning circulation. During February and March 2018, a field campaign was executed over the Iceland and southern Greenland Seas that utilized a range of observing platforms to investigate critical processes in the region, including a research vessel, a research aircraft, moorings, sea gliders, floats, and a meteorological buoy. A remarkable feature of the field campaign was the highly coordinated deployment of the observing platforms, whereby the research vessel and aircraft tracks were planned in concert to allow simultaneous sampling of the atmosphere, the ocean, and their interactions. This joint planning was supported by tailor-made convection-permitting weather forecasts and novel diagnostics from an ensemble prediction system. The scientific aims of the IGP are to characterize the atmospheric forcing and the ocean response of coupled processes; in particular, cold-air outbreaks in the vicinity of the marginal ice zone and their triggering of oceanic heat loss, and the role of freshwater in the generation of dense water masses. The campaign observed the life cycle of a long-lasting cold-air outbreak over the Iceland Sea and the development of a cold-air outbreak over the Greenland Sea. Repeated profiling revealed the immediate impact on the ocean, while a comprehensive hydrographic survey provided a rare picture of these subpolar seas in winter. A joint atmosphere–ocean approach is also being used in the analysis phase, with coupled observational analysis and coordinated numerical modeling activities underway.

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“…For LES, we use the PArallelized Large Eddy Simulation Model PALM (Maronga et al, 2015;Raasch & Schröter, 2001) with revision number 2864 in its dry version. PALM has already been used to study polar boundary layers over heterogeneous sea ice distributions (Weinbrecht & Raasch, 2001), small-scale processes above leads (L08), and large-scale processes concerning the impact of sea ice heterogeneities on the downstream ABL in cold air outbreaks (de Roode et al, 2019;Gryschka et al, 2008Gryschka et al, , 2014. PALM is based on the nonhydrostatic Boussinesq-approximated Reynolds equations with a 1.5-order subgrid scale closure according to Deardorff and Peterson (1980), in which a prognostic equation of the subgrid scale TKE is solved.…”

Section: Les Modelmentioning

confidence: 99%

Influence of Lead width on the Turbulent Flow Over Sea Ice Leads: Modeling and Parametrization

et al. 2020

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A new turbulence parametrization is developed for a non‐eddy‐resolving microscale model to study the effects of leads (elongated open‐water channels in sea ice) of different width on the polar atmospheric boundary layer (ABL). Lead‐dominated sea ice regions are characterized by large horizontal inhomogeneities of the surface temperature causing strong convection. Therefore, the new parametrization is based on a previous formulation where inhomogeneous conditions of dry convection over leads and nonlocal effects on heat fluxes had already been taken into account for a fixed lead width. A nonlocal lead width dependent approach is applied now for both heat fluxes and momentum fluxes in the convective region. Microscale model results obtained with the new, the previous nonlocal, and a local parametrization are shown, where 10 idealized cases of a lead‐perpendicular, near‐neutral ABL‐flow below a strong capping inversion are considered. Furthermore, time‐averaged large eddy simulation (LES) results of those cases are considered for analyzing the integrated effects of the dry convection on ABL characteristics. Microscale model results obtained with the new nonlocal parametrization agree well with the LES for variable lead widths and different atmospheric forcing although there is a room for further improvement. Furthermore, several features obtained with a local closure clearly disagree with LES. Thus, the microscale study also points to difficulties that might occur in mesoscale studies over regions where leads dominate the flow regime when local closures are applied.

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Turbulent Transport in the Gray Zone: A Large Eddy Model Intercomparison Study of the CONSTRAIN Cold Air Outbreak Case

Cited by 32 publications

References 76 publications

Organized Turbulence in a Cold-Air Outbreak: Evaluating a Large-Eddy Simulation with Respect to Airborne Measurements

Organized Turbulence in a Cold-Air Outbreak: Evaluating a Large-Eddy Simulation with Respect to Airborne Measurements

The Iceland Greenland Seas Project

Influence of Lead width on the Turbulent Flow Over Sea Ice Leads: Modeling and Parametrization

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