Modeling convection over arctic leads with LES and a non‐eddy‐resolving microscale model

Lüpkes, Christof; Gryanik, Vladimir M.; Witha, Björn; Gryschka, Micha; Raasch, Siegfried; Gollnik, Tim

doi:10.1029/2007jc004099

Cited by 44 publications

(65 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(6) only depends on the lead width X and not on external conditions. However, Lüpkes et al (2008a) showed that the TIBL depends on the boundary layer wind speed, the surface buoyancy over the lead and on the background mixed layer height for near-neutral inflow. It would be interesting to have more measurements taken for different external conditions to better constrain these formulae.…”

Section: The Methods Of Andreas and Cash (1999)mentioning

confidence: 99%

Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere

2012

View full text Add to dashboard Cite

Abstract. Leads are linear-like structures of open water within the sea ice cover that develop as the result of fracturing due to divergence or shear. Through leads, air and water come into contact and directly exchange latent and sensible heat through convective processes driven by the large temperature and moisture differences between them. In the central Arctic, leads only cover 1 to 2 % of the ocean during winter, but account for more than 70 % of the upward heat fluxes. Furthermore, narrow leads (several meters) are more than twice as efficient at transmitting turbulent heat than larger ones (several hundreds of meters). We show that lead widths are power law distributed, P (X) ∼ X −a with a > 1, down to very small spatial scales (20 m or below). This implies that the open water fraction is by far dominated by very small leads. Using two classical formulations, which provide first order turbulence closure for the fetch-dependence of heat fluxes, we find that the mean heat fluxes (sensible and latent) over open water are up to 55 % larger when considering the lead-width distribution obtained from a SPOT satellite image of the ice cover, compared to the situation where the open water fraction constitutes one unique large lead and the rest of the area is covered by ice, as it is usually considered in climate models at the grid scale. This difference may be even larger if we assume that the power law scaling of lead widths extends down to smaller (∼1 m) scales. Such estimations may be a first step towards a subgrid scale parameterization of the spatial distribution of open water for heat fluxes calculations in ocean/sea ice coupled models.

show abstract

Section: The Methods Of Andreas and Cash (1999)mentioning

confidence: 99%

Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere

2012

View full text Add to dashboard Cite

show abstract

“…Ebner et al, 2011). Challenges remain in the high sensitivity of winter air temperatures to sea ice concentration (Lüpkes et al, 2008a;Tetzlaff et al, 2013) in the representation of new, thin ice in atmospheric models (Tisler et al, 2008) and in the interaction of convective plumes with capping stable or near-neutral environments (Lüpkes et al, 2008b). In the dynamics of cold air outbreaks over the open ocean, the new results linking the occurrence of roll convection with surface inhomogeneities in upwind sea ice (Liu et al, 2006;Gryschka et al, 2008) are an interesting discovery, although the links are still under discussion.…”

Section: Main Advances and Remaining Challenges In Individual Researcmentioning

confidence: 99%

“…Liu et al, 2006). On the basis of airborne observations and high-resolution modelling, Lüpkes et al (2008bLüpkes et al ( , 2012b concluded that convection over 1-2 km wide leads reached altitudes of 50-300 m depending on the boundary layer structure on the upstream side of leads. On the basis of aircraft in situ, drop sonde, and lidar observations, Lampert et al (2012) observed that over areas with many leads, the potential temperature decreased with height in the lowermost 50 m and then was nearly constant due to convective mixing up to the height of 100-200 m. When the leads were frozen and their fraction was small, however, an SBL extended up to a height of 200-300 m. Ebner et al (2011) showed in a modelling study that convective plumes generated over the Laptev Sea polynya influence atmospheric turbulence even 500 km downstream of the polynya, and Hebbinghaus et al (2006) found that cyclonic vortices can be generated or intensified over polynyas due to convective processes.…”

Section: Atmosmentioning

confidence: 99%

See 1 more Smart Citation

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

et al. 2014

Self Cite

View full text Add to dashboard Cite

Abstract. The Arctic climate system includes numerous highly interactive small-scale physical processes in the atmosphere, sea ice, and ocean. During and since the International Polar Year 2007-2009, significant advances have been made in understanding these processes. Here, these recent advances are reviewed, synthesized, and discussed. In atmospheric physics, the primary advances have been in cloud physics, radiative transfer, mesoscale cyclones, coastal, and fjordic processes as well as in boundary layer processes and surface fluxes. In sea ice and its snow cover, advances have been made in understanding of the surface albedo and its relationships with snow properties, the internal structure of sea ice, the heat and salt transfer in ice, the formation of superimposed ice and snow ice, and the small-scale dynamics of sea ice. For the ocean, significant advances have been related to exchange processes at the ice-ocean interface, diapycnal mixing, double-diffusive convection, tidal currents and diurnal resonance. Despite this recent progress, some of these small-scale physical processes are still not sufficiently understood: these include wave-turbulence interactions in the atmosphere and ocean, the exchange of heat and salt at the ice-ocean interface, and the mechanical weakening of sea ice. Many other processes are reasonably well understood as stand-alone processes but the challenge is to understand their interactions with and impacts and feedbacks on other processes. Uncertainty in the parameterization of small-scale processes continues to be among the greatest challenges facing climate modelling, particularly in high latitudes. Further improvements in parameterization require new year-round field campaigns on the Arctic sea ice, closely combined with satellite remote sensing studies and numerical model experiments.

show abstract

“…This allows for the development of the typical pattern of organized turbulence over the water surface, as it has been repeatedly found for breeze circulations, e.g. induced by arctic leads (Esau, 2007;Lüpkes et al, 2008). Over the land surface, we kept H s constant in order to represent the effect of LW radiative cooling.…”

Section: Modifications To the Palm Codementioning

confidence: 99%

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

Wolf¹,

Esau²,

Reuder

2017

Atmos. Chem. Phys.

View full text Add to dashboard Cite

Abstract. Street-level urban air pollution is a challenging concern for modern urban societies. Pollution dispersion models assume that the concentrations decrease monotonically with raising wind speed. This convenient assumption breaks down when applied to flows with local recirculations such as those found in topographically complex coastal areas. This study looks at a practically important and sufficiently common case of air pollution in a coastal valley city. Here, the observed concentrations are determined by the interaction between large-scale topographically forced and local-scale breeze-like recirculations.Analysis of a long observational dataset in Bergen, Norway, revealed that the most extreme cases of recurring wintertime air pollution episodes were accompanied by increased large-scale wind speeds above the valley. Contrary to the theoretical assumption and intuitive expectations, the maximum NO 2 concentrations were not found for the lowest 10 m ERA-Interim wind speeds but in situations with wind speeds of 3 m s −1 . To explain this phenomenon, we investigated empirical relationships between the large-scale forcing and the local wind and air quality parameters. We conducted 16 large-eddy simulation (LES) experiments with the Parallelised Large-Eddy Simulation Model (PALM) for atmospheric and oceanic flows. The LES accounted for the realistic relief and coastal configuration as well as for the large-scale forcing and local surface condition heterogeneity in Bergen. They revealed that emerging local breeze-like circulations strongly enhance the urban ventilation and dispersion of the air pollutants in situations with weak largescale winds. Slightly stronger large-scale winds, however, can counteract these local recirculations, leading to enhanced surface air stagnation.Furthermore, this study looks at the concrete impact of the relative configuration of warmer water bodies in the city and the major transport corridor. We found that a relatively small local water body acted as a barrier for the horizontal transport of air pollutants from the largest street in the valley and along the valley bottom, transporting them vertically instead and hence diluting them. We found that the stable stratification accumulates the street-level pollution from the transport corridor in shallow air pockets near the surface. The polluted air pockets are transported by the local recirculations to other less polluted areas with only slow dilution. This combination of relatively long distance and complex transport paths together with weak dispersion is not sufficiently resolved in classical air pollution models. The findings have important implications for the air quality predictions over urban areas. Any prediction not resolving these, or similar local dynamic features, might not be able to correctly simulate the dispersion of pollutants in cities.

show abstract

Modeling convection over arctic leads with LES and a non‐eddy‐resolving microscale model

Cited by 44 publications

References 44 publications

Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere

Influence of sea ice lead-width distribution on turbulent heat transfer between the ocean and the atmosphere

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

Contact Info

Product

Resources

About