The Climatology, Meteorology, and Boundary Layer Structure of Marine Cold Air Outbreaks in Both Hemispheres*

2016 ◽  
Vol 29 (6) ◽  
pp. 1999-2014 ◽  
Author(s):  
Jennifer Fletcher ◽  
Shannon Mason ◽  
Christian Jakob
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Pressure Gradients ◽  
Cold Air ◽  
Surface Heat Fluxes ◽  
Cold Air Outbreak ◽  
Wide Range ◽  
Cold Air Outbreaks

Abstract A comparison of marine cold air outbreaks (MCAOs) in the Northern and Southern Hemispheres is presented, with attention to their seasonality, frequency of occurrence, and strength as measured by a cold air outbreak index. When considered on a gridpoint-by-gridpoint basis, MCAOs are more severe and more frequent in the Northern Hemisphere (NH) than the Southern Hemisphere (SH) in winter. However, when MCAOs are viewed as individual events regardless of horizontal extent, they occur more frequently in the SH. This is fundamentally because NH MCAOs are larger and stronger than those in the SH. MCAOs occur throughout the year, but in warm seasons and in the SH they are smaller and weaker than in cold seasons and in the NH. In both hemispheres, strong MCAOs occupy the cold air sector of midlatitude cyclones, which generally appear to be in their growth phase. Weak MCAOs in the SH occur under generally zonal flow with a slight northward component associated with weak zonal pressure gradients, while weak NH MCAOs occur under such a wide range of conditions that no characteristic synoptic pattern emerges from compositing. Strong boundary layer deepening, warming, and moistening occur as a result of the surface heat fluxes within MCAOs.

scholarly journals Simulations of a cold-air pool associated with elevated wintertime ozone in the Uintah Basin, Utah

2014 ◽  
Vol 14 (11) ◽  
pp. 15953-16000 ◽  
Author(s):  
E. M. Neemann ◽  
E. T. Crosman ◽  
J. D. Horel ◽  
L. Avey
Keyword(s):  
Boundary Layer ◽  
Snow Cover ◽  
Layer Structure ◽  
Inversion Layer ◽  
Cloud Microphysics ◽  
Photochemical Reactions ◽  
Near Surface ◽  
Cold Air ◽  
Air Temperatures ◽  
Uintah Basin

Abstract. Numerical simulations are used to investigate the meteorological characteristics of the 1–6 February 2013 cold-air pool in the Uintah Basin, Utah, and the resulting high ozone concentrations. Flow features affecting cold-air pools and air quality in the Uintah Basin are studied, including: penetration of clean air into the basin from across the surrounding mountains, elevated easterlies within the inversion layer, and thermally-driven slope and valley flows. The sensitivity of the boundary layer structure to cloud microphysics and snow cover variations are also examined. Ice-dominant clouds enhance cold-air pool strength compared to liquid-dominant clouds by increasing nocturnal cooling and decreasing longwave cloud forcing. Snow cover increases boundary layer stability by enhancing the surface albedo, reducing the absorbed solar insolation at the surface, and lowering near-surface air temperatures. Snow cover also increases ozone levels by enhancing solar radiation available for photochemical reactions.

A cold air outbreak near Spitsbergen in springtime — Boundary-layer modification and cloud development

1992 ◽  
Vol 61 (1-2) ◽  
pp. 13-46 ◽  
Author(s):  
Burghard Brümmer ◽  
Birgit Rump ◽  
Gottfried Kruspe
Keyword(s):  
Boundary Layer ◽  
Cold Air ◽  
Cold Air Outbreak ◽  
Cloud Development

scholarly journals Large-Eddy Simulation of a Coastal Ocean under the Combined Effects of Surface Heat Fluxes and Full-Depth Langmuir Circulation

2016 ◽  
Vol 46 (8) ◽  
pp. 2411-2436 ◽  
Author(s):  
Rachel Walker ◽  
Andrés E. Tejada-Martínez ◽  
Chester E. Grosch
Keyword(s):  
Water Column ◽  
Stable Stratification ◽  
Coastal Ocean ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Surface Heating ◽  
Surface Cooling ◽  
Surface Heat Fluxes ◽  
Wide Range ◽  
Large Eddy

AbstractResults are presented from the large-eddy simulations (LES) of a wind-driven flow representative of the shallow coastal ocean under the influences of Langmuir forcing and surface heating and cooling fluxes. Langmuir (wind and surface gravity wave) forcing leads to the generation of Langmuir turbulence consisting of a wide range of Langmuir circulations (LCs) or parallel, counterrotating vortices that are aligned roughly in the direction of the wind. In unstratified, shallow coastal regions, the largest of the LCs reach the bottom of the water column. Full-depth LCs are investigated under surface waves with a significant wave height of 1.2 m and a dominant wavelength of 90 m and wave period of 8 s, for a wind speed of 7.8 m s−1 in a 15-m-deep coastal shelf region. Both unstable and stable stratification are imposed by constant surface heat fluxes and an adiabatic bottom wall. Simulations are characterized by Rayleigh and Richardson numbers representative of surface buoyancy forcing relative to wind forcing. For the particular combination of Langmuir forcing parameters studied, although surface cooling is able to augment the strength of LC, a significantly high cooling flux of 560 W m−2 (such that the Rayleigh number is Raτ = 1000) is required in order for turbulence kinetic energy generation by convection to exceed Langmuir production. Such a transition is expected at a lower heat flux for weaker wind and wave conditions and thus weaker LCs than those studied. Furthermore, a surface heating flux of approximately 281 W m−2 (such that the Richardson number is Riτ = 500) is able to inhibit vertical mixing of LC, particularly in the bottom half of the water column, allowing stable stratification to develop.

Effects of Streamwise Pressure Gradient on Turbulent Spot Development

1996 ◽  
Vol 118 (4) ◽  
pp. 737-743 ◽  
Author(s):  
J. P. Gostelow ◽  
N. Melwani ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Pressure Distribution ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Turbulent Layer ◽  
Wide Range

A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet, which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition and the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution, strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the centerline and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot, which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

scholarly journals Sea waves impact on turbulent heat fluxes in the Barents Sea according to numerical modeling

2020 ◽  
Author(s):  
Stanislav Myslenkov ◽  
Anna Shestakova ◽  
Dmitry Chechin
Keyword(s):  
Roughness Length ◽  
Barents Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Sea Waves ◽  
Cold Air ◽  
Mean Values ◽  
The Barents Sea ◽  
Turbulent Heat Fluxes ◽  
Cold Air Outbreaks

Abstract. This paper investigates the impact of sea waves on turbulent heat fluxes in the Barents Sea. The COARE algorithm, meteorological data from reanalysis and wave data from the WW3 wave model results were used. The turbulent heat fluxes were calculated using the modified Charnock parameterization for the roughness length and several parameterizations, which explicitly account for the sea waves parameters. A catalog of storm wave events and a catalog of extreme cold-air outbreaks over the Barents Sea were created and used to calculate heat fluxes during extreme events. The important role of cold-air outbreaks in the energy exchange of the Barents Sea and the atmosphere is demonstrated. A high correlation was found between the number of cold-air outbreaks days and turbulent fluxes of sensible and latent heat, as well as with the net flux of long-wave radiation averaged over the ice-free surface of the Barents Sea during a cold season. The differences in the long-term mean values of heat fluxes calculated using different parameterizations for the roughness length are small and are on average 1–3 % of the flux magnitude. Parameterizations of Taylor and Yelland and Oost et al. on average lead to an increase of the magnitude of the fluxes, and the parameterization of Drennan et al. leads to a decrease of the magnitude of the fluxes over the entire sea compared to the Charnock parameterization. The magnitude of heat fluxes and their differences during the storm wave events exceed the mean values by a factor of 2. However, the effect of explicit accounting for the wave parameters is, on average, small and multidirectional, depending on the used parameterization for the roughness length. In the climatic aspect, it can be argued that the explicit accounting for sea waves in the calculations of heat fluxes can be neglected. However, during the simultaneously observed storm waves and cold-air outbreaks, the sensitivity of the calculated values of fluxes to the used parameterizations increase along with the turbulent heat transfer increase. In some extreme cases, during storms and cold-air outbreaks, the difference reaches 700 W m−2.

Roll Vortices and Boundary-Layer Development during a Cold Air Outbreak

1997 ◽  
Vol 84 (1) ◽  
pp. 45-65 ◽  
Author(s):  
Jörg Hartmann ◽  
Christoph Kottmeier ◽  
Siegfried Raasch
Keyword(s):  
Boundary Layer ◽  
Cold Air ◽  
Roll Vortices ◽  
Cold Air Outbreak ◽  
Boundary Layer Development ◽  
Layer Development
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