Boundary Layer and Mesoscale Structure over Lake Michigan during a Wintertime Cold Air Outbreak

1990 ◽  
Vol 47 (19) ◽  
pp. 2293-2316 ◽  
Author(s):  
Ernest M. Agee ◽  
Mary L. Hart
Keyword(s):  
Boundary Layer ◽  
Lake Michigan ◽  
Cold Air ◽  
Mesoscale Structure ◽  
Cold Air Outbreak

Convective Structures in a Cold Air Outbreak over Lake Michigan during Lake-ICE

2005 ◽  
Vol 62 (7) ◽  
pp. 2414-2432 ◽  
Author(s):  
Suzanne M. Zurn-Birkhimer ◽  
Ernest M. Agee ◽  
Zbigniew Sorbjan
Keyword(s):  
Boundary Layer ◽  
Wind Shear ◽  
Lake Michigan ◽  
Vertical Mixing ◽  
Internal Boundary Layer ◽  
Internal Boundary ◽  
Cold Air ◽  
Convective Structures ◽  
Cold Air Outbreak ◽  
Lake Effect

Abstract The Lake-Induced Convection Experiment provided special field data during a westerly flow cold air outbreak (CAO) on 13 January 1998, which has afforded the opportunity to examine in detail an evolving convective boundary layer. Vertical cross sections prepared from these data, extending from upstream over Wisconsin out across Lake Michigan, show the modifying effects of land–water contrast on boundary layer mixing, entrainment, heating, and moisture flux. Through this analysis, an interesting case of lake-effect airmass modification was discovered. The data show atypical differing heights in vertical mixing of heat and moisture, as well as offshore downwelling and subsidence effects in the atmosphere. Analysis shows evidence of a new observational feature, the moisture internal boundary layer (MIBL) that accords well with the often recognized thermal internal boundary layer (TIBL). The “interfacial” layer over the lake is also found to be unusually thick and moist, due in part to the upstream conditions over Wisconsin as well as the effectiveness of vertical mixing of moist plumes over the lake (also seen in the aircraft datasets presented). Results show that the atmosphere can be much more effective in the vertical mixing of moisture than heat or momentum (which mixed the same), and thus represents a significant departure from the classical bottom-up and top-down mixing formulation. Four scales of coherent structures (CSs) with differing spatial and temporal dimensions have been identified. The CSs grow in a building block fashion with buoyancy as the dominating physical mechanism for organizing the convection (even in the presence of substantial wind shear). Characteristic turbulence statistics from aircraft measurements show evidence of these multiple scales of CSs, ranging from the smallest (microscale) in the cloud-free path region near the Wisconsin shore, to the largest (mesoscale) in the snow-filled boundary layer near the Michigan shore. A large eddy simulation (LES) model has also been employed to study the effects of buoyancy and shear on the convective structures in lake-effect boundary layers. The model simulation results have been divided into two parts: 1) the general relationship of surface heat flux versus wind shear, which shows the interplay and dominance of these two competing forcing mechanisms for establishing convection patterns and geometry (i.e., rolls versus cells), and 2) a case study simulation of convection analogous to the CSs seen in the CFP region for the 13 January 1998 CAO event. Model simulations also show, under proper conditions of surface heating and wind shear, the simultaneous occurrence of differing scales of CSs and at different heights, including both cells and rolls and their coexisting patterns (based on the interplay between the effects of buoyancy and shear).

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

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.

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

scholarly journals The Role of Precipitation in Controlling the Transition from Stratocumulus to Cumulus Clouds in a Northern Hemisphere Cold-Air Outbreak

2017 ◽  
Vol 74 (7) ◽  
pp. 2293-2314 ◽  
Author(s):  
Steven J. Abel ◽  
Ian A. Boutle ◽  
Kirk Waite ◽  
Stuart Fox ◽  
Philip R. A. Brown ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Rapid Change ◽  
Supercooled Liquid ◽  
Cloud Layer ◽  
Liquid Water Path ◽  
Cumulus Clouds ◽  
Cold Air ◽  
Stratiform Region ◽  
Cold Air Outbreak

Abstract Aircraft observations in a cold-air outbreak to the north of the United Kingdom are used to examine the boundary layer and cloud properties in an overcast mixed-phase stratocumulus cloud layer and across the transition to more broken open-cellular convection. The stratocumulus cloud is primarily composed of liquid drops with small concentrations of ice particles and there is a switch to more glaciated conditions in the shallow cumulus clouds downwind. The rapid change in cloud morphology is accompanied by enhanced precipitation with secondary ice processes becoming active and greater thermodynamic gradients in the subcloud layer. The measurements also show a removal of boundary layer accumulation mode aerosols via precipitation processes across the transition that are similar to those observed in the subtropics in pockets of open cells. Simulations using a convection-permitting (1.5-km grid spacing) regional version of the Met Office Unified Model were able to reproduce many of the salient features of the cloud field although the liquid water path in the stratiform region was too low. Sensitivity studies showed that ice was too active at removing supercooled liquid water from the cloud layer and that improvements could be made by limiting the overlap between the liquid water and ice phases. Precipitation appears to be the key mechanism responsible for initiating the transition from closed- to open-cellular convection by decoupling the boundary layer and depleting liquid water from the stratiform cloud.

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