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Abstract
Case studies are presented which describe a type of lake-effect snowband which forms along the western shore of Lake Michigan when a cold anticyclone to the north sets up an easterly gradient over the lake. Numerical simulations indicate that the snowband coincides with a narrow band of upward motion which results from the convergence of easterly winds over the lake and north to northwesterly winds over land. The northerly winds are part of a land breeze circulation which forms when cold air is heated by the relatively warm lake surface.
Initial data for model simulations are obtained by objective analysis of upper-air data from the eight upper-air stations closest to Lake Michigan at six levels in the lower troposphere. Model results show that a pool of cold air over the lake up to about 850 mb favors rapid growth of the planetary boundary layer over the western half of the lake, and that latent heat release plays an important role in intensifying the land breeze circulation.
Abstract
Case studies are presented which describe a type of lake-effect snowband which forms along the western shore of Lake Michigan when a cold anticyclone to the north sets up an easterly gradient over the lake. Numerical simulations indicate that the snowband coincides with a narrow band of upward motion which results from the convergence of easterly winds over the lake and north to northwesterly winds over land. The northerly winds are part of a land breeze circulation which forms when cold air is heated by the relatively warm lake surface.
Initial data for model simulations are obtained by objective analysis of upper-air data from the eight upper-air stations closest to Lake Michigan at six levels in the lower troposphere. Model results show that a pool of cold air over the lake up to about 850 mb favors rapid growth of the planetary boundary layer over the western half of the lake, and that latent heat release plays an important role in intensifying the land breeze circulation.
Abstract
A three-dimensional, primitive equation, boundary-layer model is used to investigate wintertime mesoscale frontogenesis along the New England coast. Some features included in the model are a terrain-following coordinate system to study the effects of irregular terrain, a stable beating scheme to allow for the release of latent heat and to estimate precipitation, and an upper boundary condition on pressure which permits interaction with the synoptic-scale circulation.
Numerical experiments with the model have verified the hypothesis that coastal fronts form when a cold anticyclone is located just to the north or northeast of New England, and a wave disturbance at 700 mb approaches the northeast from the midwest United States. Polar continental air flowing southwestward around the eastern side of the anticyclone is modified rapidly by sensible and latent heat transfer from the relatively warm Atlantic Ocean. As the 700 mb trough approaches the northeast, surface winds over the ocean veer from northeasterly to a more easterly direction. However, over land the low-level winds do not veer with the geostrophic wind, but rather back from northeasterly to a more northerly direction. This backing results from a combination of factors including surface friction and the effects of heat fluxes from the ocean and latent heat release. The numerical experiments indicate that the effect of heal fluxes from the ocean may be more important than previously suspected. The low-level convergence of maritime air flowing from the cast and cold air over land flowing from the north results in upward motion in a narrow band along the New England coast reaching a magnitude of ∼20 cm s−1 after 15 h of integration.
Abstract
A three-dimensional, primitive equation, boundary-layer model is used to investigate wintertime mesoscale frontogenesis along the New England coast. Some features included in the model are a terrain-following coordinate system to study the effects of irregular terrain, a stable beating scheme to allow for the release of latent heat and to estimate precipitation, and an upper boundary condition on pressure which permits interaction with the synoptic-scale circulation.
Numerical experiments with the model have verified the hypothesis that coastal fronts form when a cold anticyclone is located just to the north or northeast of New England, and a wave disturbance at 700 mb approaches the northeast from the midwest United States. Polar continental air flowing southwestward around the eastern side of the anticyclone is modified rapidly by sensible and latent heat transfer from the relatively warm Atlantic Ocean. As the 700 mb trough approaches the northeast, surface winds over the ocean veer from northeasterly to a more easterly direction. However, over land the low-level winds do not veer with the geostrophic wind, but rather back from northeasterly to a more northerly direction. This backing results from a combination of factors including surface friction and the effects of heat fluxes from the ocean and latent heat release. The numerical experiments indicate that the effect of heal fluxes from the ocean may be more important than previously suspected. The low-level convergence of maritime air flowing from the cast and cold air over land flowing from the north results in upward motion in a narrow band along the New England coast reaching a magnitude of ∼20 cm s−1 after 15 h of integration.
