Wind shear

About: Wind shear is a research topic. Over the lifetime, 8023 publications have been published within this topic receiving 185373 citations.

Equatorial variability and resonance in a wind-driven Indian Ocean model

Abstract: A numerical isopycnal ocean model has been designed and applied to model the Indian Ocean north of 25°S. Vertical normal modes are used in the open boundary conditions and for selections of initial layer depths. A 21-year integration with a reduced Hellerman-Rosenstein monthly averaged wind stress has been made with 3.5-layer and 1.5-layer versions of the model. Both solutions reproduce the main features of the observed wind-driven seasonal circulation in the Indian Ocean above the main thermocline. The transient semiannual equatorial surface jets are more intense, more coherent, and in better phase agreement with observations when three layers are active. The associated undercurrents below the main thermocline are also included in the 3.5-layer model solution. Second baroclinic-mode, reflecting, equatorial Kelvin and Rossby waves combine to give a semiannual, resonant basin mode. Experiments with an equatorial band of semiannual zonal winds suggest a very strong response of the Indian Ocean to wind forcing with this period. Further, the amplitudes of the 28–30 day oscillations in the western equatorial model region are found to be strongly damped with depth; they have upward phase propagation and downward energy propagation.

A review of aeolian transport processes in cold environments

Abstract: Aeolian environments in Canada experience seasonally cold temperatures. The portion of the annual wind transport occurring between late autumn and early spring usually is perceived as trivial because low temperature transport is difficult to measure reliably, particularly in remote northern areas, and because warm climate based semi-empirical wind erosion models are intractable for temperatures below 0°C. Very little is known about the processes contributing to the phenomenal aeolian transport associated with the Pleistocene Epoch, but supply limiting factors were likely as important then as they are in contemporary high latitude environments, although the wind and solar radiation regimes of this glacial period are not exactly replicated. Field and simulation work on the boundary layer and surface controls, which include wind shear velocity, air density, sediment texture, pore water, snow, ice, and vegetation, suggests a complex system of interactions. Frozen and wet surfaces, traditionally viewed as stab...

A Numerical Study of the Variability and the Separation of the Gulf Stream, Induced by Surface Atmospheric Forcing and Lateral Boundary Flows

Abstract: A primitive equation regional model is used to study the effects of surface and lateral forcing on the variability and the climatology of the Gulf Stream system. The model is an eddy-resolving, coastal ocean model that includes thermohaline dynamics and a second-order turbulence closure scheme to provide vertical mixing. The surface forcing consists of wind stroll and beat fluxes obtained from the Comprehensive Ocean-Atmosphere Data Set (COADS). Sensitivity studies am performed by driving the model with different forcing (e.g., annual versus zero surface forcing or monthly versus annual forcing). The model climatology, obtained from a five-year simulation of each case, is then compared to observed climatologies obtained from satellite-derived SST and hydrocast data. The experiments in which surface best flux and wind stress were neglected show less realistic Gulf Stream separation and variability, compared with experiments in which annual or seasonal forcing are used. A similar unrealistic Gulf S...

Aspect Ratios of Longitudinal Rolls and Convection Cells Observed during Cold Air Outbreaks

Abstract: Atmospheric conditions in which cellular-roll cloud patterns are apparent, and dependence of the aspect ratios of the cells on depths of the convective layer and the stability ratio are investigated by examining satellite pictures and aerological data over eastern Asia during cold air outbreaks in the months January to March for 1975–82. Vertical profiles of temperature and relative humidity in the convective layer along the cloud bands over the ocean show an increase of static stability, relative humidity, and layer depth in the downwind direction. Longitudinal convective rolls are realized when vertical wind shear is between 10−3 and 10−2 sec−1, and three-dimensional open cells are realized below these values. The cloud top height is proportional to l3/5 of the cloud-band spacing for l≲20 km and to l2/5 for l≳20 km. The obtained aspect ratio for longitudinal rolls ranges from 5 to 18, increasing in the downwind direction at a rate of 1/110 km, while open cells are obtained in the range from 8 t...