Topic
Wind shear
About: Wind shear is a research topic. Over the lifetime, 8023 publications have been published within this topic receiving 185373 citations.
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TL;DR: In this article, the authors studied the statistics of wind direction fluctuations in the atmosphere for a wide range of time scales (10−4'sec to 1'h), and in both vertical and horizontal planes.
Abstract: We study some elementary statistics of wind direction fluctuations in the atmosphere for a wide range of time scales (10−4 sec to 1 h), and in both vertical and horizontal planes. In the plane parallel to the ground surface, the direction time series consists of two parts: a constant drift due to large weather systems moving with the mean wind speed, and fluctuations about this drift. The statistics of the direction fluctuations show a rough similarity to Brownian motion but depend, in detail, on the wind speed. This dependence manifests itself quite clearly in the statistics of wind-direction increments over various intervals of time. These increments are intermittent during periods of low wind speeds but Gaussian-like during periods of high wind speeds.
81 citations
TL;DR: In this article, the vertical gradient of diabatic temperature change resulting from vertical shear-induced turbulent heat flux, in layers of CAT, is proposed as the generation mechanism responsible for large values of potential vorticity on the mesoscale.
Abstract: Results from three case study investigations of upper-level jet stream systems document the existence of stratospheric mesoscale cyclonic wind shear in the layer of maximum wind. Anomalously high values of potential vorticity are shown to coincide with the mesoscale cyclonic shear zone. The high values of potential vorticity within an upper level frontal zone were shown to result from shearing vorticity in the mesoscale high potential vorticity region of the stratosphere which is transported downward into the tropospheric frontal zone and becomes transformed into curvature vorticity with little change in thermal stability. The vertical gradient of diabatic temperature change resulting from vertical shear-induced turbulent heat flux, in layers of CAT, is proposed as the generation mechanism responsible for large values of potential vorticity on the mesoscale. It is proposed that turbulent-scale mixing processes are of fast order importance in the evolution of jet stream frontal zone systems.
81 citations
TL;DR: The influence of wind shear on the life cycle of extratropical cyclones and their upper-level potential vorticity (PV) waves was investigated in this paper.
Abstract: The El Nino Southern Oscillation (ENSO) strongly influences the interannual and seasonal atmospheric circulation over the North Pacific. The present study shows that the meridional displacement of the time-mean upper-level jet associated with ENSO modulates the time-mean barotropic (meridional) wind shear over the central and eastern North Pacific storm track. Earlier theoretical and observational studies established the influence of barotropic wind shear on the life cycles of extratropical cyclones and their upper-level potential vorticity (PV) waves. The present study suggests that differences in the time-mean flow associated with the 1997-99 ENSO cycle had a similar impact on tropopause PV structure, meridional eddy fluxes of momentum and temperature, and predictability.
81 citations
TL;DR: In this article, an ERS 1 synthetic aperture radar (SAR) image of the island Hopen shows a distinct 7.6km wavelength wave phenomenon near the island, interpreted as the surface imprint on open water of atmospheric lee waves.
Abstract: An ERS 1 synthetic aperture radar (SAR) image of the island Hopen shows a distinct 7.6-km wavelength wave phenomenon near the island. This wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves. The pattern is visible in the SAR image, since the lee waves modulate the horizontal wind speed near the ocean surface which, in turn, modulates the surface roughness and the radar cross section. The physical setting for the observation is presented and discussed. The lower bound on horizontal wind speed modulation is estimated to range from 3±2 ms−1 (for the wind speed minima) to 12±2 ms−1 (for the wind speed maxima) based upon the observed radar cross-section modulation and the ERS 1 scatterometer wind retrieval model CMOD4. The wavelength and wind speed modulation are consistent with linear lee wave model predications. The model uses an atmosphere with an exponential profile of the Scorer parameter (ratio of buoyancy frequency to wind speed) to represent a shallow, ground-based inversion layer observed at Bear Island and a bell-shaped barrier to represent the forcing effects of Hopen.
81 citations