Wind shear

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

Simulation of the Wind Speed at Different Heights Using Artificial Neural Networks

Abstract: In this paper, an estimation of the wind speed at different heights with artificial neural networks is presented. It is an alternative way to compute wind shear. This method was tested using pairs of data sets from two measuring stations, installed in different topographic locations. Wind speed simulation is performed with high accuracy. The calculation of the surface friction coefficient from the actual measurements is also compared for wind shear estimation with the typical method in terms of energy output. Results showed that artificial neural networks achieve a better wind speed simulation and wind power estimation at different heights, even in complex terrains.

Physics of Stratocumulus Top (POST): turbulent mixing across capping inversion

Abstract: . High spatial resolution measurements of temperature and liquid water content, accompanied by moderate-resolution measurements of humidity and turbulence, collected during the Physics of Stratocumulus Top experiment are analyzed. Two thermodynamically, meteorologically and even optically different cases are investigated. An algorithmic division of the cloud-top region into layers is proposed. Analysis of dynamic stability across these layers leads to the conclusion that the inversion capping the cloud and the cloud-top region is turbulent due to the wind shear, which is strong enough to overcome the high static stability of the inversion. The thickness of this mixing layer adapts to wind and temperature jumps such that the gradient Richardson number stays close to its critical value. Turbulent mixing governs transport across the inversion, but the consequences of this mixing depend on the thermodynamic properties of cloud top and free troposphere. The effects of buoyancy sorting of the mixed parcels in the cloud-top region are different in conditions that permit or prevent cloud-top entrainment instability. Removal of negatively buoyant air from the cloud top is observed in the first case, while buildup of the diluted cloud-top layer is observed in the second one.

Enhancement of sporadic E by horizontal transport within the layer

Abstract: The tidal winds in the E region, acting through the wind shear mechanism, produce thin horizontal layers of metallic ions, which descend in time as the phases of the winds change. Gravity waves generated below the E region also have a downward-directed phase velocity and, if this is of the same order of magnitude (but greater than) the descent velocity of the layer, the wave ‘seen’ by the ions in the layer can be almost stationary in time. The interaction of the wave with the layer then produces a very strong horizontal redistribution of the ion density, although hardly affecting the height of the layer. We suggest that this process is responsible for enhancing the ion density at certain locations and producing experimentally observable Es. The ‘sporadic’ nature of the phenomenon then arises from the variable presence of suitable waves, while the horizontal scale of the enhanced layer region is controlled by the horizontal wave length of the gravity wave.

Maui Mesosphere and Lower Thermosphere (Maui MALT) Observations of the Evolution of Kelvin-Helmholtz Billows Formed Near 86 km Altitude

Abstract: [1] Small-scale (less than 15 km horizontal wavelength) structures known as ripples have been seen in OH airglow images for nearly 30 years The structures have been attributed to either convective or dynamical instabilities; the latter are mainly due to large wind shears, while the former are produced by superadiabatic temperature gradients Dynamical instabilities produce Kelvin-Helmholtz (KH) billows, which have been known for many years However, models and laboratory experiments suggest that these billows often spawn a secondary instability that is convective in nature While laboratory investigations see evidence of such structures, the evolution of these instabilities in the atmosphere has not been well documented The Maui Mesosphere and Lower Thermosphere (Maui MALT) Observatory, located on Mt Haleakala, is instrumented with a Na wind/temperature lidar that can detect dynamic or convective instabilities with 1 km vertical resolution over the altitude region from about 85 to 100 km The observatory also includes a fast OH airglow camera, sensitive to emissions coming from approximately 82 to 92 km altitude, which obtains images every 3 s at sufficient resolution and signal to noise to see the ripples On 15 July 2002, ripples were observed moving at an angle to their phase fronts After a few minutes, structures appeared to form approximately perpendicular to the main ripple phase fronts The lidar data showed that a region of dynamical instability existed from approximately 855 to 87 km and that the direction of the wind shear in this region was consistent with the phase fronts of the ripple features The motion of the ripples themselves was consistent with the wind velocity at 859 km Thus in this case the observed ripple motion was the advection of KH billows by the wind The perpendicular structures were seen to be associated with the KH billows: they formed at the time when the atmosphere briefly became convectively unstable within the region where the KH billows most likely formed Because of this and because the ripples were oriented approximately perpendicular to and moved with the billows, we speculate that they are the secondary instabilities predicted by models of KH evolution The primary and perpendicular features were seen to decay into unstructured regions suggestive of turbulence While the formation and decay time appear consistent with models, the horizontal wavelength of the perpendicular structures seems to be larger than models predict for the secondary instability features