Wind shear

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

A Mesoscale Convective Complex-Generated Inertially Stable Warm Core Vortex

Abstract: A long-lived mesoscale convectively-generated vortex (MCV) associated with a mesoscale convective complex (MCC) is documented. The MCV, with a Rossby number of approximately 0.5, is investigated as a feature intrinsic to the organization of the MCC. On 6–7 July 1982 a particularly large and intense MCC developed in a region of high convective available potential energy (CAPE) but weak vertical wind shear (bulk Richardson number ∼150), and weak advection of temperature and vorticity. Convection initially was organized in a narrow line with elements propagating relative to the mean environmental flow. These elements subsequently developed a large semicircular area of stratiform precipitation and a surface mesolow to the rear. Heavy rain fell over a broad area; amounts as great as 10.9 cm accompanied by flooding were reported in central Oklahoma. As the large semicircular rain area dissipated, a three layered structure became evident: a large upper tropospheric anticyclone, a rain cooled mesoscale h...

Evaluating Environmental Favorableness for Tropical Cyclone Development with the Method of Point‐Downscaling

Abstract: [1] A new method is presented to determine the favorableness for tropical cyclone development of an atmospheric environment, as represented by a mean sounding of temperature, humidity, and wind as a function of height. A mesoscale model with nested, moving grids is used to simulate the evolution of a weak, precursor vortex in a large domain with doubly periodic boundary conditions. The equations of motion are modified to maintain arbitrary profiles of both zonal and meridional wind as a function of height, without the necessary large-scale temperature gradients that cannot be consistent with doubly periodic boundary conditions. Comparisons between simulations using the point-downscaling method and simulations using wind shear balanced by temperature gradients illustrate both the advantages and the limitations of the technique. Further examples of what can be learned with this method are presented using both idealized and observed soundings and wind profiles.

Large eddy simulation of wind turbine wake dynamics in the stable boundary layer using the Weather Research and Forecasting Model

Abstract: Recently, an actuator disk parameterization was implemented in the Weather Research and Forecasting (WRF) Model for large eddy simulation (LES) of wind turbine wakes. To thoroughly verify this model, simulations of various types of turbines and atmospheric conditions must be evaluated against corresponding experimental data. In this work, numerical simulations are compared to nacelle-based scanning lidar measurements taken in stable atmospheric conditions during a field campaign conducted at a wind farm in the western United States. Using several wake characteristics—such as the velocity deficit, centerline location, and wake width—as metrics for model verification, the simulations show good agreement with the observations. Notable results include a high average velocity deficit, decreasing from 73% at a downwind distance x of 1.2 rotor diameters (D) to 25% at x = 6.6D, resulting from a low average wind speed and therefore high average turbine thrust coefficient. Moreover, the wake width expands from 1.4D at x = 1.2D to 2.3D at x = 6.6D. Finally, new features—namely rotor tilt and drag from the nacelle and tower—are added to the existing actuator disk model in WRF-LES. Compared to the rotor, the effect of the tower and nacelle on the flow is relatively small but nevertheless important for an accurate representation of the entire turbine. Adding rotor tilt to the model causes the vertical location of the wake center to shift upward. Continued advancement of the actuator disk model in WRF-LES will help lead to optimized turbine siting and controls at wind farms.

Thunderstorm cloud height-rainfall rate relations for use with satellite rainfall estimation techniques

Abstract: Observational studies of thunderstorm cloud height-rainfall rate and cloud height-volume rainfall rate relations are reviewed with significant variations being noted among climatological regimes. Analysis of the Florida (summer) and Oklahoma (spring) relations are made using a one-dimensional cloud model to ascertain the important factors in determining the individual cloud-rain relations and the differences between the two regimes. In general, the observed relations are well simulated by the model-based calculations. The generally lower predicted rain rates in Oklahoma (as compared to Florida) result from lower precipitation efficiencies which are due to a combination of larger entrainment (related to larger vertical wind shear) and drier environment. The generally steeper slope of the Oklahoma rain rate height curves is shown to be due to a stronger variation in maximum vertical velocity with cloud top height, which, in turn, is related to the greater static stability in the range of cloud tops. The impact of the regime-to-regime variations on empirical rain estimation schemes based on satellite-observed cloud height or cloud temperature information is discussed and a rain estimation approach based on model-generated cloud-rain relations is outlined.