Wind shear

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

Thermodynamic control of tropical cyclogenesis in environments of radiative-convective equilibrium with shear

Abstract: The potential for tropical cyclone formation from a pre-existing disturbance is further explored with high-resolution simulations of cyclogenesis in idealized, tropical environments. These idealized environments are generated from simulations of radiative-convective equilibrium with fixed sea-surface temperatures (SSTs), imposed mean surface winds, and an imposed profile of vertical wind shear. The propensity for tropical cyclogenesis in these environments is measured in two ways: first, in the period of time required for a weak, mid-level circulation to transition to a developing tropical cyclone; and second, from the value of an incubation parameter that incorporates environmental measures of mid-level saturation deficit and thermodynamic disequilibrium between the atmosphere and ocean. Conditions of tropospheric warming can be produced from increased SSTs or from increased mean surface winds; in either case, the time to genesis increases with atmospheric warming. As these parameters are varied, the incubation parameter is found to be highly correlated with changes in the time to genesis. The high resolution (3 km) of these simulations permits analysis of changes in tropical cyclogenesis under warming conditions at the vortex scale. For increasing SST, increased mid-level saturation deficits (dryness) are the primary reason for slowing or preventing genesis. For environments with increased surface wind, it is the decreased thermodynamic disequilibrium between the atmosphere and ocean that delays or prevents development. An additional effect in both cases is a decoupling of the low-level and mid-level vortices, primarily as a result of increased advecting flow at the altitude of the mid-level vortex, which is linked to the height of the freezing level. Copyright © 2010 Royal Meteorological Society

The SEEK chemical release experiment: Observed neutral wind profile in a region of sporadic E

Abstract: Wind measurements made with the chemical release technique during a sporadic E layer event are presented. The data were obtained as part of the Sporadic E Experiment over Kyushu (SEEK) sounding rocket campaign. The winds show a strong maximum in the lower E region approaching 150 m s−1 near 105-km altitude and a large shear below the maximum. The large shear was within a few kilometers altitude of the peak in the electron densities measured on the downleg of the rocket trajectory. Calculations of the Richardson numbers for the wind profile show that the altitude range near the layer was highly unstable.

Convective-Scale Variations in the Inner-Core Rainbands of a Tropical Cyclone

Abstract: Airborne Doppler radar documented a variety of convective-scale structures within the inner-core rainbands of Hurricane Rita (2005). As predicted by past studies, wind shear determined azimuthal variations in the convection. All convective-scale circulations had radial inflow at low levels, upward motion, and outflow in the midtroposphere. Convective cells at smaller radii contained a low-level tangential jet determined largely by tangential acceleration due to angular momentum conservation (uy/r term), while cells at larger radii contained a low-level and/or midlevel jet determined jointly by the uy/r and vertical advection terms. The outflow was at a higher (lower) altitude for the outer (inner) cells. Radial variations in the convective cells are attributable to differencesin buoyancy and vertical shear of the radial wind (›u/›z). More buoyant updrafts at larger radii enhance vertical advection of y, creating local tangential jets at midlevels. At smaller radii the stronger low-level radial inflow contributes to a greater›u/›z, confining convectively generated jets to low levels. The low-level tangential jet and convectively generated pressure gradients produce outward-pointing supergradient acceleration that decelerates the boundary layer inflow. Consequently, this supergradient flow will enhance convergence and convection at the radius of inner rainbandcells, increasing the likelihoodof secondary eyewall formation. It is hypothesized that a critical zone for secondary eyewall formation exists where sufficiently high ›u/›z consistently constrains the altitudes of convectively generated supergradient flow so that convection in this radial zone leads to a newly developed eyewall. Once an incipient secondary eyewall forms at a certain radius, subsidence occurring along its inner edge separates it from the primary eyewall.

A note on the barotropic response of sea level to time‐dependent wind forcing

Abstract: This study examines the extent to which sea level variations at periods between 30 days and 1 year and spatial scales greater than 1000 km can be described by the wind- driven linear barotropic vorticity dynamics. The TOPEX/POSEIDON altimetric observations of sea level and the wind products of the National Meteorological Center are used as the database for the study. Each term of the linear barotropic vorticity equation was evaluated by averaging over regions of 10 deg x 10 deg. In most of the open ocean the result of the analysis suggests that the sea level variabilities at the scales considered cannot be fully described by the equation; the apparent net vorticity change is more than what can be explained by the local wind stress curl. In the few regions where the wind stress curl is strong enough to balance the vorticity budget, predominantly in the northeast Pacific and the southeast Pacific, the balance is basically achieved in terms of the time-dependent topographic Sverdrup relation, namely, the balance between the advection of the planetary vorticity plus the topography-induced vorticity and the forcing by the wind stress curl.

Verification of high-speed solar wind stream forecasts using operational solar wind models

Abstract: High-speed solar wind streams emanating from coronal holes are frequently impinging on the Earth's magnetosphere causing recurrent, medium-level geomagnetic storm activity. Modeling high-speed solar wind streams is thus an essential element of successful space weather forecasting. Here we evaluate high-speed stream forecasts made by the empirical solar wind forecast (ESWF) and the semiempirical Wang-Sheeley-Arge (WSA) model based on the in situ plasma measurements from the Advanced Composition Explorer (ACE) spacecraft for the years 2011 to 2014. While the ESWF makes use of an empirical relation between the coronal hole area observed in Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images and solar wind properties at the near-Earth environment, the WSA model establishes a link between properties of the open magnetic field lines extending from the photosphere to the corona and the background solar wind conditions. We found that both solar wind models are capable of predicting the large-scale features of the observed solar wind speed (root-mean-square error, RMSE ≈100 km/s) but tend to either overestimate (ESWF) or underestimate (WSA) the number of high-speed solar wind streams (threat score, TS ≈ 0.37). The predicted high-speed streams show typical uncertainties in the arrival time of about 1 day and uncertainties in the speed of about 100 km/s. General advantages and disadvantages of the investigated solar wind models are diagnosed and outlined.