Wind shear

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

Observations and models of the energy flux from the wind to mixed-layer inertial currents

Abstract: Observations of wind stress, upper-ocean currents, and stratification from a mooring at 10 ∘ N in the Pacific are used along with two different one-dimensional mixed-layer models to investigate the horizontal kinetic energy (KE) balance for inertial motions in the mixed-layer. Results from four other sites spanning 25 ∘ N to 60 ∘ N in the Atlantic also are presented. Determining the work done by the wind on the ocean during strong resonant forcing events is of particular interest. The damped-slab mixed-layer model used in previous studies is appealing for this purpose, since it is possible to estimate the wind work using only the wind stress, prescribed mixed-layer depth, and an empirical damping constant. However, it is found that this model, which does not allow for interaction between the mixed-layer and the stratified water column below, does not reproduce the observed KE balance for strong forcing events and systematically over-estimates the wind work. A slightly more sophisticated model, which includes a shear instability mechanism to facilitate momentum transfer between the mixed-layer and a transition layer below, reproduces the observed KE balance and the cumulative wind work much more accurately. Mixed-layer inertial currents unrelated to wind forcing (e.g., due to upward propagating internal waves) are found in the observations, but are not accounted for in either model. When wind forcing is relatively weak, these background currents may be of comparable amplitude to wind-forced currents, and can have a significant impact on the inertial response.

A Dynamical Index for the East Asian Winter Monsoon

Abstract: A new index measuring the East Asian winter monsoon is defined using the mean wind shears of upper-tropospheric zonal wind based on the belief that the physical processes of both higher and lower latitudes, and at both lower and upper troposphere, should be considered to depict the variability of monsoon. When the index is high (low), the westerly jet is strong (weak), the East Asian trough is deep (shallow), the Siberian high is strong (weak), and anomalous low-level northerlies (southerlies) prevail over East Asia. As a result, the surface and lower-tropospheric temperature over East Asia decreases (increases) and the cold surges over Southeast Asia and tropical western Pacific are more (less) active. The index, which exhibits distinct interannual variations, is also strongly correlated with the Arctic Oscillation and Nino-3.4 sea surface temperature (SST) index. Compared to previous indexes, this index takes into account more influencing factors and better elucidates the physical processes ass...

Tropical Cyclone Formation in a Sheared Environment: A Case Study

Abstract: The development of Hurricane Danny (1997) from depression to hurricane was examined using cloud-to-ground lightning data, reconnaissance aircraft data, and satellite imagery. Vertical wind shear between 850 and 200 hPa of 5–11 m s−1 produced persistent downshear convective outbreaks that became progressively more intense and closer to the center during the development. Early in the period the storm intensified steadily in the presence of this downshear convection. During the last and most intense outbreak, a second vortex appeared to develop within the convection. Evidence is presented that the new downshear vortex became the dominant vortex and absorbed the original. Based on these events, it is hypothesized that the presence of moderate vertical wind shear accelerated the early development process. Equivalent potential temperature fields within 500 m of the surface were examined. Only well after the period of vortex interaction did the characteristic mature tropical cyclone radial profile of eq...