Wind shear

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

Tropical cyclone wind field forcing for surge models: critical issues and sensitivities

Abstract: Several wind fields developed for Hurricane Katrina (2005) in the US Gulf of Mexico (GOM) are applied with the ADCIRC hydrodynamic model to explore the sensitivity of predictions of coastal surges to wind fields developed by alternative methods. The alternative model predictions are evaluated against water level measurements provided by gages at two coastal locations. It is found that all the post-event analyzed wind fields yield a range of predictions of only ±10% of the available peak surge measurements regardless of whether the wind fields are produced by dynamical boundary layer models, kinematic analysis methods or a blend. However, the richness of meteorological forcing data in the GOM is not typically matched in other basins affected by tropical cyclones and errors may be much larger where storm intensity and size parameters are estimated mainly from satellite data. The attributes and remaining critical deficiencies of current methods for surface wind specification in both data-rich and data-poor environments are reviewed.

Interannual Variation of Tropical Cyclone Activity over the Central North Pacific.

Abstract: The annual mean number of tropical cyclones in the Central North Pacific (CNP) is approximately three Although this number is low in comparison to other basins, the interannual variability of tropical cyclones, which includes tropical storms and hurricanes, is high For the period 1966-1997, the annual number ranges from 0 to 10 tropical cyclones There is a large and positive correlation between CNP tropical cyclone counts and El Nino 34 region SST anomalies with a 95% significance level In the El Nino Hurricane Season (ENHS), a greater number of cyclones formed in the CNP and more cyclones propagated into this area from the east The monsoon trough, low level relative vorticity, and tropospheric vertical wind shear in the CNP undergo pronounced changes during warm and cold phases of ENSO For instance, the 1000 hPa relative vorticity values within the CNP in an El Nino autumn composite are double the values in a corresponding La Nina composite The El Nino autumn composite of tropospheric vertical wind shear shows a two to three times reduction equatorward of 16°N-17°N when compared to the La Nina autumn composite The increased values of the dynamic potential term in Gray’s (1977) seasonal genesis parameter correspond well with the increased cyclone frequency in the CNP for an ENHS composite Furthermore, a majority of initial detection points of named storms is found within a band of relatively large values of dynamic potential This suggests that this term can be used to diagnose favorable areas for tropical cyclogenesis on a seasonal time scale

On Deriving Vertical Air Motions from Cloud Radar Doppler Spectra

Abstract: A method for deriving vertical air motions from cloud radar Doppler spectrum measurements is introduced. The method is applicable to cloud volumes containing small particles, in this case liquid droplets, which are assumed to trace vertical air motions because of their limited size. The presence of liquid droplets is confirmed using multiple ground-based remote sensors. Corrections for Doppler spectrum broadening due to turbulence, wind shear, and radar beamwidth are applied. As a result of the turbulence broadening correction, the turbulent dissipation rate can also be estimated. This retrieval is demonstrated using measurements from the Department of Energy (DOE) Atmospheric Radiation Measurement Program’s (ARM) site in Barrow, Alaska, during the Mixed-Phase Arctic Cloud Experiment (MPACE) of autumn 2004. Comparisons of the retrievals with measurements by research aircraft near Barrow indicate that, on the whole, the retrievals perform well. A small bias in vertical velocity between the retriev...

Concurrent OH imager and sodium temperature/wind lidar observation of localized ripples over northern Colorado

Abstract: [1] On 3 and 5 September 2002 the OH all-sky imager at Platteville, Colorado (40.2°N, 104.7°W), observed small-scale, wavelike patterns (known as ripples), with horizontal wavelengths of ∼9 km and ∼7 km and lifetimes of ∼9 min and ∼15 min, respectively. The Colorado State University sodium lidar at nearby Fort Collins, Colorado (40.6°N, 105°W), also made concurrent observations of temperature and zonal and meridional winds, which allowed us to determine the nature of the ripples observed. Our observations suggest that the 3 September ripple was induced by a convective instability located at 87.5 km and the 5 September ripple was induced by a dynamic instability at 88.5 km. The ripples clearly advected as packets with the background wind. Lidar measurements also allowed us to relate the directions of wind shear to the phase front alignments of both the ripples and the nearby short-period atmospheric gravity waves. These spatial relationships provided a meaningful comparison with previously observed ripples as well as with current theoretical models. Using the 16-hour continuous lidar data set for each case, we deduced that long-period waves created an unusually large temperature perturbation at the ripple times on 3 September and an unusually large wind shear perturbation on 5 September. These perturbations prepared the background atmosphere to be near the verge of local instability, but, as revealed again by lidar observation, it was the superposition of smaller-scale perturbations at the time of the ripples that helped to actually reach the conditions required for instability and generation of the ripples.

Mean circulations of boundary-layer rolls in lake-effect snow storms

Abstract: An observational study of the roll-average flow fields of boundary-layer rolls is presented. Data used for this purpose were collected by dual-Doppler radar and aircraft measurements taken over southern Lake Michigan during the 1983/1984 field operations of Project Lake Snow. The roll circulations agreed well with findings of past observational, numerical and theoretical studies, with cross-roll components roughly 10% of the convective internal boundary layer (CIBL)-mean wind speeds and weaker vertical components. Along-roll winds were systematically stronger in the rollupdraft regions than in the roll-downdraft regions, probably due to distortion of the along-roll wind profile by the rolls. Comparison of observed wind profiles to those required by roll formation mechanisms found by past numerical and theoretical studies suggested that the observed rolls were formed by the along-roll wind shear (Asai, 1970) or wind shear curvature (Kuettner, 1971) in the lowest 0.2Z i, whereZ i is the height of the top of the CIBL.