The spectral width observed by Doppler radars can be due to several e€ects including the atmospheric turbulence within the radar sample volume plus e€ects associated with the background ̄ow and the radar geometry and con®guration. This study re-examines simple models for the e€ects due to ®nite beamwidth and vertical shear of the horizontal wind. Analytic solutions of 1and 2-dimensional models ...

Helicity was calculated in Hurricane Bonnie (1998) using tropospheric-deep dropsonde soundings from the NASA Convection and Moisture Experiment. Large helicity existed downshear of the storm center with respect to the ambient vertical wind shear. It was associated with veering, semicircular hodographs created by strong, vortex-scale, radial-vertical flow induced by the shear. The most extreme v...

Helicity was calculated in Hurricane Bonnie (1998) using tropospheric-deep dropsonde soundings from the Convection and Moisture Experiment conducted by NASA. Large helicity existed downshear of the storm center with respect to the ambient vertical wind shear. It was associated with veering, semi-circular hodographs created by strong, vortex-scale, radial-vertical flow induced by the shear. The ...

The theoretical predictions derived in Part I of this study for the equilibrium fluctuations of an idealized ensemble of noninteracting, pointlike cumulus clouds are tested against three-dimensional cloud resolving model (CRM) simulations of radiative–convective equilibrium. Simulations with different radiative cooling rates are used to give a range of cloud densities, while imposed vertical wi...

Rain gauge data, satellite IR brightness temperature and radar-estimated rain rate for five tropical cyclones from the 2005–06 to 2009–10 seasons that made landfall along the northwestern coast of Australia are analysed. It is the first time that the spatial rainfall distribution of landfalling tropical cyclones in the southern hemisphere has been systematically investigated. It is found that t...

Numerical simulations of tropical-cyclone-like vortices are performed to analyze the effects of unidirectional vertical wind shear and translational flow upon the organization of convection within a hurricane’s core region and upon the intensity of the storm. A series of dry and moist simulations is performed using the Pennsylvania State University–National Center for Atmospheric Research Mesos...

Ducted gravity waves are associated with potentially large perturbations in horizontal winds. It may be shown, neglecting friction, that these perturbations are maximized at the surface and minimized at the top of the wave duct, producing perturbation vertical wind shear as well. The magnitude of this shear is maximized in the wave ridge and the wave trough. The perturbation shear may be signif...

We study the atmospheric structure in response to the propagation of gravity waves under nonisothermal (nonzero vertical temperature gradient), wind-shear (nonzero vertical zonal/meridional wind speed gradients), and dissipative (nonzero molecular viscosity and thermal conduction) conditions. As an alternative to the “complex wave-frequency” model proposed by Vadas and Fritts, we employ the tra...

The climatic conditions in the Arctic, and observations of the wind-induced drift of ice made in connexion with Fridtjof Nansen’s Fram expedition, led to the discovery 100 years ago by Vilhelm Bjerknes’ pupil, V.W. Ekman, of the importance of the Earth’s rotation in limiting the depth of the wind-induced shear current in the ocean. This essay commemorates the centenary of Ekman’s seminal paper,...

Pilot reports from special turbulence-reporting periods were used t o investigate methods of analyzing and forecasting clear-air turbulence over the United States. Meteorological analyses for the special reporting periods were made objectively by computer using only standard upper air rawinsonde measurements. The wind analyses were built upward from the 400-mb level to the 200-mb level using th...