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 ...

Simplified asymptotic models are developed to investigate tropical–extratropical interactions. Two kinds of interactions are illustrated in the model: (i) MJO initiation through extraction of energy from barotropic Rossby waves and (ii) MJO termination via energy transfer to extratropical Rossby waves. A new feature, in comparison to previous simplified models, is that here these waves interact...

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...

On 30 October 2004 during a strong solar proton event, layers of enhanced backscatter from altitudes between 55 and 75 km have been observed by both ESRAD (52 MHz) and the EISCAT VHF (224 MHz) radars. These echoes have earlier been termed Polar Mesosphere Winter Echoes, PMWE. After considering the morphology of the layers and their relation to observed atmospheric waves, we conclude that the ra...

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...

Albatrosses can travel a thousand kilometres daily over the oceans. They extract their propulsive energy from horizontal wind shears with a flight strategy called dynamic soaring. While thermal soaring, exploited by birds of prey and sports gliders, consists of simply remaining in updrafts, extracting energy from horizontal winds necessitates redistributing momentum across the wind shear layer,...

■ Weather phenomena such as microburst wind shear and severe thunderstorms are major concerns to the aviation industry. A number of significant airplane accidents have resulted from wind-shear encounters during takeoff and landing, and thunderstorms are a major contributor to airplane delay. Providing fully automated and timely warnings of these phenomena by radar is challenging because it requ...

The daily weather at a particular place is largely influenced by the synoptic circulation and thermodynamic profile of the atmosphere. Heavy rainfall occurs from a particular subset of synoptic and thermodynamic states. Baseline climatologies provide objective information on heavy rainfall-producing circulation patterns and thermodynamic variables. This is how climatologically large or extreme ...

Three phenomena are involved in sand movement: erosion, wind transport, and sedimentation. This paper presents a comprehensive easy-to-use multiphase model that include all three aspects with a particular attention to situations in which erosion due to wind shear and sedimentation due to gravity are not in equilibrium. The interest is related to the fact that these are the situations leading to...

Wind shear and tower shadow are the sources of power fluctuation of grid connected wind turbines during continuous operation. This paper presents a simulation model of a MW-level doubly fed induction generator (DFIG) based variable speed wind turbine with a partial-scale back-to-back power converter in Simulink. A simple and effective method of wind power fluctuations mitigation by active curre...