The hydrodynamic model of electron transport in semiconductors is analyzed and, in analogy with vortices in fluid mechanics, the curl of electron velocity is defined as electron vorticity, and the transport equation for the electron vorticity is derived. Aside from the classical hydrodynamic sources of vorticity, collision terms in the continuity and momentum equations are identified as sources...

In this note, equations for enstrophy and enstrophy advection are derived in terms of well-known quantities, assuming horizontal frictionless flow on a beta-plane. Specifically, enstrophy can be written in terms of the geopotential (or pressure), relative vorticity, zonal wind, and resultant deformation. Enstrophy advection is shown to be related to the time evolution of deformation and ageostr...

The persistence of the southern annular mode (SAM) is studied during austral winter (June–September) and summer (December–March) using observations of the three-dimensional vorticity budget. Analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere, coupled with a secondary circulation, constitutes a positive eddy feedback that a...

Article history: Received 30 November 2007 Received in revised form 30 June 2008 Accepted 19 September 2008 This paper reviews our present understanding of tornadogenesis and some of the outstanding questions that remain. The emphasis is on tornadogenesis within supercell thunderstorms. The origin of updraft-scale rotation, i.e., mesocyclogenesis, above the ground is reviewed first, followed by...

The Roman imperial monarchy is generally studied from the vantage point of ancient Roman history: the “Roman emperor” is viewed and analyzed as an element of the Roman world. This conventional approach fails to place this institution in a broader comparative context, that of monarchical rulers across world history. Systematic comparison opens up new perspectives and is indispensable in identify...

The linear wave and baroclinic instability properties of various geostrophic models valid when the Rossby number is small are investigated. The models are the ‘‘L1’’ dynamics, the ‘‘geostrophic potential vorticity’’ equations, and the more familiar quasigeostrophic and planetary geostrophic equations. Multilayer shallow water equations are used as a control. The goal is to determine whether the...

The antiquities of Jammu and Kashmir reveal that women might have enjoyed a high status as elsewhere in India. But ,there was a marked deterioration in the position of women. Female children were not much desired and their sufferings became endless with the beginning of inroads of Turko-Afghan tribes for whom carrying away of women formed the prized item of booty. This situation gave new dimens...