No abstract

No abstract

No abstract

[1] Dynamic models of atmospheric movement over the Mount Etna volcano are used to calculate the path delays affecting radar caused by variable water vapour in the troposphere. We compare these model results with the equivalent differential radar interferogram generated by two ERS-2 SAR images taken 35 days apart and the water vapour delay retrievals from a network of fourteen GPS stations distributed over the volcano. The atmospheric model delay field agrees well with the long-wavelength spatial differences measured by InSAR and those measured by GPS.

Extended runs of a multi‐level spectral numerical model of atmospheric flow on a hemisphere have been used to investigate the effect of surface drag variations on the nature of the time‐averaged flow. It is shown that the most drastic effect of reducing the surface drag is to permit strong horizontal, barotropic shears in the zonal mean flow, which inhibit baroclinic instability. This superficially paradoxical result is implicit in many earlier calculations, most clearly in the lifecycle description of nonlinear baroclinic instability, but appears not to be widely appreciated. The kinetic energy spectra are interpreted in terms of the wavenumber of the most baroclinically unstable normal modes KR, the Rhines blocking wavenumber Kβ, and a limiting wavenumber based on surface drag KD. The changes in KR and the smaller changes in Kβ as drag is reduced account satisfactorily for the changes found in the kinetic energy spectra.