Explosive cyclogenesis over the eastern United States

Abstract

Cases of explosive cyclogenesis ("bombs') were identified over the central and eastern United States and were compared with nonexplosive cyclone development in the same region. Bombs tend to show a marked decrease of vorticity with height during their incipient and explosive states, whereas regular cyclones reveal only weak vertical vorticity gradients in the troposhere. The low-tropospheric spin-up in bombs precedes significantly that in the upper troposphere. Preexisting low-tropospheric vorticity maxima are associated with low-level jet streaks. Whereas regular cyclones posses an ill-defined level of nondivergence (ie, a broad region between 800 and 400mb, of divergence values close to zero), incipient bombs have a well-marked zero-divergence level near 500mb, associated with a sharp maximum of rising motions. We observed a marked increase in large-scale latent heat release between the incipient and the explosive phases of bomb development. There is little difference between the stability associated with bombs and regular cyclones. -from Authors