The Transient Mass-Flow Adjustment of Heated Atmospheric Circulations

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  • 1 National Center for Atmospheric Research, Boulder, CO 80307
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Abstract

The transient adjustment of the baroclinic structure of a warm core disturbance forced by heating is studied as an initial value problem. It is found that the divergent flow in convective regions adjusts on a time scale of a few hours, and the surrounding divergence field outward to about 2000 km adjusts on a time scale of about 1 day. This rapid adjustment is due to the outward radiation of gravity inertia waves. The adjustment is sufficiently rapid that diurnally periodic forcings produce divergence fields that are almost in phase, and in practically instantaneous equilibrium with the forcings.

In the case of latent heating associated with local precipitation rates in excess of a few centimeters per day, the strongly anticyclonic upper tropospheric pressure field may render the balance equation non-elliptic. When they occur in the tropics, isolated events of this magnitude can produce cross-isobaric flows on the order of 1 m s−1 outward to beyond 2000 km. A plausible influence of these tropical flows upon midlatitudes is hypothesized, following the argument in a climatological study by Blackmon et al. (1977). The present results suggest that the mechanism in question can act on time scales as short as one or two days after the inception of a strong tropical disturbance.

Abstract

The transient adjustment of the baroclinic structure of a warm core disturbance forced by heating is studied as an initial value problem. It is found that the divergent flow in convective regions adjusts on a time scale of a few hours, and the surrounding divergence field outward to about 2000 km adjusts on a time scale of about 1 day. This rapid adjustment is due to the outward radiation of gravity inertia waves. The adjustment is sufficiently rapid that diurnally periodic forcings produce divergence fields that are almost in phase, and in practically instantaneous equilibrium with the forcings.

In the case of latent heating associated with local precipitation rates in excess of a few centimeters per day, the strongly anticyclonic upper tropospheric pressure field may render the balance equation non-elliptic. When they occur in the tropics, isolated events of this magnitude can produce cross-isobaric flows on the order of 1 m s−1 outward to beyond 2000 km. A plausible influence of these tropical flows upon midlatitudes is hypothesized, following the argument in a climatological study by Blackmon et al. (1977). The present results suggest that the mechanism in question can act on time scales as short as one or two days after the inception of a strong tropical disturbance.

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