Preliminary Numerical Tests of the Modification of Mesoscale Convective Systems

J. M. Fritsch Environmental Research Laboratories, NOAA, Boulder, CO 80303

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C. F. Chappell Environmental Research Laboratories, NOAA, Boulder, CO 80303

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Abstract

A fine-mesh 20-level, primitive equation model is used as a tool for preliminary study of the potential for modification of mesoscale convective systems. The governing system of the model is hydrostatic with the non-hydrostatic convective components parametrically introduced through a convective cloud model subroutine. Two modification possibilities are tested: 1) dynamic seeding, and 2) alteration of the timing and location of initial convection.

Results of artificially changing the time and location of initial convection indicate that the evolution, structure, dynamics and precipitation of mesoscale systems are sensitive to the location where the initial convection happens to develop. Changing the time and location of initial convection may also substantially alter the location and significance of subsequent severe weather as well as potentially beneficial rainfall.

For idealized dynamic seeding (i.e., freezing occurs at −10°C in all cloud updrafts), model results suggest that seeding enhances convective precipitation and strengthens the dynamics of the mesoscale system. Although mesoscale convergence is increased by the additional latent heat release, the most promising link to additional precipitation seems to be through the enhancement of new growth by strengthening or accelerating moist downdrafts and their associated mesohigh outflow.

Abstract

A fine-mesh 20-level, primitive equation model is used as a tool for preliminary study of the potential for modification of mesoscale convective systems. The governing system of the model is hydrostatic with the non-hydrostatic convective components parametrically introduced through a convective cloud model subroutine. Two modification possibilities are tested: 1) dynamic seeding, and 2) alteration of the timing and location of initial convection.

Results of artificially changing the time and location of initial convection indicate that the evolution, structure, dynamics and precipitation of mesoscale systems are sensitive to the location where the initial convection happens to develop. Changing the time and location of initial convection may also substantially alter the location and significance of subsequent severe weather as well as potentially beneficial rainfall.

For idealized dynamic seeding (i.e., freezing occurs at −10°C in all cloud updrafts), model results suggest that seeding enhances convective precipitation and strengthens the dynamics of the mesoscale system. Although mesoscale convergence is increased by the additional latent heat release, the most promising link to additional precipitation seems to be through the enhancement of new growth by strengthening or accelerating moist downdrafts and their associated mesohigh outflow.

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