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This review is begun with a brief summary of the current status of our understanding of the physics of precipitation in warm clouds. The impact of warm-cloud precipitation processes on the evolution of the ice phase in supercooled clouds also is discussed.
This is followed by a review of experimental attempts to modify the microstructure of warm clouds. Modeling studies of warm cloud modification and observational studies of inadvertent warm cloud modification also are drawn upon to further elucidate the physics of warm cloud modification. The hypotheses, and evidence, for dynamic modification of warm clouds are then discussed. A few brief comments on modeling of warm cloud processes also are given. These comments are intended to serve as a warning to the non-modeler to be very cautious in taking the results of the modeling studies at face value. Finally, the review is concluded with specific recommendations regarding the current status of warm cloud modification, and future directions for the scientist and the weather modification practitioner.
This review is begun with a brief summary of the current status of our understanding of the physics of precipitation in warm clouds. The impact of warm-cloud precipitation processes on the evolution of the ice phase in supercooled clouds also is discussed.
This is followed by a review of experimental attempts to modify the microstructure of warm clouds. Modeling studies of warm cloud modification and observational studies of inadvertent warm cloud modification also are drawn upon to further elucidate the physics of warm cloud modification. The hypotheses, and evidence, for dynamic modification of warm clouds are then discussed. A few brief comments on modeling of warm cloud processes also are given. These comments are intended to serve as a warning to the non-modeler to be very cautious in taking the results of the modeling studies at face value. Finally, the review is concluded with specific recommendations regarding the current status of warm cloud modification, and future directions for the scientist and the weather modification practitioner.
The application of three-dimensional time-dependent models to weather modification experiments along with the ways in which mesoscale simulations may be used as an aid in clarifying and formulating the physical basis of a weather modification hypothesis is discussed. It is furthermore pointed out that such models can be an aid in the design of field experiments, in the evaluation of field experiments, and in decision making during the daily operations of the experiment. Not only does the challenge of weather modification require considerable advancement in our understanding of the complex physics and dynamics of mesoscale processes, but it is also essential that we develop parameterizations of these processes in order for a mesoscale model to be of value in the post hoc analyses of weather modification experiments and as a decision aid.
The application of three-dimensional time-dependent models to weather modification experiments along with the ways in which mesoscale simulations may be used as an aid in clarifying and formulating the physical basis of a weather modification hypothesis is discussed. It is furthermore pointed out that such models can be an aid in the design of field experiments, in the evaluation of field experiments, and in decision making during the daily operations of the experiment. Not only does the challenge of weather modification require considerable advancement in our understanding of the complex physics and dynamics of mesoscale processes, but it is also essential that we develop parameterizations of these processes in order for a mesoscale model to be of value in the post hoc analyses of weather modification experiments and as a decision aid.
Experience in performing real-time mesoscale numerical prediction forecasts using the Regional Atmospheric Modeling System (RAMS) over Colorado for a winter season on high-performance workstations is summarized. Performance evaluation is done for specific case studies and, statistically, for the entire winter season. RAMS forecasts are also compared with nested grid model forecasts. In addition, RAMS precipitation forecasts with a simple “dump bucket” scheme are compared with explicit, bulk microphysics parameterization schemes. The potential applications and political/social problems of having a readily accessible, real-time mesoscale forecasting capability on low-cost, high-performance workstations is discussed.
Experience in performing real-time mesoscale numerical prediction forecasts using the Regional Atmospheric Modeling System (RAMS) over Colorado for a winter season on high-performance workstations is summarized. Performance evaluation is done for specific case studies and, statistically, for the entire winter season. RAMS forecasts are also compared with nested grid model forecasts. In addition, RAMS precipitation forecasts with a simple “dump bucket” scheme are compared with explicit, bulk microphysics parameterization schemes. The potential applications and political/social problems of having a readily accessible, real-time mesoscale forecasting capability on low-cost, high-performance workstations is discussed.
Improving the forecasts of the intensity of tropical cyclones (TCs) remains a major challenge. One possibility for improvement is consideration of the effects that aerosols have on tropical clouds and cyclones. The authors have been pursuing this under the Hurricane Aerosol and Microphysics Program, supported by the U.S. Department of Homeland Security. This was done through observations of aerosols and resulting cloud microphysical structure within tropical cyclones and simulating their effects using high-resolution TC models that treat cloud internal processes explicitly. In addition to atmospheric aerosols, special attention was given also to the impact of the intense sea-spray-generated aerosols and convective rolls in the hurricane boundary layer (BL) under hurricane- force winds.
The results of simulations and observations show that TC ingestion of aerosols that serve as cloud condensation nuclei can lead to significant reductions in their intensities. This is caused by redistribution of the precipitation and latent heating to more vigorous convection in the storm periphery that cools the low levels and interferes with the inflow of energy to the eyewall, hence making the eye larger and the maximum winds weaker. The microphysical effects of the pollution and dust aerosols occur mainly at the peripheral clouds. Closer to the circulation center, the hurricane-force winds raise intense sea spray that is lifted efficiently in the roll vortices that form in the BL and coalesce into rain of mostly seawater already at cloud base, which dominates the microstructure and affects the dynamics of the inner convective cloud bands.
Improving the forecasts of the intensity of tropical cyclones (TCs) remains a major challenge. One possibility for improvement is consideration of the effects that aerosols have on tropical clouds and cyclones. The authors have been pursuing this under the Hurricane Aerosol and Microphysics Program, supported by the U.S. Department of Homeland Security. This was done through observations of aerosols and resulting cloud microphysical structure within tropical cyclones and simulating their effects using high-resolution TC models that treat cloud internal processes explicitly. In addition to atmospheric aerosols, special attention was given also to the impact of the intense sea-spray-generated aerosols and convective rolls in the hurricane boundary layer (BL) under hurricane- force winds.
The results of simulations and observations show that TC ingestion of aerosols that serve as cloud condensation nuclei can lead to significant reductions in their intensities. This is caused by redistribution of the precipitation and latent heating to more vigorous convection in the storm periphery that cools the low levels and interferes with the inflow of energy to the eyewall, hence making the eye larger and the maximum winds weaker. The microphysical effects of the pollution and dust aerosols occur mainly at the peripheral clouds. Closer to the circulation center, the hurricane-force winds raise intense sea spray that is lifted efficiently in the roll vortices that form in the BL and coalesce into rain of mostly seawater already at cloud base, which dominates the microstructure and affects the dynamics of the inner convective cloud bands.
