Planned and Inadvertent Weather Modification/Weather Modification Association


Potential Application of WRF/Chem to Weather Modification Problems

Steven E. Peckham, CIRES/Univ. of Colorado & NOAA/ESRL/GSD, Boulder, CO; and G. A. Grell, S. A. McKeen, J. D. Fast, and W. I. Gustafson

Over the past decades there has been a continuing interest in weather modification. However, its effectiveness has

been repeatedly questioned and a “level of proof” needs to be made to demonstrate whether or not a modification project actually meets its objectives. While a growing body of evidence is developing,that supports the effectiveness and

benefits of cloud seeding, it is also evident that conclusive proof does not exist at this time.

For example, there have been recent studies examining whether cloud seeding can produce a measurable impact upon snow pack in the Rocky Mountain region. In these studies ground-based generators are used to release silver chloro-iodide particles which can create additional ice

crystals and subsequently snowfall from winter clouds. The weather conditions were closely examined and release times were selected to optimize precipitation in targeted basins. While snow pack amounts suggest a local increase did occur, examination of release events with numerical models reveals that the efficiency in which the released particles reached their intended target (seedable clouds) was highly dependent upon the local weather conditions for each release situation. Therefore, it is questionable if the localized seeding was entirely responsible for the increase in observed snow pack .

Also, there has been some discussion of numerical model studies in recent journal articles that suggest the intensity and/or the path of hurricanes could be changed through the introduction of aerosols into or near the storm. By carefully targeting the location and amount of

released aerosols, the amount of absorbed shortwave radiation and clouds could be modified. The resulting changes to the environmental temperature, relative humidity, cloud cover, precipitation subsequently changing the

intensity and path of the storm. And by doing so, the potential damage and loss of life would be mitigated. While the results of the studies are of potential significance, the numerical studies are not complete. Additional studies need to be conducted in which released particulate transport is combined with background pollution. In addition, both the direct and indirect effects of atmospheric aerosols should be included in the study so that the cloud properties and evolution are considered. These fully-interactive numerical studies examining the effects of seeding necessitate the use of “online” chemistry.

The Weather Research and Forecast model (WRF) with chemistry is one such model being developed and evaluated for various atmospheric chemistry studies. This uniquely designed model integrates meteorology and atmospheric chemistry simultaneously. The WRF/Chem model incorporates several air chemistry mechanisms and aerosol production packages with biogenic emissions, surface deposition, convective transport, turbulence, photolysis, and advective transport.

In addition, aerosol interaction with shortwave radiation as well as microphysical parameterizations has been included. Thus, this numerical model is capable of examining problems from inert tracer transport, to regional air quality to issues associated with climate change. In addition, WRF/Chem can be used to examine the impacts of planned and/or inadvertent weather modification (e.g., cloud seeding, fire smoke, hurricane modification, etc.).

Theis presentation will we will discuss the WRF/Chem model and its current and future applications to planned and inadvertent weather modification. Itwill include the potential setup and use of the numerical model. In addition, results from recent studies demonstrating reasonable

representation of aerosol concentrations as well as their significant impact upon both shortwave radiation and cloud droplet concentration will be provided.

Session 10, Application of Numerical Models to Planned and Inadvertent Weather Modification Topics
Wednesday, 23 April 2008, 11:00 AM-12:00 PM, Standley I

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