Contact:  Dr. Brad Fritz, Agricultural Engineer, USDA-ARS, 2771 F&B Road, College Station, TX 77845  email: bfritz@apmru.usda.gov

 Summary:  Drift from aerial application of crop protection and production materials is influenced by many factors, both controllable (boom length, nozzle type and orientation, spray pressure, etc…) and uncontrollable (wind speed, wind direction, atmospheric stability).  The applicator is responsible for insuring that all factors are considered and adjusted for, to reduce as much as possible, the potential for drift.  The labels of many of the crop protection and production materials contain guidance on application parameters including meteorological considerations.  The purpose of this manuscript will be to discuss atmospheric stability and the associated meteorological parameters (such as wind speed and temperature profiles) and how these are accounted in the stability ratio.  Preliminary results for research dealing with atmospheric stability issues will be included.  In April 2003, two meteorological monitoring towers, one in central Texas and one in the Texas coastal region, were erected for the purpose of recording and documenting atmospheric stability and other meteorological conditions.  The different locations will allow for comparisons of atmospheric stability between regions.  Plots of the percent occurrence of the different atmospheric stability conditions (Unstable, Neutral, Stable, or Very Stable as defined by the stability ratio) over a 24 hour timeline will be developed.  Meteorological data will be separated by stability ratio class and analyzed for unique characteristics such as averages and ranges of wind.  Additionally, the time of occurrence, duration, and strength of temperature inversions present in the collected meteorological data will be presented.

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