TEMPORL INDICATIONS OF ATMOSPHERIC STABILITY AFFECTING OFF-TARGET SPRAY DRIFT IN THE MID-SOUTH U.S.

by

Steven Thomson, Y Huang, B Fritz

Contact: Steven J. Thomson

Research Agricultural Engineer

APTRU

USDA ARS

P.O. Box 36

Stoneville, MS 38776

steve.thomson@ars.usda.gov

Summary: This study is designed to determine atmospheric conditions favorable for long-distance spray drift deleterious to susceptible crops downwind from spray application. The ultimate goal is to incorporate this information into new guidelines for pilots on weather conditions and times of the day to reduce off-target drift potential in the Mid-south. A tall meteorological monitoring tower equipped with six precision (and periodically calibrated) thermistors at 14.7, 29.5, 59.4, 74.5, 89.6, and 95.5 m heights and four wind speed anemometers at 14.9, 39.7, 64.5, and 89.6 m heights will be logged continuously throughout the day during the entire growing season. Wind speed and temperature data will be used to calculate atmospheric stability ratios, and temporal and spatial temperature gradient patterns at different altitudes will be determined. Periods when wind patterns and stable air conditions occur that are known to favor off-target drift will be determined from tower data. Temperature inversion periods favorable for drift will be examined for strength, time of occurrence, and duration. Probabilities of inversion conditions as a function of time-of-day and weather will be outlined, and preliminary guidelines for safe spraying in the Midsouth will be developed from atmospheric stability data.

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