By Jeffrey Andresen
Temperature inversions are generally defined as layers in the atmosphere in which temperatures increase with height, which is opposite of the more common scenario of cooling temperatures with height. This has very important implications for the dispersal of materials in the atmosphere, as inversion layers are notoriously stable with very little vertical mixing or atmospheric turbulence. Most inversion events occur near the ground surface during the overnight hours under clear skies with little or no wind when the ground surface cools more rapidly than the air above it and results in pooling of cooler, denser air near the surface.
During the spring season, inversions are commonly associated with frost/freeze events that may damage crops. Many fruit growers in Michigan have incorporated large wind machines that can be used for frost protection during a temperature inversion. Here, the idea is to promote the mixing of the relatively warmer air aloft with cold air near the ground, raising the air temperature in the crop environment to a level above the threshold temperature where freeze or frost injury can occur.
Later in the season, temperature inversions are also of concern to growers for a different reason. Given their inherent atmospheric stability, inversions increase the risk of pesticide drift because during inversions, small droplets of volatile chemicals can be transported substantial horizontal distances from the intended application site before they settle. Although there are some tools and tactics that pesticide applicators use to reduce drift onto sensitive non-target vegetation or non-targeted areas (including proper nozzle type, boom position, tractor speed and field buffers), applicators should also be aware of the presence of temperature inversions and the risk of pesticide movement during periods when they occur. In recent years, there has been an increasing number of observed cases of pesticide drift where herbicides were carried far from the target area causing unintended crop or property damage.
To enable identification of periods where low level temperature inversions occur and to help growers determine if conditions are suitable for applying herbicides or other pesticides, Michigan State University Enviroweather
has deployed additional temperature sensors (positioned 1.5 and 10 feet above the ground) at seven station sites across central and southern Michigan (see picture). The Temperature Inversion Potential Tool
uses data from these additional sensors to compare the temperatures at different heights in order to determine whether there is the potential for temperature inversions in the 10-foot layer.
The Temperature Inversion Potential Tool produces the report shown in the picture. Stations where there is a potential for a temperature inversion are flagged with a red arrow pointing down, and stations where temperature inversions are not likely are marked with a green arrow that points upward. The observations are updated at least once per hour.
The link for this tool can be found on any Enviroweather station
page under the heading for “Weather Observations and Summaries” or from the “More Weather
” link on the main menu at the top of each page.