Management of surface temperature inversions

Surface temp inversions

Researchers erect a tower to measure surface temperature inversion layers.

The management of spray drift also requires growers to have an appreciation of the influence of weather parameters. It has long been recognised that the application of agricultural sprays can be influenced by the stability of the atmosphere.

The NWPPA has endorsed a new project which is examining the feasibility of using data from automatic weather stations to predict and detect the presence of surface temperature inversions. The project is planning to test a system that can provide alerts and specific forecasts in regional areas for growers and applicators when conditions are not optimal for spray application.

Project updates

The management of spray drift also requires growers to have an appreciation of the influence of weather parameters. It has long been recognised that the application of agricultural sprays can be influenced by the stability of the atmosphere. The NWPPA has endorsed a project to investigate the feasibility of using data from automatic weather stations to predict and detect the presence of surface temperature inversions. The project being conducted by Graeme Tepper and Warwick Grace is planning to test a system that can provide alerts and specific forecasts in regional areas for growers and applicators when conditions are not optimal for spray application. In collaboration with the Department of Agriculture and Food WA (DAFWA), five sites for instrumented towers have been chosen and instrumentation has been ordered. DAFWA will oversee installation during January 2014. DAFWA are modifying current systems to ingest and archive the data for subsequent analysis. Test runs of the model have accurately determined local-wind flow regimes associated with the diurnal variance of atmospheric stability. Detail down to about 100m has been achieved.
The management of spray drift also requires growers to have an appreciation of the influence of weather parameters. It has long been recognised that the application of agricultural sprays can be influenced by the stability of the atmosphere. The NWPPA has endorsed a project to investigate the feasibility of using data from automatic weather stations to predict and detect the presence of surface temperature inversions. The project is planning to test a system that can provide alerts and specific forecasts in regional areas for growers and applicators when conditions are not optimal for spray application. At the June NWPPA meeting, Warwick Grace reminded the delegates that there are some simple ‘rules of thumb’ for predicting the onset of a surface temperature inversion, namely:

  1. A reduction in wind speed to below 15 to 20kph is necessary for all seasons.
  2. In winter, a fall of at least 2°C from the maximum temperature recorded on the day promote an inversion even an hour before sunset.
  3. In summer, a fall of at least 4°C from maximum temperature recorded on the day promotes an inversion an hour after sunset.
  4. If the difference between the observed maximum temperature and forecast minimum temperature is 10°C or more then there is a 90% risk of inversion conditions at sunrise.
  5. In winter, laminar flow sets in with a fall of 4°C from maximum even before an hour after sunset.
  6. Laminar flow intensifies as overnight temperature decreases.
  7. In summer, laminar flow sets in about an hour after sunset.
  8. For laminar flow to occur wind speed must be less than 15 to 20kph for any season.