The Potential for Wind Observations from Insect Returns using UK Doppler Rain Radars

During summer time the UK operational rain radars are often able to detect the presence of insects within 10 to 30 km of the radar. The returns from insects have a lower magnitude compared to precipitation and are usually rejected by the processing software. However, on convective days the Doppler shift of the insect returns has potential information on the evolving wind fields before the precipitation echo appears. Such information could be valuable in improving forecasts of where convective showers are likely to form.

Extracting the insect information is not trivial. Firstly, the returns are of small magnitude and can be close to the noise of the radar system; secondly, if the insects are common, the radar will mistake them for permanent ground clutter echoes and thus reject them; thirdly, it can be difficult to distinguish the insect returns from clutter. We report on the analysis of data obtained during the summers of 2007, 2008 and 2009. During 2007 and 2008 methods were developed to extract the insect returns, and the resulting analysis revealed the difficulties specified above. Preliminary results from the summer of 2009 demonstrate the results from modifications to the radars' data processing system that should provide a more comprehensive data set and yield more avenues to identify and not reject the insects.

Examples of days when insect returns provided good estimates of the winds are examined, with attention to the sources and characterisation of the error associated with VADs and radial wind components. The potential for assimilation of such insect-derived wind observations into numerical weather prediction models is presented.