In Helsinki, Finland, Kumpula weather radar reflectivity on the 14th of May, 2010, 05 to 17 UTC. The radar in the centre is roughly on the northern coast of the Gulf of Finland. Precipitation is in the topmost class, while other reflectivity was due to masses of birch aphids migrating over the Gulf of Finland northwards. Reflectivity caused by insects varied due to horizontal roll vortices over the land area in Finland, and by the gust front disturbances caused by the thunderstorms. Differences in the insects’ number density in air are the primary reasons for the features in reflectivity, but measurement volume gets also higher with range, and both the convergence and upward motions contribute to the patterns. More information can be found here.