Impact of improved radar detection capability in clear air observations

The identification and monitoring of clear air phenomena by radars is a well known process implicitly connected to the radar sensitivity and regional factors related to local weather. Thus, the knowledge of the conditions for the occurrence of those phenomena for climatologically different regions is required. For times, the two moderately sensitive radars operating in the State of São Paulo, SE Brazil have provided observations of echoes in the atmosphere void of precipitation. With the new detection capability resulting from the update that these radars have undergone recently, it was already possible to verify a significant increase on the number of cases of clear air phenomena occurring throughout the year under different atmospheric conditions.

This study aims to comparatively analyze before and after the improvement of the radar performance. It is particularly focused on bores, a phenomenon which had its detection notably increased. The motivation was the fact that in some cases, radar observations indicates that bores seem to induce convection pointing out the importance of this phenomenon for nowcasting. A search for a bore passing over an automatic surface station has shown a pressure jump of about 0,5 hPa and a wind shift in the order of 90 degree.

Fires detected by radar from burning of sugar cane crops that cover large areas in the radars range are also studied. The emitted carbonlets needles constitute an ever growing environment pollutant. On the other hand, as verified in a previous field experiment, they contribute positively to the clear air detection providing a better match of the vertical wind profile derived from radars to radiosonde wind.

A large number of cases are still being analyzed including the vertical structure of the radar observations.