WRAL WeatherCenter Blog

Having a little trouble with the radar recently. The color "blue" shows up a lot as light rain but I don't think it is raining in those areas. Remember someone saying that flocks of birds sometimes show up on the radar and wondering if that is the problem?

Posted September 16, 2007

MIKE MOSS SAYS:      Jim,     Some of the light blue echoes around the region are indeed biological targets such as birds and bugs, with the amount of coverage varying according to several factors including the concentrations of those creatures (which varies with time of day, season and weather conditions), the vertical temperature and moisture structure of the lower atmosphere (which can affect the propagation of the radar beam), and the mode of operation of the radar itself. One particular impact in this regard is that we recently replaced the old Doppler 5000 with a new polarimetric model (DUALDoppler5000) that can transmit as much as 1 million watts in single polarization modes. This was installed back in mid-summer and the added power made the system more sensitive to the biological targets than it had been in the past. Thus we were more prone to see the "cloud" of biological echoes around the radar, similar to that which is commonly seen on NWS NEXRAD radars, which also transmit at up to 1 million watt power levels. As we operate the system more frequently in a dual-polarization mode which uses 500,000 watts for each of two orthogonally polarized signals, we'll likely see a little less of those targets, although still potentially more than we did with the older Doppler 5000 and its 250,000 watt transmitter.


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