Intense rainfall rates and their effects on microwave attenuation

Rainfall records at the University of Miami and at many other places throughout Florida were examined for the years 1960-1978 inclusive to determine maximum rates and durations to be expected. Radar was sometimes used to determine the dimensions of rain cells. Hourly rainfall totals greater than 2 inches occurred most frequently in central and south Florida. Recording raingages showed that most of the hours with more than 2 inches of rain were convective storms in which the total amount fell in 20 to 30 minutes giving rates of 102 mm per hour and greater. A large intense rainstorm on 25 April 1979 produced an extreme rate of 584 mm per hour that lasted for 15 minutes at the Miami Airport. The calculated attenuation at 20 GHz was 63.6 db per mile for a total of 382 db on a slant path 6 miles in length. Several rain cells in this storm produced calculated attenuation totals in excess of 50 db along slant paths at 20 GHz for periods of one-half hour. Typically, the size of rain cells and general orientation and movement of this storm suggested a space diversity of 20 GHz antennas on the order of 5 to 6 miles for high antenna elevation angles and more spacing for low angles. The report includes a bibliography and a paper describing a digital radar calibration system for rainfall monitoring.