A COMPARISON OF DOPPLER AND SPACED ANTENNA RADAR TECHNIQUES FOR THE MEASUREMENT OF TURBULENT ENERGY-DISSIPATION RATES

There has been concern in the past that spaced antenna radar measurements of energy dissipation rates in the Mesosphere using broad beam arrays may be contaminated by the effects of atmospheric gravity waves. To investigate this possibility, a 1.98 MHz Doppler radar operated by the University of Adelaide was used in two separate configurations; a narrow vertical beam (4.5-degrees half power half width) and 3 smaller spaced antenna systems with broad beams (20-degrees half power half width) were used to simultaneously measure energy dissipation rates in the height region 80 to 100km. The 3 broad beams were also used to determine winds by the spaced antenna method. Although extraction of the energy dissipation rate parameter is a difficult process, temporally and spatially coincident data were obtained enabling some important comparisons to be made. Three years of such data were analysed and the following results noted: (1) the mean energy dissipation rates as measured by the two radars are comparable, (2) the variance of the data as measured by the Doppler radar is larger than that measured by the spaced antenna radar, (3) The spaced antenna radar does not generally over-estimate energy dissipation rates at moderate and large values, but when turbulence is very weak, it may do so. The degree of over-estimation is not as serious as has been inferred in the past. However, there is considerable scatter in the short term ratio of measurements using the two methods, which emphasizes the large degree of spatial variability of turbulence strengths in the middle atmosphere.