At H + 2 minutes (1110Z), the sun was 2 degrees west of north from the Boxer, 15 degrees above the equatorial plane. A simple section through the poles in Figure 4 shows how cloud position is determined to be at 1470-km altitude and 2250-km range. debris cloud. This implies that an average southerly wind of 6750 kph moved the This motion is in general agreement with the expected direction for this global and solar posi- tion in Church's pattern, and the speed is of correct order of magnitude. The altitude is double the 2-minute cloud height from Bell's sketch but, under entirely different atmospheric conditions of low-altitude atomic tests, many ring clouds eventually reach twice their 2-minute height. Elevation angle of the cloud is the main source of error; other parameters have less effect on resulting wind speed and altitude. Even so, varying the observed elevation angle + 10 degrees changes the inferred speed and altitude by less than 30 percent, as shown in Figure 5, References 1. 2. Church, H. W., 1961: Effects of large diurnal density changes on outer atmosphere circulation. submitted to J, Meteor. Priester, W., H. A. Martin and K, Kramp, 1960: atmosphere, To be Diurnal and seasonal density variations in the upper Nature, 188, 202, 3, Steiger, W. R., and S. Matsushita, 1960: Photographs of the high-altitude nuclear explosion 'Teak." 4, Chapman, S., 48 J. Geophys. Research, 65, 545. 1940: Geomagnetism, Vol. 1, Oxford, Clarendon Press, 100.