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Abstract:

Some preliminary results are presented showing that the ISAMS instrument on board the UARS satellite has detected sun‐synchronous variations in atmospheric temperature between 15–80 km altitude. These are interpreted as the westward‐migrating diurnal and semi‐diurnal tides. Zonal mean maps of the amplitudes of these components are shown, determined from 40 days' observations during the northern hemisphere winter of 1991/92. The results show maximum amplitudes ∼5 K, with the diurnal tide strongest over the equator while the semi‐diurnal tide is strongest at mid‐latitudes. Comparisons are made with previous observations from the LIMS instrument and the lidar at Biscarrosse, France. While the ISAMS and LIMS results are consistent, several significant differences from the lidar results are noted. The conclusion is that information on the global diurnal and semi‐diurnal temperature tides in the middle atmosphere may be obtained from a relatively simple treatment of ISAMS data. Copyright 1993 by the American Geophysical Union.

Abstract:

Limitations on the precision of digitized data are identified and discussed. Apart from calibration errors, these sources of uncertainty can be divided into three types of noise; digitization, Gaussian and periodic, each of which behaves differently when data is averaged. An attempt is made to separate and quantify these contributions in the infrared channels (3, 4 and 5) of various AVHRR instruments. Typical values of total noise for these channels are also obtained. © 1989 Taylor & Francis Ltd.