Validation of O(¹S) wind measurements by WINDII: the WIND Imaging Interferometer on UARS

Abstract

This paper describes the current state of the validation of wind measurements by the wind imaging interferometer (WINDII) in the O(1S) emission. Most data refer to the 90‐to‐110‐km region. Measurements from orbit are compared with winds derived from ground‐based observations using optical interferometers, MF radars and the European Incoherent‐Scatter radar (EISCAT) during overpasses of the WINDII fields of view. Although the data from individual passes do not always agree well, the averages indicate good agreement for the zero reference between the winds measured on the ground and those obtained from orbit. A comparison with winds measured by the high resolution Doppler imager (HRDI) instrument on UARS has also been made, with excellent results. With one exception the WINDII zero wind reference agrees with all external measurement methods to within 10 m s−1 at the present time. The exception is the MF radar winds, which show large station‐to‐station differences. The subject of WINDII comparisons with MF radar winds requires further study. The thermospheric O(1S) emission region is less amenable to validation, but comparisons with EISCAT radar data give excellent agreement at 170 km. A zero wind calibration has been obtained for the O(1D) emission by comparing its averaged phase with that for O(1S) on several days when alternating 1D/1S measurements were made. Several other aspects of the WINDII performance have been studied using data from on‐orbit measurements. These concern the instrument's phase stability, its pointing, its responsivity, the phase distribution in the fields of view, and the behavior of two of the interference filters. In some cases, small adjustments have been made to the characterization database used to analyze the atmospheric data. In general, the WINDII characteristics have remained very stable during the mission to date. A discussion of measurement errors is included in the paper. Further study of the instrument performance may bring improvement, but the utimate limitation for wind validation appears to be atmospheric variability and this needs to be better understood.

Simulation study for measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground-based observations of ozone and carbon monoxide lines in the 230–250 GHz region

“…Over a 14-year period the space-borne high-resolution Doppler imager (HRDI) (Burrage et al, 1996) measured wind velocities typically between 60 • N and 60 • S and down to 50 km and contributed to the Upper Atmosphere Research Satellite (UARS) Reference Atmosphere Project (URAP) (Swinbank and Ortland, 2003) wind climatology. Also on UARS, the limb-sounding WIND Imaging Interferometer (WINDII) observed O( 1 S) airglow emission to measure winds over 90-110 km (Gault et al, 1996b). Since 2002 the TIMED Doppler Interferometer (TIDI) has been making limb-scanning measurements of O( 1 S) and O 2 (0-0) band emissions for determining horizontal winds above 60 km (Killeen et al, 2006).…”

Doppler temperatures from O(<sup>1</sup>D) airglow in the daytime thermosphere as observed by the Wind Imaging Interferometer (WINDII) on the UARS satellite

“…These temperatures correspond to an integration of the emission along the lines-of-sight. The last step consists of the inversion of these apparent quantities to obtain a temperature profile as a function of altitude, as described for wind measurements by Gault et al (1996). The detailed description of the inversion technique has been given by Rochon (2000).…”

“…The performance of the instrument over time has been described by Thuillier et al (1998). Although the wind measurements in the O( 1 S) and O( 1 D) emissions have been validated by comparisons with measurements by other instruments (Gault et al, 1996;Thuillier et al, 1996;Lathuillère et al, 1997), the Doppler temperatures have never been validated. The purpose of the present study is to examine several aspects of the WINDII daytime O( 1 D) temperature measurements to determine what level of confidence to place in them as indicators of atmospheric temperature.…”

Intercalibration of HRDI and WINDII wind measurements

“…The validation of the WINDII green-line wind observations (Gault et al, 1996) has taken a similar approach to that used for the HRDI MLT winds. In the comparisons of HRDI and WINDII observations with other techniques, it was found that medium-frequency (MF) radars can significantly underestimate the wind speeds in the mesosphere and lower thermosphere (MLT) region Gault et al, 1996;Khattatov et al, 1996). Since until the launch of UARS MF radars were the primary source of wind information, reference models also contain these biases (Fleming et al, 1996).…”