Validation of HRDI MLT winds with meteor radars

Abstract

Abstract. A validation study of the mesospheric and lower-thermospheric (MLT) wind velocities measured by the High-Resolution Doppler Imager (HRDI) on board the Upper-Atmosphere Research Satellite (UARS) has been carried out, comparing with observations by meteor radars located at Shigaraki, Japan and Jakarta, Indonesia. The accuracy of the HRDI winds relative to the meteor radars is obtained by a series of simultaneous wind measurements at the time of UARS overpasses. Statistical tests on the di erence in the wind vectors observed by HRDI and the meteor radars are applied to determine whether the wind speed has been overestimated by HRDI (or underestimated by the MF radars) as previously noticed in HRDI vs. MF radar comparisons. The techniques employed are the conventional t-test applied to the mean values of the paired wind vector components as well as wind speeds, and two nonparametric tests suitable for testing the paired wind speed. The square-root transformation has been applied before the t-tests of the wind speed in order to ®t the wind-speed distribution function to the normal distribution. The overall results show little evidence of overestimation by HRDI (underestimation by meteor radars) of wind velocities in the MLT region. Some exceptions are noticed, however, at the altitudes around 88 km, where statistical di erences occasionally reach a level of signi®cance of 0.01. The validation is extended to estimate the precision of the wind velocities by both HRDI and meteor radars. In the procedure, the structure function de®ned by the mean square di erence of the observed anomalies is applied in the vertical direction for the pro®le data. This method assumes the isotropy and the homogeneity of variance for the physical quantity and the homogeneity of variance for the observational errors. The estimated precision is about 6 m s À1 for the Shigaraki meteor radar, 15 m s À1 for the Jakarta meteor radar, and 20 m s À1 for HRDI at 90-km altitude. These values can be used to con®rm the statistical signi®cance of the wind ®eld obtained by averaging the observed winds.

An improvement of wind velocity estimation from radar Doppler spectra in the upper mesosphere

“…Using the improved method, the wind velocities measured with the MU radar were compared with UARS/HRDI winds. The wind velocities with the HRDI are smaller than those of the MU radar in the meridional component and larger in the zonal component, which is similar to the results obtained by Hasebe et al (1997) on a comparison with a meteor radar. Although the number of samples for such a comparison of the MU radar and HRDI was small, the newly developed technique shown here will contribute significantly to future comparisons of the MU radar and other instruments, or the validation of a new satellite mission.…”

“…The wind velocity with HRDI has been observed to be smaller than that with the MU radar in the meridional component and larger in the zonal component. Overestimation of the HRDI wind in the zonal component has been similarly found as a result of the validation of HRDI MLT winds with meteor radars (Hasebe et al, 1997). However, there is still some uncertainty regarding these results for a few reasons.…”

“…Validation of wind velocity measurements by HRDI has been carried out by comparison with observations from MF radars (e.g. Burrage et al, 1993) and meteor radars (Hasebe et al, 1997), etc. Hasebe et al (1997) compared wind velocities measured with HRDI, the Jakarta (6.9 • S, 107.6 • E) meteor radar, and the meteor observation mode of the MU radar.…”

“…Burrage et al, 1993) and meteor radars (Hasebe et al, 1997), etc. Hasebe et al (1997) compared wind velocities measured with HRDI, the Jakarta (6.9 • S, 107.6 • E) meteor radar, and the meteor observation mode of the MU radar. Good agreement was shown except for the eastward component at around the 88 km altitude.…”

Cooperative wind observation in the upper mesosphere and lower thermosphere with foil chaff technique, the MU radar, and Yamagawa MF radar

“…Uncertainty of the resultant wind velocity includes both estimation error and geophysical variability within the temporal and spatial sampling volume. Hasebe et al (1997) calculated the precision of the MU radar meteor winds through comparison with results of HRDI onboard the UARS satellite and the Jakarta meteor radar, the error except for the geophysical noise being estimated to be ∼6 m/s.…”