Comparison of monthly mean prevailing winds and semidiurnal tidal amplitudes and phases as calculated with and without height resolution

Reflection height measurements at Collm are performed since late 1982 (Kürschner et al., 1987). However, when analysing time series of Collm winds, we often use an extended database back to 1979, in order to increase statistical reliability of the results. When doing so, we use prevailing winds and semidiurnal tidal amplitudes that are calculated from monthly median half-hourly winds and assign the results to the height of maximum measuring density near 95 km assuming that the differences are small. To prove, whether such an assumption is justified, in Figures 1-4 we compare prevailing winds and semidiurnal tidal amplitudes and phases that are calculated using a quasi-harmonic regression analysis with height-dependent parameters with those values obtained from an analysis without taking height dependence into acount. The database used covers the period 1983 - 1999.

Figure 1: Monthly mean zonal prevailing winds calculated using a regression analysis without height-dependent parameters vs. zonal prevailing winds calculated without height information.

Figure 2: As in Figure 1, but for the meridional prevailing wind.

Figure 3: As in Figure 1, but for the zonal semidiurnal amplitude.

As can be seen from the figures, the differences are small. Mean differences and standard devailations are given in Table 1. The standard deviation for the tidal phase is relatively large, this is due to large differernces that may apprear when the tidal amplitude is small (particularly during months of wind field changes in spring/autumn or during stratwarm). It is shown in Figure 4 that the difference of tidal phase is small for large tidal amplitudes.

mean difference
(m/s), (h)
standard deviation
(m/s), (h)
zonal prevailing wind
0,62
2,25
meridional prevailing wind
-0,05
2,21
zonal semidiurnal amplitude
-0,15
2,24
zonal semidiurnal phase
-0,06
0,80
Table 1: Long-term mean differences between wind parameters calculated with and without height information, and their standard deviation.

Figure 4: Difference of zonal semidiurnal phases calculated with and without height information vs. tidal amplitude.

It can be concluded that the monthly mean winds and tidal parameters as calculated without height dependence are reasonable estimates of the wind field as determined using the full information available.

References:

Kürschner, D., Schminder, R., Singer, W. and Bremer, J., 1987: Ein neues Verfahren zur Realisierung absoluter Reflexionshöhenmessungen an Raumwellen amplitudenmodulierter Rundfunksender bei Schrägeinfall im Langwellenbereich als Hilfsmittel zur Ableitung von Windprofilen in der oberen Mesopausenregion. Zeitschrift für Meteorologie 37, 322 - 332.

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3.11.2000, last modification: 3.11.2000