Diurnal and semidiurnal tide in the upper middle atmosphere during the first year of simultaneous MF radar observations in northern and southern Japan (45°N and 31°N)

K Hocke,K Igarashi

doi:10.1007/s005850050768

Abstract

The climatology of mean wind, diurnal and semidiurnal tide during the first year (1996-1997) of simultaneous wind observations at Wakkanai (45.4Â°N, 141.7Â°E) and Yamagawa (31.2Â°N, 130.6Â°E) is presented. The locations of the radars allow us to describe the latitudinal dependence of the tides. Tidal amplitude and phase profiles are compared with those of the global scale wave model (GSWM). While the observed amplitude profiles of the diurnal tide agree well with the GSWM values, the observed phase profiles often indicate longer vertical wavelengths than the GSWM phase profiles. In contrast to the GSWM simulation, the observations show a strong bimodal structure of the diurnal tide, with the phase advancing about 6 hours from summer to winter.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

Highlights

Tides in the upper middle mesosphere over Japan were mainly observed by the Kyoto meteor radar in the past (e.g. Tsuda et al, 1988; Tsuda et al, 1983; Vincent et al, 1988)
The contours of mean wind and tidal amplitudes at Yamagawa are depicted in Fig. 1 for the time from September 1996 to September 1997
As mentioned before the mean wind and the tidal amplitudes are calculated with a sliding window of 10 days length

Summary

Observations and data analysis

We use data of the MF radars at Yamagawa (31.2°N, 130.6°E) in southern Japan and Wakkanai (45.4°N, 141.7°E) in northern Japan between September 1996 to September 1997 Both radars have an operation frequency of 1.95 MHz and measure winds at heights between 60 and 100 km with a height resolution of 2 km and time resolution of 2 min at Yamagawa and 4 min at Wakkanai. The amplitudes and phases are only calculated if the data gaps within the window are less than 1/3 of the window length. This is related to the limit chosen by Thayaparan et al (1995). Instrumental factors must be considered by the comparison between our MF radar observations, satellite observations and results of tidal models. Burrage et al (1996) showed that MF radar winds tend to be smaller in magnitude than the HRDI measurements of the UARS satellite

Mean wind and amplitudes of tides and 2-day wave

Seasonal variations of tidal phases

Comparison between the observations and the GSWM model

Concluding remarks