Abstract
Abstract. Simultaneous observations are valuable in providing further insights into the character of the quasi 2-day wave. In this study we investigate the period and amplitude for the quasi 2-day wave near 91 km using MF radars at London and Saskatoon, Canada, and in addition look at possible values of the zonal wave number. The results of the present study bring out certain new aspects of the quasi 2-day wave at mid-latitudes in the Northern Hemisphere. In particular we show that the period of the quasi 2-day wave determined from our study (specially at large amplitudes) is smaller (46–47 h) than the 51–52 h period often suggested by other Northern Hemisphere results, and that the periods also showed variability as a function of time. We also draw attention to the annual variability, and especially highlight the occurrence of the wave in non-summer months. Our observations show significant wave correlation between the London and Saskatoon sites during time intervals of strong 2-day wave activity. These results suggest that the 2-day waves of 1993/4 are westward propagating waves of zonal wave number 3, although sometimes the zonal wave number 5 is also indicated (specially at large amplitudes). Our study also contributes additional mid-latitude geographical data which should aid in developing a better picture of the quasi 2-day wave.
Highlights
Radar observations in the Northern Hemisphere indicate the presence of a 2-day wave in all seasons, maximum amplitudes occur in the months of July/August (e.g., Kingsley et al, 1978; Manson et al, 1982; Manson and Meek, 1986; Clark, 1989; Tsuda et al, 1988)
This ®gure shows that the amplitude of the meridional diurnal tide is signi®cantly reduced to less than 5 m/s during the time of largest amplitude of the 2-day wave at the London site, while the amplitude values as large as 10±20 m/s are observed at the Saskatoon site in the meridional component of years 1993 and 1994
The results show that the meridional component leads the zonal component by $ 12X6 Æ 1X7 h and $ 13X1 Æ 1X1 h at the London and Saskatoon sites respectively in 1993
Summary
The quasi 2-day wave (hereafter referred to as the 2-day wave) is a global-scale oscillation in the middle atmosphere (in the 50±100 km height region) which has been observed in both the Northern and Southern Hemi-. Most observations in the Southern and Northern Hemispheres generally suggest that the 2-day wave is consistent with a westward propagating wave of zonal wave number 3 (e.g., Muller and Nelson, 1978; Craig et al, 1983; Phillips, 1989; Poole, 1990; Clark et al, 1993). This is supported by satellite temperature observations (e.g., Rodgers and Prata, 1981; Wu et al, 1993). In this study we investigate the period and amplitude of the waves over two years, and look for possible values of the zonal wave number for the quasi 2-day wave, using MF radars located at London and Saskatoon, Canada
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