Simultaneous observations of the 2-day wave at London

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 midlatitudes 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 signi®cant 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.