A LONG-TERM STUDY OF THE QUASI-2-DAY WAVE IN THE MIDDLE ATMOSPHERE

Winds in the upper mesosphere, observed at Adelaide (35-degrees-S, 138 -degrees-E) using the spaced-antenna technique, have been used to stud y the features and long-term trends of the quasi-two-day wave over the 12 summers from 1980 to 1991. This report investigates the possibilit y that the quasi-two-day wave maintains its phase relation, with respe ct to the local solar time, from year to year. The period of this wave phenomenon over the 12 summers ranged from 46.0 to 51.0 h, with a med ian period around 48.5 h. A very long vertical wavelength (greater-tha n-or-equal-to 150 km) was found at Adelaide during most years. The pha se (in local time) was found to vary from year to year, and cycle to c ycle. This is not surprising since the period also varied by a few hou rs. Although the phase locking was not precise, there was a tendency f or the maximum northward and eastward winds of the quasi-two-day wave to occur between 1200 and 1600 h LT every year. The phase relationship between the zonal and meridional components was investigated. It was found that although the zonal tends to lead the meridional by 1/16-1/4 of a cycle (3-12 h), the mean vector phases over all summers differ b y less than 4 h, and are the same at some altitudes.