Preliminary Analysis

Westward moving disturbances are easily detected along the equator at most longitudes and during all season. Figure 1 is representative Hovmoller diagram of unfiltered, twice-daily 850 mb meridional wind at the equator over the pasific ocean from 1 november through 31 desember 1986. Numerous disturbances are evident. During this particular season they tend to originate near the date line and disappear around 130^o E. Their phase speeds are 5-10 m s^-1 with local periods of 4-10 days. similar disturbances are evident at other longitudes, particularly the africa-atlantic region. africa is though to be a region of genesis for westward propagating disturbances with periods of 3-5 days (e.g., Burpee 1972).

GAMBAR

Fig. 1. Hovmoller diagram twice-daily 850 mb meridional wind at the equator 1 november-31 desember 1986. Contours are plotted at intervals of 3 m s^-1 with negative contours dashed. Zero contour is omitted.

               The power spectrum of the 850 mb meridional wind at the equator as a function of longitude is presented in Fig. 2a. The power of calculated at 61 frequencies for each 120 day segment beginning on 1 september and then averaged over the eight years. There is subtantial power in the 3.5-6 day band (hereafter referred to as "synoptic -frequency") ar all longitudes except 20^o-30^o E¹ and 45^o -60^o W. In fact, at many longitudes there is as much power in this band as there is at periods greater than 10 days and, in particular, near the date line and over the eastern Atlantic there is more power at synoptic than at lower frequencies.