PICTURE OF THE MONTH: An Example of the “Fujiwhara Effect” in the West Pacific Ocean

Abstract

~The “Fujiwhara Effect” is the name meteorologists use to describe the most spectacular of interactions between vortex pairs, that of tropical storms. The name comes from S. Fujiwhara whose studies on this phenomenon were published several decades ago (e.g. [l]). The interaction of vortex pairs is quite complex. Vortices may either attract or repel one another. Rotation will take place about a center of gravity (c.f. [2]) located on a straight line or great circle connecting them. The specific location of this center of gravity will be determined by the relative mass and intensity of the vortices. Interaction with nearby systems will also affect the motions of the vortex pair especially if the mass of the nearby system or systems is greater than that of either of the vortices in the pair. From September 9 to 12, 1967, the ESSA 3 and ESSA 5 weather satellites photographed a splendid example of the “Fujiwhara Effect.” Figures 1 through 4 show tropical vortices Ruth and Thelma for a 4-day period as these two storms approached typhoon Opal from the east. The latter storm is visible in figures 3 and 4. Figure 5 shows the tracks of the three storms for the period of the pictures. The positions indicated on the track chart are for the time of the satellite picture. The wind speeds shown at each storm position in figure 5 were obtained from the storm advisories. The interaction between Thelma and Ruth is most obvious between the 9th and 10th as Ruth is deflected southward from her previously westward