326 BULLETIN AMERICAN METEOROLOGICAL SOCIETY The Development and Motion of Typhoon "Doris," 1950 GEORGE P. CRESSMAN Hq.y Air Weather Service, Washington, D. C. ABSTRACT The development and motion of typhoon "Doris," which was observed during the first two weeks of May, 1950, are studied. The development of the storm is examined with respect to pre- viously published theories of storm formation. The original deepening occurred in the low latitude portion of an extended trough, after the fracture of the trough. This is in agreement with a model proposed by Riehl. The motion of the deepening storm relative to the high-level flow patterns differed from previously studied examples in that the deepening occurred as the low-level cyclone moved from under the west side of an upper anticyclone toward a position un- der an upper cyclone. The storm developed as two cyclonic vortices, which gradually merged into one, in agreement with a principle of Fujiwhara. The motion of the storm northward, as it broke through the subtropical ridge line, is shown. After examination of several possibilities, this motion is attributed to the resultant of all the Coriolis forces acting on the storm, as discussed by Rossby. The suggestion is made that this resultant force becomes prominent in determining the motion of the storm due to changes in the radial velocity profile and the increasing geographical extent of the storm. "^HE development and movement of ty- southern hemisphere and the northern hemisphere phoon "Doris," which occurred in the west easterlies. This is suggested by a west wind at Pacific in the first two weeks of May 1950, 10,000 feet at Honiara (09°S, 160°E) on 1 May, offer an opportunity for the testing of several new and is confirmed by the streamline chart of 2 May. itheorie s relating to tropical cyclones. There were By 03GCT, 2 May, the northern part of the west an unusually large number of upper-air observa- tions available for this part of the world, and a reasonably complete life history of the cyclone can be derived. THE DEVELOPMENT STAGE It is convenient to trace the development by starting with the 10,000-ft streamline chart (FIG. 1) and the 700-rnb chart (FIG. 2) for 0300 GCT, 1 May 1950. The pattern of middle latitude long waves consists of a trough over Manchuria, a ridge east of Japan and Sakhalin, a trough at about 167°E, and a ridge at about 170°W. As a result of the short wavelength from trough to trough in this pattern, the west Pacific trough was moving rapidly eastward. It was shown in a previous in- vestigation [1] that if the higher-latitude portion of an extended trough is moving rapidly east- ward, it will be unable to retain its tropical ex- FIG. 1. 10,000-ft streamlines, 0300 GCT, 1 May 1950. In this and subsequent charts winds from aircraft are in- tension. In the present example, then, the portion cluded from a total period of twelve hours, centered on of the extended trough which lies in the tropics the map time. No correction in position is made in the should break off from the middle latitude trough. plotting for aircraft wind reports computed between fixes. According to Riehl and Burgner [10] this frac- Pilot balloon reports six hours off map time are indicated ture produces a situation which is favorable for by a dashed shaft. Apparent discrepancies occasionally low-latitude cyclogenesis. An additional factor seen between winds and streamlines arise primarily be- of some importance is the existence of a line of cause the winds are off time or represent mean values shear between cross-equatorial westerlies from the between fixes. Unauthenticated | Downloaded 10/04/21 08:35 AM UTC VOL. 32, No. 9, NOVEMBER, 1951 327 ception of the one ascent on 15 GCT, 4 May, strengthening of the winds through 5 May. This interpretation of the Truk winds is supported by the cloud-distribution charts. The altostratus deck over the Marshalls on 1 May moves toward the WSW as a relatively small patch until 3 May. A large extension of the area of towering cumulus in the Carolines area can be observed on the charts for 2 and 3 May. Then from 3 to 4 May the deck of altostratus increases greatly over the Carolines and over the route from Kwajalein to Guam. At the same time, the cumulus activity over the Carolines decreases along with the in- creasing horizontal circulation. It is at 21 GCT on 3 May that a 45 knot wind is reported from Truk at 3000 feet. By 4 May continuous rain is FIG. 2. 700-mb chart, 0300 GCT, 1 May 1950. In this and subsequent charts, locations where the height of the 700-mb (or other) constant pressure surface was re- ported are indicated by heavy dots. Pacific trough had moved 13° longitude eastward. As far south as 15°N the trough moved at least 5° longitude toward the east, as shown by FIGURE 3. By 5 May (see FIG. 7) the northern part of the trough is just west of Wake and Midway, which it passes before 6 May. However, the southern end of the trough broke off from the eastward mov- ing part, beginning 2 May. FIG. 4. Time section and 24-hr pressure changes from The gradual formation of a cyclonic center near 1-6 May 1950, for Truk. Truk (07°N, 152°E) is shown by the time-section for Truk (FIG. 4) and from the cloud-distribution falling at Truk and Ponape, and a closed cyclonic charts (FIG. 5). In the time section it appears circulation is drawn near Truk on FIGURE 6. that after the weak trough passage at Truk on the On 5 May (FIG. 7) a flight from Guam to first, there is a gradual veering and, with the ex- Truk passed through a new, apparently secondary, center near 11°N, 148°E. The existence of the center is indicated by a cyclonic wind circulation and by an area of cumulonimbus and bad weather which the aircraft encountered near the center of the secondary circulation. The tendency for "troughing" in the streamlines on the Kwajalein to Guam route is particularly evident on 5 May. This suggests the beginning of a split in the anti- cyclone north of this area. Such a split was defi- nitely confirmed by a flight from Tokyo to Wake on the next day. A sudden backing of the low-level winds at Truk is observed at about 00 GCT 6 May (How- ever, the surface and 1,000-ft winds are unrepre- sentative due to terrain effects). This observation might be suspected to be an error. However, the graph of 24-hr pressure change indicates a maxi- mum of falls late in the fifth, and the first thunder- FIG. 3. 10,000-ft streamlines, 0300 GCT, 2 May 1950. storm activity at Truk occurs early in the sixth. Unauthenticated | Downloaded 10/04/21 08:35 AM UTC 328 BULLETIN AMERICAN METEOROLOGICAL SOCIETY The streamline chart for 6 May (FIG. 8) is there- fore analyzed to show the original center moving eastward past Truk as the two centers begin to rotate about each other, as described by Fuji- whara [3] [4] and Haurwitz [15]. The separate identity of these centers cannot be maintained in the analysis past the sixth, as a result of the rapidly increasing circulation and a lack of sufficiently de- FIG. 5d. Cloud distribution chart 0300 GCT, 4 May 1950. FIG. 5a. Cloud distribution chart 0300, 1 May 1950. Vertical hatching indicates areas of towering cumulus (tops above 8,000 feet). Horizontal hatching indicates areas of broken or overcast altostratus. Dots indicate observation locations. FIG. 5e. Cloud distribution chart 0300 GCT, 5 May 1950. FIG. 5b. Cloud distribution chart 0300 GCT, 2 May 1950. FIG. 6. 10,000 ft streamlines, 0300 GCT, 4 May 1950. tailed data. On the sixth the surface wind at Truk remains from S to SE, and the 24-hr pressure falls continue, although at a slower rate. From this it can be concluded that the second center is moving southward in the area west of Truk. After 6 May the only further indication of two centers comes FIG. 5C. Cloud distribution chart 0300 GCT, 3 May 1950. from the Air Weather Service reconnaissance Unauthenticated | Downloaded 10/04/21 08:35 AM UTC VOL. 32, No. 9, NOVEMBER, 1951 329 double eye might be a final remnant of the origi- nal double system of circulations which, through low-level convergence operating over a period of time, gradually merged into a single system. Other solutions are also possible, in the absence of more detailed data, but they would be more complicated than the one presented above. The conclusion however, would be the same in that a system originally containing several vortices gradually intensified into a single typhoon, with the double eye as a final indication of the original complications. The development of "Doris" to typhoon strength concurrently with the appearance and amalgama- tion of the two centers is a remarkable verification of views presented by Fujiwhara in 1923 [3] and again in 1937 [5]. In these two papers Fujiwhara FIG. 7. 10,000 ft streamlines, 0300 GCT, 5 May 1950. presented a theory proposing that small adjacent vortices with the same sense of rotation will tend flight Vulture Three Doris on 8 May. The re- to amalgamate, leading to the appearance of a port of the weather observer, CWO K. R. single large vortex. Walters,1 includes the following paragraph: Recently Riehl [11] has pointed out the impor- "It is believed that there were two eyes in tance of the high-level flow pattern for the deepen- Doris at the time of this flight, a small one lying ing of tropical cyclones.