440 DANIELSEN If the concepts just discussed are valid, we should expect to find layers of stratospheric air in the troposphere and tropospheric air in the stratosphere. We should also expect a positive correlation between the radioactivity and the potential vorticity. In other words, the potential vorticity should tell us about the history or origin of the air. The conventional classification of air as stratospheric or tropospheric tells us only about the moment, because it is based on stability, and stability is not conserved during motion. MISSION OF APR. 18 AND 19, 1963 Let us now turn to the actual Springfield observations to check the concepts, Figure 3 is a hemispheric analysis of the stream function, y, on the 310°K isentropic surface.* It determines the geostrophic winds, not the actual winds. The actual windsare approximately paral- lel to the y lines. The wind speeds arerelated to their spacing and the curvatures of the air-parcel trajectories. When air speeds upit crosses to lower values of %, and when it turns cyclonically the wind speed is less than the speed implied by the gradient of /. Figure 3 does not show the actual winds, but they are on the original chart. Both the actual winds and the % analyses are necessary to construct the trajectories, Superimposed on the ¥ analysis is the area of maximum stability on the 310°K surface. Within the gray area the stabilities are greater than 0.2°6/mb; thus the air would be classified as strato- spheric, Notice that the gray area correlates with the low centers, or areas of large ¢.. Therefore this area also approximates the region of large Py. We would also expect the gray area to approximate the re- gion of maximum radioactivity on the 310°K surface. The original chart also includes an analysis of the pressure topograph of the © surface, Over most of the gray area the pressures are between 250 and 350 mb. At low latitudes the surface reachesto the 800- to 900-mb level, and over Texas, New Mexico, and Mexicoit intersects the ground, The latter area is outlined with a dashed line. On April 18, two WB50 and two RB57 aircraft were sent to obtain measurements along a northwest to southeastflight track (perpendicular to the flow) south of the low center in Wyoming. The cross section along the flight track is shown in Fig. 4. Isentropic lines are drawn for a 2°K interval; this permits a visual estimate of stability. The dashed lines depict the isotachs, lines of equal wind speed, at intervals of 10 knots. Positive values correspond to southwesterly winds. *This is the first hemispheric hand analysis prepared from the wind and the temperature observations. A smoothed machine analysis of the stream function has been developed by A, Gustafson.