a oO fh HEIGHT, KM 20 + —— —_ 40 }— —_—a been —— oh 90° t 1 [| iy 60° | 30° 3 Fig. 7— Atmospheric circulation model (after Dobson and Brewer). a. Summer. b. Winter. 6 OBJECTIONS There are two serious objections to this model: First, air that rises into the stratosphere must undergo a marked heating. This can be shown on the left side in Fig. 8. If a parcel of dry air rises and expands without gain or loss of heat from its surroundings, temperature will cool along the dashed line called the “dry adiabatic.” When it rises 1 km or 3200 ft, it will have cooled owing to expansion by 10°C. The solid curve shows the observed stratospheric temperature increase with altitude in equatorial stations. This observed picture is exceedingly persistent day after day. The rising parcel must gain heat presumably by short-wave solar and long-wave terrestrial radiation to bring the parcel’s temperature back along the dotted curve to the observed curve. Two objections to this process may be noted: (1) If the rising motion is DRY ADIABAT AMBIENT TEMPERATURE ALTITUDE —————» TROPOPAUSE EQUATOR TEMPERATURE ———— Figure 8 318