. . ' - : . ee eel Pane ed em atid ae ttnde BE el toe 141 1600 1 -” 1400 -—- ws 24 APRI969 1630 e eae APR 1969 2100 PRESSURE HEIGHT, meters 1200 F— 1Q00 F— 800 [— 600 >— \ 25 APR \N" 24 APR 1966 1220 !969 400 F— 200 t— TEMPERATURE, °C Fig. 103.—Vertical temperature profiles, Midway Airport, April 24-25, 1969 CST at Argonne. The winds were southwest at 8 to 10 mph. Clouds were broken at 10,000 feet with a 0.9 cloud cover at Midway. The Cineinnati thermistor system was flown on January 14, 1969 by Argonne personnel in a rented light plane (Cherokee 140). An adiabatic lapse rate was observed up to the solid cloud layer at 1400 feet over the Lewis Lockport Airport. (a lakefront site). A few soundings were made at. other locations. A large, strong, high pressure area was moving from NWto SE across Chicago during the flight program. As the center of the high pressure passed, the winds veered from north at 8 mph at the start of the pro- gram through ESE at 5 mph at 2100 CST on the 24th, through S at 4 mph at midnight to SE at 4 mph by the end of the period. The sky remainedclear. The airplane flights conducted between 1200 CST on April 24th and 0600 CST on April 25th are illustrative of how an aircraft can be used to measure both The time variability of lapse rate at Midway is shown in Figure 103. Considerable warm advection oc- Midway Airport (a city location} and Meigs Airport turnal inversion extended to 980 ft by 2100 CST; the intensity but not the depth of the inversion increased the space and time variability of lapse rate in the area. The thermistor-bridge system was used every four to five hours to make profile measurements at Lewis Airport in Lockport, Illinois (a rural area), curred above 1300 ft between 1220 and 2100 CST. The mixing depth decreased from 2900 ft to 1640 ft between 1220 and 1630 on the 24th. The surface noc-