Some Observations on the Thermal Behavior of the Mesosphere

Abstract

Temperature and wind soundings of the stratosphere and mesosphere using the acoustic grenade technique were made over Barrow, Alaska (71N), during the arctic winter night and during the summer. The winter mesosphere temperatures were generally warmer than at any other location and season and were variable from day to day. Temperatures oscillated with height in wavelike fashion at magnitudes up to 30?40C between 70 and 90 km. These wavelike structures were found to exist also in the winter mesosphere at Churchill (59N) and Wallops Island (38N). However, the magnitude of the oscillations decreased with latitude to a value of 20?25C at Wallops. Conversely, variability In summer armed to decrease with increasing latitude and the wavelike structure was suppressed entirely at Barrow. Temperature variations in summer at Barrow were less than 10C from sounding to sounding at any given altitude from 40 to 85 km. Extremely low mesopause temperatures ranging from 130?140K near 85 km were observed in all of these soundings. One of the Barrow soundings, conducted during a noctilucent cloud display, when compared with a sounding conducted in the confirmed absence of noctilucent clouds, failed to show any significant temperature difference at the cloud level. Simultaneous grenade soundings conducted from Wallops, Churchill and Barrow during 1965 indicate that a stratospheric warming which occurred over Barrow in late January-early February can be explained in terms of the circulation features at 50 km. Ridging of the Aleutian anticyclone over Alaska combined with the splitting and/or migration of the polar vortex center to a location southwest of Churchill, resulted in a 20?25C increase in the Barrow temperatures from 40?50 km during the 8-day period between soundings (27 January to 4 February). The third set of soundings made on 8 February shows that the original circulation pattern was restored with the polar vortex again centered north of the Arctic circle and the Aleutian anticyclone centered south of Alaska. The resulting circulation returned the Barrow temperature profile to its original value of 27 January and was accompanied by a weakening of the pressure gradient over North America which changed the strong northwesterly winds above Barrow to light and variable up to 70 km. One set of grenade soundings at Wallops in November 1964, and four sets of pitot-tube soundings at Ascension Island in April 1964 and May 1965, and aboard ship in March and April 1965, were conducted each within one diurnal cycle. Wallops temperature variations observed at 45 km indicate a tendency toward a higher temperature near midnight than near local noon. This variation, a total of 15C at 45 km, increases with altitude to above 20C at 75 km. The phase of the cycle changes considerably also, and at 70 km the maximum occurs at local sunset and the minimum occurs near local sunrise. Results from the pitot-tube soundings indicate higher temperatures at night than in daytime at the stratopause, a rapidly changing phase of maximum temperature with height, and an increasing amplitude of the variations with height.