Observations of hydrostatic instability in the free atmosphere

Abstract

The distribution of lapse rates observed with a high resolution temperature sonde on two summer balloon flights is presented. Shallow layers of relative instability are observed in the stratosphere as well as the troposphere. Ten percent of the troposphere sounding had lapse rates in excess of 9.5 deg/km, and 10% of the stratosphere sounding had lapse rates in excess of 6.5 deg/km. This fraction of relatively unstable lapse rates must play a large role in determining the over-all diffusivity of the stratosphere. , 1971]. Improvements in the pressure-altitude measurement of the sounding system permit a more quantitative description of the frequency of occurrence of the unstable layers. This note reports on data. from two summer balloon ascents made with the new system. Both flights carried the GMD sonde in addition to the experimental sonde so that conventional temperature and pressure records were available for comparison. Pressure is measured in the experimental system by an a particle pressure gage developed at the University of Minnesota [Howard et al., 1968]. The gage measures the ionizing current produced by a weak a source, and with the present circuitry and source strength a measurement of pressure is obtained once every second at sea level pressure and approximately once every 3 sec at the tropopause. The accuracy of a single pressure measurement with the a particle gage is much the same as the accuracy of a single pressure measurement of the aneroid in the GMD system. Intercomparisons of both systems gave a standard deviation of the difference in pressure altitude of approximately 25 meters. The greater sampling rate of the a gage, however, makes it possible to remove much of the noise by smoothing. Temperature measurements made with an experimental sonde have shown that shallow layers of neutral stability or possibly hydrostatic instability are a common occurrence in the free atmosphere [Mantis and PepinThe accuracy of the a gage can be judged by the comparison of the balloon ascent rates