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Measurements for Washington, DC and Boulder, CO are combined to provide a time series of midlatitude stratospheric water vapor data for the period 1964-82. The mean concentration for the data period is shown to be nearly constant with altitude for the low stratospheric layer between 16-22 km with a mass mixing ratio for the layer of 2.5-2.6 ppmm. Above 22 km the mixing ratio increases slightly with altitude. Evident in the 60 mb level time series is an annual cycle, a quasi-biennial cycle and a long-term nonlinear trend. The quasi-biennial cycle in water vapor at midlatitudes is consistent with variations in tropical stratosphere zonal winds and temperature and total ozone and suggests a modulation of the Hadley cell circulation. The long-term trend shows mixing ratio increasing during the 1960s and decreasing in the 1970s after 1972.

The development of a relatively lightweight dew-point radiosonde was coupled with a flight program to measure the water vapor in the stratosphere. The technique of obtaining data on descent as well as on ascent provided a method for checking the internal consistency of single flight observations. Data from three flights which meet the criterion of such self consistency are presented. One flight gave data which showed an essentially constant mixing ratio of approximately 4×10−5 g/g through the stratosphere with some decrease above 72,000 feet. The other two flights show a low water-vapor content in a layer just above the tropopause with a mixing ratio 1/20 that of the first flight at an altitude of 55,000 feet. An increase in water vapor with altitude above this layer is observed, the increase being such as to give a mixing ratio for the three flights which is of the same order of magnitude at 100,000 feet.