From three-hourly special radiosonde observations the diurnal pressure and temperature variation is computed for eight levels between the surface and 16 km. The quality of observations is considered, and corrections are applied for the effect of solar radiation on the radiosonde instrument. Both pressure and temperature show large diurnal variations even in the high troposphere. It is suggested that these variations cannot be caused by horizontal convergence and divergence, but must be due to non-adiabatic processes aloft.

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