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Abstract Evidence is obtained from the examination of synoptic charts to show that the horizontal components of the air movement in the vicinity of active fronts are such as to tend to increase the thermal gradient between the two air masses. The dynamical consequences of this type of frontogenetic flow are examined by numerical calculation in respect of a very simple atmosphere structure. It is shown that the characteristic upward motion of the warm air and sinking of the cold air must take place, but the calculated upward motion of the warm air is insufficient to account for the observed rainfall unless the effect on the temperature field of the release of latent heat in the cloudy air is taken into account. The characteristic slope of frontal surfaces also appears to arise from the vertical circulation which also tends to give the strongest horizontal temperature gradient near the ground and in the upper troposphere.
J. S. Sawyer (Tue,) studied this question.