Diurnal and semidiurnal variations of wind, pressure, and temperature in the troposphere at Washington, D.C.

Abstract

The diurnal and semidiurnal variations of wind, pressure, and temperature in the troposphere are obtained for a summer season by combining two series of 6-hourly observations made at different times at Washington, D.C. Order-of-magnitude estimates of terms in the equation of motion at the 5-km level suggest that a linearized form of the equation of motion describes the diurnal motions closely. On the assumptions that the pressure wave moves westward at an even rate without change of amplitude and that friction is absent, the local pressure variation is computed from the wind observations. At levels above 4 km in the case of the diurnal wave and above 1 km in the case of the semidiurnal wave, the phase computed from the wind agrees reasonably well with the observed phase of the pressure variation, although the calculated amplitude is too large. Discrepancies between the pressure changes determined from the winds and the observed pressure variation can be traced to the basic assumption of a simple progressive wave, to obvious wind errors that are revealed by an absence of vertical continuity, and probably to the vertical exchange of momentum in the layer near the earth's surface.