Showing papers by "Arthur D. Richmond published in 1975"

Thermospheric response to a magnetic substorm

Abstract: A computer model is used to simulate the winds and temperature variations in the thermosphere which result from auroral region electric currents during a large isolated magnetic substorm. A disturbance propagates with a speed of 750 m/s poleward and equatorward, with an amplitude of about 200 m/s in the north-south velocity and about 100 K in the temperature at 400-km altitude. The amplitude decays relatively little before the disturbance reaches the equator. The time history of the disturbance is roughly that of a single sinusoid whose period increases with horizontal distance from the source and with decreasing altitude. East-west winds of over 400 m/s at 400-km altitude are created in the auroral region itself by the ion drag mechanism. The spatial distribution of these ion drag winds is significantly affected by momentum convection, so that a simple interpretation in terms of local ion drag forces is generally not sufficient. A residual electric field of about 5 mV/m remains after the substorm source is turned off, due to the dynamo effect of the ion drag winds. Vertical velocities up to about 40 m/s are produced inside the auroral region, primarily by the fact that the heated air is more buoyant than the air outside. Comparison of our simulation with numerous observations shows generally good agreement.

Energy Relations of Atmospheric Tides and Their Significance to Approximate Methods of Solution for Tides with Dissipative Forces.

Abstract: The concepts of kinetic energy, potential energy and energy flux are clarified and quantified for atmospheric tides. An understanding of the tidal energy relations provides physical insight into the problem of dissipative effects an tidal structure. It is shown that mode coupling effects due to dissipative forces are related to the coupling of kinetic energy between different tidal modes, and the mode-coupling coefficients are computed for several tidal modes. A relation is derived linking energy density and variations of the eigenvalues of Laplace's tidal equation with frequency. A formalism of “analogous atmospheric oscillations” in a plane-parallel, uniformly rotating atmosphere is proposed to provide an approximate method of computing tidal structure in the presence of dissipative forces.