Upper atmosphere science is placing increased emphasis on global coupling between the magnetosphere, ionosphere, and thermosphere systems, particularly with regard to the penetration of dynamic, chemical, and electrodynamic effects from high to low latitudes during magnetically disturbed periods. An emerging potential exists for latitudinal and longitudinal chains of ionosondes to contribute uniquely to this thrust in ways complementary to the capabilities and shortcomings of other groundbased sensors and satellites. Here we illustrate a methodology whereby the fullest potential of such ionosonde data can be realized. Data from a chain of stations close to the -165¿ magnetic meridian and separated by about 5¿ in magnetic latitude are used to study the relationships between magnetic activity, hmF2, foF2, and inferred meridional winds during 17--28 April, 1979. Hourly values are fit in latitude using Legendre polynomials, and variations from quiet-time values are displayed in latitude-U.T. coordinates using a color graphics method which provides an illuminating illustration of the penetration of ionospheric disturbances in latitude and their dependence on Kp, storm time, and local time. Observed effects are interpreted in terms of plausible electric field, neutral wind, and neutral composition changes during the storm period. For instance, net depletions in foF2 occur over the entire disturbed interval down to about 25¿--30¿ latitude, apparently due to such increased N2 densities that the resulting enhanced plasma loss rates overcompensate and ''positive'' storm effects whereby southward winds elevate the F-layer peak to altitudes of reduced chemical loss.

Positive storm effects are, however, observed at lower latitudes, and may also reflect the influence of electric fields as well as winds. Interestingly, besides reflecting the anticipated southward flows and equatorward extensions in conjunction with magnetically disturbed conditions, the 24-hour average meridional winds exhibit a northward return flow after the magnetic disturbance has relaxed; this is a new feature of thermosphere dynamics which should be further investigated using general circulation models and other means of inferring the wind field. ¿ American Geophysical Union 1988