SYNOPTIC MODELS OF HIGH-LATITUDE MAGNETIC ACTIVITY AND EQUIVALENT IONOSPHERIC AND INDUCED CURRENTS

Hourly models of the northern high latitude magnetic activity and the equivalent ionospheric and induced currents have been made for the ent ire 1980 period using data from 55 magnetic observatories. Vector obse rvations and the method of spherical cap harmonic analysis are used to simultaneously model the external and internal scalar potentials from which the disturbance vector field and the corresponding equivalent c urrents can be determined anywhere and at anytime on, over and under t he cap. This modelling technique, when used with observatory mean hour ly values to reduce spatial aliasing of irregular disturbances and wit h the quiet nighttime (undisturbed) reference level, provides reasonab le synoptic (basic) models (errors 5-80 nT). Only the statistically si gnificant coefficients are retained in the hourly models so those for a full year (8784 models) can be readily stored and used on small comp uter systems. However, there are numerous regions that are in need of observatories and such additional data could significantly improve the delineation of large irregular disturbances. These synoptic models of the high latitude disturbance fields and the equivalent currents have a variety of applications. The models of the disturbance field might be used for correcting some magnetic surveys for the temporal variatio ns, for the analyses of the large scale equivalent ionospheric and ind uced current systems and for determining parameters of the activity. M aps of the external currents provide an indication of their spatial ex tent and, with other observations, can be used to study the electrodyn amics and the heating of the upper atmosphere and the magnetosphere-io nosphere coupling. Similarly, maps of the induced currents show their spatial extent, variability and the influences of the conducting ocean s and other crustal features. Timely data and models of the activity c ould be used to help mitigate the effects of active conditions on surv eys and also the hazardous effects of storms on some technological fac ilities. (C) 1997 Elsevier Science Ltd.