Tropospheric vorticity responses to the solar magnetic sector structure and geomagnetic disturbances

The responses of the Vorticity Area Index (VAI) at 500 mb to large geomagnetic disturbances and to magnetic sector boundary crossings are evaluated for the periods 1947–57 and 1963–74, during which time the geomagnetic response to sector structure were known to be distinctly different. Results indicate that the nature of the VAI response to geomagnetic disturbances is markedly similar between the two subsets. The response does not vanish even when only those geomagnetic disturbances not related to sector boundary passage are used in the analysis, which suggests that enhanced geomagnetic activity can independently influence the lower atmosphere. Unlike the geomagnetic disturbance-related effects the sector-related effects have varied with time in a very complex manner. In view of this it is concluded that geomagnetic disturbances, whose effects have shown pronounced consistency, may prove a better solar signal in future sun-weather studies.