Effect of Forbush decreases of cosmic ray flux on ozone at higher middle latitudes

The Forbush decreases of cosmic ray flux occur prevailingly together with geomagnetic storms, because these phenomena have a similar origin in solar/interplanetary processes. To study the effects of large Forbush decreases on total ozone at middle latitudes, we use the TOMS total ozone data along latitudinal circles 40 degreesN and 50 degreesN. The effects of Forbush decreases are found to occur or to be non-measurable under the same conditions as those of geomagnetic storms: certain effect occurs only at 50 degreesN (not 40 degreesN), in winter, under conditions of high solar activity and the east phase of the QBO. However, the effects of the analyzed Forbush decreases are weaker than the effects of strong geomagnetic storms. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.