Chemical ozone depletion during Arctic winter 1997/98 derived from ground based millimeter-wave observations

We present ground based millimeter-wave measurements of Arctic stratospheri c ozone at Ny-Alesund, Spitsbergen (79N, 12E), for winter 1997/98. Vortex a veraged chemical ozone depletion rates around the 475 K isentropic level we re derived from our observations using measured ozone trends for 20 day per iods and calculations of diabatic descent inside the vortex. Back trajector y calculations for air-parcels crossing Ny-Alesund show that measurements a t Ny-Alesund were representative for vortex air-masses. Significant chemica l ozone depletion was observed during one period at the end of February 199 8 with loss rates of 32 ppb/day around the 475 K isentropic level. During t his period the loss rate was higher than in February 1997. Due to the early breakup of the polar vortex! the chemical ozone depletion stopped in March and the accumulated loss is found to be 0.64 +/-0.2 ppm in 1997/98.