BURSTS OF CLOUD CONDENSATION NUCLEI (CCN) BY DISSIPATING CLOUDS AT PALMER-STATION, ANTARCTICA

We present here a case study of cloud-mediated production of cloud con densation nuclei (CCN) recorded at Palmer Station (64 degrees 46'S, 64 degrees 05'W), Antarctica on 20 Jan 1994. Four instances of CCN burst s occurred on Jan 17, 19, 20 and Feb 7, 1994 when cloud base descended to the surface and dissipated under prevailing meteorological conditi ons. The most spectacular event occurred on Jan 20 when the CCN concen tration was enhanced by a factor of four at 0.25% supersaturation (wit h respect to water) compared to the preevent concentration. At 1.25% s upersaturation, the corresponding enhancement was by a factor of seven . This indicated a larger production of aerosol particles in smaller s ize ranges. The elevated CCN concentrations were measured for over fif teen hours. The CCN activity spectrum during the event resembled the o nes that are typical of previous measurements in the urban plumes of S t. Louis and Denver.