Springtime enhancement of upper tropospheric aerosol at 45S

Monthly sonde data for Lauder in Central Otago, New Zealand show profiles of aerosol backscatter from the surface to over 30 km altitude. The tropospheric data vary by season, with greater aerosol backscatter throughout the free troposphere in springtime. Aerosol mixing ratios in layers in the upper troposphere at these times are often much higher than anywhere else above the boundary layer, suggesting that they arise from horizontal transport. Ozone measurements from the sonde show correspondence in vertical structure to the backscatter data and also seasonal enhancement. The latter correlates with aerosol, but competing causes of ozone enhancement make the correspondence indistinct. High concentrations of carbon monoxide are observed by Fourier transform spectroscopy in spring, and altitude profiles derived from line shape suggest that the peak in CO occurs in the same altitude range as the aerosol enhancement

Polar stratospheric cloud threshold temperatures in the 1995–1996 arctic vortex

Balloon-borne backscattersondes have been used to study the relationship between particle scattering and ambient temperature near the vertical edge of arctic polar stratospheric clouds (PSCs) as well as to delineate the cloud type occurrence probability as a function of temperature. The observed typical threshold temperatures as a function of altitude are about1°K warmer than the temperature TSTS expected for rapid growth of supercooled ternary solution aerosols. A more descriptive analysis shows that the threshold temperatures occur over a definable range of temperatures and tend to cluster near, but somewhat warmer than, TSTS. Considering the experimental and theoretical uncertainties, this difference may not be significant. The probability of type Ib PSC occurrence shows a dramatic increase at TSTS±1°K, while for type Ia PSCs the probability is roughly constant at 10% for temperatures below the formation point of nitric acid trihydrate (TNAT)