Comparison of Coincident Optical Particle Counter and Lidar Measurements of Polar Stratospheric Clouds Above McMurdo (77.85°S, 166.67°E) From 1994 to 1999

Macroscopic stratospheric aerosol properties such as surface area density (SAD) and volume density (VD) are required by modern chemistry climate models. These quantities are in continuous need of validation by observations. Direct observation of these parameters is not possible, but they can be derived from optical particle counters (OPCs) which provide concentration (number density) and size distributions of aerosol particles, and possibly from ground-based and satellite-borne lidar observations of particle backscatter coefficients and aerosol type. When such measurements are obtained simultaneously by OPCs and lidars, they can be used to calculate backscatter and extinction coefficients, as well as SAD and VD. Empirical relations can thus be derived between particle backscatter coefficient, extinction coefficient, and SAD and VD for a variety of aerosols (desert dust, maritime aerosols, stratospheric aerosols) and be used to approximate SAD and VD from lidar measurements. Here we apply this scheme to coincident measurements of polar stratospheric clouds above McMurdo Station, Antarctica, by ground-based lidar and balloon-borne OPCs. The relationships derived from these measurements will provide a means to obtain values of SAD and VD for supercooled ternary solutions (STS) and nitric acid trihydrate (NAT) PSCs from the backscatter coefficients measured by lidar. Coincident lidar and OPC measurements provided 15 profile comparisons. Empirical expressions of SAD and VD as a function of particle backscatter coefficient, beta, were calculated from fits of the form log(SAD/VD) = A + B log(beta) using beta from the lidar and SAD/VD from the OPC. The PSCs were classified as STS and NAT mixtures, ice being absent.

Automated summary

Macroscopic stratospheric aerosol properties such as SAD and VD are essential for modern chemistry climate models and require continuous validation through observations. By utilizing optical particle counters and lidars simultaneously, empirical relations can be derived between particle backscatter/extinction coefficients and SAD/VD for different aerosols, providing a means to approximate SAD and VD from lidar measurements. Coincident lidar and OPC measurements of PSCs classified as STS and NAT mixtures, with ice absent, provided valuable insights into the relationship between beta, SAD, and VD.