Stratospheric Aerosol Layers in the High Canadian Arctic

Some of the major uncertainties in predicting climate change are related to the effect of aerosols and clouds on the radiative forcing of the atmosphere. In the Arctic stratosphere aerosols can also assist in the destruction of ozone. Though the high-Arctic stratosphere is often said to be “clean” relative to mid-latitudes, aerosol layers exist and can persist for periods extending for more than one year. A DIAL/Raman/Rayleigh lidar located in Eureka, Nunavut (80° N, 86° W) and jointly operated by the Canadian Network for the Detection of Environmental Change (CANDAC) and Environment Canada has made measurements during the Arctic polar sunrise for the last 3 years. The lidar transmitter is in the near UV region and the backscatter returns are measured in five detection channels. The lidar measures two Rayleigh and three Raman lines (two nitrogen and one water) to obtain height profiles of ozone, temperature and water vapor. One Rayleigh profile and the corresponding Raman profile together with nightly coincident radiosonde measurements are used to calculate the aerosol extinction and backscattering coefficients independently. These measurements allow for the calculation of the extinction-to-backscatter ratio, which relates the magnitude of anisotropic scattering and possible absorption to the amount of backscattering. Since the ratio depends on the size distribution, shape and composition it can be used to characterize the microphysical properties of the aerosol. The lidar's measurements will be used to characterize the properties of stratospheric aerosols during the Arctic polar sunrise over Eureka. These measurements will give new information about the abundance of Arctic stratospheric aerosols as well as their properties.