K. A. Powell

An Advanced System to Monitor the 3D Structure of Diffuse Volcanic Ash Clouds

AbstractMajor disruptions of the aviation system from recent volcanic eruptions have intensified discussions about and increased the international consensus toward improving volcanic ash warnings. Central to making progress is to better discern low volcanic ash loadings and to describe the ash cloud structure more accurately in three-dimensional space and time. Here, dispersed volcanic ash observed by the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) space-based lidar near 20 000–40 000 ft [~(6–13) km] over Australia and New Zealand during June 2011 is studied. This ash event took place 3 weeks after the Puyehue-Cordon Caulle eruption, which disrupted air traffic in much of the Southern Hemisphere. The volcanic ash layers are shown to exhibit color ratios (1064/532 nm) near 0.5, significantly lower than unity, as is observed with ice. Those optical properties are used to develop an ash detection algorithm. A “trajectory mapping” technique is then demonstrated wherein ash clo...

Properties of the 1979 SAM II Antarctic 1.0-μm extinction coefficients: Implications of dehydration and seasonal evolution of the Antarctic polar vortex

The present study investigates the 1.0-μm extinction coefficient measurements obtained in the Antarctic region in 1979 from the Stratospheric Aerosol Measurement (SAM) II, with particular focus on the background aerosol properties. Correlative meteorological information from the National Centers for Environmental Prediction is incorporated in this investigation. The results indicate that the data frequency distribution of the background aerosol extinction coefficient in the local summer and fall can be adequately modeled by using a single-mode normal distribution, and that a binormal distribution is needed for modeling the distribution in the local winter and spring because of the different characteristics of the aerosols inside and outside the polar vortex. In general, the vertical distribution of the aerosol mean extinction coefficient exhibits two regions of different seasonal variation. Above 16 km the extinction coefficient is the highest during the local summer, and the lowest during the local spring inside the polar vortex. Below 16 km the aerosol seasonal variation is more complex, but the winter enhancement of the aerosol extinction coefficient inside the Antarctic polar vortex is clearly evident. As the season changes from winter to spring, the results inside the Antarctic polar vortex also indicate a reduction in aerosol optical depth in the stratosphere, but no significant changes in the upper troposphere. The present study further indicates that the bottom of the winter polar vortex in Antarctica is located at an altitude as low as 8 to 9 km, which is about 4 to 5 km lower than the bottom of the Arctic polar vortex. This difference may be attributable to the different strengths of the winter polar vortex and the planetary wave activities between the two hemispheres. In summary, the properties of the Antarctic background aerosol are very consistent with the effect of polar stratospheric clouds on the aerosol vertical distribution through their formation, sedimention, and evaporation, and with the seasonal evolution of the polar vortex. Finally, the result of the present study provides valuable opportunities for fully utilizing the multiyear SAM II tropospheric and stratospheric measurements to investigate the aerosol climatology and long-term variations in the Arctic and Antarctic regions.