Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling

[摘要] The day-long observation of a polar stratospheric cloud (PSC) bytwo co-located ground-based lidars at the Swedish researchfacility Esrange (67.9° N, 21.1° E) on 16January 1997 is analyzed in terms of PSC dynamics andmicrophysics. Mesoscale modeling is utilized to simulate themeteorological setting of the lidar measurements. Microphysicalproperties of the PSC particles are retrieved by comparing themeasured particle depolarization ratio and the PSC-averaged lidarratio with theoretical optical data derived for differentparticle shapes. In the morning, nitric acid trihydrate (NAT)particles and then increasingly coexisting liquid ternary aerosol(LTA) were detected as outflow from a mountain wave-induced icePSC upwind Esrange. The NAT PSC is in good agreement withsimulations for irregular-shaped particles with length-to-diameterratios between 0.75 and 1.25, maximum dimensions from 0.7 to0.9 µm, and a number density from 8 to 12 cm^-3 and thecoexisting LTA droplets had diameters from 0.7 to 0.9 µm, arefractive index of 1.39 and a number density from 7 to11 cm^-3. The total amount of condensed HNO₃ was in therange of 8–12 ppbv. The data provide further observationalevidence that NAT forms via deposition nucleation on iceparticles as a number of recently published papers suggest. Byearly afternoon the mountain-wave ice PSC expanded above thelidar site. Its optical data indicate a decrease in minimumparticle size from 3 to 1.9 µm with time. Later on,following the weakening of the mountain wave, wave-induced LTAwas observed only. Our study demonstrates that ground-based lidarmeasurements of PSCs can be comprehensively interpreted ifcombined with mesoscale meteorological data.

[学科分类] 大气科学