Formation of solid particles in synoptic-scale Arctic PSCs in early winter 2002/2003

[摘要] Polar stratospheric clouds (PSC) have been observed in early winter(December 2002) during the SOLVE II/Vintersol campaign, both from balloonscarrying comprehensive instrumentation for measurements of chemicalcomposition, size distributions, and optical properties of the particles, aswell as from individual backscatter soundings from Esrange andSodankylä. The observations are unique in the sense that the PSCparticles seem to have formed in the early winter under synoptic temperatureconditions and not being influenced by mountain lee waves. A sequence ofmeasurements during a 5-days period shows a gradual change between liquidand solid type PSCs with the development of a well-known sandwich structure.It appears that all PSC observations show the presence of a backgroundpopulation of solid particles, occasionally mixed in with more opticallydominating liquid particles. The measurements have been compared with results from adetailed microphysical and optical simulation of the formation processes.Calculated extinctions are in good agreement with SAGE-IIImeasurements from the same period. Apparently the solid particles arecontrolled by the synoptic temperature history while the presence of liquidparticles is controlled by the local temperatures at the time ofobservation. The temperature histories indicate that the solid particles arenucleated above the ice frost point, and a surface freezing mechanism forthis is included in the model. Reducing the calculated freezing rates by afactor 10-20, the model is able to simulate the observed particle sizedistributions and reproduce observed HNO₃ gas phase concentrations.

[学科分类] 大气科学