Observations of Meteoric Aerosol in the Upper Stratosphere–Lower Mesosphere by the Method of Two-Wavelength Lidar Sensing

Resumo

We present the results of two-wavelength lidar sensing of the middle atmosphere in the altitude range from 30 to 60 km over Obninsk (55.1° N, 36.6° E) in 2012–2017. Monthly average values of the ratio of aerosol and Rayleigh backscattering coefficients (RARC) at a wavelength of 532 nm, averaged over the layers of 40–50 km and 50–60 km, vary from 0 to 0.02, while the average peak RARC levels in these layers vary from 0.1 to 0.2. Short-term (shorter than 1 month) and long-term (half-year and longer) variations in backscattering are observed. Short-term variations are time concurrent with the occurrence of meteor showers. Long-term enhancements of backscattering in the layer of 50–60 km were observed in 2013 after the Chelyabinsk meteorite fall, as well as in the first half of 2016. In 2014–2015, the monthly average RARC was zero within measurement errors at altitudes from 40 to 60 km. We analyzed the possibility for meteoric aerosol to manifest in backscattering, taking into account the fluxes of meteoric material, gravitational sedimentation of aerosol, and the effect of vertical wind. The flux of visible meteors with masses larger than 10⁻⁶ kg and bolides is shown to be insufficient for a long-term enhancement of backscattering in the layer of 50–60 km. It is hypothesized that the enhancement in backscattering is most likely to be due to the occurrence of an enlarged fraction of meteoric smoke particles, formed by ablation of radio meteors and penetrating into the upper stratosphere in the region of the stratospheric polar vortex. In early 2016, this was favored by the formation of an extremely strong stratospheric polar vortex and its shift toward Eurasia.