Thin Laminations (~10m) within Arctic Clouds using a Lidar

Abstract:

The Canadian Network for the Detection of Atmospheric Composition Change (CANDAC) Rayleigh-Mie-Raman lidar (CRL) is located at Eureka, Nunavut, in the Canadian High Arctic (79.6° N, 85.6° W). It makes 7.5 m vertical resolution measurements up to 24 h/day using 532 nm and 355 nm lasers. Depolarization capability allows CRL to determine cloud particle phase.

Layers as thin as the vertical resolution limit of the lidar were found within clouds in the CRL data and interpreted to be laminated structures of liquid water alternating with layers of icy (or possibly aerosol) particles [1]. A study of four years of high resolution lidar data (2016-2019) has now been carried out, focusing on layers which are 7 - 30 m thick. Identification of days with laminated clouds was carried out using (7.5 m x 1 min) CRL plots to find laminations which met the following criteria: The laminations are quasi-horizontal, stacked at least 3 layers high within 150 m, must be located within (any type of) cloud from 0-5 km altitude, and must persist for more than 0.5 h.

We find that these laminated features occur frequently. They are found on 18-88 % of all days (and on 34-87 % of all measured cloudy days). March, April and May have more measurements than other months, and show with more precision that laminated clouds occur on about 50-75 % of all days during the spring seasons.

These measurements have been compared with local meteorological measurements from the Environment and Climate Change Canada (ECCC) Weather Station. Days with laminated clouds are strongly correlated with snow precipitation at ground level (r = 0.63), while days with non-laminated clouds (r = -0.40) and clear sky days (r = -0.43) are moderately anti-correlated with snow precipitation. Correlations of laminations with other types of weather were not significant.

[1] McCullough, E.M, Drummond, J.R., Duck, T.J.: Lidar measurements of thin laminations within Arctic clouds, ACP, 19, 4595-4614, 2019.