Dynamical and Microphysical Characteristics of Arctic Clouds during BASE

Abstract

In this study, observations from aircraft, Doppler radar, and LANDSAT are used to better understand dynamical and microphysical characteristics of low-level Arctic clouds for climate change studies. Observations during the Beaufort and Arctic Storms Experiment were collected over the southern Beaufort Sea and the northern Mackenzie River Basin during 1 September?14 October 1994. Measurements from the cases of 8 September and 24?25 September are analyzed. In situ observations were made by instruments mounted on a Convair-580 research aircraft. Reflectivity and radial winds were obtained from an X-band Doppler radar located near Inuvik. The reflectivity field from LANDSAT observations concurrent with the aircraft and radar observations was also obtained. Dynamical activity, representing vertical air velocity (wa) and turbulent fluxes, is found to be larger in cloud regions. The sizes of coherent structures (e.g., cells) are from 0.1 to 15 km as determined by wavelet analysis and time series of aircraft data. This size is comparable with LANDSAT and Doppler radar?derived cell sizes. Reflectivity in embedded cells for the 8 September case was larger than that of single convective cells for the 24?25 September case. The effective radius for ice crystals (droplets) ranged from 37(7.5) ?m to 70(9.5) ?m for both cases. Using observations, parameterization of the ice crystal number concentration (Ni) is obtained from a heat budget equation. Results showed that Ni is a function of wa, radiative cooling, particle size, and supersaturation. The large-scale models may have large uncertainties related to microphysical and dynamical processes (e.g., particle size and vertical air velocity, respectively), which can directly or indirectly influence radiative processes. Overall, the results suggest that the microphysical and dynamical properties of Arctic clouds need to be further explored for climate change studies.