Abstract
Abstract. Observations of vertically resolved turbulence and cloud microphysics in a mixed-phase altocumulus cloud are presented using in situ measurements from an instrumented aircraft. The turbulence spectrum is observed to have an increasingly negative skewness with distance below cloud top, suggesting that long-wave radiative cooling from the liquid cloud layer is an important source of turbulence kinetic energy. Turbulence measurements are presented from both the liquid cloud layer and ice virga below. Vertical profiles of both bulk and microphysical liquid and ice cloud properties indicate that ice is produced within the liquid layer cloud at a temperature of −30 ∘C. These high-resolution in situ measurements support previous remotely sensed observations from both ground-based and space-borne instruments and could be used to evaluate numerical model simulations of altocumulus clouds at spatial scales from eddy-resolving models to global numerical weather prediction models and climate simulations.
Highlights
Mixed-phase layer clouds are common in the Earth’s atmosphere (Zhang et al, 2010; Warren et al, 1988), from the tropics where detrainment from convection forms long-lived altocumulus layers (Stein et al, 2011) to the mid-latitudes where humidity is brought to the mid-troposphere by cyclonic activity (Rauber and Tokay, 1991)
The maintenance of altocumulus clouds is the result of a complex network of processes relating supercooled water to ice through long-wave radiative cooling (LWRC), turbulence, underlying aerosol properties and entrainment, similar to the network in Arctic clouds described by Morrison et al (2012)
The aim of this paper is to report on improved cloud and aerosol microphysical observations from a detailed case study and place them in the context of new highly detailed turbulence measurements in order to better understand the processes that maintain mixed-phase altocumulus clouds in the mid-latitudes
Summary
Mixed-phase layer clouds are common in the Earth’s atmosphere (Zhang et al, 2010; Warren et al, 1988), from the tropics where detrainment from convection forms long-lived altocumulus layers (Stein et al, 2011) to the mid-latitudes where humidity is brought to the mid-troposphere by cyclonic activity (Rauber and Tokay, 1991). Peak liquid water content (LWC) was found at cloud top, ice water content (IWC) reached a maximum in the lower half of the cloud system and the similarity to Arctic boundary layer mixed-phase stratocumulus was noted. The maintenance of altocumulus clouds is the result of a complex network of processes relating supercooled water to ice through long-wave radiative cooling (LWRC), turbulence, underlying aerosol properties and entrainment, similar to the network in Arctic clouds described by Morrison et al (2012)
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