Contrasting GCM simulations of Arctic Mixed Phase Boundary Layer Clouds with Observations from a Tethered Balloon Platform

Abstract. Conventional techniques to measure boundary layer clouds such as research aircrafts are unable to sample in orographic or densely-populated areas. In this paper, we present a newly developed measurement platform on a tethered balloon system (HoloBalloon) to measure in situ vertical profiles of microphysical and meteorological cloud properties up to 1 kilometer above ground. The main component of the HoloBalloon platform is a holographic imager, which uses digital in-line holography to image cloud particles in a velocity independent sample volume, making it particularly well suited for measurements on a balloon. The unique combination of holography and balloon-borne measurements allows observations with high spatial resolution, covering cloud structures from the kilometer down to the millimeter scale. We present observations of a supercooled low stratus cloud (high fog event) during a Bise situation over the Swiss Plateau in February 2018. In situ microphysical profiles up to 700 m altitude above the ground and at temperatures down to −8 °C and wind speeds up to 15 m s−1 were performed. We were able to capture unique microphysical features from the kilometer down to the meter scale. For example, we observed cloud regions with decreased cloud droplet number concentration (CDNC) and cloud droplet size at scales of 30–50 meters. These cloud inhomogeneities could arise from adiabatic compression and heating and subsequent droplet evaporation in descending air parcels. Moreover, we observed conditions favorable for the formation of boundary layer waves and Kelvin-Helmholtz instability at the cloud top. This potentially influenced the cloud structure on a scale of 10–30 kilometers, which is reflected in the variability of the CDNC.

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Impact of Aerosol Intrusions on Arctic Boundary Layer Clouds. Part I: 4 May 1998 Case

Journal of the Atmospheric Sciences ◽

10.1175/jas3454.1 ◽

2005 ◽

Vol 62 (9) ◽

pp. 3082-3093 ◽

Cited By ~ 12

Author(s):

G. G. Carrió ◽

H. Jiang ◽

W. R. Cotton

Keyword(s):

Boundary Layer ◽

Sea Ice ◽

National Laboratory ◽

Atmospheric Modeling ◽

Mixed Phase ◽

Radiative Properties ◽

Arctic Boundary Layer ◽

Water Fraction ◽

Boundary Layer Clouds ◽

The Impact

Abstract The objective of this paper is to assess the impact of the entrainment of aerosol from above the inversion on the microphysical structure and radiative properties of boundary layer clouds. For that purpose, the Los Alamos National Laboratory sea ice model was implemented into the research and real-time versions of the Regional Atmospheric Modeling System at Colorado State University. A series of cloud-resolving simulations have been performed for a mixed-phase Arctic boundary layer cloud using a new microphysical module that considers the explicit nucleation of cloud droplets. Different aerosol profiles based on observations were used for initialization. When more polluted initial ice-forming nuclei (IFN) profiles are assumed, the liquid water fraction of the cloud decreases while the total condensate path, the residence time of the ice particles, and the downwelling infrared radiation monotonically increase. Results suggest that increasing the aerosol concentrations above the boundary layer may increase sea ice melting rates when mixed-phase clouds are present.

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The effect of marine ice nucleating particles on mixed-phase clouds

10.5194/acp-2021-537 ◽

2021 ◽

Author(s):

Tomi Raatikainen ◽

Marje Prank ◽

Jaakko Ahola ◽

Harri Kokkola ◽

Juha Tonttila ◽

...

Keyword(s):

Boundary Layer ◽

High Resolution ◽

Mixed Boundary ◽

Mixed Phase ◽

Radiative Balance ◽

Boundary Layer Clouds ◽

Boundary Layer Turbulence ◽

Resolution Model ◽

High Resolution Model ◽

Mixed Phase Clouds

Abstract. Shallow marine mixed-phase clouds are important for the radiative balance, but modelling their formation and dynamics is challenging. These clouds depend on boundary layer turbulence and cloud top radiative cooling, which is related to the cloud phase. The fraction of frozen droplets depends on the availability of suitable ice nucleating particles (INPs), which initiate droplet freezing. While desert dust is the dominating INP type in most regions, remote boundary layer clouds are dependent on local marine INP emissions, which are often related to biogenic sources including phytoplankton. Here we use high resolution large eddy simulations to examine the potential effects of marine emissions on boundary layer INP concentrations and their effects on clouds. Surface emissions have a direct effect on INP concentration in a typical well-mixed boundary layer whereas a steep inversion can block the import of background INPs from the free troposphere. The importance of the marine source depends on the background INP concentration, so that marine emissions become dominant with low background concentrations. For the INP budget it is also important to account for INP recycling. Finally, with the high-resolution model we show how ice nucleation hotspots and high INPs concentrations are focused on updraught regions. Our results show that marine INP emissions contribute directly to the boundary layer INP budget and therefore have an influence on mixed-phase clouds.

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Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

Atmospheric Measurement Techniques ◽

10.5194/amt-13-925-2020 ◽

2020 ◽

Vol 13 (2) ◽

pp. 925-939 ◽

Cited By ~ 2

Author(s):

Fabiola Ramelli ◽

Alexander Beck ◽

Jan Henneberger ◽

Ulrike Lohmann

Keyword(s):

Boundary Layer ◽

Three Dimensional ◽

Cloud Droplet ◽

Sample Volume ◽

Tethered Balloon ◽

Wind Speeds ◽

Boundary Layer Clouds ◽

Main Component ◽

Balloon System

Abstract. Conventional techniques to measure boundary layer clouds such as research aircraft are unable to sample in orographically diverse or densely populated areas. In this paper, we present a newly developed measurement platform on a tethered balloon system (HoloBalloon) to measure in situ vertical profiles of microphysical and meteorological cloud properties up to 1 km above ground. The main component of the HoloBalloon platform is a holographic imager, which uses digital in-line holography to image an ensemble of cloud particles in the size range from small cloud droplets to precipitation-sized particles in a three-dimensional volume. Based on a set of two-dimensional images, information about the phase-resolved particle size distribution, shape and spatial distribution can be obtained. The velocity-independent sample volume makes holographic imagers particularly well suited for measurements on a balloon. The unique combination of holography and balloon-borne measurements allows for observations with high spatial resolution, covering cloud structures from the kilometer down to the millimeter scale. The potential of the measurement technique in studying boundary layer clouds is demonstrated on the basis of a case study. We present observations of a supercooled low stratus cloud during a Bise situation over the Swiss Plateau in February 2018. In situ microphysical profiles up to 700 m altitude above the ground were performed at temperatures down to −8 ∘C and wind speeds up to 15 m s−1. We were able to capture unique microphysical signatures in stratus clouds, in the form of inhomogeneities in the cloud droplet number concentration and in cloud droplet size, from the kilometer down to the meter scale.

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