Abstract
Balloon-borne polarimetric backscatter sonde (polarsonde) observations of aerosol and cloud during the approach of a cold front at Macquarie Island (54.499 S 158.937 E) are described. The polarsonde captures vertical profiles of cloud occurrence and phase. The cloud base and cloud top heights from the backscatter sonde compare favourably with observations made by a co-located cloud radar and ceilometer. An estimate of the total scatter probability from a liquid cloud layer at 1000 m height is used with a Monte Carlo model of the instrument to obtain cloud particle concentration, and this is compared to a measurement of cloud condensation nucleus concentration made at sea level. Backscatter from aerosol, as well as cloud, is significant. A high aerosol loading in part of the pre-frontal airmass is observed at altitudes up to 6 km. Below the melting level, the high cross-polarised return, relative to the co-polarised, indicates a substantial concentration of solid, non-spherical aerosol particles, which due to the high humidity cannot be sea salt or sulphate. A back trajectory analysis indicates that the observed aerosol includes continental dust.
Highlights
It has been recognised for some time that the cloudiness of the Southern Ocean (45◦ S to 60◦ S) is poorly captured in climate models [1,2]
The vertical profiles of scattering particles over the Southern Ocean that are shown here indicate that substantial amounts of aerosol are present in the atmosphere, extending well into to the upper troposphere, though the amounts were variable
A back trajectory analysis gave results that are consistent with the aerosols being at least partially of continental origin
Summary
It has been recognised for some time that the cloudiness of the Southern Ocean (45◦ S to 60◦ S) is poorly captured in climate models [1,2]. In addition to satellites and the campaign platforms, regular balloon soundings take place at several locations around the boundaries of the Southern Ocean, and at a few within the region These measurements have been restricted to pressure, temperature and humidity, with a few of the soundings measuring ozone concentrations. We will describe results from a new in-situ sensor, a balloon-borne polarimetric backscatter sonde that was used to obtain profiles of clouds at Macquarie Island Research Station (54.499 S, 158.937 E) in the middle of the Southern Ocean This instrument was conceived for the purpose of distinguishing super-cooled liquid water from ice particles in clouds, initially with a focus on aviation safety [21]. We will discuss a back trajectory analysis that helps to shed light on the nature of the aerosols
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