Wintertime Supercooled Liquid Water Observations Over the Snowy Mountains of Australia by Synoptic Type

A ground based microwave profiling radiometer has been operational in the Snowy Mountains in south eastern Australia and was used to build a three year climatology of supercooled liquid water (SLW). Satellite observations (MODIS) of cloud-top thermodynamic phase suggest that SLW commonly occurs over the Snowy Mountains during the winter months and at much higher rates compared to other mountain ranges such as the Sierra Nevadas.

The radiometer was able to confirm the high frequency of occurrence of SLW at 53% of the time and the observations were consistent with MODIS. Path integrated liquid water amounts observed from the radiometer compared well with MODIS and considering the complex terrain and the temporal and spatial averaging required, comparisons of quantifications of liquid water were good, although the radiometer could at times observe significantly more LW than MODIS.

Southern Ocean air masses are known to be particularly pristine and can have an order of magnitude fewer cloud condensation nuclei when compared to commonly observed pristine maritime clouds. Ice nuclei activating at temperatures warmer than -15°C are also relatively rare. Mid-latitude cyclones originating out of the Southern Ocean are the dominant cause for SLW clouds developing over the Snowy Mountains. Mid-latitude cyclones can be “embedded” within the circumpolar storm track or can become “cutoff” and move equatorward.

SLW was documented and assigned to synoptic types with 43.0% of total SLW attributed to cutoff lows (equatorward of 45°S) and 42.2% was attributed to embedded lows. Cutoff lows tended to last longer and be more dominant later in the austral winter season, while embedded lows tended to be more dominant during June and July. 7-2014-->