Polar Mesospheric Clouds (PMC) and Polar Mesosphere Summer Echoes (PMSE), caused by water vapour crystallising in the coldest region of the Earth’s atmosphere — the mesosphere — 50–92 kilometres up, were observed together for the first time by Australian Antarctic Division (AAD) scientists at Davis station last summer.
The simultaneous observation, using a radar for PMSE and a LIDAR – light detection and ranging instrument — for PMC, is the first in the Southern Hemisphere and will allow scientists to compare differences between the phenomena in the southern and northern hemispheres and to better predict the effects of climate change.
'These phenomena have been well recorded and studied in the Northern Hemisphere but we've only recently detected them above Antarctica,” AAD physicist Dr Ray Morris said.
'In the 2005–2006 austral summer we identified PMC and PMSE at the same latitude as our northern counterparts — 68.6° south versus 69° north — using similar equipment, allowing us to compare the intensity and extent of these phenomena in each hemisphere.
'Our results show that the occurrence and brightness of Southern Hemisphere PMC and PMSE are lower than those reported in the Northern Hemisphere, and that the ice clouds peak about one kilometre higher in the Southern Hemisphere. Further observation is needed to explain these differences.'
These comparisons will help scientists understand the connections between mesosphere processes in the northern and southern hemispheres and provide a baseline against which changes in PMSE and PMC can be measured. This is important if we are to better understand and model climate change.
'The mesosphere is more sensitive to climate change than other parts of the atmosphere, and there is evidence to suggest that a warming of 1.9°C at the Earth’s surface would result in a 20°C cooling in the mesosphere,' Dr Morris said.
'If this happens, we could see changes in the extent, duration and intensity of PMSE and PMC, well before we see any effects in the lower atmosphere. So we may be able to use these phenomena to monitor climate change.'
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