VHF radars (otherwise known as Mesosphere-Stratosphere-Troposphere or MST radars) are used to measure wind speed and direction over a wide range of heights in the atmosphere. The wind plays a critical role in the state of the atmosphere. It is the wind that makes the summer polar mesosphere (near 86 km in altitude) the coldest region of the earth’s environment at around −130 °C. The spring-time wind behaves in a way that holds the ozone hole together.
The behaviour of the wind in the middle atmosphere is as varied as it is important. It changes from season to season, week to week and day to day. Fine scale atmospheric waves can alter the wind dramatically in a few minutes or a few hours, or cause turbulence that leads to more chaotic behaviour. This can happen on scales as big as the earth and as small as a few metres.
Despite the insight that measuring the wind can bring, the middle atmosphere is poorly understood because it is so difficult to make these measurements.
Early atmospheric research using MST radars in the northern polar regions led to the discovery of an atmospheric phenomena called Polar Mesosphere Summer Echo (PMSE). The VHF radar return from this part of the atmosphere was much stronger than at other times of the year. The cause is the extremely cold temperatures that exist in the summer polar mesosphere. PMSE are caused by ice crystal formations. They can sometimes be observed as noctilucent clouds.
The AAD, in conjunction with the Adelaide University Physics Department and the radar designers at Atmospheric Radar Systems Pty Ltd, is making an important contribution to our understanding of the role of Antarctica in the global climate system and the processes that affect our ability to model our atmosphere into the future.