BAMOS 15
The centre of operations for CFRP Phase 3 was the Bureau’ s Mt Gambier Met Office. When Ken Wilson, who managed the operations of the office, and Barry Hanstrum as‘ chief forecaster’, declared a frontal event to be approaching, we mobilised for an intensive observations period of surface and upper air observations. From memory, we had five such events of varying intensity and definition, and collected a wealth of data for research, and the enthusiasm for the project and the comraderie of all involved was exciting. Maybe the navy, or rather the officers, sailors and Bureau observers on board HMAS Kimbla, weren’ t quite as enthusiastic as those on land though, since I am told that they dreaded to hear my voice over the radio directing them back to sea to intercept yet another cold front!
— Sue Barrell. Further field studies
Following the CFRP a data-driven approach continued in a range of significant field experiments, supported by developments in numerical modelling of idealised fronts. These studies were aimed at understanding the mesoscale features of these synoptic systems, how they were modified as they progressed over land, and also how other temperature, moisture and wind discontinuities such as gravity currents were related to fronts.
In particular, the research extended into winter events over central and northern in the Central Australian Fronts Experiments( CAFE) led by Roger Smith, Michael Reeder and Nigel Tapper from Monash University. As well as improved understanding of atmospheric processes these field experiments equipped many students for careers in meteorology.
The early part of my research career was devoted to dynamics of fronts( of all flavours), and the CFRP was the backdrop to my PhD thesis. I was especially interested in understanding their connection to baroclinic instability, and the role of the boundary layer in their structure and evolution, which had for the most part been neglected to that point. To my surprise, fronts in southern Australia looked a lot like those that grew in a nonlinear version of the classical Eady problem with a simple Ekman boundary layer( Reeder and Smith, 1986). I was chuffed when Bill Priestley read my work and took me( and my supervisor, Roger Smith) to lunch to talk about it.
Some years later, Roger Smith, Nigel Tapper, Doug Christie( from ANU) and I developed an interest in cold fronts as they headed inland. In the late winter and spring cold fronts can reach the northern parts of the continent. To me, the really astonishing thing was the unbelievably strong influence of the boundary layer. During the day when the surface is strongly heated, the fronts are almost undetectable, whereas at night the fronts quickly reform and accelerate northwards, and invariably generate large-amplitude gravity waves at their leading edge, some of which are identified in the Gulf region as southerly morning glories( Smith et al., 1995).
— Michael Reeder.
Observational studies by John Colquhoun( 1980) of the Bureau’ s NSW Regional Office had renewed interest in“ southerly busters”. Peter Baines( 1980) had suggested that postfrontal cold air was accelerated northwards along the coast after being trapped against the mountain chain to the west in the form of a coastally trapped gravity current. One key focus of research was to explore the dynamical differences between cold fronts and gravity currents in such situations. This theme is explored in depth by Smith and Reeder( 1988).
Another continuing theme was the modification of frontal systems as they moved over land. Using an idealised two-dimensional numerical model Reeder( 1986) found frontogenesis occurring as a front moved from the sea over land which had a well-mixed and heated boundary layer. Using a synoptic analysis approach, Hanstrum et al.( 1990a, b) showed how a pre-frontal trough over land can interact with a front approaching from the ocean, whereby the pre-frontal trough becomes the major front and the original front decays. Mills( 2002) continued this theme exploring how hot, dry offshore flow can reverse the coastal pressure gradient and lead to the surging of a front along the coast.
As a junior meteorologist in the Perth Office in the early 1980s I observed the effect of the warming continent in spring on fronts approaching southwest WA. One of the key tasks on the aviation desk was to forecast the low-level winds. I noticed during spring that the southwest wind change at Esperance often occurred well ahead of the approaching southern ocean front, requiring amendment of the aviation area forecast. As well as the aviation forecast, this change was also important for marine, fire weather and temperature forecasting along the southern coast of WA.
The wind change was caused by the in – situ development and translation eastwards of a pre-frontal trough. I was curious to understand the mechanism for the development of the trough, which strengthened and became the main feature of the surface weather chart as it traversed the southern coast of Australia, while the original front weakened. As a meteorologist providing forecasts during the Cold Fronts Research Program at Mount Gambier I observed a similar process of pre-frontal trough development over south eastern SA and western Victoria.
In a paper co-authored by Ken Wilson and Sue Barrell we described a climatology of the pre-frontal trough, showing its occurrence over southern Australia during the warmer months and favoured zones for formation inland from the west coast of WA and over south-eastern SA and western Victoria. In a companion paper, we presented a case study of frontogenesis within a surface prefrontal trough over southern Australia. The trough developed ahead of a surface cold front and, over a period of approximately 24 hours, intensified into a mature summertime frontal system while the original front underwent total frontolysis.
An important component of our conceptual model for continental frontogenesis was the development of a thermal ridge inland from north / south oriented coastlines in spring and summer. This led to differential thermal advection ahead of the Southern Ocean front, with warm air advection