BAMOS
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In 1978 researchers identified several problems needing attention, relating to the forecasting of weather and passage of these cool changes. The Cold Fronts Research Program( CFRP) was conceived, whose main objective was to increase understanding of the structure of the frontal transition zone over the ocean and its subsequent modification as the system passes from ocean to land. Brian Ryan led the field activities, planned and then executed in three phases between 1980 and 1984. Each of the three phases( I in 1980, II in 1981, III in 1984) took place in summer, providing an extensive dataset for the description of cool changes – aircraft, surface data, sonde ascents, and an array of precision barometers gave an unprecedented( in Australia) amount of detail on pressure perturbations associated with the pre-frontal trough, squall lines, and shallow cold fronts.
The main results identified two main types of summertime frontal system, summarised as follows:
1. The first type of cool change occurs mostly in late spring and early summer and comprises a cold front w i t h associated frontal transition zone. This zone is made up of one or more convective lines, some of which may evolve into a major squall line. The synoptically analysed cold front may have formed on the prefrontal trough ahead of the Southern Ocean front or may be the Southern Ocean front itself. The squall line outflow very often produces a sudden wind shift and sharp temperature fall at low levels.
2. The second type occurs mostly in late summer, is basically a dry cool change and is accompanied by a single discontinuity only, usually in the form of a pressure jump, wind shift and temperature fall. A regular feature of the cold air behind such a change is a levelling off of the cold-air depth after an initial steep rise in the first tens of kilometres behind the surface change, the region of near constant depth being followed by a sustained rise in the depth of cold air further upstream. This is coincident with a major, synoptically analysed, cold front with little discernible surface change, whilst the region ahead of it is termed a cold-air surge.
Results from Phases 1 and 2 of the CFRP with plans for Phase 3 are given in Ryan et al.( 1985). Main results of all three phases and a detailed discission of the role of reconnaissance aircraft in identifying weather change lines over the ocean prior to land fall are discussed in Ryan et al.( 1988). The latter authors summarise the benefits of using aircraft observations during the CFRP in which three aircraft were used. The bulk of observations were made by the CSIRO F-27 research aircraft. In phase II the RAAF flew a Canberra jet to make Doppler wind and temperature observations. In phase III two missions were flown by a RAAF Orion aircraft, with wind and temperature data recorded manually by the navigator. Information gained from the CFRP observations, particularly low-level data on change lines over the ocean led Ryan et al.( 1988) to recommend the use of a reconnaissance aircraft during the bushfire season in south-east Australia.
I was on sabbatical leave in 1980-81 and so missed out on Phase I but returned in time for Phases II and III. Working with Brian Ryan, Bill Physick, Roger Smith, and Ken Wilson in particular, we published a number of articles based on the CFRP results, then several that looked ahead to putting theory into practice. I also studied the nature of shallow cold fronts in the form of gravity currents but by 1990 had moved on to assessing boundary-layer features in climate model simulations.
— John Garratt.
Ryan noted that the CFRP fulfilled the aspirations of Andrzej Berson and associates in CSIRO in the 1950s to understand the nature of summer-time cool changes, their relation to fronts and their modification as they moved inland. These studies had been limited by the observations available at the time. The results of the CFRP included a conceptual model of the components of air flow along the lines of Browning( Wilson and Stern [ 1985 ]), but also showed the complexity of fronts. They observed that there was usually a frontal transition zone, with several change lines, with the first often being a sea breeze front.
A very comprehensive review of research during the 1980s and 1990s on cold fronts in Australia, and indeed around the southern hemisphere, is given by Reeder and Smith( 1998), and only a few highlights are noted in this paper.
Brian Ryan asked me if I was interested in being part of the CFRP. I wasn’ t that senior at the time, and my management said no – the First GARP Global Experiment( FGGE) was occupying ANMRC’ s attention.
One of my memories of the cold front debate during mid- 80’ s was the change in focus brought about by the Ash Wednesday( and the week earlier Melbourne dust storm) cool changes. The experimental parts of Phase I and Phase II of the CFRP were conducted in average to slightly above average antecedent rainfall conditions, and many of the structures in their“ frontal transition zone” were associated with moist processes. After the 1982-83 drought and Ash Wednesday there was a much greater focus on the dry cool change.( the 6-month rainfall deciles to end of December 1980, 1981, and 1982 are compelling)
— Graham Mills.
The third and last phase of the CFRP was the most ambitious, and after joining the Bureau’ s R & D Branch in 1982, I took on the role as the Bureau’ s Project Manager for Phase 3. Working closely with Brian Ryan( known to all as Uncle Brian), I managed the mobilisation of Bureau resources for the month-long observations program, which included all the Bureau’ s stations across southeast Australia, including the met observing caravan which we had deployed to King Island. Together with the field deployment of students and researchers from the three universities, units from the army( East Sale), navy(‘ Warship’ HMAS Kimbla) and air force( Orion, flown out of Edinburgh), the CSIRO research plane and international resources, all on standby for enhanced observations periods as they were declared throughout the month, it was then the biggest field experiment held in Australia.