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The Gulf Lines Experiment (GLEX)

    Investigators:

    Michael J. Reeder (Centre for Dynamical Meteorology and Oceanography, Monash University); Roger K. Smith and Robert Goler (Meteorology Institute, University of Munich, Germany); Jason Beringer and Nigel J. Tapper (School of Geography and Environmental Science, Monash University); Tom Keenan, Peter May and Harald Richter (Australian Bureau of Meteorology Research Centre); Gordon Jackson (Australian Bureau of Meteorology Northern Territory Regional Office); Brian Seymour (Department of Mathematics, University of British Columbia, Canada); Jorg M. Hacker (Flinders University, Airborne Research Australia).

    Project Overview:

    During October 2002 the Gulf Lines EXperiment (GLEX) was conducted to study the dry season cloud lines that form in the Gulf of Carpentaria. The central aim of the experiment was to take the observations necessary to determine how well these lines can be predicted using the Australian Bureau of Meteorology (ABM) Limited Area Prediction System (LAPS). The observations will help understand the initiation and maintenance of the various types of systems that constitute the cloud line. This will provide new knowledge of value to weather forecasters both in Australia and elsewhere in the tropics. The lines may be relevant to the recent observations of large-scale waves of convective activity that occur in the lee of significant north-south oriented topography in the United States and elsewhere (Carbone et al, 2002). A second field phase will focus on the generation and structure of the lines during the wet season.

    The team from the School of Geography and Environmental Science (Tapper, Beringer, Coutts) were responsible for measurements of surface energy balance at various sites as well as Tethered Balloon measurements of boundary layer structure.

    The Site

    We were located at Karumba and established a transect from the Harbour to Savanna.

    Three Energy Balance sites were established (Click to enlarge)

    Harbour Salt Flats Savanna

    Data:

    Some preliminary results from our surface energy balance observations (Click to enlarge).

    Tethered Balloon operations at the salt flat (Karumba)

    Roll clouds from Flinders Aircraft (courtesy Roger Smith)

    Andrew Coutts preparing the tethered balloon and sonde for release

    Jason Beringer adjusting eddy covariance equipment on the harbour pilon (karumba)

    Some of the group of people involved in Glex

    Southerly morning glory roll clouds (courtesy Roger Smith)

    Michael Reeder about to release a radiosonde balloon

    The view from the Bowen Ratio tower at the savanna site (Karumba)

    Background:

    (The following text is taken from an article to appear in the Bulletin of the Australian Meteoroligical Society by Reeder et al. 2003)

    Cloud Lines in Northern Australia
    Two distinct kinds of cloud lines develop over the Gulf during the dry season (April-October). The first is the North Australian cloud line (NACL), a line of cumulus clouds that may stretch the entire length of the Gulf from southeast to northwest (see e.g. Drosdowsky and Holland 1987; Drosdowsky et al. 1989). During the dry season the cloud lines are relatively shallow and generally do not produce rain, but during the wet season they may develop into thunderstorms with severe wind squalls and heavy rain showers. It is the latter type of cloud line that is of particular interest to the ABM, because these storms can affect large regions of northern Australia, and because thunderstorms are intrinsically difficult to forecast. The Geostationary Meteorological Satellite (GMS) visible image at 0632 EST 4 October 2002 (2032 UTC 3 October) in Fig. 1 shows an NACL in the eastern part of the Gulf. Such lines were the primary focus for the aircraft observations as they appear to correspond to the convergence lines generated in the LAPS runs and are linked to the development of organized convection in the transition season.
    The second kind is the well-known 'morning glory', low-level roll clouds that occur early in the morning around the southeastern part of the Gulf (see e.g. Smith 1988; Reeder and Smith 1998). Figure 1 shows a northwest-southeast oriented family of roll clouds that had propagated from the northeast; such lines are called 'northeasterly morning glories'. The image also shows east-west oriented roll clouds (known as a 'southerly morning glory') located inland from the Gulf and to the west of the northeasterly morning glory. These clouds were generated south of the Gulf as a ridge extended across northern Queensland.

    Acknowledgements
    We would like to thank the ABM for its support, especially the Queensland and Northern Territory Offices and the ABM Research Centre. We are grateful to the following participants from Monash, British Columbia, Airbone Research Australia and the University of Munich: Andrew Coutts, Rudi Gaissmaier, Thomas Hamberger, Gabriel Kalotay, Carsten Kykal, Heinz Losslein, Andreas Ropuack, Thomas Spengler, Rosemary Seymour, Bernadett Weinzierl, Hilbert Wendt, and Hongyan Zhu. Funding for the experiment came from the ABM, the German Research Council, and Monash.