Extended Abstract (288K)P1.25
Severe Thunderstorms over northeastern Queensland on 19 January 2001
Seoleun Shin, Meteorological Institute, University of Munich, Munich, Germany; and R. K. Smith and J. Callaghan
On 19 January 2001, a band of severe thunderstorms moved through the Burdekin (Ayr-Home Hill) area of northern Queensland just after 0800 UTC causing widespread damage. Two houses were demolished, six caravans were destroyed and power lines were downed. Established trees were uprooted and stripped of leaves and there was widespread crop damage. A number of reports of hail were received. More than 26,200 lightning strikes were recorded in one hour, which is an Australian record. This was an unusual event as severe thunderstorms are almost unheard of in this area of the tropics.
This paper investigates the meteorological circumstances leading to the formation of the storms and, in particular, examines the possible role of an upper trough and a surface heat low in the vicinity. The study is based mainly on an analysis of data obtained from the European Centre for Medium Range Weather Forecasts (ECMWF), complemented by satellite and other observational data. The distribution of Convective Available Potential Energy (CAPE) and Convective Inhibition (CIN) are calculated to assess the utility of these quantities as indicators of storm genesis and severity. CAPE is sometimes used as an index for estimating the severity of deep convection, being a theoretical measure the energy that an air parcel can acquire as it ascends in a convectively-unstable atmosphere, while the CIN is a measure of the energy barrier preventing the release of CAPE (see e.g. Emanuel, 1994). The possible influence of an upper-level trough on the storms and on the distribution of CAPE and CIN is examined also.
The analyses up to 12 h prior to the onset of deep convection show patterns of ageostrophic convergence into the heat low at 925 mb and corresponding regions of ascent at 850 mb. Although these regions differ between analysis times the first storm cells form broadly within the area encompassing by them. It is reasonable to presume that the CIN is locally removed by such convergence. Values of CAPE were largest in the region of the heat low also (> 1500 J kg-1) about the time of formation of the storms. We will present evidence that the upper trough had little obvious influence on the severity of the storms, at least from a thermodynamical viewpoint. It would appear that low-level processes were paramount with a major contribution to enhanced CAPE being moist air advection from the Gulf of Carpentaria into the heat low.
Poster Session 1, Posters
Wednesday, 5 May 2004, 1:30 PM-1:30 PM, Richelieu Room
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