A review of research on the dry season mesoscale meteorology of northern Australia

Convective initiation and growth are sensitive to atmospheric conditions, especially humidity, in ways that need to be understood and quantified. It is not clear, however, how well current observations and modelling systems can serve to test this understanding. We simulate multiple cases of convergent cloud lines observed during January 2016 over northeastern Australia using the Weather Research and Forecasting (WRF) model (version 3.7.1), initialized by and nudged to reanalysis data. Overall, WRF appears to skilfully simulate the convergence lines. However, the associated convective clouds as seen by satellite were not properly captured by the model. The model humidity was tested against the current version (V3‐00) of the Megha‐Tropiques satellite, which although up to 30% too moist in the lowest retrieved layer over the dry continental interior compared to radiosondes, is usually accurate to within ±10% near the cloud lines. Unperturbed WRF simulations were found to be 10–20% too dry in this region. Compensating for this humidity bias via the model initialization produced more realistic simulations of clouds and convection, and this had a comparable or larger impact than changing model physics. This result highlights the importance of observations of water vapour that are accurate and have good spatial coverage, especially in the lower troposphere, for properly constraining simulations of convective environments and for model evaluation of moist processes.

Section: Introductionmentioning

confidence: 99%

Using Megha‐Tropiques satellite data to constrain humidity in regional convective simulations: A northern Australian test case

Prasad

Sherwood

Brogniez

2020

“…Bores are generally accompanied also by an increase in wind speed and wind speed variability, and often by a change in wind direction (e.g. Smith and Reeder, ). Unlike other mesoscale disturbances such sea breezes, cold fronts or thunderstorm gust fronts, idealized bores are not associated with changes in temperature and humidity.…”

Section: Introductionmentioning

confidence: 99%

“…The cloud lines associated with bores in this region are known as Morning Glories . (For details see the reviews by Smith (), Reeder and Smith (), and Smith and Reeder () and the references therein.) One study of particular relevance is that by Nudelman et al (), who, using one year of surface observations, constructed a climatology of pressure jumps in the Gulf of Carpentaria region.…”

Section: Introductionmentioning

confidence: 99%

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A climatology of atmospheric pressure jumps over southeastern Australia

Davies

Reeder

Lane

2016

Black Saturday provided the first evidence of an atmospheric bore affecting the behaviour of a bushfire. As the bore passed, the fire unexpectedly strengthened. This behaviour highlighted the lack of understanding of how common bores are in the southeastern part of Australia, a region of relatively high bushfire risk. The present study addresses that lack of understanding. Pressure jumps are identified in the 1 min records at four automatic weather stations in southeastern Australia by correlating the pressure time series with a large-amplitude step function. These jumps are then separated into two classes: bores and frontal pressure jumps. Bores are defined as pressure jumps without a change in relative humidity whereas frontal pressure jumps are defined by jumps with an accompanying decrease in temperature greater than 3 • C. About 15 pressure jumps per station per year are found. Most jumps are found in the spring and summer and fewest in winter. Bores are found most frequently in the early morning and late evening at most stations, whereas frontal pressure jumps are most frequently found in the late afternoon or early evening. Following their passage, frontal pressure jumps are associated with higher 30 min mean wind speeds than bores (9.0 and 6.1 m s −1 respectively), both of which are higher than climatology (4.7 m s −1 ).

“…The majority of these disturbances are generated in the evening over Cape York Peninsula and move southwestwards during the night and early morning. A recent review of the Morning Glory and related phenomena is given by Smith and Reeder ().…”

Section: Introductionmentioning

confidence: 99%

Southerly nocturnal bores over northeastern Australia

Schmidt

Smith

2016

Analyses of 1-min data from automatic weather stations (AWSs) in the Gulf of Carpentaria region are used to study southerly nocturnal bores over northeastern Australia. The data cover the time period 1 August to 31 December in the three years 2012-2014. A total of 12 days on which a bore passed over the region of interest were found. Ten of the disturbances occurred between August and mid-October in the presence of synoptic-scale ridging across the continent behind a frontal trough. The other two occurred in early November in the presence of localized ridging behind an inland trough separate from a frontal trough. Six of the bores were followed some hours later by a clear air mass change. Four of the 12 cases are examined in detail wherein interpretations of the AWS data are aided by analysis fields from the European Centre for Medium-range Weather Forecasts (ECMWF). The results indicate that the longevity of the bore is related to the time of day that the cold front interacts with the stable maritime layer to the north of it. The ECMWF analyses are able to capture the frontal troughs as well as the timing of their passage through the AWS network. In the analyses, the troughs are seen as narrow strips of elevated cyclonic vorticity at 950 mb. Vertical cross-sections intersecting the troughs showed structural characteristics of a shallow cold front, but the horizontal resolution of the analyses is inadequate to capture the generation of bores ahead of the fronts.