The Extent of Antarctic Involvement in 'Cold Outbreaks' Over Southern AustraliaEntry ID: ASAC_697
Abstract: The data set derived from this project consists of the extraction of unusually cold days at Melbourne and Perth. (The basic source was the Bureau of Meteorology daily data records.) Another part of the data set is the points along the trajectories taken by the air to reach the cities as cold events.
From the abstracts of the referenced papers:
Cold air outbreaks, ... characterised by unseasonably low maximum temperatures, occurring over Melbourne between May 1972 and June 1991 have been identified and examined using an air parcel trajectory model and data from observations during the period of the outbreak events. Using a definition based on the long-term climatology of the region, thirteen outbreaks were identified during the study period.
The cold air pool source regions for each outbreak were examined via the use of the air parcel trajectory model using the assumption of travel along isobaric surfaces. Mean sea-level pressure patterns, the temporal behaviour of the maximum temperature surrounding an outbreak, three-hourly basic observational data and the determined isobaric trajectories were used to analyse the nature of each Melbourne outbreak.
It has emerged that air of recent Antarctic origin is not a feature common to the majority of outbreaks examined. It is also apparent that characteristic synoptic patterns are associated with cold outbreaks over the Melbourne region. These have been grouped into three categories, 'classic', warm front, and blocking anti-cyclone type. In the mean there is identifiable atmospheric organisation around the Antarctic continent associated with the events.
Unseasonably cold weather episodes have the potential to cause dislocation to many aspects of society, regardless of the season in which they occur. In this work we devise a method for quantitatively identifying extreme cold events in such a way that it is not biased to the winter season (as is usual in most other studies). We have applied this method to the daily maximum temperatures (over the period January 1972 to June 1991) in the southern Australian cities of Melbourne and Perth. We identify 10 cold events in winter and summer for the cities. Analyses were performed to determine the synoptic environment in which these events occurred. The most common synoptic type in these samples was the 'classic', which is characterised by, amongst other factors, the passage of a cold front over the city on the day of the outbreak, and the transport of air from subantarctic latitudes. Melbourne recorded five such events in summer and six in winter, while seven and eight occurred in the two seasons for Perth. The circulation features and characteristics of other synoptic types identified with these episodes is also examined.
The mean synoptic anomalies which are coincident with these cold events are analysed. For both cities and seasons there is a 'high-low' anomalous dipole in the regional MSLP pattern, with the high located in the 'upstream' quadrant from the anomalous cyclone. Having said this, the relative importance of the two features of the dipole in being associated with the cold event strongly depended on the city and season under consideration. The research shows that the regional structures associated with cold events in Melbourne and Perth bear some similarity, but also display a number of significant differences. These differences are associated partly with the different climatological and synoptic settings in which these cities find themselves, and the nature of their seasonality.
(Click for Interactive Map)
Start Date: 1972-01-01Stop Date: 1991-06-30
ISO Topic Category
Quality One of the referenced papers also provides some quality assertions (letter to the editor).
From the referenced paper (...origin and characteristics of cold air outbreaks...):
In this paper we perform trajectory analyses for all the cold outbreaks to determine the origin of the air. The accuracy of derived trajectories is often determined by the ... spatial and temporal resolution of data observations and errors associated with data measurement. Methods employed to analyse observed information and transfer that information into a gridded dataset, assumptions necessary in the determination of the trajectories, such as the form, whether isobaric, isentropic, 'isosigma' etc, in which the data will be used, and interpolation techniques also affect trajectory accuracy. The trajectory model used in this research is that developed by Law and uses wind fields centred on 2300 UTC that are cubically interpolated in space and linearly in time, in conjunction with a fourth-order Runge-Kutta method. The procedure is described in detail in the appendix. More frequent data would have made the air parcel tracking easier and possibly eliminated a few problems which resulted from the sampling interval.
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Role: TECHNICAL CONTACT
Phone: +61 3 9344 7216
Fax: +61 3 9344 7761
Email: simmonds at unimelb.edu.au
University of Melbourne School of Earth Sciences
Province or State: Victoria
Postal Code: 3052
Role: DIF AUTHOR
Phone: +61 3 6232 3244
Fax: +61 3 6232 3351
Email: dave.connell at aad.gov.au
Australian Antarctic Division 203 Channel Highway
Province or State: Tasmania
Postal Code: 7050
Perrin, G., and I. Simmonds, 1995: The origin and characteristics of cold air outbreaks over Melbourne. Australian Meteorological Magazine, 44, 41-59.
Simmonds, I., and T. Richter, 2000: Synoptic comparison of Cold Events in winter and summer in Melbourne and Perth. Theoretical and Applied Climatology, 67, 19-32
Perrin G., Simmonds I. (1995) Reply to Lamond. Australian Meteorological Magazine 44. 333-334
Creation and Review Dates
DIF Creation Date: 2000-07-28
Last DIF Revision Date: 2010-07-26