Climate - Australia

• see also:
  • Climate - Introduction 1 - atmosphere & temperature
  • Climate - Introduction 2 - water & rain
  • Climate - Introduction 3 - air & wind
  • Climate - Introduction 4 - Climates
  • Climate - Melbourne
  • Australian climate - mean annual data for various cities
  • online resources:
    • the El Nino phenomenon - Bureau Meteorology Australia
    • Strategy for dealing with coastal acid sulphate soils in Australia

Australian climate:

• general overview:
  • climatic variation is less than for other continents as:
    • extends only 32deg in latitude
    • 39% of its area lies north of the Tropic of Capricorn, where seasonal variations are modest, although subject to tropical cyclones and monsoonal weather
    • relief is subdued with 75% of the land lying between 200-500m above sea level
    • no high ranges exist to serve as major climatic barriers
    • long coastline means much of continent is subject to oceanic influences, but the oceans adjacent are not distinctly cold or warm, nor as persistent as those off other continents
      • there is no definite cool current along the west coast & in winter the water there is warm rather than cold
      • the East Australian Current is erratic and discontinuous
  • lies in the path of mobile anticyclones which move eastwards at a mean latitude varying with season:
    • cross east coast at 37degS in Feb and at 29degS in Aug/Sept, and as places to north of an anticyclone receives easterly winds whilst those to the south receive westerly winds, the change results in:
      • Sydney & Adelaide at 34degS, are influenced mainly by easterlies in summer & westerlies in winter & spring
      • Brisbane at 27-28degS is only occasionally affected by westerlies
      • Melbourne at 37degS & Hobart at 43degS are only occasionally affected by easterlies
      • winds are strongest when the anticyclones are most remote => windiest in Darwin in Feb & Hobart in October
    •  winds are also influenced by:
      • blocking highs over the Tasman Sea (~10 per year, mainly late winter)
      • semi-permanent stationary heat low over inland Australia during summer
        • Australian deserts are formed from subsidence of air inland and remoteness from sea, but do not reach the west coast (except near Carnarvon) as in other continents as the Indian Ocean is not as cold & the oceanic region of high pressure is not as intense or permanent as they are off the west coasts of Africa and Sth America
  • Australian climates are notable for extremes of high temperature and drought, resulting from relatively cloudless skies, whilst the blocking highs in the Tasman Sea may cause prolonged heat waves especially in Adelaide, which often cause major bushfires:
    • major bushfires are most prevalent along the east coast but particularly east Gippsland up to Sydney
• comparison of the capital cities:
  • Melbourne:
    • Koeppen classification Cfb with homoclimes including Wellington (NZ), London, San Francisco
    • weather is dominated by the eastward moving anticyclones, mid-latitude cyclones and cold fronts which take 2 days on average to come from Perth
    • lying at latitude 37degS, winds are rarely easterly and tend to be hot northerlies in summer, cold northerlies in winter, and cool south-westerlies following cold fronts and cool southerly afternoon seabreezes in summer
    • mean monthly wind speeds are average to windy ranging from 3.2m/s in April (the most settled but smoggy month) to 4.0m/s in Jan
    • mean monthly maximum temperatures range from a cool 13.2degC in July to 25.8degC in Jan
    • mean monthly minimum temperatures range from a cold 5.7degC in July to 13.9degC in Jan
    • as the anticyclonic band becomes maximally southernmost in Feb, this partly offsets the effect of summer solstice on Dec22 & contributes to Melbourne's tendency to have summer from Jan-Mar rather than Dec-Feb.
    • comparison with Sydney, Melbourne is:
      • much less humid, particularly in summer (vapour pressure 13mb vs 19mb)
      • much drier (monthly rainfall is at least half), with half the number of rainy days in summer but more in winter
      • similar temperatures in summer, but cooler evenings
      • mildly cooler winters, with less sunshine hours (3.7 vs 6.1h/day)
      • slightly more windy on average with winds being N/S whereas in Sydney they are generally E/W with stronger gusts associated with greater storm activity in Sydney
  • Sydney:
    • Koeppen classification Cfa with homoclimes including Buenos Aires, Hong Kong
    • weather, in addition to dominant effects of the anti-cyclonal band, is effected by:
      • moist onshore unstable south-easterlies (esp. if the warm East Australian current extends south of Sydney in which case Sydney's temperatures also tend to increase) over summer which contribute to the high humidity and rainfall, with thunderstorm activity and bushfires a significant risk
      • easterly afternoon seabreezes from noon to 9pm
      • generally stable warm trade winds from north east
      • Foehn winds from south west
    • rainfall is fairly uniform throughout the year, although April is the wettest and September the driest (when winds are mainly westerlies due to the highs being situated to its north). It rains on 11-14 days each month; Showers from onshore breezes usually occur at dawn whilst major storm rainfall tends to be 3am-9am.
    • fogs occur during autumn especially.
  • Canberra:
    • Koeppen classification Cfb with homoclimes including Madrid, Mar del Plata (Argentina)
    • being 100km inland and 600m elevation, its climate differs significantly from the other capital cities:
      • annual and daily ranges of temperature are greater
      • fewer raindays but more fog days but these rarely persist past noon
  • Perth:
    • Koeppen classification Csa with homoclimes including Rome, southern Turkey
    • the windiest city, with the driest (rains only 3days/month), sunniest summer, but wettest winters (rains 18 days/month) of all the cities
  • Adelaide:
    • Koeppen classification Csa with homoclimes including Seville in Spain
    • the driest city most at risk of long, very hot heatwaves
  • Brisbane:
    • Koeppen classification Cfa with homoclimes including Asuncion in Paraguay & Durban in Sth Africa
    • hot, very humid & wet summers
    • dry, mild, sunny winters
  • Darwin:
    • Koeppen classification Aw with homoclimes including mid-Brazil, Zanzibar & Bangkok
    • hot, extremely humid and extremely wet summers
    • hot, sunny, humid but arid winters