• Arnup, S. J., and M. J. Reeder, 2007: The diurnal and seasonal variation of the northern Australian dryline. Mon. Wea. Rev., 135, 29953008.

    • Search Google Scholar
    • Export Citation
  • Arnup, S. J., and M. J. Reeder, 2009: The structure and evolution of the northern Australian dryline. Aust. Meteor. Oceanogr. J., 58, 215231.

    • Search Google Scholar
    • Export Citation
  • Carbone, R. E., J. D. Tuttle, D. A. Ahijevych, and S. B. Trier, 2002: Inferences of predictability associated with warm season precipitation episodes. J. Atmos. Sci., 59, 20332056.

    • Search Google Scholar
    • Export Citation
  • Drosdowsky, W., 1996: Variability of the Australian summer monsoon at Darwin: 1957–1992. J. Climate, 9, 8596.

  • Hall, N., and P. Peyrille, 2006: Dynamics of the West African monsoon. J. Phys. IV, 139, 85103.

  • Hell, R., and R. K. Smith, 1998: A monsoon depression over northwestern Australia part I: Case study. Aust. Meteor. Mag., 47, 2140.

  • Hendon, H. H., and B. Liebmann, 1990: A composite study of onset of the Australian summer monsoon. J. Atmos. Sci., 47, 22272240.

  • Hodges, K. I., and C. D. Thorncroft, 1997: Distribution and statistics of African mesoscale convective weather systems based on the ISCCP Meteosat imagery. Mon. Wea. Rev., 125, 28212837.

    • Search Google Scholar
    • Export Citation
  • Huffman, G. J., and Coauthors, 2007: The TRMM multi-satellite precipitation analysis: Quasi-global, multi-year, combined-sensor precipitation estimates at fine scale. J. Hydrometeor., 8, 2855.

    • Search Google Scholar
    • Export Citation
  • Hung, C.-W., and M. Yanai, 2004: Factors contributing to the onset of the Australian summer monsoon. Quart. J. Roy. Meteor. Soc., 130, 739758.

    • Search Google Scholar
    • Export Citation
  • Keenan, T. D., and R. E. Carbone, 2008: Propagation and diurnal evolution of warm season cloudiness in the Australian and maritime continent region. Mon. Wea. Rev., 136, 973994.

    • Search Google Scholar
    • Export Citation
  • Knapp, K. R., M. C. Kruk, D. H. Levinson, and E. J. Gibney, 2009: Archive compiles new resource for global tropical cyclone research. Eos, Trans. Amer. Geophys. Union, 90, doi:10.1029/2009EO060002.

    • Search Google Scholar
    • Export Citation
  • Knippertz, P., and J. E. Martin, 2005: Tropical plumes and extreme precipitation in subtropical and tropical West Africa. Quart. J. Roy. Meteor. Soc., 131, 23372365.

    • Search Google Scholar
    • Export Citation
  • Kousky, V. E., 1980: Diurnal rainfall variation in northeast Brazil. Mon. Wea. Rev., 108, 488498.

  • Kuhnel, I., 1990: Tropical–extratropical cloudbands in the Australian region. Int. J. Climatol., 10, 341364.

  • Lavery, B., A. Kariko, and N. Nicholls, 1992: A historical rainfall data set for Australia. Aust. Meteor. Mag., 40, 3339.

  • McBride, J. L., and T. D. Keenan, 1982: Climatology of tropical cyclone genesis in the Australian region. J. Climatol., 2, 1333.

  • Mohr, K. I., and E. J. Zipser, 1996: Mesoscale convective systems defined by their 85-GHz ice scattering signature: Size and intensity comparison over tropical oceans and continents. Mon. Wea. Rev., 124, 24172437.

    • Search Google Scholar
    • Export Citation
  • Pope, M., C. Jakob, and M. J. Reeder, 2008: Convective systems of the north Australian monsoon. J. Climate, 21, 50915112.

  • Racz, Z., and R. K. Smith, 1999: The dynamics of heat lows. Quart. J. Roy. Meteor. Soc., 125, 225252.

  • Reynolds, R. W., N. A. Rayner, T. M. Smith, D. C. Stokes, and W. Wang, 2002: An improved in situ and satellite SST analysis for climate. J. Climate, 15, 16091625.

    • Search Google Scholar
    • Export Citation
  • Risbey, J. S., M. J. Pook, P. C. McIntosh, M. C. Wheeler, and H. H. Hendon, 2009: On the remote drivers of rainfall variability in Australia. Mon. Wea. Rev., 137, 32333253.

    • Search Google Scholar
    • Export Citation
  • Rotstayn, L. D., and Coauthors, 2007: Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols? J. Geophys. Res., 112, D09202, doi:10.1029/2006JD007712.

    • Search Google Scholar
    • Export Citation
  • Shi, G., W. Cai, T. Cowan, J. Ribbe, L. Rotstayn, and M. Dix, 2008: Variability and trend of northwest Australia rainfall: Observations and coupled climate modeling. J. Climate, 21, 29382959.

    • Search Google Scholar
    • Export Citation
  • Smith, I. N., 2004: An assessment of recent trends in Australian rainfall. Aust. Meteor. Mag., 53, 163173.

  • Spengler, T., M. J. Reeder, and R. K. Smith, 2005: The dynamics of heat lows in simple background flows. Quart. J. Roy. Meteor. Soc., 131, 31473165.

    • Search Google Scholar
    • Export Citation
  • Suppiah, R., 1992: The Australian summer monsoon: A review. Prog. Phys. Geogr., 16, 283318.

  • Tarpley, J. D., S. R. Schneider, and R. L. Money, 1984: Global vegetation indices from the NOAA-7 meteorological satellite. J. Climate Appl. Meteor., 23, 491494.

    • Search Google Scholar
    • Export Citation
  • Taschetto, A. S., and M. H. England, 2008: An analysis of late 20th Century trends in Australian rainfall. Int. J. Climatol., 29, 791807, doi:10.1002/joc.1736.

    • Search Google Scholar
    • Export Citation
  • Taylor, C. M., and T. Lebel, 1998: Observational evidence of persistent convective-scale rainfall patterns. Mon. Wea. Rev., 126, 15971607.

    • Search Google Scholar
    • Export Citation
  • Wardle, R., and I. Smith, 2004: Modeled response of the Australian monsoon to changes in land surface temperatures. Geophys. Res. Lett., 31, L16205, doi:10.1029/2004GL020157.

    • Search Google Scholar
    • Export Citation
  • Wheeler, M., and G. N. Kiladis, 1999: Convectively coupled equatorial waves: Analysis of clouds and temperature in the wavenumber–frequency domain. J. Atmos. Sci., 56, 374399.

    • Search Google Scholar
    • Export Citation
  • Wheeler, M., and J. L. McBride, 2005: Australian–Indonesian monsoon. Intraseasonal Variability in the Atmosphere–Ocean Climate System, W. K. M. Lau and D. E. Waliser, Eds., Praxis, 125–173.

    • Search Google Scholar
    • Export Citation
  • Wright, W. J., 1997: Tropical–extratropical cloudbands and Australian rainfall: I. Climatology. Int. J. Climatol., 17, 807829.

  • Yang, G. Y., and J. Slingo, 2001: The diurnal cycle in the Tropics. Mon. Wea. Rev., 129, 784801.

  • Zhao, S., and G. A. Mills, 1991: A study of a monsoon depression bringing record rainfall over Australia. Part II: Synoptic diagnostic description. Mon. Wea. Rev., 119, 20742094.

    • Search Google Scholar
    • Export Citation
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Physical Mechanisms Regulating Summertime Rainfall over Northwestern Australia

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  • 1 Monash Weather and Climate, Monash University, Clayton, Victoria, Australia
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Abstract

Summertime (December–February) rainfall over northwestern Australia has increased significantly since the middle of the twentieth century. As a prerequisite to understanding the observed trend, this investigation examines the broad characteristics of rainfall and identifies the physical mechanisms by which rainfall in the region is initiated. This is achieved using a combination of in situ, spaceborne, and numerical reanalysis datasets.

Hourly pluviograph data and the Tropical Rainfall Measuring Mission (TRMM)-3B42 dataset show distinctly different diurnal cycles of rainfall in different geographical subregions; near the coast, rainfall rates peak in the midafternoon, whereas inland (near the maximum rainfall trend) the rainfall rate is largest overnight. These data also indicate that most of the summertime rain falls in events lasting 2–5 days. Analysis of the ECMWF Re-Analysis (ERA-Interim) demonstrates that convergence into the continental heat low controls the diurnal cycle of rainfall but cannot explain the synoptic variability.

Composites of wet and dry conditions from ERA-Interim expose synoptic-scale differences in the environmental flow. Prior to rain falling in the interior of northwestern Australia, there is a distinct shift in the origins of low-level air parcels, such that air with high convective available potential energy is advected from the tropical maritime regions, rather than from over the continent. Preliminary analysis suggests that these flow changes may be linked to transient synoptic disturbances such as midlatitude cyclones and monsoon lows. Rather than reflecting a large-scale change in the ocean state, these results imply that the observed increase in rainfall may be linked more closely to changes in the synoptic weather systems.

Corresponding author address: G. Berry, Monash University, Weather and Climate, Building 28, Clayton, VIC 3800, Australia. E-mail: gareth.berry@monash.edu

Abstract

Summertime (December–February) rainfall over northwestern Australia has increased significantly since the middle of the twentieth century. As a prerequisite to understanding the observed trend, this investigation examines the broad characteristics of rainfall and identifies the physical mechanisms by which rainfall in the region is initiated. This is achieved using a combination of in situ, spaceborne, and numerical reanalysis datasets.

Hourly pluviograph data and the Tropical Rainfall Measuring Mission (TRMM)-3B42 dataset show distinctly different diurnal cycles of rainfall in different geographical subregions; near the coast, rainfall rates peak in the midafternoon, whereas inland (near the maximum rainfall trend) the rainfall rate is largest overnight. These data also indicate that most of the summertime rain falls in events lasting 2–5 days. Analysis of the ECMWF Re-Analysis (ERA-Interim) demonstrates that convergence into the continental heat low controls the diurnal cycle of rainfall but cannot explain the synoptic variability.

Composites of wet and dry conditions from ERA-Interim expose synoptic-scale differences in the environmental flow. Prior to rain falling in the interior of northwestern Australia, there is a distinct shift in the origins of low-level air parcels, such that air with high convective available potential energy is advected from the tropical maritime regions, rather than from over the continent. Preliminary analysis suggests that these flow changes may be linked to transient synoptic disturbances such as midlatitude cyclones and monsoon lows. Rather than reflecting a large-scale change in the ocean state, these results imply that the observed increase in rainfall may be linked more closely to changes in the synoptic weather systems.

Corresponding author address: G. Berry, Monash University, Weather and Climate, Building 28, Clayton, VIC 3800, Australia. E-mail: gareth.berry@monash.edu
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