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This work identifies and documents a suite of large-scale drivers of rainfall variability in the Australian region. The key driver in terms of broad influence and impact on rainfall is the El Niño–Southern Oscillation (ENSO). ENSO is related to rainfall over much of the continent at different times, particularly in the north and east, with the regions of influence shifting with the seasons. The Indian Ocean dipole (IOD) is particularly important in the June–October period, which spans much of the wet season in the southwest and southeast where IOD has an influence. ENSO interacts with the IOD in this period such that their separate regions of influence cover the entire continent. Atmospheric blocking also becomes most important during this period and has an influence on rainfall across the southern half of the continent. The Madden–Julian oscillation can influence rainfall in different parts of the continent in different seasons, but its impact is strongest on the monsoonal rains in the north. The influence of the southern annular mode is mostly confined to the southwest and southeast of the continent. The patterns of rainfall relationship to each of the drivers exhibit substantial decadal variability, though the characteristic regions described above do not change markedly. The relationships between large-scale drivers and rainfall are robust to the selection of typical indices used to represent the drivers. In most regions the individual drivers account for less than 20% of monthly rainfall variability, though the drivers relate to a predictable component of this variability. The amount of rainfall variance explained by individual drivers is highest in eastern Australia and in spring, where it approaches 50% in association with ENSO and blocking.

A database containing sub-seasonal to seasonal forecasts from 11 operational 30 centres is available to the research community and will help advance our understanding of 31 the sub-seasonal to seasonal time range.Abstract 51 52Demands are growing rapidly in the operational prediction and applications communities for 53 forecasts that fill the gap between medium-range weather and long-range or seasonal 54

Daily variations in Australian rainfall and surface temperature associated with the Southern Hemisphere annular mode (SAM) are documented using observations for the period 1979-2005. The high index polarity of the SAM is characterized by a poleward contraction of the midlatitude westerlies. During winter, the high index polarity of the SAM is associated with decreased daily rainfall over southeast and southwest Australia, but during summer it is associated with increased daily rainfall on the southern east coast of Australia and decreased rainfall in western Tasmania. Variations in the SAM explain up to ϳ15% of the weekly rainfall variance in these regions, which is comparable to the variance accounted for by the El Niño-Southern Oscillation, especially during winter. The most widespread temperature anomalies associated with the SAM occur during the spring and summer seasons, when the high index polarity of the SAM is associated with anomalously low maximum temperature over most of central/eastern subtropical Australia. The regions of decreased maximum temperature are also associated with increased rainfall. Implications for recent trends in Australian rainfall and temperature are discussed.

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We document a relationship between tropical cyclones of the Indian and western Pacific oceans and the Madden-Julian oscillation (MJO). Cyclones preferentially occur during the convective phase of the oscillation, and cluster around the low-level cyclonic vorticity and divergence anomalies that appear poleward and westward of the large-scale connective anomaly along the equator.Although the absolute numbers of storms and typhoons are enhanced during the convective phase of the oscillation, the ratios of storms and typhoons formed per depression are the same in the convective phase as the dry phase of the oscillation. There exist more storms and typhoons simply by there being more depressions in the convective phase. The third result of this study is that the increase in cyclone activity during active periods of convection is not restricted to MJO activity. In fact, we find that an equal increase occurs during the convective phase of an arbitrarily chosen, completely independent band from the MJO. We conclude that the MJO does not influence tropical cyclones in a unique fashion, but it is important because of the relatively large proportion of tropical variance that is explained by it.

Interannual variation of seasonal-mean tropical convection over the Indo-Pacific region is primarily controlled by El Niño–Southern Oscillation (ENSO). For example, during El Niño winters, seasonal-mean convection around the Maritime Continent becomes weaker than normal, while that over the central to eastern Pacific is strengthened. Similarly, subseasonal convective activity, which is associated with the Madden–Julian oscillation (MJO), is influenced by ENSO. The MJO activity tends to extend farther eastward to the date line during El Niño winters and contract toward the western Pacific during La Niña winters. However, the overall level of MJO activity across the Maritime Continent does not change much in response to the ENSO. It is shown that the boreal winter MJO amplitude is closely linked with the stratospheric quasi-biennial oscillation (QBO) rather than with ENSO. The MJO activity around the Maritime Continent becomes stronger and more organized during the easterly QBO winters. The QBO-related MJO change explains up to 40% of interannual variation of the boreal winter MJO amplitude. This result suggests that variability of the MJO and the related tropical–extratropical teleconnections can be better understood and predicted by taking not only the tropospheric circulation but also the stratospheric mean state into account. The seasonality of the QBO–MJO link and the possible mechanism are also discussed.

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