Rainfall In Australia Research Articles

Southern Hemisphere Synoptic Behavior in Extreme Phases of SAM, ENSO, Sea Ice Extent, and Southern Australia Rainfall

Abstract The association between Southern Hemisphere cyclones and anticyclones and the El Niño–Southern Oscillation (ENSO), southern annular mode (SAM), Antarctic sea ice extent (SIE), and rainfall in Perth and Melbourne is explored. Those cities are, respectively, located in the southwestern and southeastern corners of Australia, where substantial decreasing rainfall trends have been observed over the last decades. The need for a more unified understanding of large-scale anomalies in storm indicators associated with the climate features itemized above has motivated this study. The main aim is to identify cyclone-anomalous areas that are potentially important in characterizing continental rainfall anomalies from a hemispheric perspective, focusing on midlatitude Australia. The study covers the “satellite era” from 1979 to 2003 and was conducted for the southern winter when midlatitude rainfall is predominantly baroclinic. The results indicate a well-organized hemispheric cyclone pattern associated with ENSO, SAM, SIE, and rainfall anomalies. There is a moderate large-scale, high-latitude resemblance between La Niña, negative SAM, and reduced SIE in some sectors. In particular, there is a suggestion that SIE anomalies over the Indian Ocean and Western Australia sectors are associated with a large-scale pattern of cyclone/anticyclone anomalies that is more pronounced over the longitudes of Australia and New Zealand. Spatial correlation analysis suggests a robust link between cyclone density over the sectors mentioned above and rainfall in Perth and Melbourne. Statistical analyses of rainfall and SIE show modest correlations for Perth and weak correlations for Melbourne, generally corroborating the above. It is proposed that SAM and SIE are part of a complex physical system that is best understood as a coupled mechanism, and that their impacts on the circulation can be seen as partially independent of ENSO. While SAM and SIE have greater influence on the circulation affecting rainfall in the western side of Australia, ENSO is the dominant influence on the eastern half of the country. A contraction of the sea ice seems to be accompanied by a southward shift of high-latitude cyclones, which is also hypothesized to increase downstream cyclone density at midlatitudes via conservation of mass, similarly to what is observed during the extreme positive phase of the SAM. These associations build on previous developments in the literature. They bring a more unified view on high-latitude climate features, and may also help to explain the declining trends in Australian rainfall.

A comparative modeling analysis of multiscale temporal variability of rainfall in Australia

The effects of long‐term natural climate variability and human‐induced climate change on rainfall variability have become the focus of much concern and recent research efforts. In this paper, we present the results of a comparative analysis of observed multiscale temporal variability of rainfall in the Perth, Newcastle, and Darwin regions of Australia. This empirical and stochastic modeling analysis explores multiscale rainfall variability, i.e., ranging from short to long term, including within‐storm patterns, and intra‐annual, interannual, and interdecadal variabilities, using data taken from each of these regions. The analyses investigated how storm durations, interstorm periods, and average storm rainfall intensities differ for different climate states and demonstrated significant differences in this regard between the three selected regions. In Perth, the average storm intensity is stronger during La Niña years than during El Niño years, whereas in Newcastle and Darwin storm duration is longer during La Niña years. Increase of either storm duration or average storm intensity is the cause of higher average annual rainfall during La Niña years as compared to El Niño years. On the other hand, within‐storm variability does not differ significantly between different ENSO states in all three locations. In the case of long‐term rainfall variability, the statistical analyses indicated that in Newcastle the long‐term rainfall pattern reflects the variability of the Interdecadal Pacific Oscillation (IPO) index, whereas in Perth and Darwin the long‐term variability exhibits a step change in average annual rainfall (up in Darwin and down in Perth) which occurred around 1970. The step changes in Perth and Darwin and the switch in IPO states in Newcastle manifested differently in the three study regions in terms of changes in the annual number of rainy days or the average daily rainfall intensity or both. On the basis of these empirical data analyses, a stochastic rainfall time series model was developed that incorporates the entire range of multiscale variabilities observed in each region, including within‐storm, intra‐annual, interannual, and interdecadal variability. Such ability to characterize, model, and synthetically generate realistic time series of rainfall intensities is essential for addressing many hydrological problems, including estimation of flood and drought frequencies, pesticide risk assessment, and landslide frequencies.

An assessment of relationships between the Australian subtropical ridge, rainfall variability, and high‐latitude circulation patterns

AbstractThe monthly anomaly of the latitude of the subtropical ridge over eastern Australia (L) is a major regulator of synoptic‐scale influences on Australia's climate. Three datasets have been used to calculate L: observed Australia coastal mean sea level pressure (MSLP), Hadley and NCEP Reanalysis datasets. The choice of datasets used in this study appears to strongly influence results. Changes in the Southern Hemisphere Hadley cell and meridional circulation changes are associated with changes in L and it is shown that (1) L has statistically and physically significant relationships with seasonal rainfall in Australia; (2) the Antarctic Oscillation Index (AOI) has statistically significant relationships with Australian seasonal rainfall; and (3) L and Southern Annular Mode (SAM) are significantly related. Longer‐term latitudinal shifts in L are also discussed. Copyright © 2008 Royal Meteorological Society

Variability and Trend of North West Australia Rainfall: Observations and Coupled Climate Modeling

Abstract Since 1950, there has been an increase in rainfall over North West Australia (NWA), occurring mainly during the Southern Hemisphere (SH) summer season. A recent study using twentieth-century multimember ensemble simulations in a global climate model forced with and without increasing anthropogenic aerosols suggests that the rainfall increase is attributable to increasing Northern Hemisphere aerosols. The present study investigates the dynamics of the observed trend toward increased rainfall and compares the observed trend with that generated in the model forced with increasing aerosols. It is found that the observed positive trend in rainfall is projected onto two modes of variability. The first mode is associated with an anomalously low mean sea level pressure (MSLP) off NWA instigated by the enhanced sea surface temperature (SST) gradients toward the coast. The associated cyclonic flows bring high-moisture air to northern Australia, leading to an increase in rainfall. The second mode is associated with an anomalously high MSLP over much of the Australian continent; the anticyclonic circulation pattern, over northern Australia, determines that when rainfall is anomalously high, west of 130°E, rainfall is anomalously low east of this longitude. The sum of the upward trends in these two modes compares well to the observed increasing trend pattern. The modeled rainfall trend, however, is generated by a different process. The model suffers from an equatorial cold-tongue bias: the tongue of anomalies associated with El Niño–Southern Oscillation extends too far west into the eastern Indian Ocean. Consequently, there is an unrealistic relationship in the SH summer between Australian rainfall and eastern Indian Ocean SST: the rise in SST is associated with increasing rainfall over NWA. In the presence of increasing aerosols, a significant SST increase occurs in the eastern tropical Indian Ocean. As a result, the modeled rainfall increase in the presence of aerosol forcing is accounted for by these unrealistic relationships. It is not clear whether, in a model without such defects, the observed trend can be generated by increasing aerosols. Thus, the impact of aerosols on Australian rainfall remains an open question.

Interannual variability in rainfall and its impact on nutrient load and phytoplankton in Myponga Reservoir, South Australia

Rainfall in Australia is highly variable and this lends complexity to nutrient loading models. Nutrient loads are important to reservoir management from the perspective of eutrophication and associated algal problems. We describe a flow‐weighted monitoring program, nitrogen and phosphorus nutrient budgets and a hydrology based iterative phosphorus loading model. This model can predict reservoir total phosphorus load in an inter‐annually variable system, Myponga Reservoir, South Australia. Rainfall variability is partially attributed to the El Niño Southern Oscillation (ENSO), and the implications for long‐term forecasting of algal biomass for reservoir management are discussed.

Forecasting regional crop production using SOI phases: an example for the Australian peanut industry

Using peanuts as an example, a generic methodology is presented to forward-estimate regional crop production and associated climatic risks based on phases of the Southern Oscillation Index (SOI). Yield fluctuations caused by a highly variable rainfall environment are of concern to peanut processing and marketing o/Southern bodies the industtry could profitable to adjust their operations stategically. Significantly , physically based lag-relationships exist between an index of ocean/atmospher EI Niño/southern Oscillation phenomenon and future rainfall in Australia and elsewhere. Combining knowledge of SOI phases in November and December with output from a dynamic simulation model allows the derivation of yield probability distributions based on historic rainfall data. This information is available shortly after planting a crop and at least 3-5 months prior to harvest. The study shows that in years when the November-December SOI phase is positive there is an 80% chance of exceeding average district yields. Conversely, in years when the November-December SOI phase is either negative or rapidly falling there is only a 5% chance of exceeding average district yields, but a 95% chance of below average yields. This information allows the industry to adjust strategically for the expected volume of production. The study shows that simulation models can enhance SOI signals contained in rainfall distributions by discriminating between useful and damaging rainfall events. The methodology can be applied to other industries and regions.

Distribution and diversity patterns of soil mites and other microarthropods in a Chihuahuan desert site

This paper reports the results of a pilot survey of the patterns of distribution and species diversity of soil microarthropods from 12 different sites in a Chihuahuan Desert watershed in southern New Mexico. A total of 18 orders of arthropods was recorded from 49 samples, distributed across this watershed. Mites and Collembola predominated throughout. Mites were more abundant than Collembola in all sites except in Prosopis litter from the edge of a playa. At this site, collembolan density was estimated to be 24,460/m 2 . Four orders of mites occurred in the sites surveyed: Prostigmata, Cryptostigmata, Mesostigmata and Astigmata. The last-named group was so infrequent that it was not considered further. The Mesostigmata were numerous only in Atriplex litter. Prostigmata and Cryptostigmata were equally abundant at only two sites: the litter under Prosopis on the bajada site and the mineral soil under Fallugia. Elsewhere, Cryptostigmata tended to be more numerous than Prostigmata where the organic content of the substratum was high (> 30%) and vice versa. The highest total mite density occurred in the Juniperus litter (29, 486/m 2 ), the lowest in Larrea litter (8274/m 2 ). These estimates are considerably higher than those recorded from a Juniperus site in the more arid Mojave Desert, but they are much lower than densities considered typical of cool, moist temperate deciduous forests. The densities of Prostigmata and Mesostigmata compare favourably with those reported from sites with similar rainfall in Australia. Cryptostigmatid densities are much higher in the Chihuahuan sites, however. An Index of Diversity, calculated for the various groups of microarthropods at the 12 sites, was very variable, but values approximating to those reported for the microarthropod fauna of an English beech woodland were obtained for several sites. The equitability component of this species diversity provided a good indicator of the relative stability of the sites studied.

The Pattern of Mineral Return in Leaf Litter of Three Subtropical Australian Forests

SUMMARY Monthly samples of leaf litter from three contrasted forests have been analysed for nitrogen, phosphorus, potassium, calcium and aluminium. The mineral composition of the litter is remarkably constant throughout the year, despite the markedly seasonal litter-fall. In an unusually dry year the litter-fall was greater and the mineral content somewhat higher, though the discrepancy was only serious in the case of phosphorus. The mineral return of a complex forest on basalt was almost identical with that of a forest of similar structure in Ghana, suggesting that convergence of structure and life forms is related to edaphic factors as well as to climate. Leaf-fall in a subtropical vine forest was suppressed during an abnormally dry season, possibly expressing an adaptation towards evergreenness similar to that of sclerophyll types which characterize areas of erratic rainfall in Australia.

Seasonal distribution of rainfall in Australia analysed by Fourier methods

A harmonic or Fourier analysis of mean monthly rainfall data is found useful in objectively describing and mapping the seasonality of rainfall within Australia. Over large areas the seasonal component is well described by the first and second harmonic terms, leaving as a residual variance only a small proportion of the observed total variance. Care must be taken in the interpretation of second harmonic contributions within those areas of tropical Australia under strong monsoonal influences. This is because pecularities in the form of the annual rainfall regime make the first harmonic term inadequate in itself to fully describe the annual trend. The technique is found particularly useful in defining the boundaries of areas of similar seasonality, and maps based upon the first and second harmonic amplitudes are shown to bear a close relationship with known physical controls.

Artificial Rainfall in Australia

Artificial Rainfall in Australia

Australian Rainfall 1

IN the continent of Australia rainfall is by far the most important meteorological element to the agriculturist, there being large tracts of country where the annual precipitation is barely sufficient to allow of profitable use of the soil for farming or raising stock. For this reason Dr. Griffith Taylor, who is becoming well known for his work on Australian meteorology, has recently produced a volume devoted entirely to the rain fall of the continent and its control over vegetation. The subject is dealt with in a very thorough manner, and it would be hard to over estimate the value of such a work in the case of a young agricultural country looking to great developments in the near future. To obtain a just appreciation of the meteorological conditions which govern the weather of the continent it is necessary to remember that the southern tropical high-pressure belt crosses the^ southern part of the country, while the equatorial low-pressure area lies off the northern coast. These systems fluctuate north and south with the sun, causing a very marked annual period in the rainfall. Thus the northern^, districts receive most of their rainfall in the southern summer, when cyclones, from the northern low-pressure area strike the coast. On the other hand, the southern districts at this time of year lie under anticyclonic conditions and receive little rain, . but in the winter, when the high-pressure belt has moved northward, the westerly winds of the southern oceans reach this region and the rainy season occurs. This movement to the north and south of the pressure systems and associated phenomena is well illus trated by an ingenious “Solar Control Model” which forms the frontispiece of the present volume.

Rainfall in Australia

Rainfall in Australia