A teleconnection between the Southern Hemisphere mid-latitude and equatorial ocean (Abstract)

The sub-surface ocean is a pathway for climate anomalies which propagate away from high and mid-latitude water mass formation region and into the Equatorial ocean. Thus there is the potential that the existence of this sub-surface ocean pathway may lead to decadal variability of Equatorial sea surface temperature. This in turn leads to some influence upon the El Nino Southern Oscillation. In my talk, I will present some results from recent ocean modelling studies that investigate mid-latitude water mass formation processes and their passage throughout the interior of the upper ocean

Queensland rainfall decline

Queensland rainfall has been declining over much of the state in recent decades and is more regionally extensive than the winter rainfall decline that has been well described from southwestern Western Australia (SWWA). The SWWA rainfall decline has been attributed to a number of factors, but the rainfall decline in Queensland has only been recently documented and no major attributes identified. Correlation analysis of rainfall with a number of factors including seas surface temperatures and sea level pressure is presented and some of the key elements discussed that have a major role in the rainfall decline observed from this region

A study into the export of saline water from Hervey Bay, Australia

Australia's climate is one of the world's driested and locally characterised by high year-to-year rainfall variability. Due to high evaporation and low river runoff many estuaries and embayments in the region are characterised by inverse conditions with salinity increasing toward the coast and river mouths. Such conditions were also found during the first comprehensive hydrographic survey of Hervey Bay located at the east coast of Australia in early spring 2004. The survey traced a subsurface salinity maximum that was found in earlier studies within the East Australia Current east of Hervey Bay to the shallow southwest regions of the bay. These are identified as the most likely source region for locally produced saline Hervey Bay Water. Utilising a simple box model, mean evaporation rates and historical river run-off data, it is demonstrated that inverse conditions are likely to dominate throughout the year. The negative circulation is a climatological feature of this estuary that is not limited to the dry season of the year. Due to persistent drought and declining rainfall in coastal eastern Australia, these conditions are likely to persist into the near future and need to be considered in coastal management strategies

A western boundary current eddy characterisation study

The analysis of an eddy census for the East Australian Current (EAC) region yielded a total of 497 individual short-lived (7-28 days) cyclonic and anticyclonic eddies for the period 1993 to 2015. This was an average of about 23 eddies per year. 41% of the tracked individual cyclonic and anticyclonic eddies were detected off southeast Queensland between about 25 oS and 29 oS. This is the region where the flow of the EAC intensifies forming a swift western boundary current that impinges near Fraser Island on the continental shelf. This zone was also identified as having a maximum in detected short-lived cyclonic eddies. A total of 94 (43%) individual cyclonic eddies or about 4-5 per year were tracked in this region. The census found that these potentially displaced entrained water by about 115 km with an average displacement speed of about 4 km per day. Cyclonic eddies were likely to contribute to establishing an on-shelf longshore northerly flow forming the western branch of the Fraser Island Gyre and possibly presented an important cross-shelf transport process in the life cycle of temperate fish species of the EAC domain. In-situ observations near western boundary currents previously documented the entrainment, off-shelf transport and export of near shore water, nutrients, sediments, fish larvae and the renewal of inner shelf water due to short-lived eddies. This study found that these cyclonic eddies potentially play an important off-shelf transport process off the central east Australian coast

Assessing water renewal time scales for marine environments from three-dimensional modelling: a case study for Hervey Bay, Australia

We apply the three-dimensional Coupled Hydrodynamical Ecological model for Regional Shelf Seas (COHERENS) to compute water renewal time scales for Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia. Water renewal time scales are not directly observable but are derived indirectly from computational studies. Improved knowledge of these time scales assists in evaluating the water quality of coastal environments and can be utilised in sustainable marine resource management. Results from simulations with climatological September forcing are presented and compared to cruise data reported by Ribbe (2006). A series of simulations using idealised forcing provides detailed insight into water renewal pathways and regional differences in renewal timescales. We find that more than 85 % of the coastal embayment’s water is fully renewed within about 50-80 days. The eastern and western shallow coastal regions are ventilated more rapidly than the central, deeper part of the domain. The climatological simulation yields temperature and salinity patterns that are consistent with the observed situation and water renewal times scales in the range of those derived from idealised model studies. While the reported simulations involve many simplifications, the global assessment of the renewal time scale is in the range of a previous estimate derived for this coastal embayment from a simpler model and observational data

Sensitivity of middle Miocene climate and regional monsoon to palaeo-altimetry

It is well-known that plate motions and the elevation of mountains belts have played a major role in palaeoclimate evolution. The present day monsoon in southeast Asia and northern Australia is associated with the Tibetan plateau. We investigate how the Miocene Climate Optimum (MCO) developed in response to altimetry changes in Eurasia and South America impacting changes in regional monsoon, wind stress and precipitation. We carried out a number of numerical experiments with alternative paleo-altimetries, using an updated NCAR coupled climate model, CCSM3, and CAM3.1 and CLM3 with slab ocean and ice models, validated with proxies. Our model results explore the sensitivities of regional climate change to plate motions and rising mountain belts as well as sea-level change. Especially, the model simulations ground-truth the monsoon evolution in the southeast Asia, northern Australia and South America

Variability and trend of the north west Australia rainfall: observations and coupled climate modeling

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 20th century multi-member 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. We find 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 towards 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 with northwesterly flows west of 130°E and generally opposite flows in northeastern Australia, determine that when rainfall is anomalously high, west of 130oE, 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 an 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

Is the East Australian Current causing a marine ecological hot-spot and an important fisheries near Fraser Island, Australia?

The distributions of chlorophyll-a (Chl-a) blooms near the Fraser Island continental shelf along the east coast of Australia were analysed for the period 2002–2012. The blooms were found to exhibit two distinct quasi climatological patterns. The first pattern was a broad near-coast mid-shelf distribution that prevailed from about March to July each year. The second pattern was established due to re-occurring outer-shelf Chl-a blooms southeast of Fraser Island from about August to February. The outer-shelf Chl-a bloom concentration maxima appeared to be higher than those associated with the near coast pattern. Both distributions were found to be characterised by significant year-to-year variability in the number of total blooms, the length of blooms and the Chl-a bloom concentration maxima. The physical cause of the outer-shelf Chl-a concentration maxima was of particular interest, since this location overlaps with a region previously identified as a key eastern Australian marine ecological site and important fisheries. In this analysis, we found that the area also overlaps with a hot-spot in EAC-generated bottom layer stress, which appears to be the main driver of the 'Southeast Fraser Island Upwelling System'

Seasonal climate forecasts for more effective raingrown grain-cotton production systems

Cropping is a risky business. Our highly variable climate makes it difficult to decide how best to manage crops and cropping systems. What works well one year might not work well the next. To develop better risk management practices, this project uses the APSIM cropping systems model to examine the profitability and sustainability of a range of alternative dryland cotton/grain cropping systems throughout the northern grain region of eastern Australia. It involves working closely with farmer collaborators in Central Queensland, the Darling Downs, the northwest slopes of NSW and the Liverpool Plains

20th century rainfall variability and the role of large scale climate events within Indo-Pacific region from IPCC AR4 models, reanalysis and observations

[Abstract]: The performance of Intergovernmental Panel on Climate Change Assessment Report No. 4 (IPCC AR4) models in simulating rainfall variability within Indo-Pacific region is being investigated. Data from 21 different climate models together with National Centre for Environmental Prediction reanalysis and other rainfall observations is being compared. The observational data sets were taken from gridded rainfall Indonesian observation data sets as well as a comprehensive set of high-resolution grids of monthly climate for the globe from the Climatic Research Unit (CRU) datasets. The focus of the study is firstly, a model comparison in simulating historical rainfall variability in the region, and secondly, an investigation of the models sensitivity in simulating large scale climate events such as the El Nino Southern Oscillation and the Indian Ocean Dipole and its relationship with the rainfall variability over the region. Particular attention also upon the simulation of multi-decadal rainfall variability in the Indo-Pacific region