Duncan Ackerley

Monash University (Australia) · Monash Weather and Climate

General circulation models (GCMs) are valuable tools for understanding how the global ocean–atmosphere– land surface system interacts and are routinely evaluated relative to observational data sets. Conversely, observational data sets can also be used to constrain GCMs in order to identify systematic errors in their simulated climates. One such exa...

A full understanding of the causes of the severe drought seen in the Sahel in the latter part of the twentieth-century remains elusive some 25 yr after the height of the event. Previous studies have suggested that this drying trend may be explained by either decadal modes of natural variability or by human-driven emissions (primarily aerosols), but...

Tropical precipitation is caused by many processes that occur over a wide-range of temporal and spatial scales. Such processes vary from local, diurnal convection driven by a destabilisation of the boundary layer to planetary-scale systems that result in rainfall over many days. It is therefore important to assess whether general circulation models...

Palaeoclimate-proxy data provide an invaluable source of evidence for past climatic conditions, which can be compared with data from climate model simulations. This study illustrates how high-resolution regional climate model simulations can be used to estimate the difference in the climate of New Zealand between 6000 years before present (yr BP) a...

Diagnosing the climate of New Zealand from low-resolution General Circulation Models (GCMs) is notoriously difficult due to the interaction of the complex topography and the Southern Hemisphere (SH) mid-latitude westerly winds. Therefore, methods of downscaling synoptic scale model data for New Zealand are useful to help understand past climate. Ne...

The simulation of northern Australian wet season rainfall bursts by coupled climate models is evaluated. Individual models produce vastly different amounts of precipitation over the north of Australia during the wet season, and this is found to be related to the number of bursts they produce. The seasonal cycle of bursts is found to be poor in most...

General circulation models (GCMs) are routinely run under Atmospheric Modelling Intercomparison Project (AMIP) conditions with prescribed sea surface temperatures (SSTs) and sea ice concentrations (SICs) from observations. These AMIP simulations are often used to evaluate the role of the land and/or atmosphere in causing the development of systemat...

The diurnal cycle of precipitation in the tropics is represented poorly in general circulation models (GCMs), which is primarily attributed to the representation of moist convection. Nonetheless, in areas where precipitation is driven by the diurnal cycle in the synoptic-scale flow, GCMs may represent that circulation-rainfall relationship well. Ov...

This study uses the simplified patterns of temperature and effective precipitation approach from the Australian component of the international palaeoclimate synthesis effort (INTegration of Ice core, MArine and TErrestrial records – OZ-INTIMATE) to compare atmosphere–ocean general circulation model (AOGCM) simulations and proxy reconstructions. The...

The initiation of Northern Australian monsoon rainfall bursts is accompanied by an increase in cyclonic circulation in the monsoon region. In this study we show that the change in circulation at the start of the composite rainfall burst is predominantly influenced by mid-latitude front-like features. By exploiting the relationship between circulati...

Paleoclimate proxy reconstruction initiatives, such as the Australian component of the international paleoclimate synthesis effort: INTegration of Ice core, MArine and Terrestrial records (OZ-INTIMATE), are important as they provide evidence of past climatic conditions that are necessary to evaluate global General Circulation Models (GCMs). One of...

General circulation models (GCMs) are valuable tools for understanding how the global ocean-atmosphere-land surface system interacts and are routinely evaluated relative to observational datasets. Conversely, observational datasets can also be used to constrain GCMs in order to identify systematic errors in their simulated climates. One such exampl...

The high insolation during the Southern Hemisphere summer leads to the development of a heat low over north-west Australia, which is a significant feature of the monsoon circulation. It is therefore important that General Circulation Models (GCMs) are able to represent this feature well in order to adequately represent the Australian Monsoon. Given...

There are some long-established biases in atmospheric models that originate from the representation of tropical convection. Previously, it has been difficult to separate cause and effect because errors are often the result of a number of interacting biases. Recently, researchers have gained the ability to run multiyear global climate model simulati...

As general circulation models (GCMs) are routinely used to make projections of future rainfall (for example, the simulations available as part of the 5th Coupled Model Intercomparison Project, CMIP5), it is important to assess whether the processes that cause precipitation are represented well. If those processes are poorly represented then it is i...

The Australasian INTIMATE (INTegration of Ice-core, Marine and Terrestrial records) initiative (INQUA project #0809) was undertaken to develop a consistent chronological assessment of the climate of the past 30000 years over Australia, New Zealand and the Maritime Continent. Work has continued as part of SHAPE initiative (INQUA project #1302), but...

The representation of rainfall and in particular its diurnal cycle, is generally poor in general circulation models (GCMs). Nonetheless, studies make use of GCMs in future climate projections in regions where precipitation has a strong diurnal cycle. In this study we evaluate whether one GCM (ACCESS1.3) can represent the rainfall in such a region (...

Proxy data that are used to infer past climatic conditions on land are often representative of a much smaller area than that of global general circulation models (GCMs). One way to close this gap is to undertake statistical or dynamical downscaling of the coarse-resolution GCM data to a resolution comparable with the proxies. In this study, both st...

In parts of Australia there are places where the circulation and rainfall respond directly to solar heating during the day and others where a broad-scale rearrangement of the flow at night leads to convergence and rainfall (such as the north-west Australian heat low). General Circulation Models (GCMs) struggle to capture the timing and strength of...

The past 1500 years provide a valuable opportunity to study the response of the climate system to external forcings. However, the integration of paleoclimate proxies with climate modeling is critical to improving the understanding of climate dynamics. In this paper, a climate system model and proxy records are therefore used to study the role of na...

Quantifying future increases in sea level around New Zealand arising from climate change is a key factor for determining decisions on adaptation, yet most projections are expressed in terms of a global-mean rise in sea level. The work presented here makes use of the data from the Atmosphere-Ocean General Circulation Models (AOGCM) used in the 4th I...

Rainfall in north-west Australia has been shown to be increasing since the 1950s. Despite this well-known rainfall trend, there is little consensus on its actual cause with numerous competing hypotheses. GCMs have been the preferred tool in testing these hypotheses; however, the lack of consensus is likely to be driven by different GCMs representin...

Australian summertime rainfall has been shown to be increasing in the north-west of the continent. Despite this well-documented increase in rainfall, there are still several competing hypotheses as to the cause of the increase with no overall consensus. Modeling work has been undertaken to explore the current (and potential future) trend in rainfal...

Climates of the past, such as the Last Glacial Maximum (LGM), give a useful insight into the response of atmosphere and ocean processes to various forcings that were different to the present day. The use of General Circulation Models aids in understanding past climates in combination with the available proxy data. In this study, a selection of mode...

The climate of New Zealand is highly variable, both spatially and temporally, due to a mixture of complex topography and location in the Southern Hemisphere, mid-latitude westerlies. The representation of New Zealand climate in General Circulation Models (GCMs) is too coarse to provide meaningful regional climate statistics. Therefore empirical-sta...

Aeolian dust modelling has improved significantly over the last ten years and many institutions now consistently model dust uplift, transport and deposition in general circulation models (GCMs). However, the representation of dust in GCMs is highly variable between modelling communities due to differences in the uplift schemes employed and the repr...

Various studies have shown that December – February rainfall has increased significantly over the last sixty years in Northwestern Australia (NWA). However, there is little consensus on the underlying causes of this rainfall trend and General Circulation Models (GCMs) struggle to capture the processes that lead to rainfall generation in NWA, making...

Incomplete understanding of three aspects of the climate system-equilibrium climate sensitivity, rate of ocean heat uptake and historical aerosol forcing-and the physical processes underlying them lead to uncertainties in our assessment of the global-mean temperature evolution in the twenty-first century 1,2. Explorations of these uncertainties hav...

Various studies have shown that December – February rainfall has increased significantly over the last sixty years in Northwestern Australia (NWA). However, there is little consensus on the underlying causes of this rainfall trend and General Circulation Models (GCMs) struggle to capture the processes that lead to rainfall generation in NWA, making...

Diagnosing the climate of New Zealand from low-resolution General Circulation Models (GCMs) is notoriously difficult due to the interaction of the complex topography and the Southern Hemisphere (SH) mid-latitude westerly winds. Therefore, methods of downscaling synoptic scale model data for New Zealand are useful to help understand past climate. Ne...

This study provides improved estimates of fire danger for New Zealand under future climate. Fire danger ratings for two projection periods (the 2050s, 2040-2059; and 2080s, 2070-2089) were estimated using monthly changes in weather inputs (temperature, humidity, wind speed and rainfall). These ratings were obtained from downscaling IPCC 4th Assessm...

The Paleoclimate Modelling Intercomparison Project (PMIP) was undertaken to assess the climatic effects of the presence of large ice-sheets and changes in the Earth's orbital parameters in fully coupled Atmosphere-Ocean General Circulation Models (AOGCMs). Much of the previous literature has focussed on the tropics and the Northern Hemisphere durin...

Aeolian mineral dust aerosol is an important consideration in the Earth's radiation budget as well as a source of nutrients to oceanic and land biota. The modelling of aeolian mineral dust has been improving consistently despite the relatively sparse observations to constrain them. This study documents the development of a new dust emissions scheme...

A large ensemble of general circulation model (GCM) integrations coupled to a fully interactive sulfur cycle scheme were run on the climateprediction.net platform to investigate the uncertainty in the climate response to sulfate aerosol and carbon dioxide (CO2) forcing. The sulfate burden within the model (and the atmosphere) depends on the balance...

Aerosols from anthropogenic and natural sources have been recognized as having an important impact on the climate system. However, the small size of aerosol particles (ranging from 0.01 to more than 10 μm in diameter) and their influence on solar and terrestrial radiation makes them difficult to represent within the coarse resolution of general cir...