The Australian Community Climate and Earth-System Simulator (ACCESS) is a coupled climate and earth system simulator being developed as a joint initiative of the Bureau of Meteorology and CSIRO in cooperation with the university community in Australia. The main aim of ACCESS is to develop a national approach to climate and weather prediction model development. Planning for ACCESS development commenced in 2005 and significant progress has been made subsequently. ACCESS-based numerical weather prediction (NWP) systems were implemented operationally by the Bureau in September 2009 and were marked by significantly increased forecast skill of close to one day for three-day forecasts over the previously operational systems. The fully-coupled ACCESS earth system model has been assembled and tested, and core runs have been completed and submitted for the Intergovernmental Panel for Climate Change (IPCC) Fifth Assessment Report. Significant progress has been made with ACCESS infrastructure including successful porting to both Solar and Vayu (National Computational Infrastructure (NCI)) machines and development of infrastructure to allow usage by university researchers. This paper provides a description of the NWP component of ACCESS and presents results from detailed verification of the system.

The Australian Government Bureau of Meteorology completed the installation of a network of 9 new wind profiling radars across mainland Australia in 2017, which complement an existing network of 5 profilers and 5 research systems. This results in a network of 14 operational, and 19 total, profilers across Australia and Davis Station in Antarctica. Four of the new profilers are higher power stratospheric tropospheric systems, designed to measure winds from near ground level to the tropopause, and maintain the upper air network in Australia where sonde launches are no longer available. Wind measurements in the near field of the radar are demonstrated to be both possible and accurate by comparison with co-located radiosondes. Quality control procedures producing winds of sufficient accuracy for presentation to forecasters and ingestion into global numerical weather prediction models are described. The Australian network data are available on the global telecommunications system and are currently being ingested into all major models. First results from impact studies on forecast error reduction in the Australian Community Climate and Earth Systems Simulator show remote stations have the greatest impact.

Atmospheric motion vectors (AMVs) have been generated continuously from Multifunctional Transport Satellite 1 Replacement (MTSAT-1R) radiance data (imagery) since 2005, and more recently from MTSAT-2, which are operated by the Japan Meteorological Agency (JMA). These are the primary geostationary meteorological satellites observing the western Pacific, Asia, and the Australian region. The vectors are used operationally, for analysis in the Darwin Regional Forecast Office. The near-continuous AMVs have been stringently error characterized and used in near-real-time trials to gauge their impact on operational regional numerical weather prediction (NWP), using four-dimensional variational data assimilation (4DVAR). The use of these locally generated hourly vectors (the only hourly AMV source in the region at the time) and 4DVAR has resulted in both improved temporal and spatial data coverage in the operational regional forecast domain. The beneficial impact of these data on the Bureau of Meteorology's (Bureau's) current operational system is described. After these trials, the hourly MTSAT AMVs were introduced into the Bureau's National Meteorological and Oceanographic Centre's (NMOC) operational NWP suite for use by the operational Australian Community Climate Earth System Simulator (ACCESS) regional and global models, ACCESS-R and ACCESS-G, respectively. Examples of their positive impact on both midlatitude and tropical cyclone forecasts are presented.

Abstract:The impact of the Australian Bureau of Meteorology's in situ observations (land and sea surface observations, upper air observations by radiosondes, pilot balloons, wind profilers, and aircraft observations) on the short-term forecast skill provided by the ACCESS (Australian Community Climate and Earth-System Simulator) global numerical weather prediction (NWP) system is evaluated using an adjoint-based method. This technique makes use of the adjoint perturbation forecast model utilized within the 4D-Var assimilation system, and is able to calculate the individual impact of each assimilated observation in a cycling NWP system. The results obtained show that synoptic observations account for about 60% of the 24-h forecast error reduction, with the remainder accounted for by aircraft (12.8%), radiosondes (10.5%), wind profilers (3.9%), pilot balloons (2.8%), buoys (1.7%) and ships (1.2%). In contrast, the largest impact per observation is from buoys and aircraft. Overall, all observation types have a positive impact on the 24-h forecast skill. Such results help to support the decision-making process regarding the evolution of the observing network, particularly at the national level. Consequently, this 4D-Var-based approach has great potential as a tool to assist the design and running of an efficient and effective observing network.

The use of high spatial and temporal resolution data assimilation and forecasting around Australia’s capital cities and rural land provided an opportunity to improve moisture analysis and forecasting. To support this endeavour, RMIT University and Geoscience Australia worked with the Bureau of Meteorology (BoM) to provide real-time GNSS (global navigation satellite system) zenith total delay (ZTD) data over the Australian region, from which a high-resolution total water vapour field for SE Australia could be determined. The ZTD data could play an important role in high-resolution data assimilation by providing mesoscale moisture data coverage from existing GNSS surface stations over significant areas of the Australian continent. The data were used by the BoM’s high-resolution ACCESS-C3 capital city numerical weather prediction (NWP) systems, the ACCESS-G3 Global system and had been used by the ACCESS-R2-Regional NWP model. A description of the data collection and analysis system is provided. An example of the application of these local GNSS data for a heavy rainfall event over SE Australia/Victoria is shown using the 1.5-km resolution ACCESS-C3 model, which was being prepared for operational use. The results from the test were assessed qualitatively, synoptically and also examined quantitatively using the Fractions Skills Score which showed the reasonableness of the forecasts and demonstrated the potential for improving rainfall forecasts over south-eastern Australia by the inclusion of ZTD data in constructing the moisture field. These data have been accepted for operational use in NWP.

The sensitivity of the main characteristics of baroclinically unstable waves with respect to fundamental parameters of the atmosphere (the static stability parameterσ0and vertical shear of a zonal windΛ) is theoretically explored. Two types of waves are considered: synoptic scale waves and planetary scale (ultralong) waves based on an Eady-type model and model with vertically averaged primitive equations. Sensitivity functions are obtained that estimate the impact of variations inσ0andΛon the growth rate and other characteristics of unstable waves and demonstrate that waves belonging to the short-wave part of the spectrum of unstable waves are more sensitive to changes in the static stability parameter than waves belonging to the long-wave part of the spectrum. The obtained theoretical results show that the increase of the static stability and decrease of the meridional temperature gradient in midlatitude baroclinic zones in some areas of the southern hemisphere lead to a slowing of the growth rate of baroclinic unstable waves and an increasing wavelength of baroclinic unstable wave maximum growth rate, that is, a spectrum shift of unstable waves towards longer wavelengths. These might affect the favorable conditions for the development of baroclinic instability and, therefore, the intensity of cyclone generation activity.

Variational data assimilation (VDA) remains one of the key issues arising in many fields of geosciences including the numerical weather prediction. While the theory of VDA is well established, there are a number of issues with practical implementation that require additional consideration and study. However, the exploration of VDA requires considerable computational resources. For simple enough low-order models, the computational cost is minor and therefore models of this class are used as simple test instruments to emulate more complex systems. In this paper, the sensitivity with respect to variations in the parameters of one of the main components of VDA, the nonlinear forecasting model, is considered. For chaotic atmospheric dynamics, conventional methods of sensitivity analysis provide uninformative results since the envelopes of sensitivity functions grow with time and sensitivity functions themselves demonstrate the oscillating behaviour. The use of sensitivity analysis method, developed on the basis of the theory of shadowing pseudoorbits in dynamical systems, allows us to calculate sensitivity functions correctly. Sensitivity estimates for a simple coupled dynamical system are calculated and presented in the paper. To estimate the influence of model parameter uncertainties on the forecast, the relative error in the energy norm is applied.

The use of high spatial and temporal resolution data assimilation and forecasting around Australia's capital cities and rural land provides an opportunity to improve moisture analysis and forecasting. To support this endeavour, RMIT University and Geoscience Australia have worked with the Bureau of Meteorology (BoM) to provide real-time GNSS (Global Navigation Satellite System) Zenith Total Delay (ZTD) data over the Australian region, from which a high-resolution total water vapour field for SE Australia can be determined. The ZTD data can play an important role in high-resolution data assimilation by providing mesoscale moisture data coverage from existing GNSS surface stations over significant areas of the Australian continent. The data are now used by the BoM's high-resolution ACCESS-C3 capital city NWP systems, the ACCESS-G3 Global system and have been used by the ACCESS-R2-Regional NWP model. A description of the data collection and analysis system is provided. An example of the application of these local GNSS data for a heavy rainfall event over SE Australia/Victoria is shown using the 1.5km resolution ACCESS-C3 model, which is being prepared for operational use. The results from the test have been assessed qualitatively/synoptically and also have been examined quantitatively using the Fractions Skills Score which shows the reasonableness of the forecasts and demonstrates the potential for improving rainfall forecasts over south-eastern Australia by the inclusion of ZTD data in constructing the moisture field. These data have now been accepted for operational use in NWP.