Chapter 2 - Climate Data and Monitoring

The Australian Climate Network > Meteorological Observations

Land Surface

The current land-based component of Australia’s national meteorological network includes some 845 manual and automatic meteorological observing stations (Figure 2.1), more than 6,800 daily rainfall stations and around 800 rainfall intensity recorders, located on the Australian mainland, on remote islands and in Antarctica. The Bureau of Meteorology staffs 60 of the manual observing stations and approximately 420 are operated by volunteers and paid cooperative observers, with equipment and overall coordination provided by the Bureau. There are currently 500 automatic weather stations (AWS) in the network, many co-located with manual observation sites.

Figure 2.1. The Australian Land Surface Meteorological Network. Some island and Antarctic stations are not shown.

This land surface network is the foundation of Australia’s climate monitoring capability. It provides an enormous quantity of high-quality information from which our basic understanding of the spatial and temporal variability of the climate of this country derives. It is also the key to our ability to detect any changes arising from human activities or from natural climate drivers.

Australia supports the WCDMP Climate Change Detection Project through the maintenance of 103 stations in its national meteorological network as Reference Climate Stations (RCS) (Figure 2.2). These stations have been selected to provide continuous homogeneous records, of high quality, for use in detecting and monitoring long-term climate trends. Most RCS have at least 30 years of record and are relatively free from changes due to increased urbanisation. However, not all of these stations are staffed by the Bureau of Meteorology and a program has commenced to install an AWS to assist in the continuity of data which could have otherwise been at risk due to the withdrawal of an observer. Currently, 70 of these RCS stations have an AWS at the site. Electronic fieldbooks are being installed throughout the RCS network at the remaining non-AWS sites to improve data quality and to achieve increased realtime reporting.

Data from the RCS network form the back-bone of a number of high-quality research datasets that have been developed to monitor climate changes, as measured in daily and annual mean temperature, daily and monthly rainfall totals and cloud amounts over Australia. These high quality datasets have been corrected for inhomogeneities caused by changes in, for example, site location, instrumentation or observation practice.

In addition to providing information on regional climate trends, Australia’s RCS network also makes an important contribution to monitoring global climate trends, with 68 stations having been designated as part of the GCOS Surface Network (GSN) (Figure 2.2). The GSN has been established by the WMO to monitor and detect changes in temperature and atmospheric circulation at the Earth’s surface.

Figure 2.2. Australia's Reference Climate Station network and the GCOS Surface Network. Some island and Antarctic stations are not shown.

Australia also maintains a National Benchmark Network for Agrometeorology (NBNA), consisting of 179 observing stations of particular relevance to agricultural services and research. The Bureau of Meteorology established and operates the NBNA according to a concept and specifications developed by the National Committee on Agrometeorology (NCA). With the aid of specific Government funding following the 1996 Review of the Operation of the Bureau of Meteorology, the Bureau is striving to meet the data requirements for agrometeorology through the ongoing installation of automatic weather stations, electronic fieldbooks and new soil temperature and wind run sensors throughout the network.

Upper Air

Australia currently has a total of 50 upperair observation stations within its national meteorological network, 38 of which report atmospheric pressure, temperature, relative humidity and wind speed and direction, with the remaining 12 reporting wind speed and direction only. Meteorological balloons, carrying radiosondes or reflective targets, are released at six-hourly intervals every day at many of these stations. The balloons are tracked by radar, satellite navigation systems (Global Positioning System (GPS)) or, in limited instances, by optical theodolite, up to balloon-burst height (about 30 kilometres). Twelve stations are equipped with autosondes, which provide a fully automated upper air observing system, preparing and releasing the balloon train, tracking the radiosonde signal using the GPS and processing the data.

Of the 50 upper-air stations, 16 have been designated as part of the GCOS Upper-Air Network (GUAN), a network with relatively homogeneous distribution suitable for detecting the broad scale patterns of climate change throughout the atmosphere. Nine of Australia's GUAN stations are located on the Australian mainland with a further four located on remote islands and three in Antarctica (Figure 2.3).

Figure 2.3. Australia's mainland GCOS Upper Air Network.

Traditionally, Australian upper-air stations have used 350g weather balloons that usually burst between the atmospheric pressure levels of about 25 and 15 hectopascals (hPa), which is lower than the required height of 5hPa for a GUAN station. To increase the height achieved at GUAN stations, 800g balloons were gradually introduced to the network. In June 2000, 800g balloons were introduced for the 00Z flight at all GUAN stations, except for Antarctic stations and Macquarie Island. The resultant improvement in heights achieved at these stations has been excellent, with the mean height achieved for the 00Z flight increasing from 26.3km to 34.0km. The larger balloons were introduced at the remaining stations in the spring of 2001 after being tested in Antarctic conditions.

Observations from the Australian upper-air network are supplemented by observations of temperature, wind and turbulence from new-generation commercial aircraft fitted with Aircraft Meteorological Data Relay (AMDAR) systems. These observations are automatically transmitted from the aircraft in-flight using very high frequency (VHF) air-to-ground communications, and are transmitted to the Bureau of Meteorology’s communications centre where they are distributed internationally on the Global Telecommunications System (GTS).

Immediately prior to the demise of Australia’s second major domestic airline, Ansett, the AMDAR program had grown to involve 53 instrumented aircraft reporting approximately 5500 observations per day. With over half of this fleet having ceased making observations thereafter, numbers shrunk to 25 aircraft reporting approximately 2500 observations per day. The Bureau of Meteorology continues to actively pursue AMDAR fleet expansion with the major airlines, and has commenced liaison with Air Services Australia to explore the feasibility of installing AMDAR-like units on smaller aircraft with cruise altitudes in the mid-troposphere.

Satellite-based observations of the upper atmosphere are an increasingly important supplement to Australia’s ground-based observations. Tropospheric and stratospheric temperatures and moisture content are derived routinely from the radiances from the polar orbiting satellites of the US National Oceanic Atmospheric Administration (NOAA). Upper level winds are calculated by tracking cloud tracers on the visible, infrared and water vapour images of the Japanese Geostationary Meteorological Satellite (GMS-5) and the Chinese satellite Feng Yun (FY-2).

A further upper-air observing system employed within Australia in recent years involves the use of vertically profiling radar sounders to measure wind velocities in the lower and middle troposphere. Following the trial of a prototype VHF instrument at Mount Gambier as part of an ARC-funded collaborative project between the Bureau of Meteorology and the University of Adelaide, operational VHF instruments have been or are being installed at Mascot Airport, Canberra and Launceston, and a UHF instrument developed by the Bureau of Meteorology has been installed at Shanes Park, Sydney for the NSW Environment Protection Authority.

Most recently, in 2003, a new collaborative project, also partially funded by the ARC, has commenced between the University of Adelaide and the Bureau of Meteorology to develop a vertically profiling infrared lidar (laser radar) system with which to obtain measurements of tropospheric temperature and humidity.

Commencing in 2001, the Australian Antarctic Division (AAD), in collaboration with the University of Adelaide, commenced a program to monitor temperature, wind velocity and aerosol loading in the stratosphere and mesosphere, using a Doppler lidar based at Davis station in Antarctica. Northern hemisphere measurements have suggested that a general cooling is taking place in the mesosphere and stratosphere, but few published data currently exist regarding trends at southern latitudes. A program of temperature comparisons between the lidar and Bureau of Meteorology balloon-borne radiosondes and ozonesondes is being undertaken up to altitudes of 40 km to test the lidar temperature retrieval techniques.

Atmospheric Constituent Observations

Monitoring atmospheric constituents is an important component of Australia's climate activities, contributing to international efforts to understand the relationship between changing atmospheric composition and changes in global and regional climate. The WMO provides the framework for this contribution through its Global Atmosphere Watch (GAW) system.

Australia makes a major contribution to the GAW system through operation of a global observatory at Cape Grim, Tasmania. Since the Australian government established the Cape Grim Baseline Air Pollution Station (CGBAPS) in 1976 it has gained an international reputation for the excellence of its scientific outputs and is widely recognised as one of the premier stations within the GAW. Programs at the station, under the leadership of scientists from the Bureau of Meteorology, the CSIRO, universities and the Australian Nuclear Science and Technology Organisation, monitor a number of key atmospheric parameters including chemical components such as carbon dioxide, methane, chlorofluorocarbons, ozone, particulate chemistry and physical characteristics such as radiation and particulate numbers and size distributions. Air samples are also archived so that, in future, newly relevant compounds can be investigated. In addition, basic meteorological parameters of pressure, temperature, wind speed and direction, and rainfall are measured. CGBAPS has now produced long records for a large number of chemical components and physical and meteorological parameters, not least of which is the corrected record of carbon dioxide (Figure 2.4).

Figure 2.4 Monthly mean baseline levels of carbon dioxide measured in situ at Cape Grim. Note both the seasonal cycle and the upward trend. (Courtesy CSIRO Atmospheric Research).

Australia operates a second atmospheric observatory, on a much smaller scale, at Charles Point in the Northern Territory. CSIRO Atmospheric Research and the Northern Territory University manage this observatory, with an automatic weather station provided by the Bureau of Meteorology.

In a contribution to GAW ozone monitoring activities, the Bureau of Meteorology operates a network of Dobson spectrophotometers, measuring the total ozone in the atmospheric column and its vertical distribution, at four locations on the Australian mainland. Weekly observations of the vertical distribution of ozone are also made using ozone sondes flown from Melbourne and Macquarie Island. The Bureau also routinely retrieves, analyses and archives total ozone data derived from the TIROS Operational Vertical Sounder (TOVS) instruments on board NOAA polar orbiting satellites.

Australia has operated a global air sampling network of 5-20, mostly marine boundary layer, sites for varying periods since 1984 (Figure 2.5). In addition, flasks are collected on an opportunistic basis in support of regional and international campaigns. Shipboard sampling is done from Antarctic resupply and CSIRO research vessels, and aircraft sampling is done over southeastern Australia. Flasks are analysed at the CSIRO’s Global Atmospheric Sampling Laboratory (GASLAB).

Figure 2.5. The GASLAB global air-sampling network. The area enclosed by the dotted line is that most commonly sampled from Australian Antarctic resupply vessels. Shading around Cape Grim encompasses the range of sampling from aircraft (Courtesy of CSIRO Atmospheric Research).

The University of Wollongong monitors the long-term variability and change in stratospheric composition through groundbased remote sensing techniques involving solar infrared, visible and UV spectroscopy. Established in 1996, the Wollongong site contributes to the international Network for the Detection of Stratospheric Change (NDSC).

Various agencies are involved in deriving concentrations and distributions of aerosols, such as dust, sulphate and volcanic ash, from a range of satellite instruments. The Bureau of Meteorology's Volcanic Ash Advisory Centre in Darwin uses volcanic ash detection techniques based on NOAA Advanced Very High Resolution Radiometer (AVHRR) data and GMS-5 imagery, combined with ground reports from vulcanological agencies, pilot reports, meteorological knowledge and numerical models, to track and forecast ash movements from volcanoes in Indonesia, Papua New Guinea and part of the Philippines.

The Bureau of Meteorology is also active in the Tropical Rainfall Measuring Mission (TRMM). The Darwin Climate Monitoring and Research Station, which is jointly operated by the Bureau of Meteorology Research Centre (BMRC) and the Bureau's Northern Territory Regional Office, provides the mission with systematic observations of tropical rainfall in a monsoon environment, which are critical for the calibration and 'ground-truthing' of the satelliteborne precipitation radar.