Space Weather Studies in Australia

Space weather—the space-based phenomena that affect human and technological systems—can damage orbiting satellites and harm humans in space. But on a more regional level, space weather can induce currents on long conductors, such as pipelines and power lines. It can also disrupt radio communications between ground locations and aircraft. Most Northern Hemisphere countries monitor regional effects from adverse space weather in their hemisphere. Their collective research and calculations provide a comprehensive view of the phenomena that affect their region. By contrast, fewer research and monitoring efforts are directed toward understanding regional effects of space weather surrounding the South Pole region, although some programs do exist (e.g., Scientific Committee for Antarctic Research (SCAR) and activities developed during the International Polar Year). Australia has the largest ground-based, space weather network in the Southern Hemisphere, a breadth needed to provide continent-wide services over a range of geomagnetic and geographic coordinates and over a highly variable space environment. In part because Australia emerged as a regional leader after World War II, government officials created the Ionospheric Prediction Service (IPS) in 1948, an early space weather–monitoring agency to provide advice on the effective use of the ionosphere to support high-frequency (HF) radio communications. During the 1957–1958 International Geophysical Year (IGY) this role was extended to include short-term alerts for fadeouts during solar flares and ionospheric and geomagnetic storms. After IGY, a growing number of geophysical customers found the HF communicators’ alerts and storm warnings useful. Like in many countries around the world, the growing customer base, together with the immediacy of the Internet in the early 1990s, led to the development of an increasingly wide range of space weather services. Yet services to mitigate space weather effects are only one side of Australia's efforts to understand solar-terrestrial interactions. Because highly complex processes can lead to effects that the services seek to mitigate, research has a wide role to play in understanding the scope of space weather effects in Australia. Principal space weather services are provided mainly by IPS, part of the Bureau of Meteorology, through its Web site (http://www.ips.gov.au), while services are provided to Australia's Department of Defense by IPS and several other agencies. IPS customers include federal and state governments; educational groups; and private groups including HF communicators and broadcasters, airlines, engineers, pipeline operators, geophysical research groups, aeromagnetic surveyors, radio amateurs, and aurora watchers. Services cover a wide range of timescales, from analysis of space climatological patterns to prompt solar flare alerts. The services range in scope from notifying customers of disruptions to ground-based HF signals (e.g., for those involved with broadcasting, communications, radar, regulations monitoring, and direction finding), geomagnetic disturbances (e.g., for those involved with aeromagnetic surveying, constructing and maintaining pipelines, and directional drilling), and cosmic ray events (important to those flying aircraft), to alerting satellite operators of ionospheric disruptions that can cause scintillation and distort positioning systems. Some services are automated, triggered by solar wind and geomagnetic conditions. Others have complex, dedicated, and system-driven data collection programs. For example, Australia's Jindalee Operational Radar Network (JORN), an over-the-horizon radar network, bounces signals off the ionosphere to obtain a description of its current state; projects like JORN may need to collect different data depending on the type of radar operation being used. Both service and research programs in Australia capitalize on a widely dispersed observational network spanning the continent (Figure 1). Most local data sets important for space weather services are made available to the scientific community, in some cases in near real time, through the World Data Centre for Solar Terrestrial Science (http://www.ips.gov.au/World_Data_Centre). Space weather research itself bears both directly and indirectly on service problems. For example, geomagnetic surveys, carried out from aircraft, can have significant errors if the geomagnetic field is disturbed—geomagnetic pulsations interact with surveying methods, resulting in spurious results. To help assess the likely impact of pulsations on surveys, IPS develops products that map the impact of pulsations across Australia (http://www.ips.gov.au/Geophysical/1/3/2). Other research projects focus on pipeline protection—currents are run through pipelines to help them resist corrosion, but changing magnetic fields during a geomagnetic storm can render protection efforts ineffective. The need for accurate space environment forecasting has led scientists to review data sources and brainstorm better ways of displaying and quantifying how the solar wind interacts with Earth. Additionally, the relatively new area of radio astronomy at frequencies as low as 100 megahertz has led to renewed interest in ionospheric variability caused by traveling ionospheric disturbances (TIDs) and ionospheric scintillation. TIDs are neutral atmospheric waves that produce distorted isoionic contours in the ionosphere, resulting in focusing and defocusing radio waves that are reflected from or pass through the ionosphere. Large, storm-generated TIDs can be tracked over long distances and wide spatial regions. The periodic nature of these disturbances may allow signals to be corrected for their presence. By comparison, scintillation, caused by ionization instabilities, can result in sharp discontinuous changes in signal strength and phase, leading to signal degradation that cannot be corrected as easily. Research that bears indirectly on service issues involves basic science and is typically conducted in a university setting. These projects span the full scope of the solar-terrestrial environment, beginning with observations of the Sun. IPS makes solar observations at two solar observatories. In Culgoora (located near Narrabri, New South Wales), optical observations with a Razdow solar telescope provide routine patrol monitoring of the Sun in a visible (H-alpha) wavelength from dawn to dusk. During a patrol, solar observations are monitored—observed activity is logged, and relevant information is transmitted to similar patrol sites worldwide. Solar radio bursts are observed with a solar spectrograph, providing forecasters with evidence of material leaving the surface of the Sun during active periods. The Learmonth Solar Observatory (located near Exmouth, Western Australia) is jointly operated by IPS and the U.S. Air Force (USAF) and is home to the USAF Weather Agency Radio Solar Telescope Network (RSTN), which monitors radio emissions from the Sun. The Solar Observing Optical Network (SOON), is also sited at Learmonth, as is one of the six Global Oscillation Network Group (GONG) helioseismology stations, which monitors solar seismic waves that provide information about the solar interior. Much of these data are available in near real time at http://www.ips.gov.au/World_Data_Centre. Through these observatories, Australia has a strong heritage of solar emission research that persists today. For example, a realistic ecliptic plane model for the solar wind—based on data from the Advanced Composition Explorer (ACE) spacecraft and incorporating type II solar bursts, one of several types of solar emissions arising from energetic electrons moving outward from the solar surface (as shown in Figure 2)—provides an understanding of the two-dimensional structure of the solar wind, a factor useful for guiding space weather forecasts [Florens et al., 2007]. Building on this, recent work at the University of Sydney has led to improved models of solar type II burst emissions [e.g., Knock and Cairns, 2005] and to an improved analysis of solar spectrograph data [Lobzin et al., 2008, 2009] that offers new insights into the origins and speeds of solar wind disturbances. This research is aided by monitoring solar radio emissions associated with shock waves traveling in the solar wind, which potentially make it possible to track events moving outward through the solar wind toward the Earth. A key space weather prognostication required for a range of services is the likely magnitude and nature of the forthcoming solar cycle, which is proving particularly difficult to predict. Ice core studies indicate that solar energetic particle events were more prevalent in solar cycles before the space age [McCracken et al., 2001]—implying that future cycles may well pose added hazards. Australian scientists are active participants on the international solar cycle prediction panel. Magnetospheric, cosmic ray, ionospheric, and atmospheric research on the near-Earth space environment fills out Australia's space weather programs. Plasma instabilities and waves associated with ion and electron populations in the magnetosphere give rise to many types of hydromagnetic and ion cyclotron waves that are important in distributing solar wind energy throughout the magnetosphere and down to ionospheric altitudes. The ultralow-frequency (ULF) magnetic field fluctuations associated with these waves are observed as geomagnetic pulsations. Data from spatial arrays of magnetometers provide clues to how these waves form, propagate, and transfer energy into the high-latitude ionosphere [e.g., Howard and Menk, 2005]. Studying hydromagnetic and ion cyclotron waves is important because they and their effects can cause problems for the geomagnetic prospectors at midlatitudes; they may also impose phase and amplitude fluctuations on radio waves reflected from the ionosphere. Observational data from spacecraft and numerous ground stations in Australia, New Zealand, and Antarctica, including Tasman International Geospace Environment Radars (TIGER [see Ponomarenko et al., 2005]), are used to study ULF waves in the magnetosphere and the ionosphere. Understanding cosmic ray phenomena requires observations from a range of locations. The Mawson Cosmic Ray Observatory, located in Antarctica, houses underground and surface instruments that monitor and collect cosmic rays. Mawson is the largest and most sophisticated observatory of its type in the Southern Hemisphere and is the only one at polar latitudes. Similar instruments operate in Hobart, Tasmania. Both sites are part of Space Ship Earth [Bieber et al., 2004], an international project that provides the aviation industry with estimates of aircraft occupants’ exposure to natural high-energy particle radiation [Getley et al., 2005]. Ground-based observation stations that monitor the ionosphere include two radars of the Super Dual Auroral Radar Network (SuperDARN): TIGER Bruny in Tasmania, and TIGER Unwin in southern New Zealand, led by scientists at Victoria's La Trobe University in Bundoora (Figure 3). These TIGER radars provide a wealth of information about the local space environment from convection pattern studies to the development of substorms [Parkinson et al., 2003; Makarevich, 2009]. Additionally, several medium-frequency radars are operated by the University of Adelaide, in South Australia. Supplementary routine instruments including magnetometer arrays (operated by the Australian government and New South Wales's University of Newcastle) provide direct confirmation of space weather activity. An imaging riometer located at Davis, Antarctica, is part of the University of Newcastle's Southern Hemisphere Imaging Riometer Experiment (SHIRE). The riometer is an antenna array that observes changes in radio wave absorption due to the presence of energetic particles. In addition, ionosondes (vertically directed radars that monitor the structure of the ionosphere) are operated by IPS, Australia's Department of Defense, and La Trobe University. Other university-based research programs address basic and applied science problems including ionosphere-thermosphere coupling and dynamics, the formation of ionospheric irregularities and their dynamic behavior, and the effect of the ionosphere and solar emissions on the Global Positioning System (GPS). Attitude control system data from the Iridium telecommunications satellite constellations are used to monitor the South Pole's auroral regions [Waters et al., 2004]. Scientists at the University of Newcastle are using these data to understand more about the near-Earth space environment, the drivers of its dynamics, and the space weather patterns seen at such high altitudes. Australia's Federation Satellite (FedSat), launched in 2002, was the first satellite built in Australia in more than 30 years (for more information on FedSat, visit http://www.ips.gov.au/World_Data_Centre/1/5/2). Designed for a 3-year life span, it occupied a high-inclination low-Earth orbit (LEO). FedSat's NewMag fluxgate magnetometer payload (Figure 4) sampled three mutually perpendicular components of the geomagnetic field [Fraser, 2003] to measure currents and waves over southern auroral regions for comparison with data from ground magnetometer arrays. The GPS receiver on FedSat provided information on the total electron content (TEC) along ray paths from the FedSat orbit (about 800 kilometers in altitude) to GPS satellites (at about 20,200 kilometers in altitude). Because the FedSat GPS receiver detected signals simultaneously from several GPS satellites, tomographic images of the electron density in the upper ionosphere and plasmasphere were constructed by combining all the TEC measurements obtained along a segment of the FedSat orbit [Yizengaw et al., 2005, 2006]. TIGER also plays an important role in monitoring southern aurorae. The auroral zone is a major source of TIDs; TIGER has been used to study their propagation to lower latitudes and to identify the likely source regions in the auroral zone [He et al., 2004]. The Earth's magnetosphere can be described in terms of field lines that are closed around the Earth and field lines that are open and connect to the surrounding solar wind. As energy passes into the magnetosphere from the solar wind, the shape of the magnetosphere changes and, as a consequence, the boundary between the open and closed field lines changes. This results in changes in the latitude and shape of the open-closed magnetic field line boundary (OCB), which is considered to be an indication of energy coupling in the solar wind/magnetosphere-ionosphere system. Locating this boundary may help to develop a picture of the structure of the magnetosphere. Forecasters could use this information to estimate, for instance, the location of regions of increased radio absorption in the high-latitude ionosphere. Pinpointing the OCB is therefore a current topic of active research in Australia. Scientists working with SuperDARN radars often detect a distinct transition in line-of-sight Doppler velocity spread, called the spectral width boundary (SWB). It is believed that this transition may correspond to the OCB. Because TIGER is at a comparatively low latitude compared with most SuperDARN radars, it is more sensitive to the SWB, making TIGER data ideal for investigating any OCB-SWB connections. An investigation was carried out at La Trobe University to show that the SWB locations obtained using TIGER are aligned with the OCB locations obtained from satellites under a broad range of geomagnetic conditions, including small to moderate substorms occurring in the premagnetic and postmagnetic midnight sector. This revealed that the behavior of the SWB can be understood in terms of the spatial and temporal variations of energetic particle precipitation throughout the substorm cycle [Parkinson et al., 2004]. A possible link between open-closed field lines and ionospheric convection may also be studied using geomagnetic pulsations at high latitudes [Ables and Fraser, 2005], a line of research that is being pursued by scientists at the University of Newcastle. Space weather plays an important role in Australia, which extends from high to low latitudes both geographically and geomagnetically. Space weather affects this region in many ways, some of which are well understood and can be handled by familiar climatological techniques, while others require a range of research work and observations to increase understanding and to foster the development and implementation of useful techniques. This data-sparse region is dependent on international data exchange and alliances to obtain a full overview of the intricate processes pervading this historically rich region of the Earth. Finally, fundamental research into this environment trains future Australian space weather scientists while reinforcing present knowledge of the environment. Philip Wilkinson is assistant director of the Ionospheric Prediction Service, a part of Australia's Bureau of Meteorology, located in Sydney, New South Wales.

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