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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report 2 Space Weather Impacts in Retrospect The first session of the workshop offered participants a retrospective look at the impact of some recent space weather events on specific industries. The session was moderated by Peggy Shea (Air Force Research Laboratory and University of Alabama), who opened the session with an overview of the principal kinds of space weather disturbances and illustrated their effects on modern technological systems with examples that included the well-known Quebec blackout during the magnetic superstorm of March 1989 and the disruption of the Anik communications satellites in 1994, as well as some less well known events such as the disruption of Allied radars in 1942 by an intense solar outburst and the brief high-frequency communication outage experienced by Air Force One en route to China during a solar event in 1984. She ended her talk with a comparison of the magnitude of historical solar energetic particle (SEP) events, as determined from ice core samples, with that of more recent events and pointed out that the SEP event associated with the Carrington flare of 1859 was four times larger than the August 1972 SEP event, thought to be the largest SEP event of the space era (see the discussion of the Carrington event in Chapter 1). “We can go back in the past,” she concluded, “but we don’t know what will happen in the future.” Nonetheless, as she noted in the abstract of her talk (see Appendix C), “technological planners should consider the possibility of these extremely large events in the design of their operating systems.” Shea’s comments set the stage for the four presentations that followed, each of which was devoted to the impact of space weather on a particular technology or industry sector. The speakers were asked to (1) describe the effects of a recent serious space weather event in their areas of expertise, (2) assess in broader terms the monetary or service costs associated with such events, and (3) discuss the measures taken to adjust to or recover from space weather-related disturbances. Frank Koza (PJM Interconnection) and Michael Bodeau (Northup Grumman) represented, respectively, the electrical power and spacecraft industries. Leon Eldredge (Federal Aviation Administration) and Angelyn Moore (Jet Propulsion Laboratory) both addressed, with different emphases, the effects of space weather on navigation systems that rely on signals from Earth-orbiting satellites. Eldredge’s presentation focused specifically on the Wide Area Augmentation System (WAAS) developed by the FAA to augment the Global Positioning System (GPS), while Moore discussed space weather effects on GPS within the context of the International Global Navigation Satellite System Service (IGS).
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report SPACE WEATHER AND POWER GRIDS Background According to the U.S. Energy Information Administration, retail expenditures on electricity were approximately $325 billion in 2006, the most recent year for which data are available, which represents approximately 2.5 percent of that year’s GDP. These values, while consequential, significantly understate the economic contribution of this industry since they do not reflect the consumer surplus that buyers receive from their purchases of electricity. This point is illustrated in Figure 2.1, which depicts a hypothetical demand curve for electricity. At price P1, consumption of electricity equals Q1. Given this price and quantity, expenditures on electricity can be represented by area A while consumer surplus, the difference between what consumers are willing to pay for electricity in excess of what they actually pay, is represented by area B.1 Area B represents the net economic benefits to consumer from electricity and thus also represents the economic impact of a supply interruption on consumer net economic welfare. Because electricity is critical to maintaining modern lifestyles, the consumer surplus from electricity is generally believed to be very large relative to expenditures. As a result, interruptions in electricity supply are believed to be very costly in terms of lost consumer surplus. For example, a recent study by de Nooij, Koopmans, and Bijvoet estimated that for households in the Netherlands, the value of lost load, i.e., the estimated loss in consumer surplus from an electricity market shortage, was €16.4/kWh (equivalent to US$24.47 per kWh as of August 11, 2008).2 This is about 95 times the 2006 average retail price paid by households in the Netherlands.3 Consistent with this estimate, the lowest estimate of the economic costs to the United States of the August 2003 blackout in North America is $4 billion.4 To put this estimate in perspective, wholesale generation revenues in New York FIGURE 2.1 A hypothetical demand function for electricity, expenditures on electricity, and the consumer surplus from electricity.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report state, one of the states most affected by the blackout, were expected to equal approximately $46 million during the blackout period.5 The Workshop Presentation The first speaker at this session was Frank Koza, executive director of Systems Operations at PJM Interconnection. PJM is a regional transmission organization with 164,905 MW of generating capacity that coordinates the movement of wholesale electricity over 56,250 miles of transmission lines in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and the District of Columbia. Koza began his presentation by noting that the impacts of space weather on the power system have been well documented. Space weather can give rise to the superposition of extraneous currents onto the normal operational flows on power system equipment. This can create conditions capable of causing damage within seconds. Fortunately, the majority of the events result in relatively minor power system impacts. However, the occasional serious event can have wide-ranging impacts. One example of a space weather event that had a major impact was the March 1989 superstorm. During this storm, a large solar magnetic impulse caused a voltage depression on the Hydro-Quebec power system in Canada that could not be mitigated by automatic voltage compensation equipment. The failure of the equipment resulted in a voltage collapse. Specifically, five transmission lines from James Bay were tripped, which caused a generation loss of 9,450 MW. With a load of about 21,350 MW, the system was unable to withstand the generation loss and collapsed within seconds. The province of Quebec was blacked out for approximately 9 hours. Also during this storm, a large step-up transformer failed at the Salem Nuclear Power Plant in New Jersey. That failure was the most severe of approximately 200 separate events that were reported during the storm on the North American power system. Other events ranged from generators tripping out of service, to voltage swings at major substations, to other lesser equipment failures (Figure 2.2). Koza made the point that operators of the North American power grid constantly review and analyze the potential risks associated with space weather events. Grid operators rely on space weather forecasts such as those produced by NOAA’s Space Weather Prediction Center (SWPC; see http://www.swpc.noaa.gov). They also monitor voltages and ground currents in real time and have mitigating procedures in place. PJM, as an example, has monitoring devices in place at key locations on its system, which are monitored in real time. At the onset of significant ground currents at the monitoring stations, PJM will invoke conservative operations practices that will help mitigate the impacts if the solar event becomes more severe. During these operations, flows between low-cost but more distant generating stations and load centers are reduced so as to maintain power grid stability. What has changed since 1989? On one hand, space weather risks have declined because of increased awareness by system operators and improved forecasts. On the other hand, the evolution of open access on the transmission system has fostered the transport of large amounts of energy across the power system in order to maximize the economic benefit of delivering the lowest-cost energy to demand centers. The magnitude of power transfers has grown, and the risk is that the increased level of transfers, coupled with multiple equipment failures, could aggravate the impacts of a storm. With respect to this trend, the long distance between Hydro-Quebec’s hydro-generation stations and load centers is one of the factors that is believed to have contributed to its space weather vulnerability. Koza also presented his vision of a “perfect storm” space weather event. One might think that an event that occurred at peak load could produce the most severe impacts. However, at peak loads, almost all of the generators are running, and loss of a given amount of generation would have less impact on grid stability than at light load. Loss of multiple facilities at peak load, while of significant concern, can more readily be handled with emergency procedures and other well-established practices. In Koza’s opinion, the power system is more vulnerable to a severe geomagnetic storm during a period of light load with unusually heavy transfer patterns, as is prevalent in the middle of the night during the spring and the fall. Loss of multiple facilities at lighter loads, and high levels of long-distance transfers between low-cost but more distant generating plants and load centers, set up the potential for voltage collapse with minimal ability for mitigation. If several elements were lost at strategic locations, a voltage collapse and associated blackout would be possible.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report FIGURE 2.2 Power system events due to the March 13, 1989, geomagnetic storm. SOURCE: Electric Power Research Institute, Inc. There were a number of questions from the audience following the presentation. One individual asked Koza to rank the value of the space weather predictions that PJM receives from the SWPC on a scale of 1 through 10. Koza indicated that the forecasts were invaluable, namely that their value warranted a ranking of 10 out of 10. One of the committee members noted that Koza’s assessment of increased power grid vulnerability during the spring and the fall was troubling given the well-documented evidence6 that major space weather events are more likely during the spring and fall (Figure 2.3). SPACE WEATHER AND AVIATION NAVIGATION Background According to the FAA, enplanement (i.e., the number of passengers boarding airplanes) in the United States, measured in millions of passengers per year, have more than doubled over the period from 1979 to 2006 (Figure 2.4). This growth is not without consequences, as almost any user of the JFK, Atlanta, and O’Hare airports can attest. According to the FAA, nearly 27 percent of flights arrived late in 2007. The Air Transport Association (ATA) estimates that aviation congestion costs the economy $12.5 billion a year. Under the traditional aviation management system, the situation is expected to worsen, given the FAA’s projection that enplanements will increase at a faster rate than GDP over the next 20 years. For example, the FAA has estimated that total passenger traffic between the United States and the rest of the world will grow from 141.5 million in 2006 to 422.3 million in 2030.7 To accommodate this growth, the FAA has contributed to the development of the Wide Area Augmentation System. WAAS allows GPS to be used as a primary means of navigation. Specifically, the augmentation improves GPS navigation integrity so that near-Category I approaches can be made at a large and increasing number of U.S. airports.8 Being able to land in poor weather at many more airports effectively increases the robustness of the aviation system. Navigation accuracy is also improved. This capability effectively increases the capacity of the aviation system by allowing for reduced horizontal and vertical separation standards between planes without additional risk.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report FIGURE 2.3 Incidence of Kp8/Kp9 events by month, 1932-2007, based on an analysis of 222,072 observations. SOURCE: Data from World Data Center for Geomagnetism. FIGURE 2.4 Historical summary of enplanements in the United States, 1979-2006. SOURCE: FAA enplanement reports, various years.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report The Workshop Presentation Leo Eldredge, program manager of the Global Navigations Satellite Systems Group at the FAA, began his presentation by providing an overview of WAAS. WAAS relies on a network of 38 ground reference stations that collect GPS satellite data. These data are sent through ground communications lines to three master stations that evaluate GPS signal integrity and calculate clock, orbit, and ionospheric corrections to improve accuracy. The integrity messages and augmentation data are distributed to users through two geostationary satellite communications links (Figure 2.5). Eldredge noted that WAAS provides continent-wide ionospheric corrections for use by single-frequency GPS receivers through use of what is known as a thin shell model. This model takes the three-dimensional ionosphere FIGURE 2.5 The WAAS architecture. SOURCE: Leo Eldredge, Federal Aviation Administration, “Space Weather Impacts on the Wide Area Augmentation System (WAAS),” presentation to the space weather workshop, May 22, 2008.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report FIGURE 2.6 The thin shell model. SOURCE: Leo Eldredge, Federal Aviation Administration, “Space Weather Impacts on the Wide Area Augmentation System (WAAS),” presentation to the space weather workshop, May 22, 2008. (shown in green in Figure 2.6) and condenses it to a two-dimensional thin shell (purple). The accuracy of this transformation is dependent on the total electron content in the ionosphere. Most of the time little information is lost and the results are highly accurate. During periods of significant ionospheric disturbance, however, the thin shell model may be inadequate to represent the more complex three-dimensional variations, which causes unacceptable unknown errors. In this situation, integrity, or assured accuracy, is not available in the affected areas, and WAAS can only be used for two-dimensional guidance for a nonprecision approach and landing in these regions throughout the duration of the ionospheric disturbance. Eldredge noted that because of the thin shell model’s vulnerability, space weather “presents the largest limitation to vertically guided service.” While horizontal navigation guidance was continuously available, vertical navigation guidance was unavailable for approximately 30 hours during the three to four large geomagnetic storms experienced in October 2003. Figure 2.7 depicts the geographic coverage of the vertical navigation service on a non-disturbed day, while Figure 2.8 depicts the coverage at the height of the geomagnetic storm on October 29, 2003. On the non-disturbed day, vertical navigation service was available throughout North America. On October 29, 2003, vertical navigation service was not available throughout most of the United States. Eldredge noted that while space weather adversely affected the availability of vertical navigation service, lateral navigation service for non-precision approaches and integrity was maintained at all times for all users. In this sense, the system performed exactly as it was supposed to during the October 2003 storms by withholding only the vertical service. Nevertheless, there would be societal and economic consequences (e.g., flight delays) associated with the non-availability of WAAS if the aviation system were dependent on WAAS and a major space storm occurred. Eldredge concluded his remarks by noting that the movement to a dual-frequency GPS system, relying on L1 and L5, is expected to eliminate the vertical service outages for users that equip with dual-frequency avionics. However, it will be approximately a decade until the transformation to the dual-frequency system is complete.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report FIGURE 2.7 WAAS vertical service coverage on a non-disturbed day. SOURCE: Leo Eldredge, Federal Aviation Administration, “Space Weather Impacts on the Wide Area Augmentation System (WAAS),” presentation to the space weather workshop, May 22, 2008. FIGURE 2.8 WAAS vertical service non-availability at the height of the storm on October 29, 2003. SOURCE: Leo Eldredge, Federal Aviation Administration, “Space Weather Impacts on the Wide Area Augmentation System (WAAS),” presentation to the space weather workshop, May 22, 2008.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report SPACE WEATHER AND SATELLITES In his presentation, Michael Bodeau of Northrop Grumman Space Technology gave an overview of the economic services provided by commercial communications satellites and how the provision of those services can be threatened by adverse space weather conditions. The current fleet of approximately 250 satellites represents an approximately $75 billion investment with a revenue stream in excess of $25 billion per year, or greater than $250 billion over the life of these satellites. As in the case of both electric power and aviation, the latter figure understates the true economic value of commercial communications satellites, given that the value to society equals expenditures by consumers plus the consumer surplus (see Figure 2.1). Some of the specific services that commercial communications satellites provide include: Communication services that provide remote populations with news, education, and entertainment (e.g., global cell phones, satellite-to-home TV and radio, and distance learning); A cost-effective means for interconnecting geographically distributed business offices (e.g., satellite links of store registers to regional distribution centers provide automatic inventory control and pricing feedback at a major retailer, and a major auto maker utilizes a satellite-based private communication network to update its entire system of dealer sales staff on new model features and service crews on new repair procedures); A cost-effective means of connecting businesses with their customers (e.g., facilitating point-of-sale retail purchases made with credit or debit cards at gas stations and convenience stores); and Critical backup to terrestrial cable systems vital to restoring services during catastrophic events (earthquakes, hurricanes) that damage ground-based communications systems. The central thesis of Bodeau’s presentation was that satellites are critical infrastructure and that space weather has posed a constant challenge to designers and operators of satellites, and indirectly to their customers. The impacts of space weather have ranged from momentary interruptions of service to a total loss of capabilities when a satellite fails. Bodeau stressed that access to space weather data is critical to finding the cause of anomalies and failures, which is the first step in making satellites more resistant to space weather events. Bodeau indicated that there have been numerous studies correlating satellite anomalies with space weather. The data he presented indicate that more than half the anomalies experienced in 2003 occurred during the October 2003 storms (Figure 2.9). FIGURE 2.9 Space weather and satellite anomalies/failures. SOURCE: Michael Bodeau, Northrop Grumman, “Impacts of Space Weather on Satellite Operators and Their Customers,” presentation to the space weather workshop, May 22, 2008.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report One example of space weather’s impact on satellites was Telesat’s Anik experience in 1994.9 On January 20, 1994, Telesat’s Anik E1 was disabled for about 7 hours as a result of space weather-induced static-electricity-discharge damage to its control electronics. This satellite provides communication services in Canada. During this period, the Canadian press was unable to deliver news to 100 newspapers and 450 radio stations. In addition, telephone service to 40 communities was interrupted. One hour after E1 recovered, Telesat’s Anik E2 went off-air. As a result, TV and data services were lost to more than 1,600 remote communities. Backup systems were also damaged, making the US$290 million satellite useless. Approximately 100,000 home satellite dish owners were required to manually re-point their dishes to E1 and other satellites. The satellite was restored following a US$50 million-C$70 million 6-month recovery effort. The costs of interrupted services across Canada (i.e., the loss in consumer surplus to Canadians) are unknown. The Anik failures illustrate an important point that may be overlooked, given the understandable tendency to focus on dramatic “big” space weather events such as the “Halloween” storms of 2003, the March 1989 storm, and the Carrington event. Namely, the impact of space weather on spacecraft systems is not limited to anomalies or failures that occur during the CME-driven geomagnetic storms (such as those just mentioned) that occur episodically around solar maximum. Of major concern to the spacecraft industry are the periodic enhancements of the magnetospheric energetic electron environment associated with high-speed solar wind streams emanating from coronal holes during the declining phase of the solar cycle (see Figure 5.13).10 The Anik anomalies occurred during just such an energetic electron storm, which had begun a week earlier as a high-speed solar wind stream swept past Earth. It should be noted as well that space weather-related spacecraft anomalies can occur even when there is no CME-driven storm or high-speed stream. Energy transferred from the solar wind to the magnetosphere through the merging of the interplanetary and terrestrial magnetic fields builds up in the magnetotail until it is explosively released in episodic events known as magnetospheric substorms. Substorms, which occur during non-storm times as well as storm times, inject energetic plasma into the inner magnetosphere and can cause electrical charge to build up on spacecraft surfaces. The electrostatic discharge that occurs subsequently is one of the major causes of spacecraft anomalies. During the subsequent question-and-answer session, Bodeau was asked about the value of space weather forecasts. His initial response was that communications satellites are supposed to operate 24/7 and that a forecast in that sense is not useful. He then went on to indicate that behind-the-scenes repositioning and controlling of a satellite could be delayed if it were known that adverse space weather conditions were expected. On the other hand, if an anomaly that had occurred in the past had revealed a weakness in a satellite design, and if satellite operators could do something to mitigate such a weakness by changing operations, then they would like to know when adverse conditions were going to recur so that they could take preventive action. Bodeau noted that the value of forecasts is more apparent with respect to science satellites, whose instruments tend to be far more sensitive to the space environment than those of communication satellites. For science satellites, there are substantial risks and few benefits from operating under adverse space weather conditions, and thus it would make sense to put their instruments and even the whole satellite into a safe mode when adverse space weather conditions are projected. SPACE WEATHER AND GPS SERVICES Background It would be difficult to overstate the societal contribution of GPS. As discussed in the first workshop session, GPS is in the process of revolutionalizing aviation navigation. Other applications include the following:11 GPS receivers enable users to determine the time to within 100 billionths of a second, without the cost of owning and operating atomic clocks. This capability can be of enormous value to firms that need to synchronize their network computers or instruments.
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report GPS technology is revolutionizing transport logistics by making it possible to track and forecast the movement of freight. GPS may one day result in a significant reduction in highway fatalities by warning drivers when their car is about to leave the roadway. GPS-based applications enable farmers to adopt precision agricultural methods of planning, field mapping, soil sampling, tractor guidance, crop scouting, and yield mapping. For example, GPS allows more precise application of pesticides, herbicides, and fertilizers, thereby increasing output at lower cost. GPS provides the fastest and most accurate method for mariners to determine their location. This is a significant benefit, given the nation’s reliance on imported oil carried by tankers and the environmental consequences of oil spills. The Workshop Presentation Angelyn Moore of the Jet Propulsion Laboratory presented evidence on how space weather has impacted GPS services. Her talk made use of data from the International Global Navigation Satellite System (GNSS) Service (IGS; formerly the International GPS Service), a voluntary federation of more than 200 worldwide agencies that pool resources and permanent GNSS station data to generate precise GNSS products.12 Participants include, among others, mapping agencies, space agencies, research agencies, and universities. Currently the IGS supports two GNSSs: GPS and the Russian GLONASS (GLONASS, a navigation system comparable to the U.S. GPS, was developed by the former Soviet Union and is now operated by the Russian Space Forces). Over 350 permanent, geodetic GNSS stations operated by more than 100 worldwide agencies constitute the IGS network. These civilian, dual-frequency stations contribute data to multiple data centers on at least a daily basis at a 30-second sampling rate; subsets contribute hourly and four times hourly, and an IGS real-time pilot project is getting under way. The IGS maintains a vendor-neutral stance and specifies only functional requirements; the network is therefore very heterogeneous in instrumentation. In her talk Moore noted that a representative station suffered intermittent loss of tracking on some or all channels during periods of the October 2003 geomagnetic storms. The effect of such a loss of data will vary according to how many stations in the area are available and whether all of them are affected, and on the application under consideration. The IGS Ultrarapid orbits are a key IGS product that in 2003 were generated twice daily. Through the final week of October 2003, some degradation of the Ultrarapid accuracy could be discerned: not all IGS analysis centers were able to contribute orbit products, and accuracies slipped a few centimeters. Nevertheless, the combined IGS Ultrarapid product achieved better than 10-cm accuracy for most satellites throughout the week. The slight loss in accuracy would generally not have much of an impact on some types of geodetic processing, such as long-term monitoring of plate motion. However, high-rate and real-time GPS analysis is rapidly improving in detecting seismic surface waves and co-seismic displacement,13,14,15 and brief or partial loss of tracking because of space weather during a critical event could certainly degrade applications with societal and economic impacts, such as tsunami warning systems. During the subsequent question-and-answer session, Moore was asked about the value of space weather forecasts. Her response was that she would probably attach a low value to a forecast, probably 2 on a scale of 1 to 10. Her only caveat was that there might be users that would take alternative courses of action if a forecast of adverse conditions were available. Moore also was asked if the affected receiver or receivers were semi-codeless and therefore more sensitive to losing lock on the L2 signal than would be the case when L2 or L5 GPS coded signals were available. She confirmed that this was the case. SUMMARY The starting point of this workshop session was the observation that the most severe events over the past few solar cycles should not be viewed as an indicator of what could be expected in the future. For example, the Carrington event in 1859 was approximately four times larger than anything seen in the past 50 years. Nevertheless, there is evidence that space weather over the past two solar cycles has challenged the integrity of the electric power
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report system, a key infrastructure in which interruptions in supply can have major economic consequences. Specifically, the March 1989 geomagnetic space storm resulted in a major blackout in the Hydro-Quebec power grid and also contributed to power grid anomalies throughout North America. In the opinion of Frank Koza of PJM Interconnection, power grids such as PJM are most vulnerable to space weather during periods of light load with unusually heavy electricity flows from generating plants to load centers, as is prevalent in the middle of the night during the spring and the fall. This assessment of increased power grid vulnerability during the spring and the fall was found to be troubling given the well-documented evidence that major space weather events are more likely during the spring and fall. Given this coincidence between power grid vulnerability and the incidence of major space weather events, it was not surprising that Koza indicated that PJM places a high value on space weather forecasts. Evidence was also presented that space weather has impaired the provision of GPS. One notable example was the FAA’s inability to provide its GPS-augmented vertical aviation navigation guidance for approximately 30 hours during the large geomagnetic storms in late October 2003. This vulnerability is expected to persist over the next decade. The value of improved space weather forecasting may be less significant in this case than with respect to electric power, since aviation safety can be maintained by increasing vertical separation standards. However, there may be considerable interest by airlines and passengers in forecasts of severe space weather events because of the impact of these events on the capacity of the aviation navigation system. Among the important societal applications of GPS, Angelyn Moore noted that high-rate and real-time GPS analysis is rapidly improving in detecting seismic activity, which in turn can have applications for tsunami warnings. This workshop session also provided an overview of the economic value of services provided by satellites and how the provision of those services can be threatened by adverse space weather conditions. Michael Bodeau of Northrop Grumman indicated that numerous studies have correlated satellite anomalies with space weather. Specifically, more than half the anomalies experienced in 2003 occurred during the large geomagnetic storms in late October 2003. The economic impacts of these anomalies have ranged from minor to highly significant depending on the nature of the impact and whether substitute services were available. The value of improved space weather forecasts is dependent on the nature of the satellite service and the extent to which operators can mitigate the potential damage to a satellite by changing operations. NOTES 1. For more information about the concept of consumer surplus, see N.G. Mankiw, Principles of Microeconomics, Fourth Edition, 2007, pp. 138-142. 2. de Nooij, M., C.C. Koopmans, and C.C. Bijvoet, The value of supply security: The costs of power interruptions: Economic input for damage reduction and investment in networks, Energy Economics 29(2), 277-295, 2007. 3. See http://www.eia.doe.gov/emeu/international. 4. Electricity Consumers Resource Council, The economic impacts of the August 2003 blackout, 2004, available at http://www.elcon.org/Documents/EconomicImpactsOfAugust2003Blackout.pdf. 5. This estimate is based on forecasted load and day-ahead reference prices. 6. For example, C.T. Russell and R.L. McPherron, Semiannual variation of geomagnetic activity, J. Geophys. Res. 78, 92-108, 1973. 7. Office of Aviation Policy and Plans, FAA Long-Range Aerospace Forecasts: Fiscal Years 2020, 2025, and 2030, September 2007, p. 10. 8. The glide path of a descending airplane passes through a “decision height” at which the pilot must decide to abort or complete the landing. Category I precision conditions exist when the decision height is 200 feet or above and the runway visual range is 2400 feet or greater. 9. Bedingfield, K.L., R.D. Leach, and M.B. Alexander, Spacecraft System Failures and Anomalies Attributed to the Natural Space Environment, NASA Reference Publication 1390, August 2006, pp. 1 and 5. 10. Encounters with high-speed streams recur approximately every 27 days during the declining phase of the solar cycle, corresponding to the rotation period of the Sun. The geomagnetic disturbances associated with them are referred to as “recurrent” geomagnetic storms, which differ from CME-driven storms in both their cause and phenomenology. See J.E. Borovsky and M.H. Denton, Differences between CME-driven storms and CIR-driven storms, J. Geophys. Res. 111, A07S08, 2006, doi:10.1029/2005JA011447. Instruments in space and on the ground monitor the substorm and energetic electron environments,
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Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report which can provide some warning to satellite operators of hazardous conditions. These instruments are distinct from those used to detect large solar flares and CMEs. 11. These examples are drawn from the National Executive Committee for Space-Based Positioning, Navigation, and Timing, available at http://www.navcen.uscg.gov/gps/default.htm. 12. Dow, J.M., R.E. Neilan, and G. Gendt, The International GPS Service (IGS): Celebrating the 10th anniversary and looking to the next decade, Adv. Space Res. 36(3), 320-326, 2005, doi:10.1016/j.asr.2005.05.125. 13. Larson, K.M., P. Boudin, and J. Gomberg, Using 1-Hz GPS data to measure deformations caused by the Denali fault earthquake, Science 300, 1421, 2003, doi:10.1126/science.1084531. 14. Choi, K., A. Bilich, K. Larson, and P. Axelrad, Modified sidereal filtering: Implications for high-rate GPS positioning, Geophys. Res. Lett. 31, L22608, 2004, doi:10.1029/2004GL021621. 15. Bock, Y., L. Prawirodirdjo, and T. Melborne, Detection of arbitrarily large dynamic ground motion with a dense high-rate GPS network, Geophys. Res. Lett. 31, L06604, 2004, doi:10.1029/2003GL019150.