5.3 Opportunities for High-Power, High-Frequency Transmitters to Advance Ionospheric/Thermospheric Research: Report of a Workshop

A Report of the SSB Ad Hoc Committee on the Role of High-Power, High-Frequency-Band Transmitters in Advancing Ionospheric/Thermospheric Research: A Workshop

Overview

Research conducted by the ionospheric modifications (IM) community—a community that uses high-frequency(HF) transmitters to inject energy in the ionosphere and measure its effects using ground- and space-based diagnostics—is focused on understanding the interaction of radio waves with the ionospheric plasma, the local consequences of heating in the ionosphere, and studies of nonlinear plasma physics processes. At the request of the Department of Defense (DOD) Air Force Research Laboratory (AFRL) and the National Science Foundation (NSF) Directorate for Geosciences/Division of Atmospheric and Geospace Sciences, the Space Studies Board of the National Research Council held a workshop on May 20-21, 2013, in Washington, D.C., entitled “The Role of High-Power, High Frequency-Band Transmitters in Advancing Ionospheric/Thermospheric Research.” The request for this workshop was informed by the sponsors’ awareness of the possibility that tight budgets would result in DOD’s curtailment, or even termination,1 of support for the High Frequency Active Auroral Research Program (HAARP), which includes the world’s highest-power and most capable HF transmitter—“heater”—for ionospheric research. Although the workshop was organized to consider the utility of heaters in upper atmospheric research in general (see Appendix A), it had a specific focus on the HAARP transmitter facility, which is located in a remote part of southeastern Alaska (Figure S.1).2

The HAARP facility began construction in 1993; it was completed in 2007 at an estimated total cost of $290 million.3 The facility’s principal instrument for study of the ionosphere is a transmitter array of 180 crossed dipoles that are spaced over an area of about 30 acres. The dipoles are arranged in a 12 by 15 rectangular grid and are phased to provide steering; together, they can produce up to 3,600 kW of radiated power in a band from 2.8 to 10 MHz, which falls within what is commonly referred to as the HF band (3-30 MHz) of the electromagnetic spectrum.

The HAARP program is sponsored by DOD, receiving support from the Navy, the Air Force, and the Defense Advanced Research Projects Agency (DARPA). Its objectives are to “identify, investigate, and, if feasible, control ionospheric processes and phenomena that might serve to enhance future DOD Command, Control and Communications capabilities … research areas that will be explored include generation of very low and extremely low frequency waves, generation of geomagnetic field-aligned irregularities, electron acceleration, and investigation of upper atmospheric processes.”4Figure S.2 illustrates operation of the HAARP transmitter—known as an ionospheric “heater” because most of the transmitted energy goes into heating ionospheric electrons.

According to experts at the workshop, the combination of extremely high power and the capability to be rapidly reconfigured to create a variety of spatial and temporal antenna patterns is unique in the world to “HAARP,” or more properly its ionospheric research instrument (IRI).5 Further, in presentations at the workshop, participants learned how the ability to produce such large and patterned energy into the ionosphere is being used for exploring many aspects of the upper atmosphere, including the mesosphere and lower thermosphere (MLT) region, the

_______________

NOTE: “Overview” reprinted from Opportunities for High-Power, High-Frequency Transmitters to Advance Ionospheric/Thermospheric Research: Report of a Workshop, The National Academies Press, Washington, D.C., 2014, pp. 1-11.

1 At the workshop, an Air Force representative stated that current plans called for the elimination of funding for the facility starting by fiscal year 2015. Not foreseen at the time the workshop was requested, the Budget Control Act of 2011 (BCA)—“the sequester”—which took effect on March 1, 2013, resulted in further substantial cuts to the DOD budget. As noted in footnote 2 of the Preface, HAARP facility ceased operations shortly after the workshop and remains closed at the time of this printing.

2 For an overview of heaters and ionospheric modification, see Duncan and Gordon (1982). A popular article that discusses HAARP applications is Weinberger (2008).

3 According to a number of participants who, in turn, referenced fact sheets for HAARP.

4 Robertshaw et al. (1993), p. 1.

5 Throughout this report “HAARP” is used interchangeably with IRI except in those instances when reference is made to the HAARP facility, which includes the IRI, various diagnostic instrumentation, and other associated operational elements, or the “HAARP program,” which strictly speaking is not correct, because the “P” in HAARP refers to “Program,” but is common usage.



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42 Space Studies Board Annual Report—2013 5.3 Opportunities for High-Power, High-Frequency Transmitters to Advance Ionospheric/Thermospheric Research: Report of a Workshop A Report of the SSB Ad Hoc Committee on the Role of High-Power, High-Frequency-Band Transmitters in Advancing Ionospheric/Thermospheric Research: A Workshop Overview Research conducted by the ionospheric modifications (IM) community—a community that uses high-­ requencyf (HF) transmitters to inject energy in the ionosphere and measure its effects using ground- and space-based d ­ iagnostics—is focused on understanding the interaction of radio waves with the ionospheric plasma, the local consequences of heating in the ionosphere, and studies of nonlinear plasma physics processes. At the request of the Department of Defense (DOD) Air Force Research Laboratory (AFRL) and the National Science Foundation (NSF) Directorate for Geosciences/Division of Atmospheric and Geospace Sciences, the Space Studies Board of the National Research Council held a workshop on May 20-21, 2013, in Washington, D.C., entitled “The Role of High- Power, High Frequency-Band Transmitters in Advancing Ionospheric/Thermospheric Research.” The request for this workshop was informed by the sponsors’ awareness of the possibility that tight budgets would result in DOD’s curtailment, or even termination,1 of support for the High Frequency Active Auroral Research Program (HAARP), which includes the world’s highest-power and most capable HF transmitter—“heater”—for ionospheric research. Although the workshop was organized to consider the utility of heaters in upper atmospheric research in general (see Appendix A), it had a specific focus on the HAARP transmitter facility, which is located in a remote part of southeastern Alaska (Figure S.1).2 The HAARP facility began construction in 1993; it was completed in 2007 at an estimated total cost of $290 million.3 The facility’s principal instrument for study of the ionosphere is a transmitter array of 180 crossed dipoles that are spaced over an area of about 30 acres. The dipoles are arranged in a 12 by 15 rectangular grid and are phased to provide steering; together, they can produce up to 3,600 kW of radiated power in a band from 2.8 to 10 MHz, which falls within what is commonly referred to as the HF band (3-30 MHz) of the electromagnetic spectrum. The HAARP program is sponsored by DOD, receiving support from the Navy, the Air Force, and the Defense Advanced Research Projects Agency (DARPA). Its objectives are to “identify, investigate, and, if feasible, control ionospheric processes and phenomena that might serve to enhance future DOD Command, Control and Commu- nications capabilities . . . research areas that will be explored include generation of very low and extremely low frequency waves, generation of geomagnetic field-aligned irregularities, electron acceleration, and investigation of upper atmospheric processes.”4 Figure S.2 illustrates operation of the HAARP transmitter—known as an iono- spheric “heater” because most of the transmitted energy goes into heating ionospheric electrons. According to experts at the workshop, the combination of extremely high power and the capability to be ­rapidly reconfigured to create a variety of spatial and temporal antenna patterns is unique in the world to “HAARP,” or more properly its ionospheric research instrument (IRI).5 Further, in presentations at the workshop, participants learned how the ability to produce such large and patterned energy into the ionosphere is being used for explor- ing many ­ spects of the upper atmosphere, including the mesosphere and lower thermosphere (MLT) region, the a NOTE: “Overview” reprinted from Opportunities for High-Power, High-Frequency Transmitters to Advance Ionospheric/Thermospheric Research: Report of a Workshop, The National Academies Press, Washington, D.C., 2014, pp. 1-11. 1 At the workshop, an Air Force representative stated that current plans called for the elimination of funding for the facility starting by fis- cal year 2015. Not foreseen at the time the workshop was requested, the Budget Control Act of 2011 (BCA)—“the sequester”—which took effect on March 1, 2013, resulted in further substantial cuts to the DOD budget. As noted in footnote 2 of the Preface, HAARP facility ceased operations shortly after the workshop and remains closed at the time of this printing. 2 For an overview of heaters and ionospheric modification, see Duncan and Gordon (1982). A popular article that discusses HAARP applica- tions is Weinberger (2008). 3 According to a number of participants who, in turn, referenced fact sheets for HAARP. 4 Robertshaw et al. (1993), p. 1. 5 Throughout this report “HAARP” is used interchangeably with IRI except in those instances when reference is made to the HAARP facil- ity, which includes the IRI, various diagnostic instrumentation, and other associated operational elements, or the “HAARP program,” which strictly speaking is not correct, because the “P” in HAARP refers to “Program,” but is common usage.

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Summaries of Major Reports 43 FIGURE S.1  Overhead photo of the High Frequency Active Auroral Research Program Gakona Facility. SOURCE: McCarrick, M., et. al., Marsh Creek LLC, “HAARP Facility Status,” presentation to the Committee on the Role of High-Power, High- Frequency-Band Transmitters in Advancing Ionospheric/Thermospheric Research: A Workshop, April 2013. Courtesy of M. McCarrick. Available at http://www.haarp.alaska.edu/haarp/photos.html. ionosphere, and the magnetosphere. These regions form a coupled system whose nonlinear response to variable and wide-ranging energy and momentum sources have important influences on those of us living on the surface of Earth; for example, radio and satellite communications, global navigation, and the lifetime of space assets limited by atmospheric drag. Many participants in the workshop, even some who were familiar with experiments at heater facilities, said they came away with an increased appreciation for the breadth of phenomena that are addressed by the HAARP facility. Historically, military applications have been a major motivation for studies at HAARP. At the workshop, the Navy’s interest in HAARP was attributed to the prospects to use the ionosphere as an antenna to generate extremely low-frequency (ELF) waves for global submarine communication, while the Air Force interest included applications such as over-the-horizon radar and attempts to study the effects of injecting ULF, ELF, and VLF waves into the radiation belts in order to affect the lifetimes of “killer” million-electron-volt electrons that would otherwise disable low Earth orbit satellites.6 Those applications were not widely discussed in this unclassified workshop, although some of them are mentioned in Chapter 4. Some participants at the workshop cited the unusual history of the HAARP facility as a contributor to its underutilization by a broader community of researchers. In particular, they noted that initial funding for HAARP 6ELF and VLF refer to extremely low frequency and very low frequency, respectively. This part of the electromagnetic spectrum is com- monly said to range from 300 Hz to 30 kHz.

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44 Space Studies Board Annual Report—2013 FIGURE S.2 Depiction of high-frequency ionospheric heating by the High Frequency Active Auroral Research Program transmitter. SOURCE: Courtesy of Robert McCoy, Geophysical Institute, University of Alaska, Fairbanks. came from congressional earmarks that went directly to the Air Force without the same level of documentation and justification as a peer-reviewed facility. This funding history and the facilities’ origins in the defense community may have contributed to the perception, as described by some participants, that performing experiments at HAARP was unduly difficult; these participants also stated that it may have contributed to HAARP’s capabilities, as described above, not being widely appreciated. For example, CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) is an NSF-sponsored upper atmospheric research program whose goal is “to understand the behavior of atmospheric regions from the middle atmosphere upward through the thermosphere and ionosphere into the exosphere in terms of coupling, energetics, chemistry, and dynamics on regional and global scales.”7 Yet some participants noted that at summer CEDAR workshops there was little mention of research using the HAARP facility. At various points in this workshop, participants proposed ways to make the facility more welcoming and user-friendly in the future and better coordinated with the CEDAR community. Chapter 6 describes some of these proposals; in particular, NSF representatives at the workshop discussed their desire to move the Poker Flat, Alaska, advanced modular incoherent scatter radar (PFISR) to the HAARP site in Gakona, Alaska. Experiments with the combined facility could then come under the usual NSF procedures for user facilities, which are more open and familiar to many scientists. 7National Science Foundation, Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR), available at http://www.nsf.gov/ funding/pgm_summ.jsp?pims_id=5503.

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Summaries of Major Reports 45 The sponsors of the workshop posed seven questions for consideration by participants. These questions were examined in presentations and discussions that occurred in multiple sessions of the workshop; a compilation of individual participant responses follows. 1. What is the state of the art in active ionospheric and thermospheric research? Active ionospheric research is founded in controlling the extent and altitude of absorption of power delivered by ground-based heaters into the lower ionosphere, a highly nonlinear physical phenomenon. It has been found that the response of the geophysical environment changes discontinuously as the HF power delivered to the ionosphere increases, thus indicating the presence of thresholds (Figure S.3). As illustrated in Figure S.3, at modest powers one can achieve measurable electron and ion heating, create field-aligned striations, modulate the D/E region conductivity, and drive parametric instabilities accompanied by stimulated electromagnetic emissions and enhanced optical emissions. All of these phenomena were explored prior to the development of HAARP. In designing HAARP, there were requirements for flexible operation—a feature of phased arrays—and the requirement for a transmitter with effective radiated power (ERP) that exceeded the gigawatt (GW) level (1 GW is equal to 90 dBW, as plotted on Figure S.4). Recent experiments at HAARP, some only possible since 2007 when the facility was completed and operation at the full design power became possible, have resulted in observations of phenomena that multiple participants characterized as new and exciting: •  The creation of artificially ionized layers descending from near the F-peak to altitudes close to 150 km; •  The capability of sustaining high-density plasma clouds in the F-region for more than 3 h, ending only when the heater was turned off; •  Virtual antenna ULF/ELF generation with modulated F-region heating without requiring the presence of the natural electrojet; •  Triggered emissions by injection of ELF/VLF waves in the radiation belts; and •  eneration of very small size irregularities capable of enhancing total electron concentration (TEC) and G affecting gigahertz (GHz) radio wave propagation. FIGURE S.3  Hierarchy of heater effective radiated power thresholds for excitation of plasma processes in the lower atmosphere. ­ SOURCE: H.C. Carlson, Jr., High-power HF modification: Geophysics, span of EM effects, and energy budget, ­­ dvances in A Space Research 13:15-24, doi:10.1016/0273-1177(93)90046-E, 1993. Courtesy of Herbert Carlson and COSPAR.

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46 Space Studies Board Annual Report—2013 HAARP, Alaska 2007 Effective Radiated Power (ERP) (dBW) HAARP 90 crosses threshold for nonlinear effects Sura, Russia EISCAT, Norway HAARP, Alaska 80 1998 Arecibo, Puerto Rico SPEAR, Norway 70 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Frequency (MHz) FIGURE S.4 Effective radiated power (ERP) versus frequency for high-frequency heating facilities. The performance of HAARP facility before the upgrade in 2007, which enabled the recent “unique and ground-breaking” results described in this report, is also indicated. The Arecibo facility is under construction and will come on line in 2014. NOTE: EISCAT, European Incoherent Scatter Scientific Association; SPEAR, Space Plasma Exploration by Active Radar. SOURCE: E. Kennedy, Naval Research Laboratory, “Heating Facilities Update: High-Frequency Active Auroral Research Program (HAARP),” 4th Radio Frequency (RF) Ionospheric Interactions Workshop, Santa Fe, New Mexico, April 19-22, 1998. Although a host of new phenomena were discovered using the new capabilities of the HAARP heater, a compre- hensive understanding, including how the new phenomena would scale, was said by some participants to have been hindered by the following: (1) lack of proper incoherent scatter radar (ISR) radar diagnostics and (2) ­nsufficient i diagnostic satellite overflight coverage following the termination of the DEMETER8 satellite mission. During the workshop, Dennis Papadopoulos noted that the large number of satellite missions with excellent diagnostic instru- ments, including the Van Allen Probes, the Canadian e-POP/CASSIOPE,9 the Russian Resonance,10 the Air Force 8 DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) was a microsatellite mission of the French space agency CNES that ended in late 2010. See http://smsc.cnes.fr/ DEMETER/. 9 The Institute for Space Imaging Science at the University of Calgary is leading the operation of the Enhanced Polar Outflow Probe (e-POP), a scientific payload for CASSIOPE, a small satellite mission from the Canadian Space Agency that was launched successfully on September 29, 2013. (In addition to e-POP, CASSIOPE carries a commercial communications payload, CASCADE. The acronym CASSIOPE is derived from “Cascade, SmallSat and Ionospheric Polar Explorer.”) The Institute for Space Imaging has links for further information at http://­mertensiana.phys.ucalgary.ca/. 10 “Resonance is a Russian space mission consisting of four identical spacecraft in specific Earth orbits, within the same magnetic flux tube for a certain period of time. The launch is scheduled for 2015. The aim of the mission is the investigation of wave-particle interactions and plasma dynamics in the inner magnetosphere of Earth, with the focus on phenomena occurring along the same field line and within the very same flux tube of the Earth’s magnetic field. Among a variety of instruments and probes, several low- and high-frequency electric sensors will be onboard that can be used for simultaneous remote sensing and in situ measurements” (Institut für Weltraumforschung website, at http:// www.iwf.oeaw.ac.at/en/research/near-earth-space/resonance/). See also http://www.iki.rssi.ru/ people/z_et_al.pdf.

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Summaries of Major Reports 47 DSX,11 and the Japanese ERG,12 as well as several CubeSat and microsatellite missions of opportunity, is expected to resolve the latter impediment during the next few years. Other participants noted that the relocation of PFISR to Gakona (discussed below) would be of great help in addressing the former. An ISR had been part of an initial proposed design for the HAARP facility, but it was not funded;13 its addition was also advocated in an influential 2002 report of a study conducted by the director of DARPA.14 Papadopoulos asserted that the unique combination of the Russian Resonance mission, discussed more exten- sively in the Chapter 3 section “Dynamics of the Radiation Belts,” in combination with HAARP and a modern ISR, would produce “transformational science” because this combination would effectively constitute a unique type of experimental plasma physics laboratory in space. He noted that the unique magneto-synchronous orbits of the twin microsatellites would allow them to stay on the HAARP magnetic field lines, perform measurements, and guide HAARP operational modes over times in excess of 30 minutes. Further, he noted that the combination of ISR and satellite diagnostics, along with active HF ionosphere research, has important strategic implications in the overall structure and connections of space science. Papadopoulos stated that the ISR provides an intimate connection be- tween passive and active ionosphere-thermosphere-magnetosphere (ITM) research, while the satellite diagnostics provide a similar connection between active ionosphere and magnetosphere/radiation belt research. While emphasis at the workshop was placed on HAARP, the major contributions provided by the EISCAT (Eu- ropean Incoherent Scatter Scientific Association) heater facility at Tromsø, Norway, were also noted. In particular, as noted by Brett Isham, EISCAT’s lower effective radiated power and more limited operational flexibility as compared to HAARP was more than made up for by its excellent radar diag- nostics. Indeed, various participants cited the wealth of EISCAT studies of irregularities, stimulated electromagnetic radio emissions,15 optical emissions, and electrojet-modulation-based virtual antennas at ULF, ELF, and VLF fre- quencies as evidence that enhanced diagnostics at HAARP would allow the facility to quickly move into addressing the next level of challenges in active modification research. 2. What are the fundamental research areas in ITM science that can be addressed using high-power HF-band transmitters? Studies of the nonlinear interaction of HF radio waves with the ionosphere using recently developed powerful and agile ionospheric heaters, such as the EISCAT heater and more recently the completed HAARP heater, have resulted in the development of novel techniques that workshop presenters, including Herbert Carlson, described as potentially transformational in their implications for understanding ITM regions and their coupling. According to Carlson and other participants familiar with recent active experiments, science areas impacted by the novel recent discoveries at EISCAT and HAARP include the following: •  Radio science. A key tool in this research area is the development of artificial plasma layers (APLs). By controlling the location, duration, and properties of the APLs, researchers can conduct studies of guidance, redirection, enhancement, and degrading of trans-ionospheric communications links at HF, VHF, and UHF frequencies and the effects of enhanced TEC and artificial ionospheric turbulence on Global Positioning System (GPS) signals and mitigation of over-the-horizon radar signals in the Arctic. •  Mesosphere-thermosphere diagnostics. Several diagnostic techniques involving active HF heating have been tested and verified recently. These include (1) artificial periodic irregularities (APIs) formed by the interfer- ence of the incoming and reflected HF waves to diagnose the neutral density and temperature of the D and E 11 “The Air Force Research Laboratory has developed the Demonstration and Science Experiments (DSX) to research technologies needed to significantly advance the capability to operate spacecraft in the harsh radiation environment of medium Earth orbits (MEO)” (Schoenberg et al., 2006). See also Scherbarth et al. (2009). Another mission of interest that may overlap with DSX, noted during the review of this workshop summary, is TARANIS (Tool for the Analysis of Radiations from Lightnings and Sprites), a French-led mission scheduled to be ready for launch in late 2015 (see http://smsc.cnes.fr/TARANIS/). 12 “The ERG (Energization and Radiation in Geospace) project is a mission to elucidate acceleration and loss mechanisms of relativistic electrons around Earth during geospace storms. The project consists of the ERG satellite, ground-based network observations, and simulation/ modeling/theory teams” (ERG Science Center at STEL, Nagoya University, available at http://ergsc.stelab.nagoya-u.ac.jp/). 13 Joint Services Program Plans and Activities, Air Force Geophysics Laboratory, and Navy Office of Naval Research (1990). 14 Anthony Tether, Director of DARPA and Chair, Committee on Future Direction of HAARP, presentation summarizing this report’s find- ings, 2002, available at http://spp.astro.umd.edu/SpaceWebProj/Tether_Panel.ppt. 6 15 For further discussion, see, for example, Leyser (2001).

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48 Space Studies Board Annual Report—2013 regions; (2) optical emissions due to F-region heating for measurements of the neutral density, composition, drag, neutral diffusion, and thermospheric wind velocity in the F-region; and (3) probing of the properties of polar mesospheric clouds. •  Space weather. The location of the HAARP facility was cited as particularly favorable in comparison to other heater locations because under quiet conditions, it maps into the plasmasphere; during substorms, it is located inside the subauroral region and is mapped near the plasma pause; and during storms, it is inside the auroral zone. As a result, it was asserted that high-power HF heating experiments can advance understanding of space weather processes in all relevant geospace regions. These processes include (1) subauroral polariza- tion stream (SAPS)/subauroral ion drift (SAID)-related outflows;16 (2) high electron temperature excited chemistry and density troughs; and (3) high-temperature ion-outflow-created atmospheric gravity waves. •  Magnetosphere-radiation belts. Dennis Papadopoulos stated that the most important development for this topic is the concept of “virtual antennas,” which allows injection of whistler, shear Alfvén, and magnetosonic waves in the magnetosphere and the radiation belts and ULF/ELF/VLF waves in the Earth-ionosphere wave- guide. Papadopoulos noted that measurements of the propagation and interaction of these waves with the plasma and energetic radiation belt particles allow for comprehensive cause-and-effect studies of critical pro- cesses, such as the physics of triggered emissions and chorus, propagation characteristics, attenuation rates and mode conversion effects of whistler and Alfvén waves, pitch angle scattering rates of trapped particles on whistler, Alfvén and EMIC waves, excitation of field line resonances, and properties of ionospheric and magnetospheric waveguides and resonators. An additional task that can be achieved with the use of virtual antennas is the assessment of radiation belt remediation systems that will be required in case of a Carrington event and deliberate or accidental high-altitude nuclear explosion. •  HAARP as 110 MW/acre radar. In his presentation to the workshop, Todd Pedersen described a new capa- bility of HAARP he thought particularly exciting: operation as an HF radar. With the addition of a receiver, HAARP could be used for ionospheric imaging (via incoherent and coherent scatter); plasmaspheric, mag- netospheric, and solar corona/wind sounding; and planetary subsurface measurements, while retaining its capability as an active HF heater.17 3. What are the key diagnostic instruments needed in conjunction with high-power, HF-band transmit- ters to address questions 1 and 2? Many participants stated that in addition to its existing diagnostic instrumentation, addressing questions 1 and 2 will require the addition of an ISR at the HAARP site. Some participants also noted the need for extensive satel- lite heater over-flight coverage by properly instrumented satellites. Further, some participants noted that important diagnostic benefits to active experiments as well as to passive diagnostics can be derived by use of the API technique, which is described in more detail in Chapter 1 of this report. • Numerous participants, including Richard Behnke, Robert Robinson, Robert McCoy, Dennis Papadopoulos, Paul Bernhardt, Todd Pedersen, Herbert Carlson, David Hysell, and Brett Isham, stated that moving an ISR to the HAARP site would provide critical diagnostic information that would help resolve physics-related issues involving ionosphere-thermosphere diagnostics, the physics of artificial ionization, and the details of virtual antenna operation. • Other participants noted that HAARP could be operated as a radar by upgrading the existing radar receiver to an imaging array. This can be accomplished by using a few hundred antennas spread out over 100 to 1,000 m or more, co-located or remote from the HAARP site, at a cost—estimated at the workshop by Todd Pedersen by analogy to new low-frequency arrays such as the Long Wavelength Array (LWA) near the Very Large Array (VLA) in New Mexico—to be approximately $1 million. This addition would create unique 16 See Foster and Burke (2002). 17 In his presentation, Pedersen stated that with respect to applications, “What do I do with an ionospheric heater?” may be the wrong ques- tion, instead, he believes the right question is, “What could I do with a 110 MW-acre radar in the 3 to 10 MHz range?” Pedersen asserted that an imaging receive array could provide “huge” new capability for little cost and that there would be numerous unique possibilities for p ­ lasmasphere, magnetosphere, and heliosphere research, in addition to active or passive ionosphere studies, all while still having the iono- spheric heating capabilities.

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Summaries of Major Reports 49 new capabilities and enable novel research for plasmasphere, magnetosphere, and heliosphere research in addition to active or passive ionosphere studies. •  Papadopoulos stated that spacecraft overflight of HAARP in magneto-synchronous satellite orbits, such as the ones planned for the Resonance mission, promise to revolutionize the utility of HF heaters for under- standing the physics of the radiation belts; they would also be a critical complement to the science derived by the Van Allen Probes and other radiation belt missions. •  edersen and others noted that the API technique requires the ionospheric modification facility to have P at least a modest receive capability, which could be accomplished by using a specialized HF receiver and antenna. According to Pedersen, an ionosonde-class antenna would be sufficient at a minimum. Both the receiver and antenna should accommodate dual polarizations. The heater itself must be configured to use either a pulsed or pulse-code mode. An imaging array of the kind described above would be ideal for API research. 4. Are there emerging science questions that might benefit from active ionospheric experiments in the subauroral zone? The subauroral zone is the region where SAPS, the outstanding feature of the perturbed plasmasphere, occurs. As such, it is an area of great interest vis-à-vis space weather. It was argued by Dennis Papadopoulos and others that with its location in the subauroral zone during weak and moderate substorms, investigations conducted with the HAARP facility can advance understanding of key space weather processes in subauroral geospace, as well as mimic aspects of substorm dynamics, by inducing effects similar to the ones created during natural events. Such HF-driven effects were said to include (1) injection of artificially created gravity waves, (2) joule heating and con- ­ ductivity modification of the D/E region, (3) thermospheric heating and associated satellite drag effects, and (4) ion outflows and duct formation. 5. What operating parameters (e.g., power and transmission frequency) are needed to address ques- tions 1-4? While some participants noted radar applications that could benefit from access to higher HF frequencies, none mentioned difficulties in addressing questions 1-4 employing HAARP with its currently available capabilities. 6. Are there ways to combine similar facilities (e.g., EISCAT, Arecibo) to perform global ionospheric science? No direct opportunities were noted during discussions at the workshop. However, a participant observed that data acquired at each location can be compared to develop useful “scaling laws.” For example, comparing the input/ response at the high-latitude ionosphere at HAARP to that of the lower-mid-latitude ionosphere at Arecibo was said to allow illumination of the critical role of Earth’s magnetic field for accessing fundamentally different plasma instability processes and dramatically enhanced efficiency of energy deposition for injection at high latitudes. Larry Paxton noted that forcing from the lower atmosphere is thought to account for perhaps 20 to 30 percent of the observed variability in the upper atmosphere. This led to a discussion of the potential to operate heaters at a variety of latitudes to help in understanding how the global atmospheric system responds to different types of energy inputs. Reflecting a theme heard in different contexts throughout the workshop, one participant envisioned important advances in magnetospheric physics coming from the use of a combination of techniques: HF heaters located at a wide range of latitudes, the associated ISRs, and having satellite coverage of the latitudes where the HF facilities are located. 7. What research opportunities might arise from the relocation of the advanced modular incoherent scatter radar (AMISR) from the Poker Flat Research Facility in Poker Flat, Alaska, to Gakona, Alaska, the location of the HAARP facility? An ISR was included in early HAARP proposals as a way “to provide the means to monitor such background plasma conditions as electron densities, electron and ion temperatures, and electric fields, all as a function of

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50 Space Studies Board Annual Report—2013 altitude.”18 At the workshop, a participant noted that such diagnostic information is critical for a quantitative under­ tanding of the physics controlling artificially ionized layers, virtual antenna generation, triggered emissions, s field-aligned striations, and for predicting the behavior and scaling of these phenomena at facilities located at other latitudes. In addition, an ISR was said to provide the means for “closely examining the generation of plasma turbu- lence and the acceleration of electrons to high energies in the ionosphere by HF heating.”19 A workshop participant noted that over the years of operating HAARP without an ISR, researchers had developed proxies for estimating state parameters. However, these proxies have not been validated, and it was said that even temporarily relocating PFISR to Gakona would help validate the methodologies that have been developed in the absence of an ISR. Specifically, according to several participants, moving PFISR to the HAARP site is expected to •  Validate conclusions made using proxy techniques that were developed in the absence of an ISR and used to infer, for example, electron and ion temperatures and densities and drifts, all of which can be directly measured using the ISR technique. •  Allow the detailed study of Langmuir and other turbulence processes, as has been done with great scientific success at EISCAT and Arecibo. •  Dramatically improve the current limited understanding of processes occurring in the horizontal directions above the HAARP heater and answer the question, Are the recently created artificial ionospheric layers actual layers, or are they more like filaments or patches?” • Contribute to the introduction of a new methodology in ITM research by creating a facility that brings to- gether distinct research communities and experimental techniques. The new methodology would combine traditional passive observational techniques, currently used by the upper atmosphere-ionosphere and mag- netosphere communities, with active experimentation that uses geospace as an open laboratory for active cause-and-effect experimentation. According to some participants, the result would be important advances in scientific understanding of — The physics of Earth’s radiation belts. — The role of ionosphere conductivity in atmosphere-ionosphere-magnetosphere coupling. — The dynamics of ionosphere-thermosphere coupling. The benefit of the ISR technique, with its ability to directly measure the key fundamental plasma parameters with- out disturbing the ambient plasma, was cited repeatedly at the workshop. One participant stated that an ISR at HAARP would benefit all experimental activity, as evidenced by the three HF facilities that have ISRs: EISCAT, Arecibo, and SPEAR (Space Plasma Exploration by Active Radar),20 all of which were said to nearly always run their HF experi- ments taking full and productive advantage of the possibility of supporting measurements by the co-located ISRs. As noted by NSF representatives at the workshop, additional value to HAARP is expected to come via the involvement of the community of scientists that currently use the PFISR radar at Poker Flat, Alaska, the ISR that they would like to be moved and utilized at HAARP. The scientific potential of this combination was discussed at the workshop, and several participants commented on both the synergy of an ISR and HAARP and the value of bringing together the traditionally separated communities that perform strictly passive observations and those who include active perturbations in their research. Herbert Carlson stated that the involvement of NSF, brought in via the inclusion of the current PFISR radar, would also contribute to opening HAARP up to additional communities of researchers new to the possibilities and potentials of using active HF techniques.21 18 See Joint Services Program Plans and Activities, Air Force Geophysics Laboratory, and Navy Office of Naval Research (1990). 19 See Joint Services Program Plans and Activities, Air Force Geophysics Laboratory, and Navy Office of Naval Research (1990). 20 SPEAR is an HF heater located above the Arctic Circle at 78.15°N in Svalbard, Norway. 21 This point was also made in the 2013 National Research Council decadal survey Solar and Space Physics: A Science for a Technologi- cal Society (NRC, 2013). The survey report includes chapters written by each of the three study panels that reported to the overall steerting committee. The survey’s AIMI (atmospheric-ionospheric-magnetospheric interactions) panel included the following: “The DOD operates and maintains the world’s largest ionospheric modification facility, HAARP, near Gakona, Alaska. HAARP is not collocated with an incoherent scatter radar, and so its full potential has not been realized since the phenomena it creates cannot be fully diagnosed . . . . Another ionospheric modification facility is under construction at the Arecibo Radio Observatory. While this facility will be modest in power compared to HAARP, its collocation with Arecibo, the world’s most sensitive incoherent scatter radar, raises the prospect of discovery science in the areas of artificial and naturally occurring ionospheric phenomena.The Arecibo heater came about through close collaboration between DOD and NSF. The AIMI panel regards this kind of interagency cooperation as a model to be followed for the utilization of existing ionospheric modification facilities as well as the planning and development of new ones” (p. 201).

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