SA43B-1583
DEMETER observations of plasma density irregularities induced above powerful VLF transmitters and their connection with energetic proton precipitation from the radiation belts
Recent DEMETER observations show the existence of extensive induced plasma density irregularities above the powerful VLF transmitter North West Cape (NWC) in Australia. Presumably the irregularities are produced through heating of the ionospheric plasma by the VLF transmitter signals. DEMETER observations sometimes show that the E field of the NWC signals exhibits a significant doppler shift. This can be interpreted to indicate that electromagnetic whistler mode signals from the NWC transmitter excite quasi- electrostatic whistler mode waves as the input signals propagate through the induced irregularities. If the quasi-electrostatic whistler mode waves can propagate to the magnetic equator without significant attenuation, they can interact with radiation belt particles through gyro-resonance and Landau resonance to produce energetic particle precipitation. We consider the case of energetic proton precipitation, calculate the proton pitch angle diffusion coefficient on the L shells near NWC, and estimate the proton lifetime on these field lines.
SA43B-1584
Ionospheric electron density variations observed by FORMOSAT3/COSMIC during AKR experiments and the Sichuan earthquake.
Auroral kilometric radiation (AKR) experiments were conducted at the HIPAS (High Power Auroral Stimulation) Observatory (64°52'19" N, 146°50'33" W) during January-March of 2008. The GPS Occultation experiment (GOX) onboard FORMOSAT3/COSMIC (F3/C) are employed to observe the ionospheric electron density during the 2008-01-21 06:52:00UT experiment. The F3/C GOX data at 07:00-08:00UT within 10- degree lat/long from the HIPAS on the experiment day and 1-15 days before and after are isolated. A comparison between the experiment day and the associated medians of its 1-15 day before/after shows that the AKR experiment results in a pronounced ionospheric electron density cavity on 21 January 2008. Meanwhile, an earthquake was occurred at Sichuan, China (30.986° N, 103.364° E, Depth 19km) at 06:28:01UT on 12 May 2008.The F3/C GOX data show that ionospheric electron densities above the forthcoming epicenter anomalously decrease of about 30-40% in the afternoon period (13:00-16:00UT) of day 6 to 4 and in the late evening period of 3-5 day before the earthquake.
SA43B-1585
Artificial Modification of Polar Mesospheric Winter Echoes (PMWE) With an RF Heater: Do Charged Dust Particles Play an Active Role?
An investigation of Polar Mesospheric Winter Echoes (PMWE) has been carried out with the MST MORRO radar operating at 56 MHz. MORRO has been deployed recently at the EISCAT installation near Tromsoe in northern Norway home of two other large incoherent scatter radars and an RF heating facility. The main object of the investigation is to examine whether, and if yes how, RF heating influences PMWE. In particular, the experimental observation of the overshoot effect would indicate the presence of charged dust particles. On 11 February 2008 we measured several weak and variable PMWE layers and we used the RF heater with an on period of 20 s and off period of 100 s to modulate the radar scatter from the layers. We chose one layer, which for 44 minutes was the strongest and most stable layer, for further analysis. The signal intensity variation during an averaged on/off heater period shows the expected weakening of the signal intensity when heating is turned on followed by a significant small recovery of the signal during the on phase and a corresponding small overshoot of the signal strength of about 13-15% over the background level when heating is switched off. The recovery and overshoot are attributable to charge accumulation on the dust particles due to electron heating. The overshoot characteristic curve shows that a considerable increase in the electron temperature did take place during heating and that charged dust particles should be present, probably with radii of some nanometers.
SA43B-1586
HAARP-Induced Artificial Ionospheric Ducts
It is well known that strong electron heating by a powerful HF-facility can lead to electron and ion density perturbations stretching along the geomagnetic field. These density perturbations can serve as ducts for ELF waves, both of natural and artificial origin. This paper presents the experimental evidence of plasma modifications associated with ion outflows due to HF heating. The experiments were conducted using the HAARP heater and two diagnostics satellites, DEMETER and DMSP-16, flying at altitudes 700-800 km close to the magnetic zenith of HAARP. Onboard detectors provided in situ measurements of the ion temperature and composition. The experimental verification of strong ion outflows and formation of the ionospheric ducts by F-region ionospheric heating is presented. Generation of the ionospheric ducts requires strong F-region heating, which is optimum in quiet ionosphere with a distinct smooth F2 region and minimal D/E region absorption. The ion outflows and density structures are best detected by satellites passing within less than a hundred kilometers to the HAARP magnetic field line. The experimental results are in qualitative agreement with the existing numerical model of inter-hemispheric artificial ducts.
SA43B-1587
Perturbations of GPS Signals by the Ionospheric Irregularities Caused by HF- heating
Generation of artificial field-aligned irregularities of electron density due to the ionospheric heating by powerful radio wave of O-mode was first discovered in mid-seventies, and was widely studied since. It was found that the wavelength spectrum of the artificial irregularities is in the range from tens of meters to kilometers. Different mechanisms are responsible for the generation of field-aligned irregularities of electron density due to HF-heating. They include ponderomotive parametric instability, thermal instability, self- focusing instability. A new mechanism for generation of super small scale field-aligned irregularities of the size of tens centimeters was recently suggested by Gurevich and Zybin [2006]. According to this model the upper hybrid waves due to HF-heating can be trapped inside striations producing standing Bernstein waves. The latter have large amplitude, and thus produce the ponderomotive force which in turn pushes plasma away from the electric field peaks. As a result the plasma irregularities will be created having the transverse scale size λ/2 where λ~10-40 cm is the Bernstein wavelength, while the longitudinal scale size is of about 1 km. These field aligned irregularities were termed super small scale irregularities (SSS). In this talk we present the first experimental evidence of strong perturbations of GPS signals by the SSS irregularities of the electron density caused by the HF-heating of the F2 region of the ionosphere. The experiments were conducted using the HAARP Ionospheric Research Instrument with the radiating frequency close to the triple electron gyro frequency. The critical diagnostic instrument was GPS receiver located at HAARP which detects the changes in differential phase of GPS signals passing through the HF-heated spot. It was found that after the start of the HF-heating differential phase of the probe GPS signals changed abruptly in about 10 s, and then oscillated with the heating period 20 s. The oscillations lasted for 4-5 minutes and then disappeared, presumably when the resonance condition was not satisfied, although the HF-heating continued. The phase oscillations indicate the presence of SSS irregularities of the electron density caused by the HF-heating at the frequency matching the triple electron gyro frequency. Gurevich A. V., and K. P. Zybin (2006), Phys. Lett. A, 358, 159.
SA43B-1588
Propagation of ULF Waves Under Different Ionospheric Conditions
We perform a numerical study of the lateral propagation of ULF compressional Alfven waves produced by a localized source, like the HAARP facility. We consider different modes of generation modulation, including pulsed, continuous, sawtooth sweep, and sinusoidal sweep, as well as different F-layer densities. Both 2D and 3D simulations were carried out. We find that propagation is strongly dependent on F-layer density, with virtually no propagation taking place for F-layer electron number densities below 105/cm3 (foF2 < 3.0 MHz). Under conditions of robust F-layer (foF2 > 6.0 MHz) ULF waves can travel lateral distances in excess of 2000km. However, ground detection of these waves may be hampered by the "skip distance" effect; ULF waves initially travel upwards, are reflected in the upper ionosphere, and generally "skip" a horizontal distance of ~1400km before reaching the bottom of ionosphere.
SA43B-1589
Ground Observations of Artificial E Region Field-Aligned Irregularities Over HAARP
Heating experiments were performed at HAARP intended to create E region field aligned plasma irregularities (FAIs) at midday in July of 2008 when the critical frequency of the E layer is a maximum. Field-aligned backscatter was observed using a 30 MHz imaging coherent scatter radar located close to Homer, Alaska. Three experiment modes were used, involving 1) heating alternately at zenith and magnetic zenith, 2) heating using triangular power modulation, and 3) heating slightly above and below the second electron gyroharmonic. Strong echoes were observed in all cases. Radar imaging and other diagnostic methods are used to examine the degree to which irregularities can be observed outside the Spitze angle, the possible effects of predonditioning on thermal parametric instability, and the effects of the double resonance on backscatter intensity and irregularity formation.
SA43B-1590
The OI 135.6nm Observations of the Weddell Sea Anomaly and the Nighttime Mid- Latitude Enhancement
The paper reports the OI 135.6nm airglow emission observation of the ionospheric Weddell sea anomaly (WSA) and the middle-latitude region observed by the TIMED-GUVI. The WSA was first observed by single point ground-based ionosonde located in the Antarctica and featured by a greater nighttime ionospheric electron density than that in daytime in the Weddell sea region during local summer. Recently the anomaly was observed by wide-range total electron content (TEC) measurements collected by the TOPEX satellite and the GPS receiver network. From the TEC observation, the WSA spans in a large area. This study utilizes the two-dimensional global airglow map and vertical profiles derived from the limb scan of the TIMED- GUVI 135.6nm observations to further explore the three-dimensional structure of the WSA. From our observation, the WSA appears as the most prominent feature of the nighttime ionosphere at mid-latitude. Meanwhile, a similar feature also occurs in the northern hemisphere during local summer. The similar feature occurs in both the northern and southern hemispheres suggests that it is actually a nighttime mid-latitude enhancement. Our global and monthly observation of the nighttime mid-latitude enhancement reveals some possible physical mechanisms of the peculiar mid-latitude structure.
SA43B-1591
Wave Injection with the HAARP HF Heater: Conditions and Coherence Limits for Magnetospheric Amplification
Controlled magnetospheric wave injection experiments are carried out with ELF/VLF waves generated by heated modulation of the ionospheric auroral electrojet currents. In an on-going experiment with the High Frequency Active Auroral Research Program (HAARP) facility located at L = 4.9, 500 Hz - 5 kHz waves are used to trigger wave-particle interactions that result in the non-linear amplification of the wave, known as the coherent whistler mode instability of VLF triggered emission phenomenon. The amplified signals show temporal growth rates of 15-30 dB/sec as well as triggering of free running emissions. The amplification process is sensitive to select frequency bands and to selectively amplify specific frequency-time formats in these bands. It is found that propagation to the magnetospheric interaction region via magnetospheric ducts may be one of the factors determining the occurrence of observations. Special formats designed to test the coherence limits of the input wave for the interaction are transmitted. Results show that while increasing the bandwidth of the input wave does not quench amplification, a minimum temporal duration for input pulses is necessary.
SA43B-1592
Kilometer-scale Structure in HF-induced Airglow at the HAARP Facility
The High Frequency Active Auroral Research Program (HAARP) is a joint Air Force and Navy facility which is used to conduct ionospheric modification experiments. Artificial airglow was first observed at HAARP in 1999 [Pedersen and Carlson, 2001] and a successful optics campaign in 2001 showed that this airglow could be consistently produced by directing the HF beam along the magnetic field lines [Pedersen et al., 2003]. Artificial airglow experiments at HAARP since then have been used to explore the relationship of electron gyroharmonic transmissions and airglow intensity [Djuth et al., 2005; Kosch et al., 2005], compare airglow measurements to coherent and incoherent scatter radar data [Kosch et al., 2005; Kosch et al., 2007], and observe the altitude profiles and tomography of the airglow with the aid of multiple camera locations [Pedersen et al., 2008]. In 2003, a heating experiment during auroral conditions unexpectedly resulted in artificial airglow intense enough to be viewed by the naked eye [Pedersen and Gerken, 2005]. Images of small-scale features in artificial airglow serve as a passive means of measuring ionospheric structure. It is important to understand ionospheric structure not only for basic research purposes but also for applications such as improved satellite communications. Telescopic observations of artificial airglow have been conducted at HAARP since 2000, first with a prototype instrument deployed by Stanford University and then by the HAARP telescopic imaging system. Recently, bright airglow emissions were observed on multiple nights during the 2008 winter campaign. Two nights of particular interest were February 26 and 27 with small-scale structure observed by the telescope on both nights. An overview of this system's capabilities and key observations thus far will be presented.
SA43B-1593
High-Resolution Ranging of the ELF/VLF Source Region Generated by the HAARP HF Transmitter
During the 2008 PARS Summer School a novel technique was employed to determine the location of the dominant ELF/VLF source region using ground-based ELF/VLF receivers located between 30 and 100 km from the HAARP HF transmitter in Gakona, Alaska. Previous ELF/VLF wave generation studies have approximated the altitude of the dominant ELF/VLF source region assuming the location is directly above the HF heater (e.g., Rietveld et al. [1989]). It may be the case, however, that different portions of the spatially distributed HF-heated region dominate the ELF/VLF signals observed at ground-based receivers located different radial distances from the HF transmitter. We employ the dual-beam capabilities of the HAARP array together with a specific modulation frequency-time format to provide bounds for the dominant ELF/VLF source region location. In this paper, we experimentally determine (with ±1 km ranging accuracy) the location of the dominant ELF/VLF source region within the larger HF-heated ionospheric patch and analyze its dependence on receiver location.
SA43B-1594
ELF/VLF Wave Radiation by an Equatorial Ionospheric Heater
The equatorial electrojet current, which is modulated by an ionospheric heating facility, radiates ELF/VLF waves. The calculation of this radiation is performed using a new stable full-wave method for a horizontally- stratified arbitrary anisotropic medium, with arbitrary harmonically-varying current distribution. This method is capable of calculating the radiation into both the ionosphere and the Earth-ionosphere waveguide. Unlike heating at high latitudes with significant emission of whistlers, at the geomagnetic equator the radiation goes only into the Earth-ionosphere waveguide. The radiated energy flux is in general higher than that for a similar high-latitude heater, and is also found to be anisotropic in the horizontal direction.
SA43B-1595
Comparison of Ionospheric Radiance and Electron Density Over the Auroral Oval With FORMOSAT-3/COSMIC Measurements
Ionospheric radiance and electron density observed by FORMOSAT-3/COSMIC GOX and TIP payloads respectively are applied to display the boundaries of the auroral oval in the northern hemisphere for study of the auroral ionosphere. The auroral ionosphere were usually observed with incoherent scatter radar (ISR) or in situ measurement along the path of a spacecraft, which provided ionospheric information in a partial region. Due to global observation of FORMOSAT-3/COSMIC satellites, global ionospheric structure can be monitored with the GPS radio occultation technique, especially in high latitude for denser data distribution. Comparing with the ionospheric radiance, which is measured by on-board tiny ionospheric photometer (TIP), this paper reports the boundary of the auroral oval and its variations in the northern hemisphere.
SA43B-1596
Spacecraft Observations of a ULF Wave Injected Onto Field Lines by SPEAR
SPEAR (Space Exploration by Active Radar) is an ionospheric heating facility situated on Svalbard which is capable of exciting ULF waves on local magnetic field lines. Field-guided ULF waves can interact with the ionospheric Alfvén resonator (IAR) and produce parallel electric fields, which then accelerate electrons along the field line. Detection and study of these waves thus provides information on the properties of the IAR and auroral acceleration processes. We examine an interval from 1 February 2006 when SPEAR was transmitting with a 5 min on-off cycle. During this interval the Cluster spacecraft passed over the heater site. We discuss signatures of the SPEAR-generated wave identified in the Cluster field and electron measurements. One feature of interest is the periodic enhancement of electron fluxes in two broad energy bands (~10-100 eV and ~100-1000 eV) which occur out of phase with each other in the two different energy bands.
SA43B-1597
Characterization of the Ionosphere Above the HAARP HF Heater Using DEMETER Satellite Data
One of the goals of the High Frequency Active Auroral Research Program (HAARP) is to study the properties of the ionosphere and the overlying plasma, especially those which can be modified and controlled by electromagnetic waves [Kennedy and Kossey, 2002]. For this purpose, a phased array of HF transmitters (3.6 MW, 2.8 - 10 MHz) is used to radiate intense electromagnetic waves up into the ionosphere. There are many possible applications of HF transmitter operation, and one of the most important is generation of ELF waves via modulation of the auroral electrojet current [Stubbe and Kopka, 1977]. All these applications depend on the natural parameters of the ionosphere during an experiment and on the change of the parameters produced by the HAARP transmitter on its own. In this work we present measurements of ionospheric parameters carried out during many passes of the DEMETER satellite over HAARP, both when HAARP is transmitting and when not. DEMETER is a low-earth orbit satellite (660 km) capable of simultaneous measurements of electron and ion densities, electron and ion temperatures, and electromagnetic waves in different frequency bands from 0 to 3.3 MHz. It should be noted that the use of the upper band of the receiver enables observation of the HAARP HF signal which directly reaches the spacecraft in some cases of close passes and favorable ionospheric conditions. The purpose of this work is to differentiate the effects naturally existing over HAARP and those created by HAARP. One such effect considered in detail is the depletion of ionospheric densities and formation of a duct for ELF/VLF waves. The first results of direct satellite observations suggested that depletion of electron and ion densities up to one order of magnitude and corresponding increase in electron temperatures can occur during HAARP heating experiments. However, a thorough analysis of a number of DEMETER passes revealed that such depletions also exists over HAARP when the transmitter is not operating. Further correlation of the position of this depletion region with Kp indices suggested that this depletion is in fact an ionospheric trough [Rodgers et al.,1992]. Even though such depletion is not created by HAARP it can substantially affect the propagation of ELF/VLF generated by HAARP and also influences on other experiments conducted with HAARP.
SA43B-1598
ISUAL side-way observations of the OI(1D) night airglows
Recently, ISUAL/FORMOSAT-2 Satellite has devoted more observation time to investigate the OI(1D) nightglow from the sideway, which provides the first comprehensive survey of 630.0nm emission in the pre- midnight sector at F layer. It is found that the OI(1D) nightglow enhancement exhibited remarkable seasonal variations. In this study, we want to highlight the following three points. First, semiannual anomaly and winter anomaly existed in the form of the brightening emission in the region of equatorial anomaly. Second, the data indicates that the tidally enhanced regions show significant longitudinal variability. Third, the latitudinal variability of OI(1D) nightglow can be contributed to both the Equatorial Ionization Anomaly (EIA) effect and the upward propagation tides.
SA43B-1599
The Arecibo HF Facility: maximizing the science return on a constrained budget
Ground-based active experiments in aeronomy and space plasma physics require facilities that are moderate in price compared to some in situ experiments, but nonetheless, the costs are significant and increasing rapidly, especially from the effect of the recent increase of the price of energy on the costs of construction and operation. The Arecibo heating facility, now under construction, was designed from the start to minimize the capital investment necessary for a facility designed to transmit a high power high frequency wave into the earth's ionosphere. The required large effective area of the antenna already exists: the Arecibo 300 m dish. A feed using dipoles and a subreflector is being constructed to illuminate the dish efficiently. The high power transmitters and transmission lines have been obtained surplus. After some study, we have been able to identify some changes that can reduce expenses without affecting the primary goals of the project, but perhaps resulting in some loss in flexibility of operation and some restrictions on future modifications to the facility. We have simplified the switching system for selecting which of the two dipole arrays is in use. This is only possible if we run separate transmission lines for the two systems. The additional lines can be obtained for the shipping costs, but we must use smaller ones in order to keep the installation costs down. This results in a slight increase in loss at the current frequencies of interest, but precludes eventual modification of the facility to use the highest frequency band of the transmitters. The antenna costs are lowered, and the facility will be easier to maintain. We will also lower operating costs by altering the biasing of the final transmitter stages. This somewhat restricts the kinds of waveforms that can be transmitted. For special experiments we would be able re-tune in order to regain the original capabilities.