Generation of acoustic-gravity waves in ionospheric HF heating experiments : simulating large-scale natural heat sources

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 203-208).In this thesis, we investigate the potential role played by large-scale anomalous heat sources (e.g. prolonged heat wave events) in generating acoustic-gravity waves (AGWs) that might trigger widespread plasma turbulence in the ionospheric layer. The main hypothesis is that, the thermal gradients associated with the heat wave fronts could act as a source of powerful AGW capable of triggering ionospheric plasma turbulence over extensive areas. In our investigations, first we are going to examine a case study of the summer 2006 North American heat wave event. Our examination of GPS-derived total electron content (TEC) data over the North American sector reveals a quite noticeable increase in the level of daily plasma density fluctuations during the summer 2006 heat wave period. Comparison with the summer 2005 and summer 2007 data further confirms that the observed increase of traveling ionospheric disturbances (TIDs) during the summer 2006 heat wave period was not simply a regular seasonal phenomenon. Furthermore, a series of field experiments had been carried out at the High-frequency Active Auroral Research Program (HAARP) facility in order to physically simulate the process of AGW/TID generation by large-scale thermal gradients in the ionosphere. In these ionospheric HF heating experiments, we create some time-varying artificial thermal gradients at an altitude of 200-300 km above the Earth's surface using vertically-transmitted amplitude-modulated 0-mode HF heater waves. For our experiments, a number of radio diagnostic instruments had been utilized to detect the characteristic signatures of heater-generated AGW/TID. So far, we have been able to obtain several affirmative indications that some artificial AGW/TID are indeed being radiated out from the heated plasma volume during the HAARP-AGW experiments. Based on the experimental evidence, we may conclude that it is certainly quite plausible for large-scale thermal gradients associated with severe heat wave events to generate some AGW which might induce widespread plasma turbulence far in space.by Rezy Pradipta.Ph.D

Case studies of intense ionospheric plasma turbulence associated with natural heat sources

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (p. 97-100).We report on observations of a series of highly-structured ionospheric plasma turbulence over Arecibo on the nights of 22/23 and 23/24 July, 2006. Incoherent scatter measurements by Arecibo radar, airglow measurements using MIT PSFC's all-sky imaging system (ASIS), together with TEC measurements from GPS satellite network provide well-integrated diagnostics of turbulent plasma conditions. Two kinds of turbulent structures were seen as slanted stripes and filaments/quasi-periodic echoes on the range-time-intensity (RTI) plots of radar measurements. Detailed analyses of radar, airglow, and GPS data allow us to determine the drift velocity/direction, the orientation/geometry, and the scale lengths of these plasma turbulence structures. They are large plasma sheets with tens of kilometer scale lengths, moving in the form of traveling ionospheric disturbances (TIDs) southward within the meridional plane or westward in zonal plane at tens of meter per second. The signatures of observed TIDs indicate that they were triggered by internal gravity waves that had reached the altitudes of ionospheric F region. All possible sources producing gravity waves have been examined. We rule out solar/geomagnetic conditions which were quiet, and the atmospheric weather anomalies which were absent, during the period of time for our experiments. It is found that the heat wave fronts, which occurred in US, were plausible sources of free energy generating intense gravity waves and triggering large plasma turbulence over Arecibo. In other words, anomalous heat sources can be responsible for the occurrence of intense space plasma turbulence all over the world. The reported research suggests that global warming may affect the space weather conditions significantly. Further GPS data analysis is outlined as our future efforts to verify some predictions based on the current research outcomes.(cont.) Simulation experiments can be conducted at Gakona, Alaska using the powerful high-frequency active auroral research programs (HAARP) heating facility, to generate gravity waves for the controlled study of concerned intriguing phenomenon.by Rezy Pradipta.S.M

Generation of Artificial Acoustic-Gravity Waves and Traveling Ionospheric Disturbances in HF Heating Experiments

We report the results of our ionospheric HF heating experiments to generate artificial acoustic-gravity waves (AGW) and traveling ionospheric disturbances (TID), which were conducted at the High-frequency Active Auroral Research Program facility in Gakona, Alaska. Based on the data from UHF radar, GPS total electron content, and ionosonde measurements, we found that artificial AGW/TID can be generated in ionospheric modification experiments by sinusoidally modulating the power envelope of the transmitted O-mode HF heater waves. In this case, the modulation frequency needs to be set below the characteristic Brunt–Vaisala frequency at the relevant altitudes. We avoided potential contamination from naturally-occurring AGW/TID of auroral origin by conducting the experiments during geomagnetically quiet time period. We determine that these artificial AGW/TID propagate away from the edge of the heated region with a horizontal speed of approximately 160 m/s.United States. Air Force Office of Scientific Research (grant FA9550-09-1-0391)United States. Office of Naval Research (High-frequency Active Auroral Research Program (HAARP) grant N00014-07-1-0999

ISR detection of enhanced plasma line in ionospheric E-region over Arecibo

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006.Includes bibliographical references (p. 45).A series of incoherent scatter radar (ISR) observation were conducted at the Arecibo Observatory from December 27, 2005 until January 3, 2006. From plasma line measurements that were taken during this radar campaign, we found that plasma line enhancement was quite frequently seen in the ionospheric E-region. We hypothesized that the E-region plasma line enhancement over Arecibo was caused by precipitated electrons from the radiation belts. The precipitated electrons will enhance the population of suprathermal electrons in the E-region. Subsequently, suprathermal electrons will cause excitation of Langmuir waves that could be detected by incoherent scatter radar as plasma lines. In this thesis, we are going to examine and discuss the observed features of E-region plasma line enhancement over Arecibo to test this hypothesis. In addition, a theoretical discussion on Langmuir waves is also presented in a chapter of this thesis. Finally, we also introduce the Spread F Index (SFI) as a convenient bookkeeping method to summarize spread F condition over a certain period of time.by Rezy Pradipta.S.B

Replication Data for Ionospheric Effects during the Total Solar Eclipse over Southeast Asia-Pacific on 9 March 2016

We report the results of our experimental investigation on a number of ionospheric effects that were observed during the total solar eclipse over the Southeast Asia-Pacific region on 9 March 2016. In particular, here we discuss a set of experimental observations that reveal a rapid uplift of the ionospheric F-layer during the eclipse, and prompt reduction of ionospheric plasma density in the areas around the eclipse totality. Data from ionosonde measurements at Biak (in eastern part of Indonesia) and Guam (in the Pacific) indicate an upward vertical drift velocity in the range of 21-40 m/s in the ionospheric F-region during the eclipse. Over Biak, foF2 decreased from 10 MHz to 6 MHz (a 40% reduction) during the eclipse. Meanwhile, foF2 over Guam during the eclipse was suppressed for a few hours; lower than the 7-day average normal level by 3 MHz. A comparison with the total electron content (TEC) data from MIT Haystack Observatory's Madrigal Database further confirms the findings from these ionosonde measurements. In addition, observational data from an HF radio link between Biak and Manado (~1300 km apart, cutting across the eclipse totality trajectory) also indicate that the D-region ionosphere had diminished considerably during the solar eclipse. We attribute these eclipse-related ionospheric effects to the interruption of solar photoionization within the eclipse totality, and to the consequential disruption of the background ionospheric current by the localized ionospheric density reduction --- which leads to a build-up of polarization electric field that gives rise to an upward vertical plasma drift. We report some key findings from our experimental observations and data analyses on a number of ionospheric effects that had occurred during the total solar eclipse over the Southeast Asia-Pacific region on 9 March 2016. Specifically, here we present the observations of traveling ionospheric disturbances (TIDs) likely to have been caused by the passage of the total solar eclipse in the region. Moreover, we also discuss the observed spatio-temporal pattern of changes in the total electron content (TEC) distribution in the areas traversed by the eclipse totality. Signatures of eclipse-related TIDs were seen in the Doppler signals from ionosonde measurements at Guam, and in the TEC perturbation (TECP) signals from several GPS receiver stations in eastern part of Indonesia. These TIDs were observed at F-region heights with a period of 30-45 minutes, Doppler velocity amplitude of 15 m/s, and TEC fluctuations of 0.3-0.4 TECU. In addition to the TID signatures, the data from GPS receiver stations also show that the level of absolute TEC was significantly affected by the passage of the eclipse. TEC reductions in the range of 10-14 TECU were observed over the eastern part of Indonesia and over Guam. In the surveilled areas, the TEC reduction due to the solar eclipse was generally found to be more prominent at the coordinate points located further east --- closer to the point of greatest eclipse duration in the middle of the Pacific. We posit that the variability in the TEC reduction (as well as the non-uniformity in the TID wave patterns) during the eclipse was caused in part by the varying lunar shadow speed at different parts of the eclipse trajectory

Unseasonal development of post-sunset F-region irregularities over Southeast Asia on 28 July 2014: 1. Forcing from above?

Abstract This contribution is the first of a two-part investigation into an unseasonal post-sunset equatorial F-region irregularity (EFI) event over the Southeast Asian region on the evening of 28 July 2014. Ground-based GPS scintillation data, space-based GPS radio occultation (RO) data, and ionosonde data show the existence of EFIs shortly after sunset over a region spanning 30° in longitude and 40° in latitude, centered on the geomagnetic equator. This post-sunset EFI event was observed during a time of the year when post-sunset equatorial plasma bubbles (EPBs) are very infrequent in the Southeast Asian longitude sector. GPS RO data shows that the EFI event over Southeast Asia coincided with the suppression of peak-season EPBs in the African and Pacific longitude sectors. Ionosonde data shows the presence of a strong pre-reversal enhancement (PRE) in the upward plasma drift over Southeast Asia prior to the detection of EFIs. Further, it is reported that this PRE was significantly stronger than on any other day of July 2014. An analysis of the geophysical conditions during this event reveals that this enhanced PRE was not caused by disturbed geomagnetic activity. Therefore, it is hypothesized that forcing from lower altitudes, perhaps tidal/planetary waves, was the potential cause of this strong PRE, and the subsequent EPB/EFI activity, on this day over the Southeast Asian sector