Current Research Projects
Ionospheric Connection Explorer (ICON)
Led by Dr. Thomas Immel of the University of California, Berkeley, was launched in 2019, ICON probes the extreme variability of Earth’s ionosphere with in-situ and remote-sensing instruments from its orbit 550 kilometers (345 miles) above Earth. The ionosphere is the region at the edge of space where the sun ionizes the air to create constantly shifting streams and sheets of charged particles. Fluctuations in the ionosphere, which are a form of space weather, cause interference in signals from communications and global positioning satellites. Such space weather effects are deleterious to numerous electronic technologies on which modern society relies and as a result can have a significantly adverse economic impact on the nation.
ICON collects data needed to establish the connection between space-weather storms in the ionosphere and storms that occur closer to Earth’s surface, allowing scientists to better predict space weather. These results could help airliners, for example, which today cannot rely solely on GPS satellites to fly and land because signals from these satellites can be distorted by charged-particle storms in the ionosphere.
We are working on the analysis and interpretation of the scientific data that will come from the four science instruments on ICON, including the MIGHTI and FUV instruments. These instruments will provide measurements of both the neutral atmosphere and the electrified ionosphere needed to understand the connection between our weather and space weather.
As NASA’s oldest continuous program, the Explorer program has launched more than 90 missions since 1958, including Explorer 1 which discovered the Earth’s radiation belts and the Nobel Prize-enabling mission Cosmic Background Explorer (COBE) mission. It is designed to provide frequent, low-cost access to space for principal investigator-led space science investigations relevant to the heliophysics and astrophysics programs in NASA’s Science Mission Directorate in Washington.
Collaborative Research: DASI Track 2: An optical network to study the vertical propagation resulting in spatio-temporal variability in the thermosphere
While a key science challenge of this decade is to “determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs”, [National Research Council, 2012], the complex interactions, coupled with the sheer vastness of the geospace system, make it difficult to address this challenge. The global whole-atmosphere models have been able to produce the state of this coupled system in a statistical sense, yet the ability to reproduce or validate the instantaneous or small-scale dynamics is missing. This is primarily due to unavailability of key measurements of geophysical parameters characterizing plasma and neutral dynamics at various scales. Much about the neutral dynamics has been learned by measuring atomic oxygen as it is a dominant species in the thermosphere. However, historically the measurements have been conducted by stand-alone instruments with limited coverage and the large-scale system dynamics are not captured. We propose to create a distributed network of all-sky airglow imagers and Fabry-Perot interferometers measuring atomic oxygen nightglow and neutral winds to enable investigations of plasma-neutral dynamics caused both by lower atmospheric and magnetospheric forcing across a range of spatial and temporal scales in the mid- latitude region. The proposed network infrastructure will contain ten OI 557.7 nm airglow imagers in the southwestern United States, forming a contiguous field-of-view spanning 15-20 degrees in latitude/longitude, three FPIs with combined OI 630.0 nm and 557.7 nm capabilities, and augmentation of a previously deployed network of 630.0 nm imagers across the continental US extending into northern Mexico. The new combined network will provide overlapping 630.0 nm and 557.7 nm airglow images between approximately 25-45 degrees N, and 95-120 degrees W geographic regions, in addition to the thermospheric temperatures and neutral wind fields from the three FPIs. The data products will be made publicly available through a project website, the Madrigal database, and the NSF-funded Integrated Geosciences Observatory (InGeO) collaborative platform, and software products through a GitHub repository under an open source license.
Past Research Projects
CEDAR Collaborative Proposal: Casual Relationships of Ion-Neutral Coupling Processes at Mid-Latitudes
This project will address two fundamental questions: 1) What is the cause/effect relationship between high-latitude forcing on the neutral winds and the response of electron densities at mid-latitudes, especially during geomagnetic storm conditions? 2) What is the relationship between spatial/temporal variability within the high-latitude drivers and the variability observed within the mid-latitude neutral winds and ionospheric structure? Observations of mid-latitude thermospheric winds and temperatures made by the North American Thermosphere-Ionosphere Observation Network (NATION) of Fabry-Perot interferometers (FPI) will be coupled with time-dependent 3D electron density estimates from the Ionospheric Data Assimilation Four Dimensional (IDA4D) assimilative model. The source of the dynamics observed in the thermospheric neutral winds and electron density will be investigated through exercising an inversion algorithm (Estimating Model Parameters from Ionospheric Reverse Engineering; EMPIRE) developed to estimate the ionospheric drivers from three-dimensional, time-evolving distributions of ionospheric electron densities. The first-principles Global Ionosphere Thermosphere Model (GITM) will also be used to elucidate the underlying physics responsible for the coupling. This study will contribute to the education and training of graduate students at the University of Illinois and the University of Michigan.
Hazards SEES: GIC Hazard Prediction: From the Solar Wind to Power System Impacts
Led by Dr. Thomas Overbye of the University of Illinois at Urbana-Champaign, this project is intended to improve the scientific understanding of the processes governing the impacts on our power distribution system of severe solar storms. The team is studying the relationship between solar wind drivers and magnetic field perturbations on the ground, developing improved models of induced electric fields, and enhancing prediction capabilities for GIC hazards. The team is developing algorithms that both advance the science of induced electric fields and operate as a predictive tool of GIC hazards in the bulk power system, including transformer heating and damage and loss of voltage stability. Impact models are being developed, enhanced, and validated to provide better prediction of the effects of GMDs on power systems for both real-time response and longer-term resilience.
Imaging Earth’s Near-Space Environment for Better Understanding of Ionospheric Spatial Structuring
We operate a network of ground-based ionospheric imaging systems. Current locations include Hawaii, Tahiti, Chile, Brazil, and Morocco. These images provide detailed information on the spatial distribution of plasma in the ionosphere. Under the correct geophysical conditions, irregularities in the ionosphere, known as equatorial plasma bubbles (EPBs), can form in the nighttime ionosphere. EPBs are easily imaged by these ground-based sensors (e.g., Makela and Miller, 2011; Makela et al., 2010; Makela, 2006) and have been shown to coexist with regions of the ionosphere that ￼cause scintillations on trans-ionospheric radio signals (e.g., Miller and Makela, 2008; Ledvina and Makela, 2005), causing these radio links to be unusable. Thus, being able to image and characterize these regions is of primary importance to ensure reliable communication and navigation channels.
In this project, we utilize data collected by this network of imagers to study the properties of EPBs and participate in the Defense Meteorological Satellite Program (DMSP) CalVal effort by validating the ability of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) on the DMSP vehicles to observe EPBs. Preliminary work (Kelley et al., 2003) comparing ground-based images and the precursor instrument to SSUSI (the Global Ultraviolet Imager on NASA’s Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics satellite) are shown in the figure and demonstrate the ability of the ground-based imager to validate the space-based observations.
Vertical Winds: Possible Forcing and Influence on the Upper Atmosphere
The overall goal of this project is to improve the description of the dynamics in the upper atmosphere associated with vertical winds and to advance our understanding of the coupling between the ionosphere and thermosphere, which can significantly influence the variation of the neutral density. Specifically, the goals are:
(1) Analyze FPI vertical wind observations at F-region altitudes in the aurora zone.
(2) Simulate vertical winds in the cusp during storm periods with GITM in high resolution.
(3) Process data of FPI observations at F-region heights from equatorial Brazil and conduct a climatological study of vertical wind at low latitudes for the first time.
(4) Investigate the influence of vertical wind caused by the perpendicular ion-drag force on the equatorial thermosphere anomaly (ETA) for the first time using the non-hydrostatic GITM.
Observation and modeling of tsunami-generated gravity waves in the earth’s upper atmosphere
In the aftermath of the large Tohoku earthquake on 11 March 2011, a tsunami was launched across the Pacific Ocean. As the wave approached the islands of Hawaii, a wide-angle imaging system on the Haleakala Volcano operated by the University of Illinois in collaboration with Cornell University obtained the first-ever optical images of waves in the ionosphere/ thermosphere system linked to an underlying perturbation on the ocean. The ocean-ionospheric coupling associated with tsunamis had been predicted as early as the 1970s and had been observed previously by various radio frequency techniques, including large arrays of groundbased Global Positioning System (GPS) receivers [e.g., Liu et al., 2006; Lognonné et al., 2006; Rolland et al., 2010]. However, the observations of Makela et al.  confirmed that these waves have an optical signature, opening up exciting new avenues for studying oceanatmosphere coupling mechanisms. These observations represented a breakthrough for two primary reasons. First, using a single wide-angle imaging system, a 1000°—1000 km2 region of the ionosphere/thermosphere system can be observed. In contrast, previous results using the GPS technique required arrays of receivers, and the quality of the resultant GPS “image” was directly related to the number of receivers in the array. As such, the coverage over islands with only a few GPS receivers, such as Hawaii, resulted in very poor coverage. Secondly, the demonstration of the ability to observe the tsunami signature in the airglow layers opens up the possibility of creating a detection system utilizing a satellite-based imaging system, which would provide continuous monitoring capabilities for large portions of the globe for tsunamis in real time.
Although these observations confirmed the existence of the tsunami airglow signature first predicted by Hickey et al. , much work is still needed in order to fully understand the coupling mechanism and allow for the development of an effective satellite-based tsunami detection/warning system. These challenges include the need for:
- additional observations of the tsunami ionospheric signature to better constrain the conditions under which ocean-atmospheric coupling is effective;
- creation of efficient detection algorithms to analyze optical data in (near) real time in order to detect tsunami signatures in the airglow; and
- development of a more realistic ocean-atmosphere coupling model that can be used to study the physical mechanisms responsible for the coupling as well as to simulate potential viewing modalities and test detection algorithms.
The observations described in Makela et al.  were made using a wide-angle imaging system located atop the Haleakala Volcano on Maui, HI. The pertinent observations were obtained using a narrowband (2.0-nm FWHM) filter centered at 630.0 nm, an emission sensitive to density and height fluctuations of the ionospheric layer. A detailed analysis utilizing a block of FIR filters was performed to extract the tsunami-related waves in the images, such as the one shown to the right, which reveals the presence of several tsunami-related waves as greyscale features. Overlain on this figure is a red curve showing the location of the ocean tsunami at the time of the image. The arrival directions, timing, periods, and velocities of the waves in the ionosphere all matched those of waves present in the underlying tsunami wave, confirming their linkage [Makela et al., 2011]. In addition, several detailed structures matched those predicted from a simple, non-viscous, three-dimensional gravity wave model [Occhipinti et al., 2011]. Through this single observation, we have confirmed that the wide-angle optical imaging systems we typically deploy to study ionospheric irregularities, such as equatorial plasma bubbles and medium scale traveling ionospheric disturbances, do indeed have the sensitivity to observe the small (5%) fluctuation in the 630.0-nm emission caused by AGWs generated by a tsunami. In addition, we have developed filtering techniques that can be applied to analyze the properties of the waves and compare them to the underlying properties of the source tsunami. However, this single example is not enough to effectively constrain the physics-based models required to understand the complex physical process at play, nor can it inform the development of more efficient analysis algorithms. Additional observations and more detailed data-model comparisons using more realistic models are, thus, required.
The North American Thermosphere-Ionosphere Observing Network
The North American Thermosphere Ionosphere Observing Network (NATION), comprising a new network of Fabry-Perot interferometers (FPIs), will be deployed in the Midwest of the United States of America. FPIs will initially be deployed to four sites to make coordinated measurements of the neutral winds and temperature in the Earth’s thermosphere using measurements of the 630-nm redline emission. The observing strategy of the network will take in to account local observing conditions and common volume measurements from multiple sites will be made in order to estimate local vector wind quantities. The network is expandable, and as additional FPI sites are installed in North America, or elsewhere, the goal of providing the upper atmospheric research community with a robust dataset of neutral winds and temperatures will be achieved.
Each site in the initial NATION deployment has been chosen for having relatively good observing conditions as well as ease of access. The sites each have Internet access, allowing for their operation as a single distributed sensing network. The typical observing strategy will be to coordinate observations of the CV locations shown in the Figure. Typical integration times will be on the order of 3 minutes for each operation, but will be dynamically determined based on the actual observing conditions. The sequences of observations will be specified depending on the goals of a given experiment. High temporal resolution (~3 minutes) could be obtained by continually observing the same common volume points. The resulting temporal resolution would allow for the tracking of dynamic features in the thermosphere, such as TADs or gravity waves. Alternately, observing all of the available orthogonal common volume locations, resulting in the largest spatial coverage, could be achieved in a sequence taking less than 30 minutes. Thus, there is a trade off between spatial coverage and temporal resolution.
The initial NATION sites are located at the University of Illinois (UI), the Pisgah Astronmoical Research Institute (PARI), Peach Mountain near the University of Michigan (UM), and Eastern Kentucky University (EKU).It is important to note that the NATION concept is fully scalable and is expected to expand as additional instruments are deployed to new sites. Additional FPIs will soon be deployed in New Jersey and New Mexico, providing important longitudinal diversity to the NATION measurements that will be useful in studying, among other topics, the penetration of mid-latitude tidal structure into thermospheric dynamics.
Each site will also have a Boltwood cloud sensor, from which the local viewing conditions can be made. These conditions will be taken in to account as the realtime observing strategy for NATION is determined. For example, if one site is determined to be clouded over, a common volume (CV) observing strategy involving that site will not be made, allowing for a higher temporal cadence for the other CV locations. In the event that no CV observations are possible from a given site due to cloud conditions at the other sites, a site would revert to a cardinal direction observing mode.
The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR)
The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) project is a joint collaboration between researchers from several institutions, including The University of Illinois at Urbana-Champaign, Clemson University, Cornell University, the Brazilian National Institute for Space Research (INPE) and the Federal University at Campina Grande (UFCG). Through the construction and deployment of a RENOIR station, we hope to come to a better understanding of the variability in the nighttime ionosphere and the effects this variability has on critical satellite navigation and communication systems.
The instruments included in a RENOIR station allow for the study the ionospheric effects caused by equatorial plasma instabilities and thermosphere-ionosphere coupling. These two areas are critical to characterizing the ionosphere and the effects it can have on radiowave propagation. The occurrence of equatorial plasma instabilities, commonly referred to as equatorial spread-F, equatorial plasma bubbles, or depletions, can cause radio signals propagating through the disturbed region to scintillate. This results in a fade in received signal power translating to a loss of the signal. Scintillations on frequencies from several GHz and below are known to occur and are a concern to many sectors, both civilian and military. The is demonstrated in the figure to the right, which shows data collected from a collocated imaging system and GPS SCINTMON on the Haleakala Volcano on Maui, HI. Scintillations are seen (as an increase in the S4 index in the top-right panel) when the look direction from the receiver to the satellite (the green square on each image) passes through the dark region of the image.
As this system is highly dynamic, with both the satellites and the airglow depletions in motion, it is sometimes better to visualize the data using a movie. This movie shows images collected by two imaging systems on the Haleakala Volcano and tracks three different GPS satellites. As with the image above, the scintillation index (S4) increases when the look direction passes through the depleted regions of the images.
Since the first observations of these instabilities in the late 1920s, much has been learned. We have gained a general understanding of the seasons when they are most likely to occur for a given location. For example, two year’s worth of occurrence statistics is summarized in the image to the left for the data collected from the Haleakala Volcano. The enigma comes from the fact that for a given location and season conducive to the growth of the instability, on a day-to-day basis, we are not very good at predicting if it will actually occur. In other words, within the “spread-F” season of a given location, instabilities do not always occur. The converse is also true, in that we sometime will see instabilities outside of the typical season for a given location. Understanding this day-to-day variability has become a highly active area of research in the ionospheric community, and much work remains to be done before we have a complete understanding of this phenomenon.
The equipment comprising a single RENOIR station will consist of:
- one wide-field ionospheric imaging system,
- two miniaturized Fabry-Perot interferometers (FPI),
- a dual-frequency GPS receiver,
- an array of five single-frequency GPS scintillation monitors.
The wide-field imaging system will be used to characterized the two-dimensional (latitude vs longitude) structure of the depletions. This will be done by measuring the natural emissions occurring in the ionosphere at wavelengths of 630.0 and 777.4 nm. The two FPI systems will be used to measure the background thermospheric neutral winds and the neutral temperature. From the FPI data, we will be able to deduce what, if any, control neutral dynamics have on the development of these irregularities. Two systems are included so we can field them at sites separated in latitude in order to study wind gradients and gravity waves known to be present in the thermosphere. The dual-frequency GPS receiver is used to characterize the electron density present in the ionosphere. This data will be used to deduce how the background electron density affects the development of irregularities. Having a GPS receiver collocated with the other equipment is crucial as the severe gradients associated with the depletions can create ambiguities when using data from instruments separated by even a relatively short distance. The array of single-frequency GPS receivers will be used to measure the drift velocities of the small-scale irregularities internal to the large-scale plasma depletions observed by the imaging system. In this way, we will be able to deduce how the internal velocities of the small-scale irregularities relate to the overall drift velocity of the depletions and the background thermospheric neutral wind. The GPS equipment will also be used to characterize the adverse effects these irregularities have on L-band transionospheric signals.
In May 2009, the installation of the RENOIR equipment was completed by Prof. Makela, Prof. Meriwether, and two students (graduate students from UI and Clemson University) in collaboration with Brazilian colleagues from INPE and UFCG. The two sites, Cajazeiras (geographic: -6.89 N, -38.56 E; geomagnetic: -5.75 N, 32.97 E) and Cariri (geographic: -7.39 N, -36.53 E; geomagnetic: -6.81 N, 34.69 E), are located in eastern Brazil. This region of Brazil was selected in order to accomplish the scientific goals of RENOIR by locating the equipment under the bright equatorial anomaly region south of the magnetic equator. This will increase the optical signal measured by the FPI and imaging systems, while also maximizing the effects that the equatorial plasma bubbles will have on trans-ionospheric wave propagation. This region is arid and skies are particularly clear during the winter dry season and has prooven to be conducive to optical observations in past campaigns. Data collected can be viewed in our database.
Data from Brazil have been collected since 2009. This has encompassed both deep solar minimum conditions through the current rise towards solar maximum. As such, the results represent a unique and near-continuous characterization of the temperatures and neutral winds at low latitudes. Summaries of the collected data are found below.
Future Deployment Scenarios
As additional funding and instrumentation become available, we are interested in constructing and fielding addition RENOIR stations in collaboration with the United Nations International Space Weather Initiative (ISWI). We are particularly interested in deployment possibilities in Africa. Ideally, the RENOIR stations would be fielding in Africa at a longitude of approximately 7 degrees from the magnetic equator. Scientists who are interested in collaborating in hosting a RENOIR station are encouraged to contact Professor Jonathan J. Makela.
The instrumentation that make up a RENOIR station have all been used in the field in previous experiments and are at a moderately mature level of development. The optical systems can be housed in individual, self-contained housing units, requiring very little infrastructure. If an optical facility is available at a host institution, the optical equipment could easily be modified to interface with available optical domes. The facility should be located in a region with relatively dark skies (away from any major cities) and away from any tall structures (buildings and trees). If two Fabry-Perot interferometers are to be fielded, the second system should be located approximately 300 km away from the main site. The dual-frequency GPS receiver is quite rugged and simply requires a location to mount the antenna and minimal space to locate the control computer. The array of single-frequency GPS scintillation monitors requires a space of approximately 100 m x 100 m over which to space the 5 antenna in a cross formation. Again, minimal space is needed to locate the control computers for each receiver. The facility should be located away from any tall strucutres (buildings and trees).
This material is based upon work supported by the National Science Foundation under Grant Number (AGS-0940253). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Parties interested in collaborating in the RENOIR project are encouraged to contact Professor Jonathan J. Makela. We are actively seeking partners who are interested in hosting a RENOIR station. The requirements for potential sites are described above.
Specification of Nighttime Ionospheric Irregularities: Occurrence, Spatial, and Dynamic Properties
In this project, we will develop automated analysis algorithms to extract pertinent spatio-temporal properties of ionospheric structures from an imaging database collected over the previous solar cycle. Effects on trans-ionospheric radiowave propagation will be studied using collocated radio (GPS) measurements. A database of structure occurrence, drift velocity, widths, and altitudes as a function of longitude, season, and solar cycle will be created and analyzed. The analysis routines will be developed such that they can be run in near real-time as part of an ionospheric structure specification network.
Studying nighttime ionospheric irregularity processes at low latitudes has become a major focus of the space weather and Aeronomy communities over the past decade. This is due to the recent proliferation of space-based assets, such as satellite communication and navigation systems, and our increasing reliance on such systems, both for civilian and military purposes. Irregularities in the ionosphere can cause these systems to become temporarily unreliable or unusable. Current specification methodologies rely on climatology-based metrics, such as the known longitudinal, seasonal and solar-cycle dependence of these structures at low-latitudes. These climatologies have been developed over decades of data collection, primarily based on scintillation measurements from radio receivers (e.g., Aarons et al., 1993, Makela et al., 2004) or from in-situ satellite measurements (e.g., Gentile et al., 2006). However, little attention has been given to the spatio-temporal properties of the individual irregularity regions, which have a pronounced affect on which transmitter-receiver channels are available/unavailable. This lack of attention is primarily driven by the available datasets and the information that can be extracted from them. For example, ground-based radio receivers measure integrated effects of the irregularities along a single line-of-site to a given satellite transmitter. Information on the spatial extent of the scintillation-causing irregularities cannot easily be gleaned from such point measurements, as the structures can be extended in several hundreds of kilometers in the meridional direction and tens of kilometers in the zonal direction. Arrays of radio receivers, such as dual-frequency GPS receivers, can be used to create a map of depletion structure (Lee et al., 2008), but there are very few suitably dense arrays in the world currently operating and the obtainable spatial/temporal resolutions obtained by such techniques is limited.
Imaging is the only observing modality that can easily provide high-resolution measurements of the spatio-dyamical properties of two-dimensional (latitude/longitude) ionospheric structures. Using an all-sky imaging system, such as the Portable Ionospheric Camera And Small-Scale Observatory (PICASSO) developed at the Naval Research Laboratory, observations of nighttime ionospheric structures can be obtained at spatial resolutions on the order of 1 km and temporal resolutions of 90 s over a 1000 km × 1000 km area. Higher resolution images (sub-km spatial resolution) can be obtained over smaller areas using a modified PICASSO system with a smaller field of view. Images obtained from these, and similar, systems show incredible spatio-temporal dynamics as ionospheric structures develop, drift, and decay over time. These dynamics have a direct affect on which transmitter-receiver links are available at a given time. Thus, a better understanding and specification of these properties will lead to more robust communication schemes in both the civilian and military regimes.
Over the past seven years, we have amassed a large dataset of optical and collocated radio observations of ionospheric irregularities from several locations. In the proposed work, we would develop automated analysis algorithms to extract pertinent spatio-temporal properties of ionospheric structures from the imaging database. Effects on trans-ionospheric radiowave propagation would be studied using the collocated radio (GPS) measurements. A database of structure occurrence, drift velocity, widths, and altitudes as a function of longitude, season, and solar cycle would be created and analyzed. The analysis routines would be developed such that they could be run in near real-time as part of an ionospheric structure specification network. In addition, if optional funding were provided, we would conduct a ground campaign in New Mexico to study the linkage between lightning, gravity waves in the mesosphere and the occurrence of mid-latitude structure in the ionosphere. This would provide valuable insight into the linkage of different atmospheric regions and the upward coupling of energy which is believed to have a significant impact on the ionosphere.
Multi-Instrument Study to Investigate the Formation and Growth of Equatorial Irregularities
In this project, we will analyze data to be obtained from a distinctive suite of optical instruments located throughout South America in order to advance our understanding of the generation and development of Equatorial Spread-F (ESF), a plasma instability known for disrupting radio communications and GPS signals near Earth’s magnetic equator. These data include:
- the first ever 24-hour thermospheric and mesospheric winds and temperatures observed by the Second-generation Optimized Fabry-Perot Doppler Imager (SOFDI) to be located at Huancayo, Peru in the fall of 2007,
- nighttime thermospheric and mesospheric all-sky imagery from the Cornell All-Sky Imager co-located with SOFDI,
- nighttime thermospheric winds and temperatures observed by Fabry-Perot interferometry from Arequipa, Peru, and
- nighttime thermospheric narrow field-of-view sky imagery from an imager located near La Serena, Chile.
The data from these instruments, along with supporting data from the Jicamarca Radio Observatory and the results of gravity wave modeling efforts, will be analyzed in a synoptic manner. Distinctive quantitative information will be gained on the behavior of the key parameters responsible for the onset and strength of ESF. These results will be invaluable for ground-based validation of the measurements to be obtained by the Communication/Navigation Outage Forecasting System as implemented in part by the Air Force Research Laboratory. This proposed study is unique in that it involves collaborative data sets never before used to simultaneously study a common volume during ESF formation. The measurements of the thermospheric and mesospheric winds will be the first of their kind at low latitudes during the sunset period, which is believed to be the crucial period for ESF development. Such information will advance our understanding of the plasma physics along Earth’s magnetic equator by providing fundamental thermospheric base-state parameters. It will also further the state-of-the-art of ESF prediction providing much improved specifications of the space environment and its impact on space systems.
CAREER: Multi-Technique Study of Ionospheric Irregularities at Mid-Latitudes
Traditionally, it was thought that the only highly active portions of the terrestrial ionosphere lay at high and low latitudes. In the polar region, the magnetic field is coupled to the magnetosphere and interstellar medium, allowing energy to flow directly into the ionosphere. This coupling results in many phenomena, most familiarly the aurora, and can create a very turbulent state leading to intense scintillations on trans- ionospheric radio signals. At low latitudes, the nearly horizontal magnetic field is conducive to the generation of irregularities by the generalized Rayleigh-Taylor instability. The requirements for this mechanism are met in the post-sunset equatorial ionosphere, resulting in the explosive release of the stored gravitational energy in the ionosphere. Irregularities across many decades of scale sizes (centimeters to kilometers) develop and an intense scintillation environment is created, leading to communication and navigational outages. In contrast to these highly active regions, the mid-latitude ionosphere has generally been considered benign and quiescent. However, as more technology and infrastructure located in this latitude range becomes dependent on satellite-based systems, it is important to study this region in greater detail. Recent experiments indicate that severe space weather can indeed occur at mid-latitudes. For example:
- A campaign carried out in the Caribbean during the later portion of the 1990s showed conclusive evidence that severe gradients in electron density, rivaling those seen at low latitudes, can exist in the nighttime mid-latitude ionosphere (Makela et al., 2000).
- During the major magnetic storms that occurred near the end of 2003, localized “plumes” of enhanced total electron content (TEC) were observed to develop over the contiguous United States (CONUS), surging from the south. These plumes severely degraded the accuracy of the GPS system (Doherty et al., 2004) and led to scintillations over CONUS (Basu et al., 2005). Similar structures have been observed during other major magnetic storms (e.g., Foster et al., 2002, 2004) extending from the Caribbean, through CONUS, to the polar region.
- An extreme event of the Rayleigh-Taylor instability was observed at the beginning of October 2002 using the incoherent scatter radar (ISR) at the Arecibo Observatory in Puerto Rico, where the instability is generally believed not to occur (Nicolls and Kelley, 2005).
These case studies, as well as several others over the years, indicate without a doubt that the mid-latitude ionosphere can awaken from its typical dormancy and behave as violently as that at high and low latitudes. Only recently has the space science community begun to operate enough equipment at mid-latitudes to systematically observe these phenomena. This has primarily been driven by the explosion of satellite- based technologies, both in civilian and military settings, over the past decade. For example, the Federal Aviation Administration (FAA) has implemented, and declared operational, the Wide Area Augmentation System (WAAS), used to aid commercial airline navigation. During times of intense geomagnetic activity,the severe gradients that occur in the ionosphere over CONUS can force the WAAS system to shut down (e.g., Doherty et al., 2004). Similarly, with the increased use of HF and higher frequencies for communications, an uncharacterized and unexpected development of ionospheric structure can lead to a temporary loss of that communication channel (e.g., Groves et al., 1997). What is proposed is to deploy a suite of complimentary instruments to two sites in the Caribbean that will observe and characterize the space weather that occurs at the transition from low- to mid-latitudes. The instruments will augment those already in place at the Arecibo Observatory in Puerto Rico, vastly increasing the amount of the ionosphere that can be simultaneously observed. Measurements will be made over several years to gain a better understanding of the background conditions conducive to local irregularity growth and coupling of the low- and mid-latitude ionosphere. Equipment will be characterized, deployed, and maintained with the assistance of students, providing valuable hands-on engineering experience. The specific scientific questions to be addressed under this proposal are:
- What are the physical extent, seasonal properties, and lifetimes of nighttime F-region structures observed over the Caribbean? This will be accomplished using the extended fields of view provided by the two ionospheric imaging systems to be deployed in conjunction with the Arecibo facility imaging system. A long-term database needs to be constructed to make progress on detailing the morphology of these structures. Thus, the equipment will remain in the field for several years.
- What is the genesis region and mechanism for the different types of structures present in the nighttime F-region ionosphere? Do they grow locally, or are they coupled from low latitudes? What effect on trans-ionospheric radio wave propagation do these irregularities have? Progress on this front will be made possible by combining the extended fields of view of the various imaging systems (to study the genesis region) with quantitative data on the background ionospheric conditions provided by the incoherent scatter radar and Fabry-Perot interferometer at the Arecibo Observatory.
- Are the enhancements in electron density commonly seen in the American sector during severe geomagnetic storms effective in creating scintillations on critical trans-ionospheric radio links? Information gathered from the GPS receivers deployed under this proposal will be used to study these effects. The receivers will also serve to bridge the gap in GPS coverage between South America and CONUS. When storms occur in the local night sector, the imaging systems will be used to study any resultant structuring in the ionosphere.
Two types of instrumentation will be deployed to study the mid-latitude ionosphere under this project:
- a wide-field ionospheric imaging system,
- a dual-frequency GPS receiver capable of making 50-Hz scintillation measurements.
The wide-field imaging system will be used to characterized the two-dimensional (latitude vs longitude) properties of the ionospheric structure. This will be done by measuring the natural emissions occurring at wavelengths of 630.0 and 777.4 nm. The imaging system to be used is called the Portable Ionospheric Camera and Small-Scale Observatory (PICASSO) and is a miniaturized version of systems that have been used in the past. The reduction in size allows for easier deployment and the need need for minimal infrastructure. These systems have been successfully deployed in the US, S. America, and the Pacific sectors. The dual-frequency GPS receiver is used to characterize the electron density present in the ionosphere. The system to be deployed is a NovAtel GSV4004B, modified by GPS Silicon Valley. This data will be used to deduce how the background electron density affects the development of irregularities. Having a GPS receiver collocated with the PICASSO is crucial as the severe gradients associated with the depletions can create ambiguities when using data from instruments separated by even a relatively short distance. The high-rate (50-Hz) data collected by the receiver will be used to characterize the adverse effects these irregularities have on L-band transionospheric signals. In addition to the instrumentation that will be deployed specifically for this project, we intend to collaborate with colleagues at the Arecibo Observatory to utilize the ISR, GPS receivers, Fabry-Perot interferometers (FPI), and all-sky imaging system located there. The ISR and FPI will be especially useful in constructing the physical framework in which the irregularities being studied occur. They will provide information on the background electron densities, electric fields, and neutral winds that are not obtainable from the other instruments.
The previous Caribbean Ionospheric Campaigns focused on fielding instrumentation near the island of Puerto Rico in order to take advantage of the Arecibo ISR. One of the limitations of these campaigns was that most of the time, structure drifted into the fields of view of the instruments fully developed. This made determining the seeding region and mechanisms impossible.
In order to address this deficiency, we have installed instrumentation at two new locations in the southern Caribbean for this study. The first site, operated in conjunction with the University of the West Indies, is located in Trinidad. The second is located on the island of Bonaire. Combined with the imaging system operating at the Arecibo Observatory, an unprecedented view of the ionosphere over the Caribbean can be obtained.
We are actively collecting and analyzing data to find events to study. You can view the data collected to this point by browsing through our database.
This project is funded through a grant from the US National Science Foundation.