Jeff Klenzing | NASA Goddard Space Flight Center (original) (raw)

Papers by Jeff Klenzing

Research paper thumbnail of Exploring the role of ionospheric drivers during the extreme solar minimum of 2008

Annales Geophysicae, Dec 2013

During the recent solar minimum, solar activity reached the lowest levels observed during the spa... more During the recent solar minimum, solar activity reached the lowest levels observed during the space age, resulting in a contracted atmosphere. This extremely low solar activity provides an unprecedented opportunity to understand the variability of the Earth's ambient ionosphere. The average E × B drifts measured by the Vector Electric Field Instrument (VEFI) on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite during this period are found to have several differences from the expected climatology based on previous solar minima, including downward drifts in the early afternoon and a weak to non-existent pre-reversal enhancement. Using SAMI2 (Sami2 is Another Model of the Ionosphere) as a computational engine, we investigate the effects of these electrodynamical changes as well as the contraction of the thermosphere and reduced EUV ionization on the ionosphere. The sensitivity of the simulations to wind models is also discussed. These modeled ionospheres are compared to the C/NOFS average topside ion density and composition and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate average NmF2 and hmF2. In all cases, incorporating the VEFI drift data significantly improves the model results when compared to both the C/NOFS density data and the F3/C GOX data. Changing the MSIS and EUVAC models produced changes in magnitude, but not morphology with respect to local time. The choice of wind model modulates the resulting topside density and composition, but only the use of the VEFI E × B drifts produces the observed post-sunset drop in the F peak.

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Research paper thumbnail of Using Schumann Resonance Measurements for Constraining the Water Abundance on the Giant Planets—Implications for the Solar System's Formation

ABSTRACT The formation and evolution of the solar system is closely related to the abundance of v... more ABSTRACT The formation and evolution of the solar system is closely related to the abundance of volatiles, namely water, ammonia, and methane in the protoplanetary disk. Accurate measurement of volatiles in the solar system is therefore important for understanding not only the nebular hypothesis and origin of life but also planetary cosmogony as a whole.

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Research paper thumbnail of Ground and space-based measurement of rocket engine burns in the ionosphere

Abstract On-orbit firings of both liquid and solid rocket motors provide localized disturbances t... more Abstract On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams.

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Research paper thumbnail of Performance of the IRI-2007 model for equatorial topside ion density in the African sector for low and extremely low solar activity

Advances in Space Research, 2013

The recent availability of new data sets during the recent extreme solar minimum provides an oppo... more The recent availability of new data sets during the recent extreme solar minimum provides an opportunity for testing the performance of the International Reference Ionosphere in historically undersampled regions. This study presents averages and variability of topside ionospheric densities over Africa as a function of season, local time, altitude, and magnetic dip latitude as measured by the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The results are compared to the three topside model options available in IRI-2007. Overall, the NeQuick model is found to have the best performance, though during the deepest part of the solar minimum all three options significantly overestimate density.

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Research paper thumbnail of The fixed-bias Langmuir probe on the Communication/Navigation Outage Forecast System satellite: Calibration and validation

Review of Scientific Instruments, Nov 12, 2012

A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument... more A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument (VEFI) suite on the Communication/Navigation Outage Forecast System (C/NOFS) satellite. C/NOFS gathers data in the equatorial ionosphere between 400 and 860 km, where the primary constituent ions are H+ and O+. The ion current collected by the probe surface per unit plasma density is found to be a strong function of ion composition. The calibration of the collected current to an absolute density is discussed, and the performance of the spherical probe is compared to other in situ instruments on board the C/NOFS satellite. The application of the calibration is discussed with respect to future fixed-bias probes; in particular, it is demonstrated that some density fluctuations will be suppressed in the collected current if the plasma composition rapidly changes along with density. This is illustrated in the observation of plasma density enhancements on C/NOFS.

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Research paper thumbnail of Topside equatorial ionospheric density and composition during and after extreme solar minimum

During the recent solar minimum, solar activity reached the lowest levels observed during the spa... more During the recent solar minimum, solar activity reached the lowest levels observed during the space age. This extremely low solar activity has accompanied a number of unexpected observations in the Earth's ionosphere-thermosphere system when compared to previous solar minima. Among these are the fact that the ionosphere is significantly contracted beyond expectations based on empirical models. Altitude profiles of ion density and composition measurements near the magnetic dip equator are constructed from the Communication/Navigation Outage Forecast System (C/NOFS) satellite to characterize the shape of the topside ionosphere during the recent solar minimum and into the new solar cycle. The variation of the profiles with respect to local time, season, and solar activity are compared to the IRI-2007 model. Building on initial results reported by Heelis et al. (2009), here we describe the extent of the contracted ionosphere, which is found to persist throughout 2009. The shape of the ionosphere during 2010 is found to be consistent with observations from previous solar minima.

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Research paper thumbnail of A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multid... more Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave observations in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfvén waves and particle precipitation related to solar and magnetospheric processes. We review ionospheric processes as well as surface and space weather phenomena that drive the coupling between the troposphere and the ionosphere. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface perturbations and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and to solve inverse problems and outline in a final section a few challenging subjects that are important to advance our understanding of tropospheric-ionospheric coupling.

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Research paper thumbnail of Observations of low-latitude plasma density enhancements and their associated plasma drifts

Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by ... more Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed ±15° away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous data have shown that the peak perturbation in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the results in this paper show that the peak perturbation in parallel flow typically occurs 25–100 km to the east of the peak perpendicular flow. The absence of such a longitudinal offset in previous observations suggests that multiple physical mechanisms may be responsible for creating plasma density enhancements as observed by satellite-borne instrumentation.

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Research paper thumbnail of Multi-Instrument Observations of an MSTID over Arecibo Observatory

The Penn State All-Sky Imager (PSASI) at Arecibo Observatory provides planar horizontal context t... more The Penn State All-Sky Imager (PSASI) at Arecibo Observatory provides planar horizontal context to the vertical ionospheric profiles obtained by the Incoherent Scatter Radar (ISR). Electric field measurements from the Communication/Navigation Outage Forecast System (C/NOFS) satellite are mapped down geomagnetic field lines to the height of the airglow layer, allowing multi-instrument studies of field-aligned irregularities with radar, imager, and satellite. A Medium-Scale Traveling Ionospheric Disturbance (MSTID) was observed during such a conjunction near the December solstice of 2009.

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Research paper thumbnail of Monitoring D-region Variability from Lightning Measurements

ursi.org

In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly ... more In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly on sounding rockets. Remote sensing techniques employing Very Low Frequency (VLF) transmitters can provide electron density estimates from subionospheric wave propagation modeling. Here we discuss how lightning waveform measurements, namely sferics and tweeks, can be used for monitoring the D-region variability and day-night transition, and for local electron density estimates. A brief comparison among D-region aeronomy models is also presented.

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Research paper thumbnail of Science of opportunity: Heliophysics on the FASTSAT mission and STP-S26

Aerospace …

The FASTSAT spacecraft, which was launched on November 19, 2010 on the DoD STP-S26 mission, carri... more The FASTSAT spacecraft, which was launched on November 19, 2010 on the DoD STP-S26 mission, carries three instruments developed in joint collaboration by NASA GSFC and the US Naval Academy: PISA, TTI, and MINI-ME. As part of a rapid-development, low-cost instrument design and fabrication program, these instruments were a perfect match for FASTSAT, which was designed and built in less than one year. These instruments, while independently developed, provide a collaborative view of important processes in the upper atmosphere relating to solar and energetic particle input, atmospheric response, and ion outflow. PISA measures in-situ irregularities in electron number density, TTI provides limb measurements of the atomic oxygen temperature profile with altitude, and MINI-ME provides a unique look at ion populations by a remote sensing technique involving neutral atom imaging. Together with other instruments and payloads on STP-S26 such as the NSF RAX mission, FalconSat-5, and NanoSail-D (launched as a tertiary payload from FASTSAT), these instruments provide a valuable “constellation of opportunity” for following the flow of energy and charged and neutral particles through the upper atmosphere. Together, and for a small fraction of the price of a major mission, these spacecraft will measure the energetic electrons impacting the upper atmosphere, the ions leaving it, and the large-scale plasma and neutral response to these energy inputs. The result will be a new model for maximizing scientific return from multiple small, distributed payloads as secondary payloads on a larger launch vehicle.

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Research paper thumbnail of The NSF Firefly CubeSat mission: Rideshare mission to study energetic electrons produced by lightning

Aerospace …

The NSF Firefly CubeSat is a 3U mission designed to perform cutting-edge science, as a secondary ... more The NSF Firefly CubeSat is a 3U mission designed to perform cutting-edge science, as a secondary payload. Firefly will be the first dedicated mission launched to study Terrestrial Gamma ray Flashes (TGFs), their link to lightning, and their effect in producing energetic electrons that may become stably trapped in the inner radiation belt. Firefly demonstrates the capability of small missions such as CubeSat to do important, focused science, with maximal student involvement, and with a minimal budget and available resources. This presentation will focus on the Firefly mission design, as well as important lessons learned in the development, testing, and design. Future developments in CubeSat-class spacecraft for measurements of energetic radiation will be discussed.

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Research paper thumbnail of Observations of DC electric fields in the low-latitude ionosphere and their variations with local time, longitude, and plasma density during extreme solar minimum

DC electric fields and associated E × B plasma drifts detected with the double-probe experiment o... more DC electric fields and associated E × B plasma drifts detected with the double-probe experiment on the C/NOFS satellite during extreme solar minimum conditions near the June 2008 solstice are shown to be highly variable, with weak to moderate ambient amplitudes of ∼1–2 mV/m (∼25–50 m/s). Average field or drift patterns show similarities to those reported for more active solar conditions, i.e., eastward and outward during day and westward and inward at night. However, these patterns vary significantly with longitude and are not always present. Daytime vertical drifts near the magnetic equator are largest in the prenoon sector. Observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects. Enhanced meridional drifts are observed near sunrise in certain longitude regions, precisely where the enhanced eastward flow that persisted from earlier local times terminates. The nightside ionosphere is characterized by larger-amplitude, structured electric fields dominated by horizontal scales of 500–1500 km even where local plasma densities appear relatively undisturbed. Data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude. The high duty cycle of the C/NOFS observations and its unique orbit promise to expose new physics of the low-latitude ionosphere.

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Research paper thumbnail of Low-latitude measurements of neutral thermospheric helium dominance near 400 km during extreme solar minimum

Since the middle of 2008 solar activity has been unusually low, resulting in unusual atmospheric ... more Since the middle of 2008 solar activity has been unusually low, resulting in unusual atmospheric conditions, including significant changes in the pressure and neutral constituents at altitudes near 400 km at low latitudes. These attributes have been measured by the Coupled Ion-Neutral Dynamics Investigation instruments aboard the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The cross-track sensor aboard C/NOFS is designed to measure the neutral pressure in an atmosphere with pressures larger than 10−8 Torr, from which the atmospheric scale height can be estimated. In the contracted thermosphere during the current solar minimum (analyzed from June 2008 to August 2009), the instrument data indicate a dominance of neutral helium near the satellite perigee (400 km). This conclusion is found to be consistent with the measured mean drag on the satellite, thus validating the basic functionality of the cross-track sensor.

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Research paper thumbnail of A numerical study of geometry dependent errors in velocity, temperature, and density measurements from single grid planar retarding potential analyzers

Planar retarding potential analyzers (RPAs) have been utilized numerous times on high profile mis... more Planar retarding potential analyzers (RPAs) have been utilized numerous times on high profile missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellite Program to measure plasma composition, temperature, density, and the velocity component perpendicular to the plane of the instrument aperture. These instruments use biased grids to approximate ideal biased planes. These grids introduce perturbations in the electric potential distribution inside the instrument and when unaccounted for cause errors in the measured plasma parameters. Traditionally, the grids utilized in RPAs have been made of fine wires woven into a mesh. Previous studies on the errors caused by grids in RPAs have approximated woven grids with a truly flat grid. Using a commercial ion optics software package, errors in inferred parameters caused by both woven and flat grids are examined. A flat grid geometry shows the smallest temperature and density errors, while the double thick flat grid displays minimal errors for velocities over the temperature and velocity range used. Wire thickness along the dominant flow direction is found to be a critical design parameter in regard to errors in all three inferred plasma parameters. The results shown for each case provide valuable design guidelines for future RPA development.

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Research paper thumbnail of A statistical analysis of systematic errors in temperature and ram velocity estimates from satellite-borne retarding potential analyzers

The use of biased grids as energy filters for charged particles is common in satellite-borne inst... more The use of biased grids as energy filters for charged particles is common in satellite-borne instruments such as a planar retarding potential analyzer (RPA). Planar RPAs are currently flown on missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellites Program to obtain estimates of geophysical parameters including ion velocity and temperature. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to inherent errors in the inferred parameters. A simulation of ion interactions with various configurations of biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, the simulation calculates collected flux from Maxwellian ion distributions with three-dimensional drift relative to the instrument. Perturbations in the performance of flight instrumentation relative to expectations from the idealized RPA flux equation are discussed. Both single grid and dual-grid systems are modeled to investigate design considerations. Relative errors in the inferred parameters for each geometry are characterized as functions of ion temperature and drift velocity.

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Research paper thumbnail of Errors in ram velocity and temperature measurements inferred from satellite-borne retarding potential analyzers

Retarding potential analyzers (RPAs) [ Heelis and Hanson, Measurement Techniques in Space Plasmas... more Retarding potential analyzers (RPAs) [ Heelis and Hanson, Measurement Techniques in Space Plasmas, in Geophys. Monogr. Ser., Vol. 102 (AGU, Washington, D.C., 1998), p. 61 ] have been used extensively in space science over the past five decades to provide in situ estimates of ion velocities and temperatures. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to errors in inferred parameters. A simulation of ion interactions with biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, perturbations to the idealized RPA equation are discussed with the intent of developing quantitative corrections for the inferred parameters. The transparency of the grid stacks is found to be a function of particle energy and angle of attack. A preliminary case study is presented and compared to previous work.

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Research paper thumbnail of A new satellite-borne neutral wind instrument for thermospheric diagnostics

The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important fact... more The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important factor in predicting the onset of plasma instabilities that are known to distort and/or disrupt high frequency radio communications. These neutral winds have historically been quite difficult to measure, especially from a moving spacecraft. A new space science instrument called the ram wind sensor has been developed to measure the component of the neutral gas velocity that lies along the orbit track of a satellite in low Earth orbit. Laboratory tests of an engineering model of the instrument have been carried out using a supersonic neutral argon beam, in order to validate the measurement concept. The results show that the technique is viable for measurements of neutral flow velocities in future satellite missions.

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Research paper thumbnail of A novel empirical study of the photoelectric effect in thin gold films

We describe a simple experiment designed to stimulate deeper understanding of the photoelectric e... more We describe a simple experiment designed to stimulate deeper understanding of the photoelectric effect, including the effects of thin metal films on both incident ultraviolet photons and liberated photoelectrons. Interpretation of the results teaches principles of critical thinking and curve-fitting that can benefit students throughout their scientific careers.

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Research paper thumbnail of Exploring the role of ionospheric drivers during the extreme solar minimum of 2008

Annales Geophysicae, Dec 2013

During the recent solar minimum, solar activity reached the lowest levels observed during the spa... more During the recent solar minimum, solar activity reached the lowest levels observed during the space age, resulting in a contracted atmosphere. This extremely low solar activity provides an unprecedented opportunity to understand the variability of the Earth's ambient ionosphere. The average E × B drifts measured by the Vector Electric Field Instrument (VEFI) on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite during this period are found to have several differences from the expected climatology based on previous solar minima, including downward drifts in the early afternoon and a weak to non-existent pre-reversal enhancement. Using SAMI2 (Sami2 is Another Model of the Ionosphere) as a computational engine, we investigate the effects of these electrodynamical changes as well as the contraction of the thermosphere and reduced EUV ionization on the ionosphere. The sensitivity of the simulations to wind models is also discussed. These modeled ionospheres are compared to the C/NOFS average topside ion density and composition and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate average NmF2 and hmF2. In all cases, incorporating the VEFI drift data significantly improves the model results when compared to both the C/NOFS density data and the F3/C GOX data. Changing the MSIS and EUVAC models produced changes in magnitude, but not morphology with respect to local time. The choice of wind model modulates the resulting topside density and composition, but only the use of the VEFI E × B drifts produces the observed post-sunset drop in the F peak.

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Research paper thumbnail of Using Schumann Resonance Measurements for Constraining the Water Abundance on the Giant Planets—Implications for the Solar System's Formation

ABSTRACT The formation and evolution of the solar system is closely related to the abundance of v... more ABSTRACT The formation and evolution of the solar system is closely related to the abundance of volatiles, namely water, ammonia, and methane in the protoplanetary disk. Accurate measurement of volatiles in the solar system is therefore important for understanding not only the nebular hypothesis and origin of life but also planetary cosmogony as a whole.

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Research paper thumbnail of Ground and space-based measurement of rocket engine burns in the ionosphere

Abstract On-orbit firings of both liquid and solid rocket motors provide localized disturbances t... more Abstract On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O+) yields energetic ion beams.

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Research paper thumbnail of Performance of the IRI-2007 model for equatorial topside ion density in the African sector for low and extremely low solar activity

Advances in Space Research, 2013

The recent availability of new data sets during the recent extreme solar minimum provides an oppo... more The recent availability of new data sets during the recent extreme solar minimum provides an opportunity for testing the performance of the International Reference Ionosphere in historically undersampled regions. This study presents averages and variability of topside ionospheric densities over Africa as a function of season, local time, altitude, and magnetic dip latitude as measured by the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The results are compared to the three topside model options available in IRI-2007. Overall, the NeQuick model is found to have the best performance, though during the deepest part of the solar minimum all three options significantly overestimate density.

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Research paper thumbnail of The fixed-bias Langmuir probe on the Communication/Navigation Outage Forecast System satellite: Calibration and validation

Review of Scientific Instruments, Nov 12, 2012

A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument... more A fixed-bias spherical Langmuir probe is included as part of the Vector Electric Field Instrument (VEFI) suite on the Communication/Navigation Outage Forecast System (C/NOFS) satellite. C/NOFS gathers data in the equatorial ionosphere between 400 and 860 km, where the primary constituent ions are H+ and O+. The ion current collected by the probe surface per unit plasma density is found to be a strong function of ion composition. The calibration of the collected current to an absolute density is discussed, and the performance of the spherical probe is compared to other in situ instruments on board the C/NOFS satellite. The application of the calibration is discussed with respect to future fixed-bias probes; in particular, it is demonstrated that some density fluctuations will be suppressed in the collected current if the plasma composition rapidly changes along with density. This is illustrated in the observation of plasma density enhancements on C/NOFS.

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Research paper thumbnail of Topside equatorial ionospheric density and composition during and after extreme solar minimum

During the recent solar minimum, solar activity reached the lowest levels observed during the spa... more During the recent solar minimum, solar activity reached the lowest levels observed during the space age. This extremely low solar activity has accompanied a number of unexpected observations in the Earth's ionosphere-thermosphere system when compared to previous solar minima. Among these are the fact that the ionosphere is significantly contracted beyond expectations based on empirical models. Altitude profiles of ion density and composition measurements near the magnetic dip equator are constructed from the Communication/Navigation Outage Forecast System (C/NOFS) satellite to characterize the shape of the topside ionosphere during the recent solar minimum and into the new solar cycle. The variation of the profiles with respect to local time, season, and solar activity are compared to the IRI-2007 model. Building on initial results reported by Heelis et al. (2009), here we describe the extent of the contracted ionosphere, which is found to persist throughout 2009. The shape of the ionosphere during 2010 is found to be consistent with observations from previous solar minima.

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Research paper thumbnail of A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multid... more Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave observations in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfvén waves and particle precipitation related to solar and magnetospheric processes. We review ionospheric processes as well as surface and space weather phenomena that drive the coupling between the troposphere and the ionosphere. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface perturbations and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and to solve inverse problems and outline in a final section a few challenging subjects that are important to advance our understanding of tropospheric-ionospheric coupling.

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Research paper thumbnail of Observations of low-latitude plasma density enhancements and their associated plasma drifts

Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by ... more Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed ±15° away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous data have shown that the peak perturbation in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the results in this paper show that the peak perturbation in parallel flow typically occurs 25–100 km to the east of the peak perpendicular flow. The absence of such a longitudinal offset in previous observations suggests that multiple physical mechanisms may be responsible for creating plasma density enhancements as observed by satellite-borne instrumentation.

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Research paper thumbnail of Multi-Instrument Observations of an MSTID over Arecibo Observatory

The Penn State All-Sky Imager (PSASI) at Arecibo Observatory provides planar horizontal context t... more The Penn State All-Sky Imager (PSASI) at Arecibo Observatory provides planar horizontal context to the vertical ionospheric profiles obtained by the Incoherent Scatter Radar (ISR). Electric field measurements from the Communication/Navigation Outage Forecast System (C/NOFS) satellite are mapped down geomagnetic field lines to the height of the airglow layer, allowing multi-instrument studies of field-aligned irregularities with radar, imager, and satellite. A Medium-Scale Traveling Ionospheric Disturbance (MSTID) was observed during such a conjunction near the December solstice of 2009.

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Research paper thumbnail of Monitoring D-region Variability from Lightning Measurements

ursi.org

In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly ... more In situ measurements of ionospheric D-region characteristics are somewhat scarce and rely mostly on sounding rockets. Remote sensing techniques employing Very Low Frequency (VLF) transmitters can provide electron density estimates from subionospheric wave propagation modeling. Here we discuss how lightning waveform measurements, namely sferics and tweeks, can be used for monitoring the D-region variability and day-night transition, and for local electron density estimates. A brief comparison among D-region aeronomy models is also presented.

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Research paper thumbnail of Science of opportunity: Heliophysics on the FASTSAT mission and STP-S26

Aerospace …

The FASTSAT spacecraft, which was launched on November 19, 2010 on the DoD STP-S26 mission, carri... more The FASTSAT spacecraft, which was launched on November 19, 2010 on the DoD STP-S26 mission, carries three instruments developed in joint collaboration by NASA GSFC and the US Naval Academy: PISA, TTI, and MINI-ME. As part of a rapid-development, low-cost instrument design and fabrication program, these instruments were a perfect match for FASTSAT, which was designed and built in less than one year. These instruments, while independently developed, provide a collaborative view of important processes in the upper atmosphere relating to solar and energetic particle input, atmospheric response, and ion outflow. PISA measures in-situ irregularities in electron number density, TTI provides limb measurements of the atomic oxygen temperature profile with altitude, and MINI-ME provides a unique look at ion populations by a remote sensing technique involving neutral atom imaging. Together with other instruments and payloads on STP-S26 such as the NSF RAX mission, FalconSat-5, and NanoSail-D (launched as a tertiary payload from FASTSAT), these instruments provide a valuable “constellation of opportunity” for following the flow of energy and charged and neutral particles through the upper atmosphere. Together, and for a small fraction of the price of a major mission, these spacecraft will measure the energetic electrons impacting the upper atmosphere, the ions leaving it, and the large-scale plasma and neutral response to these energy inputs. The result will be a new model for maximizing scientific return from multiple small, distributed payloads as secondary payloads on a larger launch vehicle.

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Research paper thumbnail of The NSF Firefly CubeSat mission: Rideshare mission to study energetic electrons produced by lightning

Aerospace …

The NSF Firefly CubeSat is a 3U mission designed to perform cutting-edge science, as a secondary ... more The NSF Firefly CubeSat is a 3U mission designed to perform cutting-edge science, as a secondary payload. Firefly will be the first dedicated mission launched to study Terrestrial Gamma ray Flashes (TGFs), their link to lightning, and their effect in producing energetic electrons that may become stably trapped in the inner radiation belt. Firefly demonstrates the capability of small missions such as CubeSat to do important, focused science, with maximal student involvement, and with a minimal budget and available resources. This presentation will focus on the Firefly mission design, as well as important lessons learned in the development, testing, and design. Future developments in CubeSat-class spacecraft for measurements of energetic radiation will be discussed.

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Research paper thumbnail of Observations of DC electric fields in the low-latitude ionosphere and their variations with local time, longitude, and plasma density during extreme solar minimum

DC electric fields and associated E × B plasma drifts detected with the double-probe experiment o... more DC electric fields and associated E × B plasma drifts detected with the double-probe experiment on the C/NOFS satellite during extreme solar minimum conditions near the June 2008 solstice are shown to be highly variable, with weak to moderate ambient amplitudes of ∼1–2 mV/m (∼25–50 m/s). Average field or drift patterns show similarities to those reported for more active solar conditions, i.e., eastward and outward during day and westward and inward at night. However, these patterns vary significantly with longitude and are not always present. Daytime vertical drifts near the magnetic equator are largest in the prenoon sector. Observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects. Enhanced meridional drifts are observed near sunrise in certain longitude regions, precisely where the enhanced eastward flow that persisted from earlier local times terminates. The nightside ionosphere is characterized by larger-amplitude, structured electric fields dominated by horizontal scales of 500–1500 km even where local plasma densities appear relatively undisturbed. Data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude. The high duty cycle of the C/NOFS observations and its unique orbit promise to expose new physics of the low-latitude ionosphere.

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Research paper thumbnail of Low-latitude measurements of neutral thermospheric helium dominance near 400 km during extreme solar minimum

Since the middle of 2008 solar activity has been unusually low, resulting in unusual atmospheric ... more Since the middle of 2008 solar activity has been unusually low, resulting in unusual atmospheric conditions, including significant changes in the pressure and neutral constituents at altitudes near 400 km at low latitudes. These attributes have been measured by the Coupled Ion-Neutral Dynamics Investigation instruments aboard the Communication/Navigation Outage Forecast System (C/NOFS) satellite. The cross-track sensor aboard C/NOFS is designed to measure the neutral pressure in an atmosphere with pressures larger than 10−8 Torr, from which the atmospheric scale height can be estimated. In the contracted thermosphere during the current solar minimum (analyzed from June 2008 to August 2009), the instrument data indicate a dominance of neutral helium near the satellite perigee (400 km). This conclusion is found to be consistent with the measured mean drag on the satellite, thus validating the basic functionality of the cross-track sensor.

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Research paper thumbnail of A numerical study of geometry dependent errors in velocity, temperature, and density measurements from single grid planar retarding potential analyzers

Planar retarding potential analyzers (RPAs) have been utilized numerous times on high profile mis... more Planar retarding potential analyzers (RPAs) have been utilized numerous times on high profile missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellite Program to measure plasma composition, temperature, density, and the velocity component perpendicular to the plane of the instrument aperture. These instruments use biased grids to approximate ideal biased planes. These grids introduce perturbations in the electric potential distribution inside the instrument and when unaccounted for cause errors in the measured plasma parameters. Traditionally, the grids utilized in RPAs have been made of fine wires woven into a mesh. Previous studies on the errors caused by grids in RPAs have approximated woven grids with a truly flat grid. Using a commercial ion optics software package, errors in inferred parameters caused by both woven and flat grids are examined. A flat grid geometry shows the smallest temperature and density errors, while the double thick flat grid displays minimal errors for velocities over the temperature and velocity range used. Wire thickness along the dominant flow direction is found to be a critical design parameter in regard to errors in all three inferred plasma parameters. The results shown for each case provide valuable design guidelines for future RPA development.

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Research paper thumbnail of A statistical analysis of systematic errors in temperature and ram velocity estimates from satellite-borne retarding potential analyzers

The use of biased grids as energy filters for charged particles is common in satellite-borne inst... more The use of biased grids as energy filters for charged particles is common in satellite-borne instruments such as a planar retarding potential analyzer (RPA). Planar RPAs are currently flown on missions such as the Communications/Navigation Outage Forecast System and the Defense Meteorological Satellites Program to obtain estimates of geophysical parameters including ion velocity and temperature. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to inherent errors in the inferred parameters. A simulation of ion interactions with various configurations of biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, the simulation calculates collected flux from Maxwellian ion distributions with three-dimensional drift relative to the instrument. Perturbations in the performance of flight instrumentation relative to expectations from the idealized RPA flux equation are discussed. Both single grid and dual-grid systems are modeled to investigate design considerations. Relative errors in the inferred parameters for each geometry are characterized as functions of ion temperature and drift velocity.

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Research paper thumbnail of Errors in ram velocity and temperature measurements inferred from satellite-borne retarding potential analyzers

Retarding potential analyzers (RPAs) [ Heelis and Hanson, Measurement Techniques in Space Plasmas... more Retarding potential analyzers (RPAs) [ Heelis and Hanson, Measurement Techniques in Space Plasmas, in Geophys. Monogr. Ser., Vol. 102 (AGU, Washington, D.C., 1998), p. 61 ] have been used extensively in space science over the past five decades to provide in situ estimates of ion velocities and temperatures. It has been shown previously that the use of biased grids in such instruments creates a nonuniform potential in the grid plane, which leads to errors in inferred parameters. A simulation of ion interactions with biased grids has been developed using a commercial finite-element analysis software package. Using a statistical approach, perturbations to the idealized RPA equation are discussed with the intent of developing quantitative corrections for the inferred parameters. The transparency of the grid stacks is found to be a function of particle energy and angle of attack. A preliminary case study is presented and compared to previous work.

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Research paper thumbnail of A new satellite-borne neutral wind instrument for thermospheric diagnostics

The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important fact... more The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important factor in predicting the onset of plasma instabilities that are known to distort and/or disrupt high frequency radio communications. These neutral winds have historically been quite difficult to measure, especially from a moving spacecraft. A new space science instrument called the ram wind sensor has been developed to measure the component of the neutral gas velocity that lies along the orbit track of a satellite in low Earth orbit. Laboratory tests of an engineering model of the instrument have been carried out using a supersonic neutral argon beam, in order to validate the measurement concept. The results show that the technique is viable for measurements of neutral flow velocities in future satellite missions.

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Research paper thumbnail of A novel empirical study of the photoelectric effect in thin gold films

We describe a simple experiment designed to stimulate deeper understanding of the photoelectric e... more We describe a simple experiment designed to stimulate deeper understanding of the photoelectric effect, including the effects of thin metal films on both incident ultraviolet photons and liberated photoelectrons. Interpretation of the results teaches principles of critical thinking and curve-fitting that can benefit students throughout their scientific careers.

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