Matthew G. McHarg

An overview of the early November 1993 geomagnetic storm

This paper describes the development of a major space storm during November 2-11, 1993. We discuss the history of the contributing high-speed stream, the powerful combination of solar wind transients and a corotating interaction region which initiated the storm, the high-speed flow which prolonged the storm and the near-Earth manifestations of the storm. The 8-day storm period was unusually long; the result of a high-speed stream (maximum speed 800 km/s) emanating from a distended coronal hole. Storm onset was accompanied by a compression of the entire dayside magnetopause to within geosynchronous Earth orbit (GEO). For nearly 12 hours the near-Earth environment was in a state of tumult. A super-dense plasma sheet was observed at GEO, and severe spacecraft charging was reported. The effects of electrons precipitating into the atmosphere penetrated into the stratosphere. Subauroral electron content varied by 100% and F layer heights oscillated by 200 km. Equatorial plasma irregularities extended in plumes to heights of 1400 km. Later, energetic particle fluxes at GEO recovered and rose by more than an order of magnitude. A satellite anomaly was reported during the interval of high energetic electron flux. Model results indicate an upper atmospheric temperature increase of 200°K within 24 hours of storm onset. Joule heating for the first 24 hours of the storm was more than 3 times that for typical active geomagnetic conditions. We estimate that total global ionospheric heating for the full storm interval was ∼190 PJ, with 30% of that generated within 24 hours of storm onset.

Comparison of acceleration, expansion, and brightness of sprite streamers obtained from modeling and high‐speed video observations

Received 2 September 2008; revised 10 December 2008; accepted 15 January 2009; published 26 March 2009. [1] We compare sprite streamer modeling results with high-speed video recordings of sprites made with 50-mstemporal resolution. Both the modeling results and the sprite videos show that sprite streamers propagate with acceleration and expansion during the initial stage of sprite development. The acceleration computed from the modeling for the applied electric fields close to the conventional breakdown threshold field is on the order of (0.5–1)10 10 ms 2 andisingoodagreementwiththepeakvaluesobservedexperimentally. We further discuss the effects of different spatial and temporal resolutions of an observational system on the visual appearances of sprite streamers. It is found that the large variation in brightness of sprites estimated from several observational studies can be directly attributed to different temporal and spatial resolutions of used instruments. Mainly due to the increasing radius of the streamer head of an accelerating streamer, the brightness of the streamer head increasesaswell.Thecomparisonresultsdemonstratethatthebrightnessofaspritestreamer head increases exponentially with time and can span more than 4 orders of magnitude in a very short period of about 1 ms. We propose a method for remote sensing of the spritedriving electric field in the mesospheric and lower ionospheric region by measuring the rate of the change of the brightness.

Polar cap index as a proxy for hemispheric Joule heating

The polar cap (PC) index measures the level of geomagnetic activity in the polar cap based on magnetic perturbations from overhead ionospheric currents and distant field-aligned currents on the poleward edge of the nightside auroral oval. Because PC essentially measures the main sources of energy input into the polar cap, we propose to use PC as a proxy for the hemispheric Joule heat production rate (JH). In this study, JH is estimated from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure. We fit hourly PC values to hourly averages of JH. Using a data base approximately three times larger than studies, we find a quadratic relationship between JH and PC, differentiated by season. A comparison during the November 1993 storm interval with earlier reported methods using the AE index and the cross polar cap potential, shows that the PC-based Joule heating estimate is as equally accurate. Thus the single station PC index appears to provide a quick estimate of, and is an appropriate proxy for, the hemispheric Joule heating rate.

Plasma-induced force and self-induced drag in the dielectric barrier discharge aerodynamic plasma actuator

§Through high-time-resolution laser interferometry, we observe the motion of a test article under the influence of a dielectric barrier discharge aerodynamic plasma actuator, and from this motion we deduce the time history of the force produced by the actuator to a resolution substantially smaller than the period of the actuator’s AC cycle. We find that the negative- and positive-going half cycles of the plasma discharge produce a force on the surrounding neutral air in the same direction, but that only the negative-going half cycle produces a force sufficient to substantially overcome the drag induced by accelerating the air in the immediate vicinity of the aerodynamic surface (within the boundary layer under normal circumstances).

Fast photometry of flickering in discrete auroral arcs

We present high speed photometric measurements of the auroral intensity of flickering aurora. These measurements reveal the existence of intensity modulations in the discrete aurora above the Nyquist frequency of standard 30 frame per second TV cameras. The intensity fluctuations observed are primarily below 80 Hz, although frequencies up to 180 Hz have been detected. Changes in the spectral characteristics from essentially band-limited to broadband intensity fluctuations and then to narrowband fluctuations are seen in individual discrete arcs within a few minutes. The center frequency of the observed fluctuations also change during this period. Data obtained from a standard narrow field TV camera observing the same arc show that only the low ( ≈ 10 Hertz) narrowband modulations would be considered standard flickering aurora.

Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation

Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere.

Sprite streamer initiation from natural mesospheric structures

Sprites are large, luminous electrical discharges in the upper atmosphere caused by intense cloud-to-ground lightning flashes, manifesting an impulsive coupling mechanism between lower and upper atmospheric regions. Their dynamics are governed by filamentary streamer discharges whose propagation properties have been well studied by past work. However, how they are initiated is still under active debate. It has recently been concluded that ionospheric/mesospheric inhomogeneities are required for their initiation, but it is an open question as to what the sources of those inhomogeneities are. Here we present numerical simulation results to demonstrate that naturally-existing, small-scale mesospheric structures such as those created by gravity waves via instability and breaking are viable sources. The proposed theory is supported by a recent, unique high-speed observation from aircraft flying at 14-km altitude. The theory naturally explains many aspects of observed sprite streamer initiation and has important implications for future observational work.

Analysis and observation of spacecraft plume/ionosphere interactions during maneuvers of the space shuttle

This work employs in situ measurement data and constructive simulations to examine the underlying physical mechanisms that drive spacecraft plume interactions with the space environment in low-Earth orbit. The study centers on observations of the enhanced flux of plasma generated during a maneuver of Space Shuttle Endeavour as part of the Sensor Test for Orion Relative Navigation Risk Mitigation experiment in May 2011. The Canary electrostatic analyzer (ESA) instrument mounted on the portside truss of the International Space Station indicated an elevated ion current during the shuttle maneuver. The apparent source of enhanced ion current is a result of interaction of the spacecraft thruster plume with the rarefied ambient ionosphere, which generates regions of relatively high density plasma through charge exchange between the neutral plume and ambient ions. To reconstruct this event, unsteady simulation data were generated using a combined direct simulation Monte Carlo/particle-in-cell methodology, which employed detailed charge exchange cross-section data and a magnetic field model. The simulation provides local plasma characteristics at the ESA sensor location, and a sensor model is subsequently used to transform the local properties into a prediction of measured ion current. The predicted and observed total currents are presented as a function of time over a 30 s period of pulsed thruster firings. A strong correlation is observed in the temporal characteristics of the simulated and measured total current, and good agreement is also achieved in the total current predicted by the model. These results support conclusions that (1) the enhanced flux of plasma observed by the ESA instrument is associated with Space Shuttle thruster firings and (2) the simulation model captures the essential features of the plume interactions based on the observation data.

Distributed space-based Ionospheric Multiple Plasma Sensor networks

Distributed small satellite mission concepts are emerging for commercial, scientific, and military applications requiring constellations of many hundreds of satellites. Massively distributed missions allow both simultaneous multipoint observations and significant redundancy. This paper presents an application case study based on the US Air Force Academys (USAFA) Ionospheric Multiple Plasma Sensors (IMPS) mission. IMPS is an integration of the satellite-on-a-Printed Circuit Board (PCBSat) miniaturization approach developed at the University of Surrey with the Miniaturized Electrostatic Analyzer (MESA) sensor developed at USAFA.

FalconSAT-7: a membrane space solar telescope

The US Air Force Academy of Physics has built FalconSAT-7, a membrane solar telescope to be deployed from a 3U CubeSat in LEO. The primary optic is a 0.2m photon sieve – a diffractive element consisting of billions of tiny circular dimples etched into a Kapton sheet. The membrane its support structure, secondary optics, two imaging cameras and associated control, recording electronics are packaged within half the CubeSat volume. Once in space the supporting pantograph structure is deployed, extending out and pulling the membrane flat under tension. The telescope will then be directed at the Sun to gather images at H-alpha for transmission to the ground. We will present details of the optical configuration, operation and performance of the flight telescope which has been made ready for launch in early 2017.