MICA sounding rocket observations of conductivity‐gradient‐generated auroral ionospheric responses: Small‐scale structure with large‐scale drivers

Lynch, K. A.; Hampton, D. L.; Zettergren, M. D.; Bekkeng, T. A.; Conde, M.; Fernandes, P. A.; Horák, P.; Lessard, M.; Miceli, R. J.; Michell, R.; Moen, J.; Nicolls, M. J.; Powell, Steven P.; Samara, M.

doi:10.1002/2014ja020860

Cited by 35 publications

(60 citation statements)

References 66 publications

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“…We use these measurements to estimate the Alfvén velocity v A = δ E / δ B ≈ 200 km s −1 . This corresponds to an Alfvén conductance Σ A = 0.25 S which is much smaller than the Pedersen conductance Σ P = 20 S (calculated for the MICA case study by Lynch et al []), as is typical for Alfvén waves [ Paschmann et al , ]. These evidences of Alfvénic activity (an indirect source for ELF WPI) from a variety of ground‐based and in situ observations lead us to consider heating of the bulk thermal ion population by wave‐particle interactions.…”

Section: Discussion and Comparison To Previous Observationsmentioning

confidence: 87%

“…The first is a fine‐scale, high‐resolution simulation that uses Venetie medium‐field imager data to specify electron precipitation (0.5 s cadence) and MICA DC electric fields as measured by the COWBOY instrument [ Lynch et al , ]. This simulation encapsulates the apogee portion of the MICA flight.…”

Section: Discussion and Comparison To Previous Observationsmentioning

confidence: 99%

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Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

et al. 2016

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We present an analysis of in situ measurements from the MICA (Magnetosphere‐Ionosphere Coupling in the Alfvén Resonator) nightside auroral sounding rocket with comparisons to a multifluid ionospheric model. MICA made observations at altitudes below 325 km of the thermal ion kinetic particle distributions that are the origins of ion outflow. Late flight, in the vicinity of an auroral arc, we observe frictional processes controlling the ion temperature. Upflow of these cold ions is attributed to either the ambipolar field resulting from the heated electrons or possibly to ion‐neutral collisions. We measure trueE→×trueB→ convection away from the arc (poleward) and downflows of hundreds of m s−1 poleward of this arc, indicating small‐scale low‐altitude plasma circulation. In the early flight we observe DC electromagnetic Poynting flux and associated ELF wave activity influencing the thermal ion temperature in regions of Alfvénic aurora. We observe enhanced, anisotropic ion temperatures which we conjecture are caused by transverse heating by wave‐particle interactions (WPI) even at these low altitudes. Throughout this region we observe several hundred m s−1 upflow of the bulk thermal ions colocated with WPI; however, the mirror force is negligible at these low energies; thus, the upflow is attributed to ambipolar fields (or possibly neutral upwelling drivers). The low‐altitude MICA observations serve to inform future ionospheric modeling and simulations of (a) the need to consider the effects of heating by WPI at altitudes lower than previously considered viable and (b) the occurrence of structured and localized upflows/downflows below where higher‐altitude heating rocesses are expected.

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Section: Discussion and Comparison To Previous Observationsmentioning

confidence: 87%

Section: Discussion and Comparison To Previous Observationsmentioning

confidence: 99%

Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

et al. 2016

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“…The predominant driver of broadband precipitation is the convergence of Alfvénic Poynting flux (S ⟂ ) in the auroral acceleration region (AAR, located at altitudes between ∼0.2 and 2 Earth radii [Forsyth et al, 2012]) causing a divergence of particle kinetic energy flux (KE || ) over a broad range of energies into the ionosphere [Lotko, 1986;Thayer and Semeter, 2004;Newell et al, 2009]. The predominant driver of broadband precipitation is the convergence of Alfvénic Poynting flux (S ⟂ ) in the auroral acceleration region (AAR, located at altitudes between ∼0.2 and 2 Earth radii [Forsyth et al, 2012]) causing a divergence of particle kinetic energy flux (KE || ) over a broad range of energies into the ionosphere [Lotko, 1986;Thayer and Semeter, 2004;Newell et al, 2009].…”

Section: Relationship Between Eof3 and Alfvén Poynting Fluxmentioning

confidence: 99%

High‐latitude ionospheric conductivity variability in three dimensions

McGranaghan

Knipp

Matsuo

2016

Geophysical Research Letters

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We perform the first ever global‐scale, altitude‐dependent analysis of polar ionospheric conductivity variability using spectrally resolved in situ satellite particle measurements. With an empirical orthogonal function analysis we identify three primary modes of three‐dimensional variability related to ionospheric footprints of the quiet and disturbed geospace environment: (1) perturbation of the quasi‐permanent auroral oval, (2) differing projections of electron precipitation during southward and northward interplanetary magnetic field, and (3) a likely imprint of variation in Alfvénic Poynting flux deposition. Together, these modes account for >50% of the total conductivity variability throughout the E region ionosphere. Our results show that height‐integrated conductance and height‐dependent conductivities are distinctly different, underscoring the importance of studying the ionosphere in three dimensions. We provide the framework for future three‐dimensional global analysis of ionosphere‐magnetosphere coupling.

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“…(top) In situ electric fields in geomagnetic coordinates in blue and green (adapted from Lynch et al []). Black corresponds to the perpendicular component of the electric field from the simulations.…”

Section: Resultsmentioning

confidence: 99%

“…Overview of the MICA flight (adapted from Lynch et al []). (first panel) Electric field, (second panel) magnetic field, (third panel) the Poynting flux calculated from E and B fields (positive is downward), (fourth panel) the optical intensity measured by the medium‐field camera, and (fifth panel) the plasma density measured by the mNLP probe.…”

Section: Mica Datamentioning

confidence: 99%

Ionospheric Alfvén resonator and aurora: Modeling of MICA observations

Tulegenov

Streltsov

2017

JGR Space Physics

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We present results from a numerical study of small‐scale, intense magnetic field‐aligned currents observed in the vicinity of the discrete auroral arc by the Magnetosphere‐Ionosphere Coupling in the Alfvén Resonator (MICA) sounding rocket launched from Poker Flat, Alaska, on 19 February 2012. The goal of the MICA project was to investigate the hypothesis that such currents can be produced inside the ionospheric Alfvén resonator by the ionospheric feedback instability (IFI) driven by the system of large‐scale magnetic field‐aligned currents interacting with the ionosphere. The trajectory of the MICA rocket crossed two discrete auroral arcs and detected packages of intense, small‐scale currents at the edges of these arcs, in the most favorable location for the development of the ionospheric feedback instability, predicted by the IFI theory. Simulations of the reduced MHD model derived in the dipole magnetic field geometry with realistic background parameters confirm that IFI indeed generates small‐scale ULF waves inside the ionospheric Alfvén resonator with frequency, scale size, and amplitude showing a good, quantitative agreement with the observations. The comparison between numerical results and observations was performed by “flying” a virtual MICA rocket through the computational domain, and this comparison shows that, for example, the waves generated in the numerical model have frequencies in the range from 0.30 to 0.45 Hz, and the waves detected by the MICA rocket have frequencies in the range from 0.18 to 0.50 Hz.

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MICA sounding rocket observations of conductivity‐gradient‐generated auroral ionospheric responses: Small‐scale structure with large‐scale drivers

Cited by 35 publications

References 66 publications

Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

Measuring the seeds of ion outflow: Auroral sounding rocket observations of low‐altitude ion heating and circulation

High‐latitude ionospheric conductivity variability in three dimensions

Ionospheric Alfvén resonator and aurora: Modeling of MICA observations

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