Citizen scientists, along with satellite and ground-based sensors, have revealed a new arc boundary at subauroral latitudes.

[1] This paper is a companion to a paper by Liang et al. (2011) which reports a causal connection between the intensification of electrostatic ECH waves and the postmidnight diffuse auroral activity in the absence of whistler mode chorus waves at L = 11.5 on the basis of simultaneous observations from THEMIS spacecraft and NORSTAR optical instruments during 8-9 UT on February 5, 2009. In this paper, we use the THEMIS particle and wave measurements together with the magnetically conjugate auroral observations for this event to illustrate an example where electrostatic electron cyclotron harmonic (ECH) waves are the main contributor to the diffuse auroral precipitation. We use the wave and particle data to perform a comprehensive theoretical and numerical analysis of ECH wave driven resonant scattering rates. We find that the observed ECH wave activity can cause intense pitch angle scattering of plasma sheet electrons between 100 eV and 5 keV at a rate of >10 À4 s À1 for equatorial pitch angles a eq < 30°. The scattering approaches the strong diffusion limit in the realistic ambient magnetic field to produce efficient precipitation loss of <$5 keV electrons on a timescale of a few hours or less. Using the electron differential energy flux inside the loss cone estimated based upon the energy-dependent efficiency of ECH wave scattering for an 8-s interval with high resolution wave data available, the auroral electron transport model developed by Lummerzheim (1987) produced an intensity of $2.3 kR for the green-line diffuse aurora. Separately, Maxwellian fitting to the electron differential flux spectrum produced a green-line auroral intensity of $2.6 kR. This is in good agreement with the $2.4 kR green-line auroral intensity observed simultaneously at the magnetic foot point (as inferred using the event-adaptive model of Kubyshkina et al. (2009Kubyshkina et al. ( , 2011) of the location where the in situ observations were obtained. Our results support the scenario that enhanced ECH emissions in the central plasma sheet (CPS) can be an important or even dominant driver of diffuse auroral precipitation in the outer magnetosphere. This paper is an important compliment to recent work that has shown lower band and upper band chorus to be mainly responsible for the occurrences of diffuse aurora in the inner magnetosphere.Citation: Ni, B., J. Liang, R. M. Thorne, V. Angelopoulos, R. B. Horne, M. Kubyshkina, E. Spanswick, E. F. Donovan, and D. Lummerzheim (2012), Efficient diffuse auroral electron scattering by electrostatic electron cyclotron harmonic waves in the outer magnetosphere: A detailed case study,

We present a statistical study of relativistic electron counts in the electron radiation belt across a range of drift shells (L * > 4) combining data from nine combined X-ray dosimeters (CXD) on the global positioning system (GPS) constellation. The response of the electron counts as functions of time, energy and drift shell are examined statistically for 67 solar wind stream interfaces (SIs); two-dimensional superposed epoch analysis is performed with the CXD data. For these epochs we study the radiation belt dropouts and concurrent variations in key geophysical parameters.At higher L * we observe a tendency for a gradual drop in the electron counts over the day preceding the SI, consistent with outward diffusion and magnetopause shadowing. At all L * , dropouts occur with a median time scale of 7 h and median counts fall by 0.4-1.8 orders of magnitude. The central tendencies of radiation belt dropout and recovery depend on both L * and energy. For 70 per cent of epochs Sym-H more than −30 nT, yet only three of 67 SIs did not have an associated dropout in the electron data. Statistical maps of electron precipitation suggest that chorus-driven relativistic electron microbursts might be major contributors to radiation belt losses under high-speed stream driving.

We present the first observations of ionospheric phenomena using the newly deployed Transition Region Explorer (TREx) Spectrograph. On the night of 10 April 2018, STEVE (Strong Thermal Emission Velocity Enhancement) and the Picket Fence optical structures were observed by the spectrograph in Lucky Lake, Saskatchewan. STEVE contains an enhancement of the OI red‐line (630‐nm) emission and a continuum which spans the visible wavelengths. Based upon its spectrum, we assert that the characteristic mauve color of STEVE is a result of this continuum. The spectrum of the Picket Fence contains a strong OI green‐line (557.7‐nm) emission similar to that produced in typical auroral structures. From their spectra, we assert that the Picket Fence is caused by particle precipitation and thus that the Picket Fence is a form of aurora, while STEVE's spectrum confirms that it is not aurora.