An analysis of multiscale observations of a substorm auroral breakup are presented which clarify the role of wave dispersion in the formation of elemental (<100 m) auroral structure. At coarse resolution (all‐sky white light camera, 1 frame/s), observations fit the established substorm morphology—namely, arc brightening, formation of spatial distortions, and breakup into multiple “rayed” structures. At fine‐scale resolution (electron multiplying charge‐coupled device [EMCCD] camera, 9‐degree field of view, prompt emission filter, 30 frames/s), an entirely different type of coherence is observed. The “arc,” as identified at lower resolution, is observed to be a dynamic structure composed of bifurcating elemental arcs that propagate outward from the center of an “arc packet.” This dynamic process is well captured in time‐brightness histories (keograms) along a cut bisecting the structure. The observations are interpreted with respect to theoretical predictions for inertial Alfvén wave dispersion. Specifically, the arc packets are interpreted as the B⊥ projection of the parallel electric field within the Alfvén resonant cone. Prebreakup observations are found to be qualitatively consistent with this model. However, some difficulties are encountered for the more active postbreakup period. The article includes a discussion of perspective considerations in interpreting small‐scale auroral features; in particular, it is shown that the “rayed” appearance of discrete breakup aurora is, in fact, a consequence of sharply kinked sheets viewed obliquely.

[1] Experimental results obtained with the 449-MHz Poker Flat Incoherent Scatter Radar (PFISR) show unusual features in both the ion line and plasma line measurements during an auroral breakup event. The features are a greatly enhanced flat ion acoustic spectrum (believed to indicate the presence of an additional peak at zero Doppler), and two peaks in the plasma line spectrum. Similar spectral morphologies are observed during active HF ionospheric modification experiments and are considered unmistakable indications of Strong Langmuir Turbulence (SLT). In SLT theory, the central peak in ion acoustic spectrum is caused by Bragg scattering from non-propagating density fluctuations (cavitons), and the two peaks in the plasma line spectrum are associated with (1) Langmuir waves trapped in the cavitons, at the cold plasma frequency, and (2) a "free mode" at the Langmuir frequency. Free modes are radiated Langmuir waves from collapsing cavitons that follow the linear dispersion relation. The observed turbulence was confined to a thin layer ($10-km) centered at $230 km altitude. Citation: Akbari, H., J. L.

AJ, Reyes RV. Store-operated channels in the pulmonary circulation of high-and low-altitude neonatal lambs. Am J Physiol Lung Cell Mol Physiol 304: L540 -L548, 2013. First published February 15, 2013 doi:10.1152/ajplung.00024.2012.-We determined whether store-operated channels (SOC) are involved in neonatal pulmonary artery function under conditions of acute and chronic hypoxia, using newborn sheep gestated and born either at high altitude (HA, 3,600 m) or low altitude (LA, 520 m). Cardiopulmonary variables were recorded in vivo, with and without SOC blockade by 2-aminoethyldiphenylborinate (2-APB), during basal or acute hypoxic conditions. 2-APB did not have effects on basal mean pulmonary arterial pressure (mPAP), cardiac output, systemic arterial blood pressure, or systemic vascular resistance in both groups of neonates. During acute hypoxia 2-APB reduced mPAP and pulmonary vascular resistance in LA and HA, but this reduction was greater in HA. In addition, isolated pulmonary arteries mounted in a wire myograph were assessed for vascular reactivity. HA arteries showed a greater relaxation and sensitivity to SOC blockers than LA arteries. The pulmonary expression of two SOC-forming subunits, TRPC4 and STIM1, was upregulated in HA. Taken together, our results show that SOC contribute to hypoxic pulmonary vasoconstriction in newborn sheep and that SOC are upregulated by chronic hypoxia. Therefore, SOC may contribute to the development of neonatal pulmonary hypertension. We propose SOC channels could be potential targets to treat neonatal pulmonary hypertension.hypoxia; pulmonary vasoconstriction; pulmonary hypertension; 2-aminoethydiphenylborinate; pulmonary vascular reactivity PULMONARY ARTERIES HAVE AN intrinsic vasoconstrictor response to low oxygen levels when exposed to acute hypoxia. This is a reversible, rapid and physiological response, known as hypoxic pulmonary vasoconstriction (HPV), that redirects blood flow from poorly oxygenated to better oxygenated alveoli. Thus, when total lung is exposed to hypoxia, HPV results in an increase in pulmonary artery pressure (PAP) that reverses when normoxia is reestablished (31). However, exposure to chronic hypoxia produces an imbalance between vasodilator and vasoconstrictor mechanisms, and there is pulmonary vascular remodeling that includes proliferation of pulmonary artery myocytes among other cellular processes (46). The result is a pathological and persistent increase in pulmonary artery contractile tone and pulmonary arterial hypertension, which in many cases leads to right ventricular hypertrophy, right heart failure, and eventually death (13).In pulmonary artery smooth muscle cells, an increase in intracellular calcium concentration ([Ca 2ϩ ] i ) is essential for HPV, proliferation, and remodeling (13,19,20,42). This increase in [Ca 2ϩ ] i greatly depends on an influx of extracellular calcium (13, 59), which may enter the smooth muscle cell through store-operated channels (SOC) among other pathways (5,8,22,40). These are channels physiologically ...

Abstract. The work presents a data-model synthesis examining the response of the auroral F-region ion temperature, composition, and density to short time scale (<1 min) electric field disturbances associated with auroral arcs. Ion temperature profiles recorded by the Sondrestrom incoherent scatter radar (ISR) are critically analyzed with the aid of theoretical calculations to infer ion composition variability. The analyses presented include a partial accounting for the effects of neutral winds on frictional heating and show promise as the groundwork for future attempts to address ion temperature-mass ambiguities in short-integration ISR data sets. Results indicate that large NO + enchancements in the F-region can occur in as little as 20 s in response to impulsive changes in ion frictional heating. Enhancements in molecular ion density result in recombination and a depletion in plasma, which is shown to occur on time scales of several minutes. This depletion process, thus, appears to be of comparable importance to electrodynamic evacuation processes in producing auroral arc-related plasma depletions. Furthermore, the potential of ionospheric composition in regulating the amounts and types of ions supplied to the magnetosphere is outlined.

[1] A method is developed for estimating F region ion composition from incoherent scatter radar (ISR) measurements during times of frictional ion heating. The technique addresses ion temperature-mass ambiguities in the IS spectra by self-consistently modeling ion temperature profiles, including the effects of ion temperature anisotropies and altitude-independent neutral winds. The modeled temperature profiles are used in a minimization procedure to estimate ion composition consistent with the recorded IS spectra. The proposed method is applicable to short-integration (<5 min) data sets from either single-beam or multiple-beam experiments. Application of the technique to Sondrestrom ISR measurements shows increases in F region molecular ions in response to frictional heating, a result consistent with previous theoretical and observational work. Estimates of ion composition are shown to be relatively insensitive to moderate variations in the neutral atmospheric model, which serves as input to the method. The technique developed in this work is uniquely qualified for studying highly variable ion composition near auroral arcs and associated processes such as molecular ion upflows. It also addresses a systematic source of error in standard ISR analysis methods when they are applied in such situations.