Solar cycle variability of nighttime topside helium ion concentrations over Arecibo

González, S. A.; Sulzer, M. P.; Nicolls, M. J.; Kerr, Robert B.

doi:10.1029/2003ja010100

Cited by 29 publications

(45 citation statements)

References 30 publications

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“…A reservoir of He + forms at altitudes where dissociative recombination is slow. Helium ions may even become the dominant species at some altitudes (Heelis et al, 1990;González et al, 2004). At the magnetic equator, however, helium ions are arrested at the flux tube apexes.…”

Section: Discussionmentioning

confidence: 99%

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Topside measurements at Jicamarca during solar minimum

2009

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Abstract. Long-pulse topside radar data acquired at Jicamarca and processed using full-profile analysis are compared to data processed using more conventional, range-gated approaches and with analytic and computational models. The salient features of the topside observations include a dramatic increase in the T e /T i temperature ratio above the F peak at dawn and a local minimum in the topside plasma temperature in the afternoon. The hydrogen ion fraction was found to exhibit hyperbolic tangent-shaped profiles that become shallow (gradually changing) above the O + -H + transition height during the day. The profile shapes are generally consistent with diffusive equilibrium, although shallowing to the point of changes in inflection can only be accounted for by taking the effects of E×B drifts and meridional winds into account. The SAMI2 model demonstrates this as well as the substantial effect that drifts and winds can have on topside temperatures. Significant quiet-time variability in the topside composition and temperatures may be due to variability in the mechanical forcing. Correlations between topside measurements and magnetometer data at Jicamarca support this hypothesis.

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Section: Discussionmentioning

confidence: 99%

“…González, 1994;González and Sulzer, 1996;González et al, 2004). Diffusive equilibrium is met when the force balance equations for the electrons and ions are satisfied:…”

Section: Discussionmentioning

confidence: 99%

Topside measurements at Jicamarca during solar minimum

2009

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“…The transition height, h t , between the O + dominated ionosphere and the H + dominated protonosphere, collapses following sunset as seen in Figure A1c. This collapse is associated with the formation of a He + layer near h t ( Figure A1d), which forms under ambipolar diffusion and attains a maximum peak density near 0400 LT [González and Sulzer, 1996;Wilford et al, 2003;González et al, 2004].…”

Section: A1 Ionospheric Density Temperature and Velocitymentioning

confidence: 99%

“…The correct specification of light ion partitioning in Arecibo data analysis is a necessity first described by González and Sulzer [1996], who demonstrated superior agreement between the measured incoherent scatter spectrum and spectral fits which incorporated three ions (H + , O + , and He + ) instead of two (H + and O + only). A detailed description of the ionospheric composition and temperature extraction technique is presented by González et al [2004] using several examples of Arecibo topside observations, including those from 8 to 9 October 1988 used in this investigation. In general, a nonlinear least squares fit for temperature and composition is performed on measured spectra after reducing the noise at high altitudes (above 889 km) by averaging the spectra across range.…”

Section: A1 Ionospheric Density Temperature and Velocitymentioning

confidence: 99%

“…[44] As described by González et al [2004], the experimental technique used at Arecibo to acquire the 1988 topside measurements consists of 1-ms transmission pulses at 430 MHz with an interpulse period (IPP) of 20 ms. Although range gates are computed every 77 km between $413 and 2700 km, the true range resolution of 150 km (determined by the 1-ms pulse length) frequently is not sufficient to resolve short scale heights very near the F peak [Isham et al, 2000].…”

Section: A1 Ionospheric Density Temperature and Velocitymentioning

confidence: 99%

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Derivation of neutral oxygen density under charge exchange in the midlatitude topside ionosphere

et al. 2006

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[1] We describe a new technique to derive neutral atomic oxygen density, [O], in the upper thermosphere using coincident incoherent scatter radar (ISR) and airglow emission observations from Arecibo Observatory. The technique exploits the nearly resonant charge exchange coupling between neutral and ionized hydrogen and oxygen that serves as the dominant chemical source and sink of protons near and above the F region peak. Under charge exchange production and loss of H + , the proton continuity equation can be solved for [O] using twilight H density profiles derived from measured H emission brightness at 656.3 nm together with ion density, temperature, and flux obtained simultaneously by the Arecibo ISR. We present both equilibrium and nonequilibrium solutions for [O] between 500 and 1500 km during a single quiescent nighttime interval under moderate solar activity. Comparisons with theoretical expectations and with MSIS-model calculations of O density are used to identify the altitude and local time extent over which the technique is justified. These comparisons generally support technique validity between $600 and 800 km, where sufficient reactant densities are present to validate the charge exchange formulation of the continuity equation. Equilibrium solutions for [O] near 650-700 km exhibit excellent agreement with MSIS estimates before midnight, but deviations arising from ion transport become increasingly significant both above this height and as dawn approaches. Incorporation of measured proton flux gradients into the nonequilibrium solutions improves agreement between the derived and modeled estimates significantly after midnight, while the minor nonequilibrium contributions during several hours before midnight lend additional support for the presence of charge exchange equilibrium.

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Topside equatorial ionospheric density, temperature, and composition under equinox, low solar flux conditions

et al. 2015

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We present observations of the topside ionosphere made at the Jicamarca Radio Observatory in March and September 2013, made using a full‐profile analysis approach. Recent updates to the methodology employed at Jicamarca are also described. Measurements of plasma number density, electron and ion temperatures, and hydrogen and helium ion fractions up to 1500 km altitude are presented for 3 days in March and September. The main features of the observations include a sawtooth‐like diurnal variation in ht, the transition height where the O+ ion fraction falls to 50%, the appearance of weak He+ layers just below ht, and a dramatic increase in plasma temperature at dawn followed by a sharp temperature depression around local noon. These features are consistent from day to day and between March and September. Coupled Ion Neutral Dynamics Investigation data from the Communication Navigation Outage Forecast System satellite are used to help validate the March Jicamarca data. The SAMI2‐PE model was able to recover many of the features of the topside observations, including the morphology of the plasma density profiles and the light‐ion composition. The model, forced using convection speeds and meridional thermospheric winds based on climatological averages, did not reproduce the extreme temperature changes in the topside between sunrise and noon. Some possible causes of the discrepancies are discussed.

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Solar cycle variability of nighttime topside helium ion concentrations over Arecibo

Cited by 29 publications

References 30 publications

Topside measurements at Jicamarca during solar minimum

Topside measurements at Jicamarca during solar minimum

Derivation of neutral oxygen density under charge exchange in the midlatitude topside ionosphere

Topside equatorial ionospheric density, temperature, and composition under equinox, low solar flux conditions

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