Solar cycle variations of trapped proton flux in the inner radiation belt

Qin, Murong; Zhang, Xianguo; Ni, Binbin; Song, Hongqiang; Zou, Hong; Sun, Yueqiang

doi:10.1002/2014ja020300

Cited by 48 publications

(79 citation statements)

References 33 publications

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“…The westward drift rate as well as latitudinal and longitudinal solar cycle oscillations are well recovered in agreement with results from other recent studies (e.g. Qin et al, 2014). In Qin et al (2014), they identify a 685 days time delay between the F10.7 solar index and the proton flux longitudinal evolution.…”

Section: Discussionsupporting

confidence: 91%

“…Qin et al, 2014). In Qin et al (2014), they identify a 685 days time delay between the F10.7 solar index and the proton flux longitudinal evolution. They obtain these results studying protons with energies > 70 MeV, so no direct comparisons can be made with our results which focus on protons with energy > 16 MeV.…”

Section: Discussionmentioning

confidence: 99%

“…We use monthly data charts with a spatial grid spacing of 2.5 • in both latitude and longitude. Qin et al (2014) have recently analysed the proton flux measured by NOAA-15 from 1999 to 2009. They used a Gaussian function to approximate the geometry of the SAA and investigated the variability of the anomaly on decadal time-scales.…”

Section: Poes -Particle Flux Datamentioning

confidence: 99%

“…Gaussian functions were proposed to describe the spatial distribution of particle flux over the South Atlantic region, both longitudinally and latitudinally (e.g. Casadio and Arino, 2011;Qin et al, 2014). To account for an apparent West-East morphological asymmetry, Weibull and Gumbel functions have also been tested (Fürst et al, 2009;Hell, 2010).…”

Section: Principal Component Analysis Applied To Saamentioning

confidence: 99%

“…The neutral atmosphere expands during the ascending phase of the solar cycle and, at altitudes above 100 km, its density increases (Solomon et al, 2013). As a result, in regions where mirror points are low enough, protons are removed from the inner belt through nuclear collisions with atmospheric neutral particles (Gledhill, 1976), explaining why the particle flux in the SAA region is anti-correlated with the solar activity as measured by the 10.7 cm radio flux of the Sun (Fürst et al, 2009;Casadio and Arino, 2011;Qin et al, 2014). This effect is maximized for the low values of L that correspond to the highest energy proton shells (Vacaresse et al, 1999).…”

Section: Introduction: the Particle Flux In The South Atlantic Anomalymentioning

confidence: 99%

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The South Atlantic Anomaly throughout the solar cycle

Domingos

Jault

Pais

et al. 2017

Earth and Planetary Science Letters

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The Sun-Earth's interaction is characterized by a highly dynamic electromagnetic environment, in which the magnetic field produced in the Earth's core plays an important role. One of the striking characteristics of the present geomagnetic field is denoted the South Atlantic Anomaly (SAA) where the total field intensity is unusually low and the flux of charged particles, trapped in the inner Van Allen radiation belts, is maximum. Here, we use, on one hand, a recent geomagnetic field model, CHAOS-6, and on the other hand, data provided by different platforms (satellites orbiting the Earth -POES NOAA for 1998 and CALIPSO for 2006. Evolution of the SAA particle flux can be seen as the result of two main effects, the secular variation of the Earth's core magnetic field and the modulation of the density of the inner radiation belts during the solar cycle, as a function of the L value that characterises the drift shell, where charged particles are trapped. To study the evolution of the particle flux anomaly, we rely on a Principal Component Analysis (PCA) of either POES particle flux or CALIOP dark noise. Analysed data are distributed on a geographical grid at satellite altitude, based on a L-shell reference frame constructed from the moving eccentric dipole. Changes in the main magnetic field are responsible for the observed westward drift. Three PCA modes account for the time evolution related to solar effects. Both the first and second modes have a good correlation with the thermospheric density, which varies in response to the solar cycle. The first mode represents the total intensity variation of the particle flux in the SAA, and the second the movement of the anomaly between different L-shells. The proposed analysis allows us to well recover the westward drift rate, as well as the latitudinal and longitudinal solar cycle oscillations, although the analysed data do not cover a complete (Hale) magnetic solar cycle (around 22 yr). Moreover, the developments made here would enable us to forecast the impact of the South Atlantic Anomaly on space weather. A model of the evolution of the eccentric dipole field (magnitude, offset and tilt) would suffice, together with a model for the solar cycle evolution.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Poes -Particle Flux Datamentioning

confidence: 99%

Section: Principal Component Analysis Applied To Saamentioning

confidence: 99%

Section: Introduction: the Particle Flux In The South Atlantic Anomalymentioning

confidence: 99%

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The South Atlantic Anomaly throughout the solar cycle

Domingos

Jault

Pais

et al. 2017

Earth and Planetary Science Letters

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Short‐term variations of the inner radiation belt in the South Atlantic anomaly

Zou

Zong

et al. 2015

JGR Space Physics

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Long‐term variations of South Atlantic anomaly (SAA) are generally derived by fitting a Gaussian‐like function to an averaged distribution of the proton flux at a certain altitude accumulated over time periods for a month or longer. These data do not show the short‐term variation of SAA arising from geomagnetic storm effects whose time scale is less than a month. To investigate the short‐term variations, the features of SAA for the high‐energy protons detected by NOAA Polar Orbiting Environmental Satellites during 1998–2008 have been investigated with a 5 day running average method. It is found that the two SAA parameters for three proton channels reflect the maximal proton flux in SAA and the extension of SAA decreases several percent during geomagnetic storms. Possible reasons for the decreases of the two SAA parameters for high‐energy protons are discussed. Proton losses at the outer boundary of the inner radiation belt can be explained by the field line curvature scattering mechanism, while the decrease of the proton flux near the center of SAA is probably caused by the enhanced neutral atmospheric density during geomagnetic storms. The study of the behavior of high‐energy protons in SAA is useful for understanding of storm time and long‐term variations of the radiation environment near Earth and for constructing dynamic radiation belt models.

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Observation and modeling of the South Atlantic Anomaly in low Earth orbit using photometric instrument data

et al. 2016

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We present a new model of the South Atlantic Anomaly (SAA) particle flux intensity for low Earth orbit, based a new data set, i.e., particle noise pulses in an ultraviolet photomultiplier. The data set is unique in that it provides daily monitoring of the strength of the particle radiation at a fixed altitude and local time and provides a consistent set of observations across the deep solar minimum. The observations show the following: (1) a development over the decline of solar cycle 23 into a deep solar minimum and the subsequent rise of cycle 24, (2) the slow motion drift of the SAA centroid with time at the rate—longitude drift =0.36 ± 0.06°W/yr, and latitude drift =0.16 ± 0.09°N/yr, (3) a higher particle flux at solar minimum than at solar maximum, and (4) a yearly cyclical variation. These particle rates are deduced from electric noise pulses generated in the photometers when an energetic charged particle hits the detector and causes an electron to be liberated from the detector material. The model described here can be used to monitor and even spatially predict the changes in particle fluxes seen by instruments in contemporaneous low Earth orbits through the SAA.

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Solar cycle variations of trapped proton flux in the inner radiation belt

Cited by 48 publications

References 33 publications

The South Atlantic Anomaly throughout the solar cycle

The South Atlantic Anomaly throughout the solar cycle

Short‐term variations of the inner radiation belt in the South Atlantic anomaly

Observation and modeling of the South Atlantic Anomaly in low Earth orbit using photometric instrument data

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