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Initial measurements of O-ion and He-ion decay rates observed from the Van Allen probes RBSPICE instrument.

Gerrard A, Lanzerotti L, Gkioulidou M, Mitchell D, Manweiler J, Bortnik J, Keika K - J Geophys Res Space Phys (2014)

Bottom Line: These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements.Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio.We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date.

View Article: PubMed Central - PubMed

Affiliation: Center for Solar-Terrestrial Research, New Jersey Institute of Technology Newark, New Jersey, USA.

ABSTRACT

: H-ion (∼45 keV to ∼600 keV), He-ion (∼65 keV to ∼520 keV), and O-ion (∼140 keV to ∼1130 keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L shells, on the order of ∼0.8 day at L shells of 3-4, and decay more slowly with higher L shell, on the order of ∼1.7 days at L shells of 5-6. Conversely, O-ions decay very rapidly (∼1.5 h) across all L shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher-energy (> 500 keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date.

Key points: We report initial observations of ring current ionsWe show that He-ion decay rates are consistent with theoryWe show that O-ions with energies greater than 500 keV decay very rapidly.

No MeSH data available.


Related in: MedlinePlus

(first and third panels) He-ion/H-ion and O-ion/H-ion ratios across the entire RBSPICE instrument energy ranges, respectively, from Figure 3 but plotted over 2013 day of year (DOY) 70–196. (second and fourth panels) Time traces of the average (log) ratio in three L shell bins; black for L = 3–4, green for L = 4–5, and red for L = 5–6. L here is determined by a dipole L model.
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fig05: (first and third panels) He-ion/H-ion and O-ion/H-ion ratios across the entire RBSPICE instrument energy ranges, respectively, from Figure 3 but plotted over 2013 day of year (DOY) 70–196. (second and fourth panels) Time traces of the average (log) ratio in three L shell bins; black for L = 3–4, green for L = 4–5, and red for L = 5–6. L here is determined by a dipole L model.

Mentions: This difference in the persistence of the He-ion and O-ion abundances as a function of L value is quantified in Figure 5 for a sample period of 2013 day of year 70 to 195. In this figure, the values of the He/H and O/H ratios are plotted as a function of time, orbit by orbit, averaged over the ratio values in three L bands: L = 3–4 (black data points), L = 4–5 (green), and L = 5–6 (red). Through exponential fits to 20 injection events, we report that the average decay rate, as determined by the e-folding time, for He-ions in the L = 3–4 band to be ∼0.8 days, for He-ions in the L = 4–5 band to be ∼1.1 days, and in the L = 5–6 band to be ∼1.7 days. Uncertainties on each of these fits are estimated to be ∼0.2 days and due to constraints on the initial amplitude and baseline value of the He/H ratio. At the times of increase (times of particle injection) in the relative He-ion abundance, the He/H ratio can reach values between ∼5% and 10%. After the decay of the He-ion population relative to the H-ion in this energy band, the He/H ratios at all L values can fall to less than 1%.


Initial measurements of O-ion and He-ion decay rates observed from the Van Allen probes RBSPICE instrument.

Gerrard A, Lanzerotti L, Gkioulidou M, Mitchell D, Manweiler J, Bortnik J, Keika K - J Geophys Res Space Phys (2014)

(first and third panels) He-ion/H-ion and O-ion/H-ion ratios across the entire RBSPICE instrument energy ranges, respectively, from Figure 3 but plotted over 2013 day of year (DOY) 70–196. (second and fourth panels) Time traces of the average (log) ratio in three L shell bins; black for L = 3–4, green for L = 4–5, and red for L = 5–6. L here is determined by a dipole L model.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497452&req=5

fig05: (first and third panels) He-ion/H-ion and O-ion/H-ion ratios across the entire RBSPICE instrument energy ranges, respectively, from Figure 3 but plotted over 2013 day of year (DOY) 70–196. (second and fourth panels) Time traces of the average (log) ratio in three L shell bins; black for L = 3–4, green for L = 4–5, and red for L = 5–6. L here is determined by a dipole L model.
Mentions: This difference in the persistence of the He-ion and O-ion abundances as a function of L value is quantified in Figure 5 for a sample period of 2013 day of year 70 to 195. In this figure, the values of the He/H and O/H ratios are plotted as a function of time, orbit by orbit, averaged over the ratio values in three L bands: L = 3–4 (black data points), L = 4–5 (green), and L = 5–6 (red). Through exponential fits to 20 injection events, we report that the average decay rate, as determined by the e-folding time, for He-ions in the L = 3–4 band to be ∼0.8 days, for He-ions in the L = 4–5 band to be ∼1.1 days, and in the L = 5–6 band to be ∼1.7 days. Uncertainties on each of these fits are estimated to be ∼0.2 days and due to constraints on the initial amplitude and baseline value of the He/H ratio. At the times of increase (times of particle injection) in the relative He-ion abundance, the He/H ratio can reach values between ∼5% and 10%. After the decay of the He-ion population relative to the H-ion in this energy band, the He/H ratios at all L values can fall to less than 1%.

Bottom Line: These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements.Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio.We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date.

View Article: PubMed Central - PubMed

Affiliation: Center for Solar-Terrestrial Research, New Jersey Institute of Technology Newark, New Jersey, USA.

ABSTRACT

: H-ion (∼45 keV to ∼600 keV), He-ion (∼65 keV to ∼520 keV), and O-ion (∼140 keV to ∼1130 keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L shells, on the order of ∼0.8 day at L shells of 3-4, and decay more slowly with higher L shell, on the order of ∼1.7 days at L shells of 5-6. Conversely, O-ions decay very rapidly (∼1.5 h) across all L shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher-energy (> 500 keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date.

Key points: We report initial observations of ring current ionsWe show that He-ion decay rates are consistent with theoryWe show that O-ions with energies greater than 500 keV decay very rapidly.

No MeSH data available.


Related in: MedlinePlus