Stormtime Evolution of the O + ${\mathrm{O}}^{+}$ Density: Magnetoseismic Analysis of Van Allen Probes Data

IF 2.6 2区 地球科学 Q2 ASTRONOMY & ASTROPHYSICS
Kazue Takahashi, Richard E. Denton, Peter Chi
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We apply a magnetoseismic technique to Van Allen Probes data to statistically determine the spatial and temporal development of the region of elevated <span></span><math>\n <semantics>\n <mrow>\n <msup>\n <mi>O</mi>\n <mo>+</mo>\n </msup>\n </mrow>\n <annotation> ${\\mathrm{O}}^{+}$</annotation>\n </semantics></math> number density <span></span><math>\n <semantics>\n <mrow>\n <mfenced>\n <msub>\n <mi>n</mi>\n <msup>\n <mi>O</mi>\n <mo>+</mo>\n </msup>\n </msub>\n </mfenced>\n </mrow>\n <annotation> $\\left({n}_{{\\mathrm{O}}^{+}}\\right)$</annotation>\n </semantics></math>, referred to as the oxygen torus, during geomagnetic storms. This study is motivated by previous studies that reported magnetic local time (MLT) localization of the torus to the morning side. In our study, we first determine the frequencies of the fundamental through third harmonics of toroidal standing Alfvén waves to estimate the mass density <span></span><math>\n <semantics>\n <mrow>\n <mo>(</mo>\n <mi>ρ</mi>\n <mo>)</mo>\n </mrow>\n <annotation> $(\\rho )$</annotation>\n </semantics></math> and then use the electron density <span></span><math>\n <semantics>\n <mrow>\n <mfenced>\n <msub>\n <mi>n</mi>\n <mi>e</mi>\n </msub>\n </mfenced>\n </mrow>\n <annotation> $\\left({n}_{\\mathrm{e}}\\right)$</annotation>\n </semantics></math> derived from plasma wave spectra to define the average ion mass <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>M</mi>\n <mi>i</mi>\n </msub>\n </mrow>\n <annotation> ${M}_{\\mathrm{i}}$</annotation>\n </semantics></math> (=<span></span><math>\n <semantics>\n <mrow>\n <mi>ρ</mi>\n <mo>/</mo>\n <msub>\n <mi>n</mi>\n <mi>e</mi>\n </msub>\n </mrow>\n <annotation> $\\rho /{n}_{\\mathrm{e}}$</annotation>\n </semantics></math>). We obtain <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>n</mi>\n <msup>\n <mi>O</mi>\n <mo>+</mo>\n </msup>\n </msub>\n </mrow>\n <annotation> ${n}_{{\\mathrm{O}}^{+}}$</annotation>\n </semantics></math> from <span></span><math>\n <semantics>\n <mrow>\n <msub>\n <mi>M</mi>\n <mi>i</mi>\n </msub>\n </mrow>\n <annotation> ${M}_{\\mathrm{i}}$</annotation>\n </semantics></math> by making an assumption about the <span></span><math>\n <semantics>\n <mrow>\n <msup>\n <mtext>He</mtext>\n <mo>+</mo>\n </msup>\n </mrow>\n <annotation> ${\\text{He}}^{+}$</annotation>\n </semantics></math> number density relative to the <span></span><math>\n <semantics>\n <mrow>\n <msup>\n <mi>H</mi>\n <mo>+</mo>\n </msup>\n </mrow>\n <annotation> ${\\mathrm{H}}^{+}$</annotation>\n </semantics></math> number density. All quantities are evaluated in a 15 min moving data window that moves in 5 min steps. 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Abstract

Measurements of singly ionized oxygen ( O + ${\mathrm{O}}^{+}$ ) ions in the inner magnetosphere during geomagnetic storms are important because the ions affect various magnetospheric processes. We apply a magnetoseismic technique to Van Allen Probes data to statistically determine the spatial and temporal development of the region of elevated O + ${\mathrm{O}}^{+}$ number density n O + $\left({n}_{{\mathrm{O}}^{+}}\right)$ , referred to as the oxygen torus, during geomagnetic storms. This study is motivated by previous studies that reported magnetic local time (MLT) localization of the torus to the morning side. In our study, we first determine the frequencies of the fundamental through third harmonics of toroidal standing Alfvén waves to estimate the mass density ( ρ ) $(\rho )$ and then use the electron density n e $\left({n}_{\mathrm{e}}\right)$ derived from plasma wave spectra to define the average ion mass M i ${M}_{\mathrm{i}}$ (= ρ / n e $\rho /{n}_{\mathrm{e}}$ ). We obtain n O + ${n}_{{\mathrm{O}}^{+}}$ from M i ${M}_{\mathrm{i}}$ by making an assumption about the He + ${\text{He}}^{+}$ number density relative to the H + ${\mathrm{H}}^{+}$ number density. All quantities are evaluated in a 15 min moving data window that moves in 5 min steps. By generating L $L$ -MLT maps of M i ${M}_{\mathrm{i}}$ for different phases of 102 storms with SYMH minimum lower than 50 ${-}50$  nT, we find that a region of high M i ${M}_{\mathrm{i}}$ appears on the morning side during the storm main phase and lasts for a few days. n O + ${n}_{{\mathrm{O}}^{+}}$ is also high on the morning side during the main phase, but this MLT skewing disappears during the recovery phase. Therefore, the MLT asymmetry of the oxygen torus depends on what parameter is considered.

Abstract Image

单电离氧(O +)的测量 ${\mathrm{O}}^{+}$ )离子在地磁暴期间内磁层是重要的,因为离子影响各种磁层过程。我们将磁震技术应用于范艾伦探测器数据,以统计确定O +升高区域的时空发展 ${\mathrm{O}}^{+}$ 数密度n O + $\left({n}_{{\mathrm{O}}^{+}}\right)$ 在地磁风暴期间,被称为氧环面。这项研究的动机是由以前的研究报道磁局部时间(MLT)定位环到早晨侧。在我们的研究中,我们首先通过确定环面驻波的三次谐波来估计质量密度(ρ)。 $(\rho )$ 然后用电子密度ne $\left({n}_{\mathrm{e}}\right)$ 由等离子体波谱推导出平均离子质量mi ${M}_{\mathrm{i}}$ (= ρ / n e $\rho /{n}_{\mathrm{e}}$ )。我们得到n O + ${n}_{{\mathrm{O}}^{+}}$ 源自M i ${M}_{\mathrm{i}}$ 通过对He +的假设 ${\text{He}}^{+}$ 相对于H +的数密度 ${\mathrm{H}}^{+}$ 数字密度。所有的数量都在一个15分钟移动数据窗口中评估,该数据窗口以5分钟的步骤移动。通过生成L $L$ - mi的mlt映射 ${M}_{\mathrm{i}}$ 102个最小SYMH值小于- 50的风暴的不同阶段 ${-}50$ nT,我们发现一个高mi的区域 ${M}_{\mathrm{i}}$ 在风暴主阶段出现在早晨,并持续几天。n O + ${n}_{{\mathrm{O}}^{+}}$ 在主要阶段,早晨侧也很高,但这种MLT倾斜在恢复阶段消失。因此,氧环面的MLT不对称性取决于所考虑的参数。
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来源期刊
Journal of Geophysical Research: Space Physics
Journal of Geophysical Research: Space Physics Earth and Planetary Sciences-Geophysics
CiteScore
5.30
自引率
35.70%
发文量
570
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