Sounding of the plasmasphere by Mid‐continent MAgnetoseismic Chain (McMAC) magnetometers
Sounding of the plasmasphere by Mid‐continent MAgnetoseismic Chain (McMAC) magnetometers
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通过中大陆磁震链 (McMAC) 磁力计探测等离子体层
DOI：
10.1002/jgra.50274
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
J. P. Gibson
中科院分区：
文献类型：
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作者：
Peter J. Chi;Mark J. Engebretson;M. Moldwin;C. Russell;Ian R. Mann;M. Hairston;M. Reno;Jerry Goldstein;L. I. Winkler;J. L. Cruz;Donghoon Lee;K. Yumoto;R. Dalrymple;B. Chen;J. P. Gibson
本文对中大陆磁震链（McMAC）的场线共振（FLR）观测得到的等离子体质量密度进行了统计分析。McMAC由美国和墨西哥沿330°磁经度的9个站点组成，L值在1.5到3.4之间。利用梯度法和自动FLR检测程序，研究了2006年7月至2007年6月一整年的McMAC观测数据。我们发现，当L = 2.7时，FLR的检出率在当地中午左右可高达56%，而在较高和较低L‐值时，检出率分别由于偶尔存在等离子体ause和较弱的FLR信号而下降。当L值在1.8和3.1之间时，推断出的赤道等离子体质量密度遵循L−4的L依赖性。通过比较质量密度和电子密度，我们发现离子质量从L = 1.8时的1.7 amu逐渐减小到L = 3.1时的1 amu。等离子体质量密度呈年变化，在1月达到最大值，当L = 2.4时，1月与7月密度之比为1.6。我们的观测还表明，等离子体质量密度在上午保持稳定，中午后上升，这一现象可能归因于赤道电离异常，这是低纬度等离子体中性耦合的一部分。
We present a statistical analysis on the plasmaspheric mass density derived from the field line resonance (FLR) observations by the Mid‐continent MAgnetoseismic Chain (McMAC). McMAC consists of nine stations in the United States and Mexico along the 330° magnetic longitude, spanning L‐values between 1.5 and 3.4. Using the gradient method and an automated procedure for FLR detection, we studied a full year of McMAC observations between July 2006 and June 2007. We find that the rate of FLR detection can reach as high as 56% around local noon at L = 2.7, and the detection rates at higher and lower L‐values decline due to the occasional presence of the plasmapause and weaker FLR signals, respectively. At L‐values between 1.8 and 3.1, the inferred equatorial plasma mass density follows the L‐dependence of L−4. By comparing the mass density with the electron density, we found that the ion mass gradually decreased from 1.7 amu at L = 1.8 to 1 amu at L = 3.1. The plasma mass density exhibits an annual variation that maximizes in January, and at L = 2.4 the ratio between January and July densities is 1.6. Our observations also show a local time dependence of plasmaspheric mass density that stays steady in the morning and rises postnoon, a phenomenon that may be attributed to the equatorial ionization anomaly as a part of the plasma neutral coupling at low latitude.