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Analysis of suprathermal tails using hourly-averaged proton velocity distributions at 1 AU

机译:使用每小时平均质子速度分布(1 AU)分析超热尾

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摘要

We obtain hourly values of tail densities and of power law indices, γ, of suprathermal (speeds above 2.48 times the solar wind speed) protons from power law fits to hourly velocity distribution functions in the solar-wind-frame. ACE/SWICS and ULEIS data, which often include very low counting statistics, are used to derive hourly proton phase space densities. We find that during part of the recent deep solar minimum (first 82 days in 2009): (a) the spectrum averaged over the entire 82 day period reveals the bulk and the halo solar wind components, interstellar pickup protons (seldom seen at 1 AU), and the common Fisk and Gloeckler (F&G) suprathermal tail (v^(−5) in velocity v with an exponential rollover at some higher speed); (b) hourly values of the tail densities range from ~1•10^(−6) to ~3•10^(−3) cm^(−3) and vary by a factor of ~2-10 over periods of hours as well as in a quasi-periodic manner by factors of 20 to 50 over 4 to 10 days; (c) about 95% of the nearly 2000 hourly spectra have complex shapes and that are not power laws; (d) about half of the ~5% of the hourly spectra that are monotonically decreasing with increasing speed (e.g. exponentials or Max-wellians, or F&G) are observed at times of high tail densities (>−5•10^(−5) cm^(−3)) where the spectra have the common F&G shapes; (e) each of the six sharp (few day long), large (tail density > 5•10^(−4) cm^(−3)) increases observed during this time period is associated with solar wind compression regions; (f) the eight shocks recorded locally that were not contained in compression regions did not produce signif-icant increases in the tail densities. We conclude that during times of low solar activity the higher energy portions of locally accelerated suprathermal tail spectra are often obscured by significant contributions from remotely accelerated particles whose spectra below (1-3)•10^8 cm/s are modified (modulated) by propagation from this remote acceleration region. In those instances where strong acceleration occurs locally, the observed tail spectra have the common F&G spectral shapes.
机译:我们从功率定律获得了超热质子的尾部密度和功率定律指数γ的小时值,该质子符合太阳风框架中的每小时速度分布函数。 ACE / SWICS和ULEIS数据通常包括非常低的计数统计信息,用于导出每小时的质子相空间密度。我们发现,在最近的一次深太阳最低值的一部分(2009年的前82天)中:(a)在整个82天期间的平均频谱揭示了大部分和光晕的太阳风分量,星际拾取质子(很少出现在1 AU ),以及常见的Fisk和Gloeckler(F&G)超热尾部(速度v中的v ^(-5),并且以更高的速度发生指数翻转); (b)每小时的尾巴密度值范围从〜1•10 ^(− 6)到〜3•10 ^(− 3)cm ^(-3),并且在几个小时内变化约2-10倍以及在4到10天内以准周期方式减少20到50; (c)近2000小时的频谱中约有95%具有复杂的形状,并且不是幂律; (d)在高尾巴密度(> -5•10 ^(− 5)时,观察到约5%的小时光谱中约有一半随速度单调减小(例如,指数或Max-wellian或F&G)。 )cm ^(− 3)),其中光谱具有常见的F&G形状; (e)在这段时间内观察到的六个急剧(几天之内)大(尾密度> 5•10 ^(-4)cm ^(-3)的增加)中的每一个都与太阳风压缩区域有关; (f)局部记录的八次冲击未包含在压缩区域内,并未使尾巴密度显着增加。我们得出的结论是,在太阳活动低的时期,局部加速的超热尾光谱的较高能量部分经常被远加速粒子的显着贡献所遮盖,这些粒子的光谱在(1-3)•10 ^ 8 cm / s以下被修饰(调制)从这个远程加速区域传播。在局部发生强加速度的那些情况下,观察到的尾部光谱具有常见的F&G光谱形状。

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