The Sodium and Potassium Atmospheres of the Moon
The Sodium and Potassium Atmospheres of the Moon
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月球的钠和钾大气
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
W. Smyth
中科院分区：
文献类型：
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作者：
M. Marconi;W. Smyth
本文对汞外大气层钠、钾的源、汇、气-地相互作用和输运动力学进行了理论综述。这四个因素的信息，控制这两个碱性基团气体的空间分布的行星，被纳入数值模型。初始源原子大气和环境（弹道跳跃）原子大气的空间性质和相对重要性，然后检查，并示出控制和耦合在很大程度上由钠和钾经历的极大的和可变的太阳辐射加速，因为它们共振散射太阳光子。横向（antisunward）运输率的热容纳钠和钾环境原子被证明是由太阳辐射加速驱动，并在水星的轨道上的一个重要部分围绕太阳，是足够快的竞争力与这些原子的短光电离寿命时，他们位于峰会表面附近或约30度内的终结者。横向传输速率的特征在于迁移时间，该迁移时间由最初在表面上的点源处开始的原子系综的模型计算确定（即，数值时空相关的绿色函数）。四个动画的时空演化的钠（或钾）大气产生的表面上的点源的录像带格式。对于钠和钾的扩展表面源，局部柱密度由来自不同表面源位置的原子的光电离寿命和横向传输时间之间的竞争决定。钠表面源通量（参考近日点处的水星）是在有阳光照射的半球上再现典型观测到的几兆瑞利的D2发射线亮度所需的，推断出的柱密度为1-2 x 10（exp 11）原子/平方厘米，范围约为2-5 x 10（exp 7）原子/平方厘米/秒。钠模式被应用于研究观测数据，记录在平均钠柱密度和太阳辐射加速的关系。由太阳辐射加速驱动的横向运输显示产生这种行为的组合不同的来源和表面调节系数。最佳拟合模型拟合的观测数据需要一个显着程度的热适应的周围钠原子的表面和源率，减少作为一个反幂的1.5至2日心距离。
A general theoretical overview for the sources, sinks, gas-surface interactions, and transport dynamics of sodium and potassium in the exospheric atmsophere of Mercury is given. Information for these four factors, which control the spatial distribution of these two alkali-group gases about the planet, is incorporated in numerical models. The spatial nature and relative importance of the initial source atom atmosphere and the ambient (ballistic hopping) atom atmosphere are then examined and are shown to be controlled and coupled to a great extent by the extremely large and variable solar radiation acceleration experienced by sodium and potassium as they resonantly scatter solar photons. The lateral (antisunward) transport rate of thermally accommodated sodium and potassium ambient atoms is shown to be driven by the solar radiation acceleration and, over a significant portion of Mercury's orbit about the Sun, is sufficiently rapid to be competitive with the short photoionization lifetimes for these atoms when they are located on the summit surface near or within about 30 deg of the terminator. The lateral transport rate is characterized by a migration time determined by model calculations for an ensemble of atoms initially starting at a point source on the surface (i.e., a numerical spacetime dependent Green's function). Four animations for the spacetime evolution of the sodium (or potassium) atmosphere produced by a point source on the surface are presented on a videotape format. For extended surface sources for sodium and potassium, the local column density is determined by competition between the photoionization lifetimes and the lateral transport times of atoms originating from different surface source locations. Sodium surface source fluxes (referenced to Mercury at perihelion) that are required on the sunlit hemisphere to reproduce the typically observed several megarayleighs of D2 emission-line brightness and the inferred column densities of 1-2 x 10(exp 11) atoms per sq cm range from approximately 2-5 x 10(exp 7) atoms/sq cm/sec. The sodium model is applied to study observational data that document an anticorrelation in the average sodium column density and solar radiation acceleration. Lateral transport driven by the solar radiation acceleration is shown to produce this behavior for combinations of different sources and surface accomodation coefficients. The best fit model fits to the observational data require a significant degree of thermal accommodation of the ambient sodium atoms to the surface and a source rate that decreases as an inverse power of 1.5 to 2 in heliocentric distance.