On the nature of equatorial spread F
On the nature of equatorial spread F
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DOI：
10.1029/jz066i004p01081
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发表时间：
1961-04
影响因子：
--
通讯作者：
R. Cohen;K. Bowles
中科院分区：
文献类型：
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作者：
R. Cohen;K. Bowles
通过F区散射的电离层传播是以50兆赫兹/秒的速度在一个跨赤道路径上（中点在秘鲁的万卡约附近）采用2580公里的发射机-接收机间隔来寻求的。通过F散射传播是目前在这条道路上约10%的时间，但只有在夜间。与F散射发生密切相关的一个条件是万卡约电离图上存在赤道扩展F构形。支持这种F散射的传播介质的高度通常可以用电离图上相关赤道扩展F的最低高度来识别。实验结果的解释的基础上，赤道扩展F示出所产生的散射的电子密度发生在底部的F层或高达100公里以下的不规则性相对较薄的床单。这些补丁的厚度估计在50公里的顺序。组成这些补丁的散射不规则性被发现是延长沿着地球的磁力线。电子不规则性的规模10米或更小的测量在至少一个维度横向的磁场线，和1000米或更长的测量沿着磁场线，被证明存在高达450公里的夜间赤道F区在赤道扩展F条件。在万卡约观测到的赤道扩展F回波被证明是在磁东西平面的所有仰角到达。一个特定的散射片在磁东西方向上的地理延伸有时高达1000公里。本文提出了一个观测程序，用以区分赤道电离图上出现的两种基本的扩展F回波。一个必要的条件，即平均电子密度的轮廓平行于磁力线，提出了作为一个控制因素的发生扩展F在赤道电离层。
Ionospheric propagation via scattering from the F region was sought at 50 Mc/s over a transequatorial path (with midpoint near Huancayo, Peru) employing a 2580-km transmitter-receiver separation. Propagation via F scatter was present over this path about 10 per cent of the time, though only at night. A condition closely related to the occurrence of F scatter was the presence of equatorial spread-F configurations on the Huancayo ionograms. The height of the propagation medium supporting this F scatter was usually identifiable with the lowest height of the associated equatorial spread F on the ionograms. On the basis of an interpretation of experimental results, equatorial spread F is shown to arise from scattering by relatively thin sheets of irregularities in electron density which occur at the bottom of the F layer or as much as 100 km lower. The thickness of these patches is estimated at the order of 50 km. The scattering irregularities comprising these patches are found to be elongated along the earth's magnetic lines of force. Electron irregularities of scale 10 meters or smaller measured in at least one dimension transverse to the magnetic field lines, and 1000 meters or longer measured along the magnetic field lines, are shown to exist as high as 450 km in the nocturnal equatorial F region during equatorial spread-F conditions. Equatorial spread-F echoes observed at Huancayo are demonstrated to be arriving at all elevation angles in the magnetic east-west plane. The geographical extension of a given scattering sheet in the magnetic east-west direction was at times as great as 1000 km. An observational procedure is suggested for distinguishing two fundamental varieties of spread-F echoes appearing on the equatorial ionograms. A necessary condition, that the contours of mean electron density be parallel to the magnetic lines of force, is proposed as a controlling factor for the occurrence of spread F in the equatorial ionosphere.