Some investigations of ionospheric diurnal variation
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摘要: 电离层具有非常鲜明的日变化特性. 电离层日变化特性是认识包括逐日变化等众多电离层现象的出发点,也是电离层经验模型需要呈现的最基本特性. 本文简要介绍了有关电离层日变化的一些研究工作,重点关注以电场为核心的电离层日出变化、电离层午时咬失现象、电离层夜间增强,特别是以威德海异常为典型代表的中纬电离层夏季夜间异常变化. 评述了这些方面相关研究进展、目前存在的争议、需要特别注意的地方及应进一步探讨的问题.Abstract: The most significant and fundamental feature of the ionospheric variations is the diurnal pattern of the ionosphere, which has very interesting and complicated phenomenon. In this brief review, we will introduce some works related with the ionospheric diurnal variations. Our topics includes the sunrise ionosphere with a focus on the enhancement of equatorial electric field around sunrise hours, the phenomenon of the daytime double peaks or noontime bite-out, and the nighttime enhancements in electron density, especially the summer mid-latitude nighttime anomalies represented by the Weddell Sea anomaly. We further discuss some points which are still under debate and remain elusive.
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图 1 2004年6月10日Jicamarca非相干散射雷达观测的垂直漂移速度、及测高仪探测的foF2和hmF2日变化. (上图)带圆点线是非相干散射雷达观测垂直漂移速度,无圆点实线是由S-F经验模型给出的漂移. (中、下图)带圆点线表示测高仪foF2和hmF2当日观测值,无圆点实线是其27天滑动值(修改自Zhang et al., 2016)
Figure 1. Diurnal variation of the vertical plasma drift from Jicamarca incoherent scatter radar and foF2 and hmF2 from Jicamarca ionosonde observations on June 10, 2004. (Top) vertical drift from Jicamarca incoherent scatter radar observations (curve with circles) and from S-F model (line without circles); (middle and bottom) foF2 and hmF2 from ionosonde observations (curve with solid circles denotes the observations and line without circles for 27-day moving values) (modified from Zhang et al., 2016)
图 2 基于ROCSAT-1观测统计的赤道电场日出增强事件随经度分布. 从上到下分别是等分季节、六月至季和十二月至季. 竖条给出日出时段卫星轨道跨过赤道的数目,填充条为存在电场日出增强的轨道数目(修改自Zhang et al., 2015)
Figure 2. Longitudinal distribution of the number of the events with sunrise enhancements in the equatorial zonal electric field and orbits of ROCSAT-1 observations in (top) Equinox, (middle) June solstice, and (bottom) December solstice. Bars denote the total numbers of orbits crossing the equator and filled part plots the number of the orbits with a sunrise enhancement in electric field (modified from Zhang et al., 2015)
图 3 高太阳活动水平期间F2层峰值电子密度(NmF2)随地方时和月份的变化,自左至右依次为磁赤道Kodaikanal站、磁赤道北侧Manila站和磁赤道南侧Singapore站的结果. Kodaikanal站子图中的虚线框指示了午时咬失现象(修改自Chen Y et al., 2020)
Figure 3. Diurnal and seasonal variations of the peak electron density of F2 layer (NmF2) at (left) Kodaikanal, (middle) Manila, and (right) Singapore stations for high solar activity. The vertical dash line in the left panel denotes the appearance of the noontime bite-out feature at Kodaikanal (modfied from Chen Y et al., 2020)
图 4 在高(Smax)低(Smin)太阳活动条件下6月份Okinawa、Wakkanai和Yakutsk台站F2层临界频率(foF2,有圆点曲线)和峰高(hmF2)的周日变化. 图中阴影部分表示300 km高度无光照时间段(修改自Chen et al., 2021)
Figure 4. Diurnal variations of the critical frequency (foF2, with solid circles) and peak height (hmF2) of F2 layer at (left) Okinawa, (middle) Wakkanai, and (right) Yakutsk stations for low (Smin) and high (Smax) solar activity. The grey area denotes the time interval without sun light at 300 km altitude (modified from Chen et al., 2021)
图 5 Alma-Ata台站测高仪F2层临界频率(foF2)夜间增强典型事例. 图中箭头表示日落时刻以及地面与300 km高度日出时刻(修改自Yakovets et al., 2009)
Figure 5. Cases of nighttime enhancements in the F2 layer critical frequency (foF2) at Alma-Ata. The arrows denote the time of ground sunset and sunrise at ground and 300 km altitude, respectively (modified from Yakovets et al., 2009)
图 6 典型夜间增强事例中北京台站测高仪F2层临界频率(foF2)、hmF2和TEC日变化(修改自Li et al., 2020)
Figure 6. Diurnal variations of the F2 layer critical frequency (foF2) and peak height (hmF2) and total electron content (TEC) during three cases of nighttime enhancements at Beijing (modified from Li et al., 2020)
图 7 2012年148~150天期间三亚台站测高仪F2层临界频率(foF2)、hmF2和标高以及地磁活动Kp指数变化. 带圆圈线为观测值,带误差棒曲线为月中值及上下四分值,黑色短竖线标示当地子夜,阴影区域为夜间时段(修改自Liu et al., 2013)
Figure 7. Diurnal variations of the F2 layer critical frequency (foF2), hmF2 and scale height at Sanya during 148~150 days in 2012. The geomagnetic activity Kp index is plotted in the bottom panel. The curve with circles denotes the observations and line with bars shows the monthly median values and upper and lower quartiles. The vertical solid lines mark the local midnight and the gray regions outline the nighttime intervals(modified from Liu et al., 2013)
图 8 2014年4月8日我国曲靖台站电离层最大密度NmF2及四个高度上电子密度的日变化. 灰色区域展示在NmF2增强发生时,在峰高以上电子密度出现下降,而底部电离层出现增强(修改自Liu et al., 2020)
Figure 8. Diurnal variations of the electron density at the F2 layer peak and four altitudes at Qujing on April 8, 2014. The grey area denotes the time interval of NmF2 enhancement (modified from Liu et al., 2020)
图 9 六月至季COSMIC掩星观测在(120°E, 60°N)附近NmF2日变化. COSMIC观测值以散点表示,而平均值及方差以曲线和误差棒画出(修改自Chen et al., 2016)
Figure 9. Local time variation of COSMIC NmF2 around (120°E, 60°N) at June solstice. Dots show the COSMIC measurements, the line with bars are the average and deviations of NmF2 (modified from Chen et al., 2016)
图 10 2007~2009年期间冬季NmF2夜间增强幅度△NmF2. 黑实线对应零地磁偏角(修改自Chen et al., 2015b)
Figure 10. The amplitude of the enhancement of NmF2 in December solstice and June Solstice determined from COSMIC observations in 2007~2009. Dark lines plot the zero magnetic declination, and the gray lines show the iso-dip contours (modified from Chen et al., 2015b)
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