Phase reversal of the diurnal cycle in the midlatitude ionosphere
Phase reversal of the diurnal cycle in the midlatitude ionosphere
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DOI：
10.1029/2009ja014689
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发表时间：
2010-01-30
影响因子：
2.8
通讯作者：
Yamamoto, Mamoru
中科院分区：
文献类型：
--
作者：
Liu, Huixin;Thampi, Smitha V.;Yamamoto, Mamoru
中纬度F区电子密度的典型昼夜周期由中午最大值和午夜最小值组成。然而，人们发现地球上三个不同的地区发生了这种昼夜周期的相位反转。它们是以（北纬53度，东经150度）为中心的东亚（EA）区域，以（北纬45度，西经50度）为中心的北大西洋（NA）区域和以（南纬60度，西经110度）为中心的南太平洋（SP）区域。被广泛报道的威德尔海异常现象位于 SP 区域内。 EA和NA地区的相位反转发生在3月至8月，SP地区的相位反转发生在8月至3月，在当地夏季最为突出。此外，这种昼夜异常在太阳极小期比太阳极大期更明显，并且在SP区域比NA和EA区域更明显，因为昼夜星等更大，一年中持续的月份也更多。需要强调的是，昼夜异常不仅包括夜间的增强，还包括同时存在的中午的消耗。因此，先前研究中报告的中纬度夏季夜间增强只是这种反向昼夜周期的一部分。相位反转的原因涉及几个相互作用的物理过程。其中，中性风与地磁场配置相结合起着举足轻重的作用。它在南部中纬度地区产生一波纵向模式，在北部中纬度地区产生两波模式，其波峰分别对应于SP、EA和NA区域的中心。中性风的季节变化和日落时电离层热收缩引起的电离向下运动可能在很大程度上控制夜间密度增强的发生时间以及不同月份持续的时间。相位反转是由于离子-中性紧密耦合而发生的。进一步指出，EA、NA 和 SP 地区的冬季异常非常弱或缺失。
The typical diurnal cycle of the midlatitude F region electron density consists of a midday maximum and a midnight minimum. However, a phase reversal of this diurnal cycle has been found to occur in three distinct regions on the globe. They are the East Asian (EA) region centered around (53 degrees N, 150 degrees E), the Northern Atlantic (NA) region centered around (45 degrees N, 50 degrees W) and the South Pacific (SP) region centered around (60 S, 110 degrees W). The intensively reported Weddell Sea Anomaly falls inside the SP region. The phase reversal occurs during March-August in EA and NA regions, and between August and March in SP region, being most prominent in local summer. Furthermore, this diurnal anomaly is more pronounced at solar minimum than at solar maximum, and more pronounced in SP region than in NA and EA regions, in terms of larger diurnal magnitude and more months it lasts in a year. It is emphasized that the diurnal anomaly consists of not only a nighttime enhancement, but also a concurrent noontime depletion. Hence, midlatitude summer nighttime enhancements reported in previous studies are just part of this reversed diurnal cycle. The cause for the phase reversal involves several interplaying physical processes. Among these, the neutral wind combined with the geomagnetic field configuration plays a pivotal role. It generates a one-wave longitudinal pattern at southern middle latitudes and a two-wave pattern at northern middle latitudes, whose wave peaks correspond to the center of the SP, EA, and NA regions, respectively. The seasonal variation of neutral winds and downward motion of the ionization induced by thermal contraction of the ionosphere at sunset may largely control the occurring local time of the nighttime density enhancement and how long it persists in different months. The phase reversal occurs as a result of close ion-neutral coupling. It is further noted that winter anomaly in the EA, NA, and SP regions is very weak or missing.