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Alternative TitleLow ionization level of northern midlatitude ionosphere in solar cycle 24
于世美; 郝永强; 张东和; 肖佐
Source Publication地球物理学报
Keyword太阳活动周 电离层 子午工程
Abstract延续2008—2009年的太阳极低活动期,第24太阳活动周开始后太阳活动性上升缓慢,即使在趋近峰年时太阳极紫外(EUV)辐射通量的水平仍显著低于前几个活动周.比较第23、24周的太阳辐射水平,及日本国分寺和子午工程武汉站的电离层测高仪观测,发现第24周的太阳EUV辐射、电离层F区临界频率(foF2)和峰值高度(hmF2)都显著低于第23周的同期水平;在较低高度上,偏低的EUV辐射带来的电子密度变化不明显,而峰值电子密度(NmF2)和0.1~50 nm太阳EUV辐射通量在多数时候都同步的偏低25%~50%;但是在夏季NmF2与EUV辐射的关联性较差,即NmF2的偏低在夏季较少。分析认为这与热层中性风的季节特点有关:在夏季午后,吹向极区的子午向风总是较弱,在第24周偏低的EUV辐射背景下,减弱的离子曳力使其他季节的极区向风得到增强,进一步进了NmF2和hmF2的降低,使这一机制的效果非常显著.基于上述结论,在对第24周电离层进行预测预报时,需更多地考虑非直接电离机制的影响。总体而言,第24周的热层和电离层变化特征可能将有别于之前几个活动周的观测,并偏离人们在此基础上所形成的认识。
Other AbstractFollowing prolonged and extremely quiet solar activity from 2008 to 2009, the 24th solar cycle (SC24) started slowly, and the solar extreme ultraviolet (EUV) irradiance level in cycle 24 was significantly lower than that in the cycles 19 to 23. The ionosonde observations at Kokubunji and Chinese Meridian Project Wuhan Station showed that, the ionospheric F-2 region critical frequency (f(o)F(2)) and peak height (h(m)F(2)) in SC24 were notably lower, compared to SC23. Around solar maximum, the solar cycle difference of electron density at lower altitude was not obvious, while both the peak electron density (NmF2) and 0.1 similar to 50 nm solar EUV flux were 25%similar to 50% lower in SC24. However, exceptions existed in summer when the negative deviation of NmF2 was much less. This can be explained by the interaction between ionospheric plasma and neutral wind in the presence of geomagnetic field. The poleward thermospheric wind at local noon is very weak in northern hemisphere summer, while it is much stronger in the other seasons and decrease NmF2 and h(m)F(2) significantly. This seasonal difference is even obvious when the wind is enhanced due to weakened ion-drag effect, under such a low level of solar EUV flux in SC24. The manifestation of wind effect reminds us to take mechanisms other than direct EUV ionization into account when modeling the ionosphere in such a weak solar cycle. The results showed here indicate that the thermosphere-ionosphere system in SC24 would probably differ from what we, have learned from the previous cycles.
Indexed BySCI ; EI
Document Type期刊论文
Recommended Citation
GB/T 7714
于世美,郝永强,张东和,等. 第24太阳活动周中纬度电离层低电离水平的观测研究[J]. 地球物理学报,2014,57(11):3512-3522.
APA 于世美,郝永强,张东和,&肖佐.(2014).第24太阳活动周中纬度电离层低电离水平的观测研究.地球物理学报,57(11),3512-3522.
MLA 于世美,et al."第24太阳活动周中纬度电离层低电离水平的观测研究".地球物理学报 57.11(2014):3512-3522.
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