Model results for the ionospheric E region: solar and seasonal changes
Model results for the ionospheric E region: solar and seasonal changes
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DOI：
10.1007/s00585-997-0063-9
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发表时间：
1997-01
影响因子：
1.9
通讯作者：
J. Titheridge
中科院分区：
文献类型：
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作者：
J. Titheridge
开发了一个新的NO密度经验模型，该模型包括当地时间、季节、纬度和太阳周期的物理合理变化。模型计算充分考虑了二次生产，以及波长低至25 Å的电离辐射，然后给出了峰值密度的值，该值仅比夏季太阳活动最小值的经验IRI值低6%。在太阳活动极大期，这种差异增加到16%。EUVAC辐射模式中的太阳周期变化似乎不足以解释观测到的inme变化，对当前大气常数进行任何合理的修改。辛特格辐射给出了正确的变化，整个太阳周期的结果仅比IRI值低2%，但在E-F山谷地区电离太少。为了与观测到的太阳增加inme相匹配，EUVAC模式中的高通量参考光谱需要总体增加约20%（如果变化仅限于不太明确的辐射atλ< 150 Å，则需要增加33%）。在中纬度地区，nmess的观测值呈现季节性异常，冬季密度比夏季高10%左右（太阳天顶角恒定）。在MSIS86大气模式中，成分的变化导致北半球的夏季到冬季的inme1变化约为-2%，南半球为+3%。NO的季节变化在冬季产生约5%的额外增加，在太阳极小期附近，南半球的整体季节异常为8%。在太阳活动极大期附近，报告的NO密度表明季节变化要小得多，不足以产生任何冬季的inme增加。其他机制，如风或电场的影响，似乎不足以解释观测到的inme变化。因此，目前的卫星数据可能低估了太阳极大期附近NO的平均季节变化。数据中的一个并非不合理的变化，即与太阳极小期相同的2:1变化，可以产生inme的季节性异常，该异常在任何时候都占观测到的效应的35-70%。
A new, empirical model for NO densities is developed, to include physically reasonable variations with local time, season, latitude and solar cycle. Model calculations making full allowance for secondary production, and ionising radiations at wavelengths down to 25 Å, then give values for the peak densityNmEthat are only 6% below the empirical IRI values for summer conditions at solar minimum. At solar maximum the difference increases to 16%. Solar-cycle changes in the EUVAC radiation model seem insufficient to explain the observed changes inNmE, with any reasonable modifications to current atmospheric constants. Hinteregger radiations give the correct change, with results that are just 2% below the IRI values throughout the solar cycle, but give too little ionisation in the E-F valley region. To match the observed solar increase inNmE, the high-flux reference spectrum in the EUVAC model needs an overall increase of about 20% (or 33% if the change is confined to the less well defined radiations atλ< 150 Å). Observed values ofNmEshow a seasonal anomaly, at mid-latitudes, with densities about 10% higher in winter than in summer (for a constant solar zenith angle). Composition changes in the MSIS86 atmospheric model produce a summer-to-winter change inNmEof about –2% in the northern hemisphere, and +3% in the southern hemisphere. Seasonal changes in NO produce an additional increase of about 5% in winter, near solar minimum, to give an overall seasonal anomaly of 8% in the southern hemisphere. Near solar maximum, reported NO densities suggest a much smaller seasonal change that is insufficient to produce any winter increase inNmE. Other mechanisms, such as the effects of winds or electric fields, seem inadequate to explain the observed change inNmE. It therefore seems possible that current satellite data may underestimate the mean seasonal variation in NO near solar maximum. A not unreasonable change in the data, to give the same 2:1 variation as at solar minimum, can produce a seasonal anomaly inNmEthat accounts for 35–70% of the observed effect at all times.