For the investigation of time variations of critical frequency (foF2), solar radiation flux at 10.7 cm wavelength (F10.7 index) and geomagnetic activity index Kp, we use conditional independence graphical models which describe and transparently represent the structure of relationships in the time series. We employ multivariate statistic methods applied to daily observational data obtained from midlatitude ionosondes within the period 1994–2009 (23rd Solar Cycle). It is demonstrated that conditional independence graphical models represent a robust method of multivariate statistical analysis, useful for finding a relation between one of the main ionospheric parameters and space weather conditions. This method appears to be more appropriate than correlation analysis between foF2 and the main geomagnetic and solar indices, especially for long‐term data for which the model characteristics may change or time series can be interrupted. We compare the results obtained by the graphical models method with cross‐correlation analysis. We found that the method is suitable for the analysis of the dependence between foF2 values and time‐shifted F10.7 time series. In particular, we clearly identified +0 day shift in all cases, and +1‐, +2–3‐, and +4–5‐day shifts in European, American, and East Asia sector, respectively. The conditional independence graphs method can be applied even in the case when classical parametric methods are not convenient.

中文翻译：

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利用图形模型分析电离层与太阳参数之间的关系

为了研究临界频率（foF2），10.7厘米波长的太阳辐射通量（F10.7指数）和地磁活动指数Kp的时间变化，我们使用条件独立性图形模型来描述和透明地表示时间序列中的关系结构。我们采用多元统计方法，将其应用于1994-2009年（第23个太阳周期）中纬度离子探空仪获得的每日观测数据。结果表明，条件独立性图形模型代表了一种可靠的多元统计分析方法，可用于发现电离层主要参数之一与空间天气状况之间的关系。该方法似乎比foF2之间的相关分析更合适以及主要的地磁和太阳指数，尤其是对于长期数据而言，其模型特征可能会更改或时间序列可能会中断。我们将通过图形模型方法获得的结果与互相关分析进行比较。我们发现该方法适用于分析foF2值与时移F10.7时间序列之间的相关性。特别是，我们清楚地确定了所有情况下的+0天班次，以及欧洲，美洲和东亚地区的+ 1，+ 2–3–天和+ 4–5天班次。即使在经典参数方法不方便的情况下，也可以应用条件独立图方法。