A modified index for the description of the ionospheric short- and long-term activity

Abstract

Abstract.A modified ionospheric activity index AI has been developed on the basis of ionospheric foF2 observations. Such index can be helpful for an interested user to get information about the current state of the ionosphere. Using ionosonde data of the station Juliusruh (54.6 • N; 13.4 • E) this index has been tested for the time interval from January 1996 until December 2008. This index has no diurnal and seasonal variations, only a small positive dependence on the solar activity could be found. The variability of this index has, however, a marked seasonal variability with maxima during the equinoxes, a clear minimum in summer, and enhanced values in winter. The observed variability of AI is strongly correlated with the geomagnetic activity, most markedly during the equinoxes, whereas the influence of the solar activity is markedly smaller and mostly insignificant. Strong geomagnetic disturbances cause in middle latitudes in general negative disturbances in AI, mostly pronounced during equinoxes and summer and only partly during winter, thus in agreement with the current physical knowledge about ionospheric storms.

A new ionospheric storm scale based on TEC and foF2 statistics

“…As shown in Mielich and Bremer [], AI had a seasonal variation. Figure b shows a histogram of P TEC , the same as in Figure a, but during 3 months around the June solstice (JS) season.…”

“…In previous studies, some parameters were suggested to describe an ionospheric state by using TEC and/or f o F 2 . One of the most widely used parameters is a percentage deviation of the current observables from the corresponding median at the same local time and location [e.g., Bremer et al , ; Mielich and Bremer , ]. In this paper, the percentage deviations are referred to as the ionospheric activity index (AI) and calculated from O TEC and O foF 2 .…”

“…For example, the ionospheric activity index (AI) was proposed by Bremer et al [] on the basis of measurements of f o F 2 in Europe. It was revised to describe ionospheric storms at midlatitudes by Mielich and Bremer []. They used 13 year data obtained at one European station and investigated the seasonal dependence of ionospheric storms.…”

Brazilian active GNSS networks as systems for monitoring the ionosphere

“…They can be obtained from (a) ionosondes data such as AI index (Bremer et al 2006), or AI modified index (Mielich and Bremer 2010); (b) IONEX files: W p and W-index Stanislawska 2008 andGulyaeva et al 2013); and (c) GNSS measurements: I ROT (Wanninger 1993), ROTI (Pi et al 1997), f P and F P (Mendillo et al 2000), and DIX (Jakowski et al 2012). The scintillations that GNSS signals suffer due to irregularities in the ionosphere can be quantified by the indexes r U (Van Dierendonck et al 1993), S4 (Conker et al 2003), S U (Forte 2005), and r CHAIN (Mushini et al 2012). There are also solar and geomagnetic indexes that provide the level of ionospheric ionization and the strength of ionospheric distortions in the vertical and horizontal plasma distribution, such as Zurich sunspot number, solar radio flux at 10.7 cm (Jakowski et al 1999), and geomagnetic K p , A p , and D st (Campbell 1996).…”

A new pair of indices to describe the relationship between ionospheric disturbances and geomagnetic activity

“…Gulyaeva et al [] used logarithmic deviations of TEC to construct an ionospheric weather index W , and subsequently, Gulyaeva and Stanislawska [] used the W index to construct a planetary ionospheric storm index, W P , which describes global ionospheric disturbances. Subsequently, Mielich and Bremer [] developed an ionospheric activity index, AI , which correlates with geomagnetic activity during equinoxes. To identify ionospheric disturbances, all authors used the monthly median value of a specific ionospheric parameter as the background value.…”