Impact factor for the ionospheric total electron content response to solar flare irradiation

Abstract

[1] On the basis of ionospheric total electron content (TEC) enhancement over the subsolar region during flares, and combined with data of the peak X-ray flux in the 0.1-0.8 nm region, EUV increase in the 0.1-50 and 26-34 nm regions observed by the SOHO Solar EUV Monitor EUV detector, also with the flare location on the solar disc, the relationship among these parameters is analyzed statistically. Results show that the correlation between ionospheric TEC enhancement and the soft X-ray peak flux in the 0.1-0.8 nm region is poor, and the flare location on the solar disc is one noticeable factor for the impact strength of the ionospheric TEC during solar flares. Statistics indicate clearly that, at the same X-ray class, the flares near the solar disc center have much larger effects on the ionospheric TEC than those near the solar limb region. For the EUV band, although TEC enhancements and EUV flux increases in both the 0.1-50 and 26-34 nm regions have a positive relation, the flux increase in the 26-34 nm region during flares is more correlative with TEC enhancements. Considering the possible connection between the flare location on the solar disc and the solar atmospheric absorption to the EUV irradiation, an Earth zenith angle is introduced, and an empirical formula describing the relationship of TEC enhancement and traditional flare parameters, including flare X-ray peak and flare location information, is given. In addition, the X-ray class of the flare occurring on 4 November 2003, which led the saturation of the X-ray detector on GOES 12, is estimated using this empirical formula, and the estimated class is X44.

Statistical analysis of solar EUV and X-ray flux enhancements induced by solar flares and its implication to upper atmosphere

“…As is known, the most important source of external forcing to the ionosphere and thermosphere is solar extreme ultraviolet (EUV) irradiation which is absorbed by the upper atmosphere from roughly 90 km to 200 km and causes the large enhancement in ionization rate and heating rate in the ionosphere and thermosphere. Zhang et al [2011] also show the relationship between TEC enhancement and the EUV flux increases in 26–34 nm EUV flux during a flare is more correlative than that in 0.1–0.8 nm soft X‐ray flux.…”

“…Our statistical results show the modified X‐ray flux with Cos(CMD) have a much improvement relationship with the EUV flux for X‐class flares; however, there is not any improvement for M and C‐class flares. In addition, Zhang et al [2011] also show that the different ionospheric response exists even for the flares with the same value of CMD and the same X‐ray class. That also illustrates the variability of the irradiation spectrum of flare to flare.…”

Thermospheric Density: An Overview of Temporal and Spatial Variations

“…However, flare response of neutral density in the upper thermosphere is 2 to 3 times stronger for a disk-center flare than for a limb flare, due to the fact that neutral gas heating through ionization by solar EUV is dominant in the 150-300 km region. Zhang et al (2011) conducted statistical analysis and found that at the same X-ray class, flares near the solar disc center have much larger effects on the ionospheric TEC than those near the solar limb region.…”

Modeling ionospheric <I>fo</I>F2 by using empirical orthogonal function analysis

“…Different types of variability in ionosphere are subject to a number of interconnecting drivers which can be broadly characterized as follows: (a) solar ionizing radiation; (b) geomagnetic activity; and (c) meteorological influences (e.g., Forbes et al, 2000;Rishbeth and Mendillo, 2001;Lei et al, 2008b;Zhang et al, 2011). The ability to model and eventually anticipate the solar cycle, annual, semi-annual and seasonal variations as well as irregularities in ionosphere is of great use for both ionospheric research and space weather applications (Tóth et al, 2005).…”