Does theF_10.7index correctly describe solar EUV flux during the deep solar minimum of 2007-2009?

Abstract

This paper shows that the relationship between solar EUV flux and the F10.7 index during the extended solar minimum (Smin) of 2007–2009 is different from that in the previous Smin. This difference is also seen in the relationship between foF2 and F10.7. We collected SOHO/SEM EUV observations and the F10.7 index, through June 2010, to investigate solar irradiance in the recent Smin. We find that, owing to F10.7 and solar EUV flux decreased from the last Smin to the recent one with different amplitudes (larger in EUV flux), EUV flux is significantly lower in the recent Smin than in the last one for the same F10.7. Namely, F10.7 does not describe solar EUV irradiance in the recent Smin as it did in the last Smin. That caused remarkable responses in ionospheric foF2. For the same F10.7, foF2 in the recent Smin is lower than that in the last one; further, it is also lower than that in other previous Smins. Therefore, F10.7 is not an ideal indicator of foF2 during the recent Smin, which implies that F10.7 is not an ideal proxy for solar EUV irradiance during this period, although it has been adequate during previous Smins. Solar irradiance models and ionospheric models will need to take this into account for solar cycle investigations.

Are the sunspots really vanishing?

“…Since 2000-2003, UV flux proxies relevant to Earth aeronomy overestimate the actual fluxes by 10 to 15% (Kane 2003;Solomon et al 2010;Chen et al 2011;Lean et al 2011b;Liu et al 2011aLiu et al , 2011bWintoft 2011). This breakdown of standard pre-2000 proxies is also reported for f 0 F 2 , TEC and thermospheric density, with typical overestimates by >10% (Bergeot et al 2010;Bruinsma & Forbes 2010;Emmert et al 2010;Lürh & Xiong 2010;Lean et al 2011b;Liu et al 2011b).…”

“…In response to those low fluxes, the density of the Earth thermosphere dropped 20% lower than earlier minima Solomon et al 2010Solomon et al , 2011, while in the ionosphere, the f 0 F 2 index was depressed by 10% (Coley et al 2010;Chen et al 2011;Lean et al 2011b;Liu et al 2011b).…”

Electron Density Comparison Between IRI 2007 and DEMETER Satellite Data in Solar Minimum Year

“…As for quick electron density reduction at the equatorial area and the big differences between DEMETER andIRI in 2008, Lühr andXiong (2010) thought that the chemical and dynamic processes might change in the mesosphere and the lower ionosphere due to the decrease in thermospheric mass density ) during the deep minimum of the solar cycle from CHAMP and GRACE N e data. Simulation results implied that the decline in solar EUV during this period is the primary contributor to the upper atmospheric cooling (Chen et al 2011). In contrast the greenhouse gases such as CO 2 play only a secondary role in this unusual change (Solomon et al 2010).…”

“…The spatial-temporal variation of plasma parameters in the ionosphere during the deep solar minimum for the years 2008 -2009 has become a critical issue in various space physics fields such as the solar-heliospheric-geospace system, the ionosphere and upper atmosphere physics, the solar EUV intensity on thermosphere cooling simulation and the predictive ability of the current IRI model (Gibson et al 2009;Heelis et al 2009;Lühr and Xiong 2010;Russell et al 2010;Solomon et al 2010;AraujoPradere et al 2011;Chen et al 2011;Liu et al 2011aLiu et al , b, c, 2012. As we all know the IRI model has been widely used to provide electron density profiles and other plasma parameters for telecommunications, satellite navigation and positioning systems.…”

GPS-TEC Variation during Low to High Solar Activity Period (2010-2014) under the Northern Crest of Indian Equatorial Ionization Anomaly Region

“…and found a linear positive correlation (r = 0.56) between diurnal maximum GPS-TEC against corresponding solar EUV flux. A research of Chen et al [82] shows that the relationship between the solar EUV flux and the previous solar minimum. The main reason that controls TEC variations and the variability of thermospheric electron density, composition and temperature of neutral atmosphere is the solar EUV radiation [83] [84].…”