Attribution of interminimum changes in global and hemispheric total electron content

Abstract

We use a new data product of electron column density (total electron content, or TEC) maps to estimate and attribute the interminimum changes (the differences between annual averages centered on the 2008 and 1996 solar minima) in TEC global and hemispheric averages (dividing the globe in three different ways). We attribute the observed changes to corresponding changes in solar and geomagnetic activity. The new TEC map product was constructed with temporally consistent processing, and it resolves some of the apparent inconsistencies of earlier studies. The estimated global average TEC interminimum change is −19.3% ± 1.0% (2σ uncertainty), of which −9.1% is attributable to the interminimum change in solar extreme ultraviolet (EUV) irradiance (as represented by the F10.7 index), −2.2% is attributable to the change in geomagnetic activity (Kp index), and −9.3% remains unattributed. The hemispheric results are very similar to the global results, but the values tend to be slightly larger in the Southern Hemisphere, at low latitudes, and at night, compared to the opposing respective hemispheres. The interminimum changes and temporal variations of thermospheric mass density anomalies (i.e., the difference between the data and the empirical model) are very similar to those of the global and hemispheric TEC residuals, suggesting that they are driven by a common, globally distributed mechanism. Thermospheric composition changes and additional (unobserved) decreases in solar EUV irradiance are possible mechanisms behind the TEC and mass density unattributed changes; we estimate a plausible range of −6% to −13% for the solar EUV irradiance interminimum change.

Interminimum foF1 Differences and Their Physical Interpretation

“…Satellite drag observations indicate a 36% neutral gas density decrease (Emmert et al, ), and a ~40 K decrease in T ex is expected from model simulations (Solomon et al, ). Further analyses by Emmert et al () gave the interminimum change of −27.7% at 275 km in global mass density.…”

Long‐term trends in the total electron content

“…These data are available since 1998. We use the same TEC data asLean et al [2011]; IGS as well as CODE TEC data/maps are taken from ftp://cddis.gsfc.nasa.gov/pub/gps/products/ionex Emmert et al [2017]. We use the same TEC data asLean et al [2011]; IGS as well as CODE TEC data/maps are taken from ftp://cddis.gsfc.nasa.gov/pub/gps/products/ionex Emmert et al [2017].…”

“…For the period 1995-1997Lean et al [2011] used a database of TEC geographical maps constructed by the Center for Orbit Determination (CODE) at the University of Bern, Switzerland. For this purpose they created among others a homogeneous data series of global TEC based on 35 stations (JPL35), which measured throughout the period 1994-2014 and were evaluated by the JPL technique[Emmert et al, 2017, supporting information, Data Set S1]. analyzed carefully the interminimum (1996-2008) difference in TEC.…”

Global Ionosphere Mapping and Differential Code Bias Estimation during Low and High Solar Activity Periods with GIMAS Software

“…The ionosphere variation was correlated with the solar activity and the geomagnetic activity [31]. Figure 1 shows the mean global TEC (MGEC) [12] evolution from 1998 to 2016, and it is equivalent to the Global Electron Content (GEC) that was proposed as the ionospheric index in the work of Afraimovich, E.L et al [32].…”