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Team title: Solar Indices and Irradiance Working Team

Team ID: S2-02

Team Leads:

Carl Henney (Air Force Research Laboratory (AFRL), USA),

Karin Muglach (NASA GSFC, USA),


Keywords (impact): Navigation/Communication

Keywords (activity type): Understanding, Requirements, Modeling, Forecasting, Data Utilization


Solar XUV (0.1-10 nm), EUV (10-120 nm), and FUV (120-200 nm) radiation is absorbed in the Earth's upper atmosphere, driving ionization and heating of the neutral atmosphere. Current Ionosphere-Thermosphere (IT) models are capable of using measured VUV (0 to 200 nm) spectral information to drive the models, as well as modeled EUV spectra based on solar indices (e.g. F10.7, the solar radio flux at 10.7 cm, along with Mg II core-to-wing ratio, total magnetic flux) used as a proxy for EUV activity.

Day-to-day variability: Many of these solar indices are averaged over long periods of time (81 days to 1 year). When compared with EUV spectral lines (such as the He II 30.4 nm line) over a solar rotation cycle, indices such as F10.7 may peak several days before the EUV peak or several days after, depending on the propagation path through the solar atmosphere. The questions for the group are: 1) How well do solar indices reproduce the observed variability of radiation bands within the VUV that drive the IT models on a cadence of 24 hours? 2) Are there other proxies or direct measurements we should use? 3) How do we develop solar spectral irradiance models for input to IT models?

Long-term variability: During the minimum between solar cycles 23 and 24 the ionosphere and thermosphere were unusually contracted. This has been frequently attributed to EUV radiation decreasing more than usual during the minimum whilst traditional solar proxies remained consistent. Additionally, F10.7 is typically capped at values of 200 sfu in IT models. So another one of the questions for the group is: Are other proxies such as MgII c-w better to represent solar EUV long-term variability?

The questions for the group are: 1) How accurate are these indices that drive the models relative to the ionizing radiation on these shorter time scales, and 2) Are there other proxies or direct measurements we should use?


  • Identify the current and future input needs of IT models.
  • Identify the effectiveness of available solar proxies (F10.7, MgII c-w, total magnetic field strength) in reproducing the variability of bands within the observed VUV spectrum (0-200 nm) on timescales appropriate to measure the 27-day solar rotation cycle, as well as in terms of overall long-term (11-year) variability.
  • Agree on long-term datasets of EUV that could be used to calibrate and validate these indices on these daily timescales, as well as IT data to validate the response. 

Action topics:

Clusters with overlapping topics: S1

Link to team external website: