# Solar Extreme and Far Ultraviolet Radiation Modeling for Aeronomic Calculations
## 2 Source Data
### Lyman Alpha Data  
There is a question about which time series which time series L\(\alpha\) to choose for building models. In particular, the longest and most accessible continuous series are the Lyman-alpha (L\(\alpha\) composite, hereinafter L\(\alpha\)C) composite series [29] and the TIMED (L\(\alpha\)T) measurement series. The L\(\alpha\)C series, based on satellite measurements and ground-based observatory data, presents daily Lyman \(\alpha\) values starting in 1947, spanning nearly seven solar cycles. Several versions of the L\(\alpha\) Composite are presented on the Internet in different years due to expansion, data revision and calibration refinement. An improved and revised version 4 is currently recommended [29]. The L\(\alpha\)C data series, with daily updates, is available at [[https://lasp.colorado.edu/lisird/data/composite_lyman_alpha/](https://lasp.colorado.edu/lisird/data/composite_lyman_alpha/)]([https://lasp.colorado.edu/lisird/data/composite_lyman_alpha/](https://lasp.colorado.edu/lisird/data/composite_lyman_alpha/)) (2 March 2021). These data are presented in Figure 1. The dotted lines represent the 81-day moving average. It can be seen from the figure that the composite data (L\(\alpha\)C, that includes both measurements on various spacecrafts and model calculations using the MgII-index) and the data of direct measurements (L\(\alpha\)T) onboard TIMED spacecraft, change in time in a similar way, and L\(\alpha\)C systematically exceeds L\(\alpha\)T.  
It should be noted that practically the same L\(\alpha\)C values correspond to the minima of cycles 23-24 and 24-25, while for L\(\alpha\)T the values at the activity minima differ by almost 7%. This is apparently caused by the degradation of the SEE hardware on TIMED. Figure 1 shows also the time variation of the difference \(d\) between the composite series and the  
Figure 1: Changes in L\(\alpha\)C (**red**) and L\(\alpha\)T (**green**) in 23 and 24 cycles of activity. (**Blue**)—difference d between data. Color lines correspond to daily data. Black lines represent 81-day moving averages.  
data measured. It can be seen that the difference between the intensities of LaC and LaT increases noticeably, and then, starting from 2005, fluctuates around a certain average value of \(\sim\)1 mW\(\cdot\)m\({}^{-2}\), which is most likely caused by a decrease in the sensitivity of the SEE equipment. An alternative reason may be a systematic decrease in the flux of extreme ultraviolet radiation during the epoch of a decline in solar activity during the 24 th solar cycle. However, this hypothesis is contradicted by the behavior of LaC, which corresponds to the equality of fluxes at the epochs of minimum solar activity, typical for time series of EUV.  
When developing the model, the index N (LaC) was chosen, which will allow the reconstruction of the EUV and FUV spectra from 1947. Nevertheless, current measurements on TIMED can be used for estimates, since the intensities of LaC and LaT are closely related to each other as can be seen in Figure 1. If it is necessary to replace one of the indices with another, the replacement can be performed using the ratio obtained from the regression analysis of the corresponding time series:  
\[\text{N (LaT)}=0.865\text{ N (LaC)}, \tag{1}\]  
where N is the photon flux density in units of \(10^{15}\) m\({}^{-2}\)s\({}^{-1}\).