## 2 Materials and Methods  
### Study Area and Datasets Used  
In this study, data were collected from various solar monitoring stations located across several different countries, including Cabauw, in the Netherlands; Cener, in Spain; Abashiri and Tateno, in Japan; Gobabeb, in Namibia; USAid Venda, in South Africa; and Saudi West Coast, in Saudi Arabia. Ground data were sourced from different networks, such as the World Radiation Monitoring Center-Baseline Surface Radiation Network (BSRN--[[https://bsrn.avi.de/](https://bsrn.avi.de/)]([https://bsrn.avi.de/](https://bsrn.avi.de/)), accessed on 19 April 2024) [5] and the Southern African Universities Radiometric Network (SAURAN--[[https://sauran.ac.za/](https://sauran.ac.za/)]([https://sauran.ac.za/](https://sauran.ac.za/)), accessed on 19 April 2024) [28] ([[https://dataportals.pangaea.de/bsrn/stations](https://dataportals.pangaea.de/bsrn/stations)]([https://dataportals.pangaea.de/bsrn/stations](https://dataportals.pangaea.de/bsrn/stations)), accessed on 19 April 2024), while some stations utilized SCADA (Supervisory Control and Data Acquisition) systems for ground data collection. The details of metadata of the locations used in the present study have been given in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Station** & **Short** & **Lat** & **Lon** & **Country** & **Ground** & **Satellite** & **Analysis Period** & **Reference** \\  
The global positioning of the locations can be determined using Figure 1. Quality controls undertaken for the SAURAN data can be assessed from [28]. Similarly, quality control information for the BSRN data is available in [5]. Additionally, all irradiance data collected for this study undergo a quality control routine, as described by [34], whereby irradiance data points are tested as to their physical acceptability and extreme limits. We also remove any time step with zenith angles above 85\({}^{\circ}\) due to the questionable accuracy of measured data at these times. The choice of satellite data sources for these stations depended on the availability and coverage of satellite scans over the respective regions. In the cases of locations in Japan, such as Abashiri (ABS) and Tateno (TAT), the Himawari-8 satellite system was utilized due to its comprehensive coverage and high-resolution imagery, which is specifically tailored for East Asian regions. Conversely, for stations in other countries like the Netherlands, Spain, Namibia, South Africa, Saudi Arabia, and India, the MSG satellite system was employed, as its coverage extends to a broader geographical area outside of East Asia. We leveraged images from the 0.64 micrometer (\(\upmu\)m) band in the visible (red) channel of the \"Advanced Himawari Imager (AHI)\" on the Himawari-8 geostationary satellite, operated by the Japan Meteorological Agency (JMA), accessible at [[https://himawari8.nict.go.jp/](https://himawari8.nict.go.jp/)]([https://himawari8.nict.go.jp/](https://himawari8.nict.go.jp/)), accessed on 19 April 2024. The VIS0.64 channel of the Himawari-8 AHI measures data in the spectral band ranging from 0.555 to 0.721 \(\upmu\)m, with a central wavelength of 0.6399; it is accessible at [[https://www.data.jma.go.jp/mscweb/en/himawari89/space_segment/spsg_ahi.html](https://www.data.jma.go.jp/mscweb/en/himawari89/space_segment/spsg_ahi.html)]([https://www.data.jma.go.jp/mscweb/en/himawari89/space_segment/spsg_ahi.html](https://www.data.jma.go.jp/mscweb/en/himawari89/space_segment/spsg_ahi.html)), accessed on 19 April 2024. The full-disk images from Himawari-8 used in this study spanned from 60\({}^{\circ}\) N to 60\({}^{\circ}\) S in latitude and from 80\({}^{\circ}\) E to 160\({}^{\circ}\) W in longitude. These images, updated every 10 min, had a spatial resolution of 5 km and can be accessed at [[https://www.eorc.jaxa.jp/ptree/userguide.html](https://www.eorc.jaxa.jp/ptree/userguide.html)]([https://www.eorc.jaxa.jp/ptree/userguide.html](https://www.eorc.jaxa.jp/ptree/userguide.html)), accessed on 19 April 2024.