## 2 Modeling Method
### Dataset  
In this study, daily hourly measured values of \(f_{o}\)F\({}_{2}\) and its monthly median values have been obtained from eighteen ionosonde stations in east Asia as shown in Figure 2 and Table 1. These stations include Akita, Beijing, Chongqing, Guangzhou, Haikou, Irkutsk, Jeju, Khabarovsk, Magadan, Manzhouli, Okinawa, Seoul, Taipei, Tokyo, Tunguska, Wakkanai, Yakutsk, and Yamagawa, which used for model reconstruction and verification. The geographical coordinates and geomagnetic latitudes of ionosonde stations are listed in Table 1 and are shown in Figure 2.  
Measured data comes from various resources of National Oceanic and Atmospheric Administration (NOAA) and World Data Centre (WDC). The data source includes four parts: (1) The ionosonde data of Akita, Okinawa, Kokubunji, Wakkanai, and Yamagawa station was downloaded from the World Data Centre website ([[http://wdc.nict.go.jp/IONO/HP2009/ISDJ/manual_txt-E.html](http://wdc.nict.go.jp/IONO/HP2009/ISDJ/manual_txt-E.html)]([http://wdc.nict.go.jp/IONO/HP2009/ISDJ/manual_txt-E.html](http://wdc.nict.go.jp/IONO/HP2009/ISDJ/manual_txt-E.html))); (2) the ionosonde data covering the years of 1957- 2012 of Khabarovsk station was downloaded from the World Data Centers in Russia and Ukraine ([[http://www.wdcb.ru/stp/data/ionosphere](http://www.wdcb.ru/stp/data/ionosphere)]([http://www.wdcb.ru/stp/data/ionosphere](http://www.wdcb.ru/stp/data/ionosphere)), ionosphere_1, ionosphere_2, ionosphere_4); (3) the ionosonde data covering the years of 1950-2008 of Irkutsk, Seoul, Taipei, Manila, Beijing, Chongqing, Guangzhou, Haikou, and Manzhouli station was downloaded from Australian government-Bureau of Meteorology Space Weather service ([[ftp://ftp-out.sws.bom.gov.au/wdc/iondata/medians](ftp://ftp-out.sws.bom.gov.au/wdc/iondata/medians)]([ftp://ftp-out.sws.bom.gov.au/wdc/iondata/medians](ftp://ftp-out.sws.bom.gov.au/wdc/iondata/medians))); (4) Other ionosonde data was downloaded from National Oceanic and Atmospheric Administration website ([[ftp://ftp.swpc.noaa.gov/pub/lists/iono_month](ftp://ftp.swpc.noaa.gov/pub/lists/iono_month)]([ftp://ftp.swpc.noaa.gov/pub/lists/iono_month](ftp://ftp.swpc.noaa.gov/pub/lists/iono_month))). The total data volume of \(f_{o}\)F\({}_{2}\) monthly median values is 168674 entries, and that of each station is listed in Table 1.  
Figure 1: The flow chart of the model reconstruction and verification. Figure 2: Comparison of geomagnetic and geographic coordinates in the analysis region. (**a**) Geographic coordinates and geomagnetic coordinates, (**b**) geographic coordinates and geomagnetic dip latitudes, and (**c**) geographic coordinates and modified geomagnetic dip latitudes. Data of different years are measured by different ionosondes. The early ionosondes are analog modulation with high cost, high transmitting power (up to 10 kW) and long observation time. While today's ionosondes are digital modulation with lower cost, lightweight, lower peak transmission power (less than 1000 W), wider frequency range (up to 30 MHz), various and self-customized frequency sweep resolution (such as 25 kHz, 50 kHz, 75 kHz or self-customized), greater flexibility (less than \(-\)120 dBm), easy to install and unattended \"lights-off\" remotely controlled operation with very little maintenance expense [38; 39; 40; 41]. The measured database is spread across three ionospheric regions which cover high, middle and low latitudes (shown in Figure 2) and covers the years of 1949-2017 which are up to six solar activity cycles (shown in Figure 3). The time periods of 1949-2017 are used in the present study because it covers about six solar cycles as long as possible with the maximum data availability. Although not all the stations have data that are equally distributed within this period, the best use of the available data form each station is made.