## 2 A Multi-Source Real Data Model for Intercity Link Communication Propagation Computing  
### WRF Models Regional Duct Distribution  
The new generation of the mesoscale advanced research WRF model system is a flexible and advanced atmospheric simulation system. It is suitable for a wide range of electromagnetic applications from meters to thousands of kilometers. The WRF modeling system is shown in Figure 1 and mainly consists of the following main programs: 1. WRF pre-processing system (WPS); 2. WRF data assimilation (WRF-DA) assimilation system; 3. advanced research WRF (ARW) solver; 4. post-processing and visualization tools. We used the WRF pre-processing system (WPS) to specify the static terrain data path of the processing area and perform interpolation on the terrain data (including terrain, land use, and soil type). The background field and boundary field data used in WPS were NCEP FNL (final) business global analysis data [21; 22]. The global meteorological data in GRIB2 (Gridded Binary2) format were downloaded. The grid data resolution was \(1^{\circ}\times 1^{\circ}\) and the time interval was 6 h.  
The latitude and longitude coordinate ranged of the selected area were (25.846\({}^{\circ}\)N-36.224\({}^{\circ}\)N, 117.472\({}^{\circ}\)E-123.528\({}^{\circ}\)E). We set the number of coarse grids and fine grids, and their relative positions. There were several cities that we simulated in the fine grids,of which, the latitude and longitude coordinates were Wuxi (120.3166\({}^{\circ}\)E, 31.5072\({}^{\circ}\)N), Hangzhou (120.1602\({}^{\circ}\)E, 30.2856\({}^{\circ}\)N), Nanjing (118.7988\({}^{\circ}\)E, 32.0651\({}^{\circ}\)N), Shanghai (121.4802\({}^{\circ}\)E, 31.2389\({}^{\circ}\)N), and Jiaxing (120.7635\({}^{\circ}\)E, 30.7509\({}^{\circ}\)N), respectively. Using the Lambert conformal projection, the simulation area was used as a coarse grid, and the key selected urban area was a fine grid. The schematic diagram of the simulation area is shown in Figure 2, and the parameter settings are shown in Table 1. After the initialization parameters were set, we executed _geogrid.exe_ to define the model domain to be processed, and imported the static terrain data into the grid; secondly, we commanded _ungrib.exe_ to extract the meteorological fields from the imported grid-formatted terrain fields; finally, we executed _metgrid.exe_ to horizontally interpolate the meteorological fields extracted by ungrib.exe in the second step into the grid model defined by _geogrid.exe_ in the first step. The vertical interpolation of the meteorological field to the WRF eta level was realized in the actual program. The background field data of 1 March 2018, 1 June 2018, 1 September 2018, and 1 December 2018 UTC were selected, respectively, to simulate the duct distribution in the selected plain area by seasons. The duct distribution located in East China is shown in Figure 3.  
As shown in Figure 3, it can be seen that the ducts were distributed in the sea area throughout the year, while the inland ducts were less distributed and scattered in March. The inland ducts were densely distributed in June and December, and the inland ducts were also widely distributed in September, but not continuous. Due to the large amount of data to be analyzed in the selected area, only the first day of each quarter was selected for numerical simulation. The actual occurrence of the duct was also related to sudden changes in weather, such as rainfall and snowfall, or the diurnal temperature variation. However, based on the numerical simulation results of WRF in the East China Plain, it is fully proven that the ducting phenomenon occurs in this area all year around. Therefore, the surface duct with the base layer is used to evaluated the CCI of the