## 3 Results and Discussion
### Institution Analysis  
Figure 4a depicts the yearly count of publications for the top ten institutions since 2000. These institutions, in descending order of publications, are the Chinese Academy of Sciences (CAS), U.S. Department of Energy (DOE), University of California System (UC), National Aeronautics and Space Administration (NASA), French National Centre for Scientific Research (CNRS), National Oceanic and Atmospheric Administration (NOAA), Nanjing University of Information Science and Technology (NUIST), China Meteorological Administration (CMA), Helmholtz Association (HZ), and Swiss Federal Institute of Technology (ETU Domain). It is worth noting that several institutions consist of multiple branches. For instance, within the Chinese Academy of Sciences, significant branches in this field include the University of Chinese Academy of Sciences, the Institute of Atmospheric Physics, and the Institute of Earth Environment. Similarly, the U.S. Department of Energy encompasses branches such as the Pacific Northwest National Laboratory, the Lawrence Berkeley National Laboratory, and the Argonne National Laboratory. In Figure 4a, if both the main institution and its branches are present, only the main institution is considered. Before 2009, NASA was the most active institution in this field. From 2010 to 2013, the U.S. Department of Energy (DOE) and the University of California System (UC) took the lead. Since 2014, the Chinese Academy of Sciences (CAS) has been the most active institution. Notably, NUIST experienced significant growth in this field after 2014, with its publications ranking second only to CAS in both 2022 and 2023. Annual publication data for the top 10 institutions in the BCL dataset can be found in Table S4. The institutional network diagram generated by CiteSpace provides a qualitative overview of collaborative relationships among institutions. The analysis of CiteSpace involves a time slicing method, segmenting the data into three-year intervals. The top 30 institutions by publications are selected for each interval, and these slices are then overlaid and locally adjusted to obtain Figure 4b. Each node represents an institution, with its size reflecting the number of publications. Abbreviated names are used for clarity, and a table mapping full institution names to abbreviations can be found in Table S5. The relative positions of institutions and their connections qualitatively represent the  
Figure 3: (**a**) International cooperation network, with the node size representing its total link strength, and the color representing the average citations. (**b**) Development trends in cooperation between major developed and developing countries. The green line with diamond nodes represents the proportionate link strength of USA–China to the total link strength of China, and the green line with triangular nodes represents the proportionate link strength of USA–China to the total link strength of the USA. Orange lines represent the collaboration trends between the USA and Germany, and blue lines represent those between China and India. degree of association, with the color of the links indicating the time slice in which the earliest collaboration was established. As Figure 4b can present a greater number of institutions, it includes both major institutions and sub-institutions. This allows for the clearer identification of key sub-institutions within the field. It can be observed that the purple dashed ellipse primarily consists of institutions from China, the green dashed ellipse predominantly comprises institutions from the United States, the red dashed ellipse mainly includes European institutions, and the blue dashed ellipse encompasses institutions from both India and the United States. Figure 4b illustrates that institutions from the United States hold central positions within the network, consistent with our earlier analysis in Section 3.1.2, indicating that the United States has the highest total link strength.