In order to alleviate global warming and the energy crisis, it is of great significance to develop and utilize solar energy resources. Sunshine duration (SD) is considered to be the best substitute for solar radiation and a key factor in evaluating solar energy resources. Therefore, the spatial and temporal characteristics of SD and the reasons for its changes have received extensive attention and discussion. Based on the data of 415 meteorological stations from 1970 to 2019, this paper uses linear trend analysis, Mann–Kendall mutation analysis, the Hurst index, empirical orthogonal decomposition, correlation analysis and partial correlation analysis to analyze the spatiotemporal characteristics of SD and its relationship with influencing factors. The results show that the annual SD in China shows a downward trend, with a climate trend rate of −37.93 h/10a, and a significant decline from 1982 to 2019. The seasonal SD shows a downward trend, and the downward trend is most obvious in summer. The annual and seasonal SD will still show a downward trend in the future. The spatial distribution of SD not only has an overall consistent distribution but also takes the Yellow River from Ningxia to Shandong as the boundary, showing a north–south opposite distribution. Annual SD has a significant positive correlation, a significant negative correlation, a positive correlation and a negative correlation with wind speed, precipitation, temperature and relative humidity, respectively, and it is most closely related to wind speed and precipitation. In addition, the change in SD may also be related to human activities.

This paper is aimed to investigate the mutual relationship between ozone‐density at cold‐point mesopause (O₃‐CPM) and solar activity globally using Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements and the 10.7 cm‐solar‐radio‐flux (F_10.7) data set. For this purpose, the global latitude regions are divided into 16 latitude bins. The global changes of O₃‐CPM are presented in mesopause region during 2002–2016. SABER has documented dramatic variability in O₃‐CPM on time scale of the 11‐year solar cycle. The observed changes in the global O₃‐CPM correlate well with the changes in solar activity during 2002–2016 with correlation coefficient of 0.92, and the global solar response of O₃‐CPM is (20.18 ± 2.24)%/100 solar flux units in mesopause. Then, the latitudinal distribution of O₃‐CPM and its solar cycle dependence are presented for 16 latitude bins. The latitudinal correlation analysis shows that the O₃‐CPM is significantly correlated to the solar cycle at or above the 95% confidence level for each latitude bin from 84°S to 70°N, and the correlation coefficients are remarkably higher in the southern hemisphere than for corresponding latitudes in the northern hemisphere. The latitudinal distribution of O₃‐CPM takes on a W shape on a global scale, and the distribution of solar response of O₃‐CPM is seen in a strong south‐north asymmetry between the two hemispheres. The solar response of O₃‐CPM in latitudinal distribution decreases gradually from the southern hemisphere to the northern hemisphere, and the standard deviation of solar response increases gradually from the equator to the pole in each hemisphere.

The global distribution and variations of NO infrared radiative flux (NO‐IRF) are presented during 2002–2016 in the thermosphere covering 100–280 km altitude based on Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) data set. For investigating the spatial variations of the mutual relationship between NO‐IRF and solar activity, the altitude ranges from 100 km to 280 km are divided into 90 altitude bins, and the latitude regions of 83°S–83°N are divided into 16 latitude bins. By processing about 1.8E9 NO‐IRF observation values from about 5E6 vertical nighttime profiles recorded in SABER data set, we obtained more than 4.1E8 samples of NO‐IRF. The annual‐mean values of NO‐IRF are then calculated by all available NO‐IRF samples within each latitude and altitude bin. Local latitudinal maxima in NO‐IRF are found between 120 and 145 km altitude, and the maximum NO‐IRF located at polar regions are 3 times more than that of the minimum at equatorial region. The influences of solar and geomagnetic activity on the spatial variations of NO‐IRF are investigated. Both the NO‐IRF and its response to solar and geomagnetic activity show nearly symmetric distribution between the two hemispheres. It is demonstrated that the observed changes in NO‐IRF at altitudes between 100 and 225 km correlate well with the changes in solar activity. The NO‐IRF at solar maximum is about 4 times than that at solar minimum, and the current maximum of NO‐IRF in 2014 is less than 70% of the prior maximum in 2001. For the first time, the response ranges of the NO‐IRF to solar and geomagnetic activity at different altitudes and latitudes are reported.

The time-frequency domain analysis of the sea surface temperature (SST) in the tropical western Indian Ocean was conducted using wavelet analysis, cross wavelet transform (XWT), the Mann–Kendall (MK) test, and other methods based on COBE-SST data for the last 50 years (1974–2020). From the perspective of time-frequency combination, examining the data of precipitation, sea surface heat flux, total cloud cover, and long-wave radiation, helped contribute to exploring the periodic changes of SST. Moreover, the Western Hemisphere Warm Pool (WHWP) was selected to analyze the role of SST from 1974 to 2020. Present results have demonstrated that the SST in the western Indian Ocean was in a stage of rising, particularly in 1998. According to the fast Fourier transform of the filtered SST time series, the tropical western Indian Ocean SST has a short period of 3–6 years, a medium period of about 10 years, and a long period of 40 years. The SST in the tropical western Indian Ocean has a resonance period of 2–6 years with precipitation, a resonance period of 2–6 years with sea surface heat flux, a resonance period of 4–5 years with total cloud cover, and a resonance period of 2–5 years with long-wave radiation. Importantly, SST was negatively associated with precipitation, total cloud cover, and long-wave radiation, and positively for sea surface heat flux before 1997. Seasonal migration activities are significantly correlated with the WHWP and the tropical western Indian Ocean SST. The spatial lattice point correlation coefficient is generally from 0.6 to 0.9, and the inter-annual serial correlation value is more than 0.89. Furthermore, the two exist with a resonance period of 2–5 years.