Research on total electron content (TEC) empirical models is one of the important topics in the field of space weather services. Global TEC empirical models based on Global Ionospheric Maps (GIMs) TEC data released by the International GNSS Service (IGS) have developed rapidly in recent years. However, the accuracy of such global empirical models has a crucial restriction arising from the non-uniform accuracy of IGS TEC data in the global scope. Specifically, IGS TEC data accuracy is higher on land and lower over the ocean due to the lack of stations in the latter. Using uneven precision GIMs TEC data as a whole for model fitting is unreasonable. Aiming at the limitation of global ionospheric TEC modelling, this paper proposes a new global ionospheric TEC empirical model named the TECM-GRID model. The model consists of 5183 sections, corresponding to 5183 grid points (longitude 5°, latitude 2.5°) of GIM. Two kinds of single point empirical TEC models, SSM-T1 and SSM-T2, are used for TECM-GRID. According to the locations of grid points, the SSM-T2 model is selected as the sub-model in the Mid-Latitude Summer Night Anomaly (MSNA) region, and SSM-T1 is selected as the sub-model in other regions. The fitting ability of the TECM-GRID model for modelling data was tested in accordance with root mean square (RMS) and relative RMS values. Then, the TECM-GRID model was validated and compared with the NTCM-GL model and Center for Orbit Determination in Europe (CODE) GIMs at time points other than modelling time. Results show that TECM-GRID can effectively describe the Equatorial Ionization Anomaly (EIA) and the MSNA phenomena of the ionosphere, which puts it in good agreement with CODE GIMs and means that it has better prediction ability than the NTCM-GL model.

Urban ecosystem health evaluation can assist in sustainable ecological management at a regional level. This study examined urban agglomeration ecosystem health in the middle reaches of the Yangtze River with entropy weight and extension theories. The model overcomes information omissions and subjectivity problems in the evaluation process of urban ecosystem health. Results showed that human capital and education, economic development level as well as urban infrastructure have a significant effect on the health states of urban agglomerations. The health status of the urban agglomeration’s ecosystem was not optimistic in 2013. The majority of the cities were unhealthy or verging on unhealthy, accounting for 64.52% of the total number of cities in the urban agglomeration. The regional differences of the 31 cities’ ecosystem health are significant. The cause originated from an imbalance in economic development and the policy guidance of city development. It is necessary to speed up the integration process to promote coordinated regional development. The present study will aid us in understanding and advancing the health situation of the urban ecosystem in the middle reaches of the Yangtze River and will provide an efficient urban ecosystem health evaluation method that can be used in other areas.

Over the past four decades, land use/land cover (LU/LC) change, coupled with persistent drought, has resulted in the decline of groundwater levels in Horqin Sandy Land. Accordingly, this study quantifies changes in LU/LC and groundwater storage (GWS). Furthermore, it investigates the effects of LU/LC changes on GWS. GWS changes are estimated using Gravity Recovery and Climate Experiment (GRACE) data and ground-based measurements obtained from July 2003 to December 2010. Soil moisture and snow water equivalent data derived from the Global Land Data Assimilation System (GLDAS) are used to isolate GWS changes from GRACE-derived terrestrial water storage changes. The result shows that the groundwater depletion rate in Horqin Sandy Land is 13.5 ± 1.9 mm·year⁻¹ in 2003–2010, which is consistent with the results of monitoring well stations. LU/LC changes are detected using bitemporal imageries (2003 and 2010) from Landsat Thematic Mapper through the post-classification comparison method. The result shows that LU/LC significantly changed during the aforementioned period. Bare soil and built-up land have increased by 76.6% and 82.2%, respectively, while cropland, vegetation, and water bodies have decreased by 14.1%, 74.5%, and 82.6%, respectively. The analysis of GWS and LU/LC changes shows that LU/LC changes and persistent drought are the main factors that affect groundwater resources.

The response of the global ionosphere to solar flares is an important topic in the field of space weather. The global ionospheric response to solar flares is comprehensively analyzed from the perspectives of total electron content (TEC) and very low frequency (VLF) signals by using solar flare data on the eruption days of X-class flares from 2006 to 2019, including flare level, flare duration, geographical location, and local time. In addition, the relationship between X-ray flux and VLF phase variation is studied through correlation analysis. The concepts of disturbance intensity (DI) and disturbance angle are defined, and a DI evaluation model is established to help detect the difference in sensitivity to solar flares between TEC and VLF signals. Results show the following. (1) The higher the flare level and the longer the duration, the greater the disturbance to the ionosphere. Simultaneously, a phenomenon exists in which the disturbance caused by low-level and long-lasting flares is greater than that caused by high-level flares. (2) VLF phase variation and flare level exhibit a good correlation, and they are also closely related to geographical location and local time. The disturbance degree of a station facing the sun is more evident than that of a station facing away from the sun. The TEC disturbance of stations in the morning (local time) is more obvious than that in the afternoon, and disturbance increases along the direction of Earth's rotation. (3) When DI is at the same level, the lowest flare level that causes TEC response is higher than the lowest flare level that causes VLF signal response. The disturbance angle of TEC is unevenly distributed within the interval [0°, 90°], and that of VLF signals is more than 85°. The sensitivity of VLF signals to flare response is considerably higher than that of TEC, and the difference between the two even stride across DI level.