The Earth's magnetosheath and cusps emit soft X-rays due to the charge exchange between highly charged solar wind ions and exospheric hydrogen atoms. The Lunar Environment Heliospheric X-ray Imager and Solar wind Magnetosphere Ionosphere Link Explorer missions are scheduled to image the Earth's dayside magnetosphere system in soft X-rays to investigate global-scale magnetopause reconnection modes under varying solar wind conditions. The exospheric neutral hydrogen density distribution, especially the value of this density at the subsolar magnetopause is of particular interest for understanding X-ray emissions near this boundary. This paper estimates the exospheric density during solar minimum using the X-ray Multimirror Mission (XMM) astrophysics observatory. We selected an event on 12 November 2008 from the XMM data archive, which detects soft X-rays of magnetosheath origin while solar wind and interplanetary magnetic field conditions are relatively constant. During the event the location of the magnetopause was measured in situ by the THEMIS mission, thus the location of the solar wind ions responsible for the magnetosheath emission is well constrained by observation. We estimated the exospheric density using the Open Geospace Global Circulation Model (OpenGGCM) and a spherically symmetric exosphere model. The ratio of the magnetosheath plasma flux between the OpenGGCM model and the THEMIS, was nearly 1, which means the magnetohydrodynamic model reasonably reproduces the magnetosheath plasma conditions. The OpenGGCM magnetosheath parameters were used to deconvolve soft X-rays of exospheric origin from the XMM signal. The lower-limit of the exospheric density of this solar minimum event is 36.8 +/- 11.7 cm(-3) at 10 R-E subsolar location.

With a typical alpine grassland ecosystem, the Tibetan Plateau (TP) is a highly representative region to observe the effects of climate change on ecosystems. Continued global warming has increased the drought risk of TP, yet the response of vegetation to drought remains unclear. To understand the spatial heterogeneity of the vegetation response to drought and identify the key control factors of vegetation response to drought in different elevation intervals on TP, we introduced three vegetation indexes (EVI, LAI, and GPP) and multi-scale drought indexes, including the Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI), to determine the spatial response of vegetation growth to drought from 2000 to 2015. Land surface temperature (LST), land cover, snow cover, population density, and soil texture were selected as potential control factors. The mean values of the maximum correlation coefficients for the six combinations indicated that 14.3%/12.0% (SPI/SPEI) of the vegetation growth on TP was significantly affected by water conditions (p < 0.05). The extent of vegetation growth responses to drought were mainly influenced by LST with the highest contribution rate of 65.8% at 3000-4500 m intervals. The response time is mainly dependent on the proportion of grassland, with the highest contribution rate of 81.7% at 4500-6000 m intervals. The results provide reasonable evidence for understanding the spatial heterogeneity of the elevation dependence of the alpine ecosystem response to drought.