In the frame of the research project IOGA⁴MET, a new ground-based GNSS network is being deployed in the Southwest Indian Ocean (SWIO) since November 2017. This new network opens up for new research opportunities in geodesics and atmospheric sciences in this area regularly exposed to natural hazards, and significantly expands the International GNSS System (IGS) network, which only includes eight stations so far in the SWIO. After a description of the current status of IOGA⁴MET, several examples of regional applications in meteorology (climatology and numerical modeling) and geodesy (monitoring of ground deformations) are presented using data collected in northern Madagascar and small neighboring islands in 2018–2020. The observed water vapor cycle is shown to exhibit different characteristics and important variability at all locations. At the seasonal scale, maximum IWV values are similar everywhere, minimum values decrease away from the equator and a sharp IWV gradient can be noticed during the wet–dry transition period. At this time scale, the seasonal IWV cycle analyzed with the high-resolution NWP system AROME-IO matches observations with little discrepancies. At the diurnal scale, IWV characteristics show different behavior on each side of Madagascar, which emphasizes the important role of this island in driving the regional circulation. Finally, examination of ground displacements measured by GNSS stations in relationship with the ongoing Mayotte seismic-volcanic crisis indicates that ground deformation associated with the current off-shore volcanic activity east of Mayotte does not extend up to 250 km, or is currently too low to be detected in very far field.

在研究项目IOGA ⁴ MET的框架内，自2017年11月起在西南印度洋（SWIO）部署了新的地面GNSS网络。这一新网络为该地区的大地测量学和大气科学领域提供了新的研究机会定期暴露在自然灾害中，并大大扩展了国际GNSS系统（IGS）网络，该网络到目前为止在SWIO中仅包括八个台站。描述IOGA ⁴的当前状态之后气象部利用2018-2020年在马达加斯加北部和邻近小岛收集的数据，介绍了气象学（气候学和数值模拟）和大地测量学（监测地面变形）中区域应用的几个例子。观察到的水蒸气循环显示在所有位置均表现出不同的特性和重要的可变性。在季节尺度上，最大IWV值在任何地方都是相似的，最小值在赤道附近逐渐减小，并且在干湿过渡期间可以看到急剧的IWV梯度。在此时间范围内，使用高分辨率NWP系统AROME-IO分析的季节性IWV周期与观测值相符，差异很小。在昼夜尺度上，IWV特征在马达加斯加的每一侧表现出不同的行为，强调了这个岛屿在推动区域流通中的重要作用。最后，对由GNSS站测量的地面位移与正在进行的Mayotte地震火山危机的关系进行的检查表明，与当前Mayotte以东的近海火山活动相关的地面变形没有延伸到250 km，或者目前太低而无法在很远的地方被发现。