<p>The negative impacts of space weather conditions on human activity have become a vital concern over the last decades, as humans increasingly use satellite communications, Positioning-Navigation-Timing (PNT) with Global Navigation Satellite Systems (GNSS), Earth&#8217;s observation and forecasting with in-situ and remote sensing satellites, and countless other applications. This situation underscores the necessity to better understand and predict the effects of Magnetosphere-Ionosphere-Thermosphere (MIT) processes and coupling in the near-Earth environment and to prevent potential detrimental influences on orbiting, aerial, and ground-based technologies (e.g., the radio signal propagation delay in the ionosphere affecting GNSS and communications, the drag force disturbances on Low Earth Orbit satellites, the power and internet outages due to intense electric currents induced during geomagnetic storms, etc.). For instance, the variability of the ozone layer has strong dependence on space weather, and it connects with the troposphere and the surface temperature variability. The ozone is a strong absorber of Solar ultraviolet (UV) and Earth&#8217;s long-wave radiations, playing thus a key role in global warming and climate change, which is affected by natural and human contributions such as solar activity and powerful ground-based radio transmitters. In the intricate MIT coupling, the UV and extreme UV (EUV) radiation are mostly absorbed by the thermosphere to create the ionosphere through ionization/dissociation of neutrals, and the thermosphere and ionosphere are strongly influenced by wave motions from the lower atmosphere, and also by energetic particle precipitation and field&#8208;aligned currents through the magnetosphere and solar wind. Addressing the challenge of completely understanding the coupled MIT processes requires significant advances in geodetic observations of plasma and neutral density, &#8220;compositions&#8221;, and &#8220;velocities&#8221;, observations of energetic particles and &#8220;magnetic field perturbations&#8221; both in space and on the ground, as well as advanced theoretic and numerical modelling capabilities. The Joint Study Group 1 &#8216;Coupling processes between Magnetosphere, Ionosphere, and Thermosphere and (MIT)&#8217; is implemented at the International Association of Geodesy (IAG) Inter-Commission Committee on Theory (ICCT), joint with the IAG Global Geodetic Observing System (GGOS), Focus Area on Geodetic Space Weather Research (FA-GSWR), the IAG Commission 4 &#8216;Positioning & Applications&#8217;, and the IAG Sub-Commission 4.3 &#8216;Atmosphere Remote Sensing&#8217;. The JSG1 aims to better understand Space Weather phenomena within the coupled MIT system, and formulate predictive models of the near-Earth space environment. We provide an introduction of the coupled MIT system and recent updates and results achieved by the group.</p>
