Geospace is a complex system comprising multiple interconnected sub-systems, each characterized by plasma in different physical regimes - collisional plasma in the ionosphere and collisionless plasma in the magnetosphere. This complexity is further enhanced by interactions between the upper layers of Earth's neutral atmosphere and the surrounding ionospheric plasma. The solar wind injects energy into this coupled system primarily through dayside magnetic reconnection, initiating the global magnetospheric electric fields and 'convection' motion called Dungey cycle. This global plasma convection moves anti-sunward at polar (high geomagnetic) latitudes and sunward at middle and low latitudes. Enhanced energy input during geomagnetic storms and substorms leads to increased Joule heating and particle precipitation rates.

Global alterations in electric fields redistribute the cold (a few eV), dense (up to 10⁴ cm^-3 at geomagnetic equator at R~2 R_E ) magnetospheric plasma population of ionospheric origin, known as plasmasphere. The plasmasphere is a critical component of the coupled Geospace system because it regulates global momentum exchange between the ionosphere and magnetosphere, and potentially contributes to the mass loss of Earth's ionized atmospheric components. However, our current understanding of fundamental plasmaspheric processes remains incomplete.

We illustrate how contemporary global coupled Geospace models advance the study of this integrated system. As an example of ongoing research, we present a case study examining plasmaspheric dynamics during December 2015 using observational data from the MMS and Van Allen Probes spacecraft, along with simulations from the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. Finally, we discuss potential avenues for future collaborative research