Physical Links Between Weather in Space and Weather in the Lower Atmosphere

Abstract Identifying the coupling mechanisms that operate in the two directions, upward and downward, between Earth's lower atmosphere and geospace (ionosphere, magnetosphere, and beyond) is currently one of the greatest scientific challenges to be addressed by the atmosphere and space science communities. To meet this challenge, an ISSI Forum on “Physical Links between Weather in Space and Weather in the Lower Atmosphere” was organized in Bern in November 2022. This paper presents a synthesis of the scientific discussions, conclusions and recommendations of this Forum, aimed primarily at the space- and atmospheric-science communities while also identifying implications for operational services, space agencies and other stakeholders. The Forum discussed how the lower atmosphere influences the upper layers through gravity waves, atmospheric tides and planetary waves, thunderstorms, chemical transport and seismic activity, and conversely how solar and space phenomena may affect chemistry, dynamics and climate in the lower atmosphere. It also considered the redistribution of chemical species, momentum and energy within the thermosphere–ionosphere, where forcing from above and below interact. Based on this analysis, the Forum identified observational gaps and needs for new observations, particularly in the lower thermosphere (~ 90 to 200 km), as well as modeling needs. Rather than implying that whole-atmosphere models lack all upper-atmosphere electrodynamics, we identify the need to strengthen quantitative coupling between neutral dynamics, ionospheric electrodynamics and magnetospheric forcing, together with systematic model validation and data assimilation. In order to implement its recommendations, the Forum highlighted the need for co-ordinated international efforts to understand the whole atmosphere as a coupled system. It emphasized the importance of developing at the international level a “Great Ionosphere–Thermosphere–Mesosphere (ITM) Observatory”, understood as an interoperable framework linking distributed space- and ground-based assets and models rather than as a single physical observatory. Finally, the Forum emphasized the need for closer collaboration between space scientists, meteorologists and climate scientists, and the importance of upper atmospheric processes for appropriately addressing space sustainability and for understanding possible links between space weather and lower atmospheric climate. The conclusions and recommendations of the Forum motivated the organization of the ISSI Workshop on “Physical Links Between Weather and Climate in Space and the Lower Atmosphere”, held in Bern in January 2024.