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.
The degree-depth relation links the spherical harmonic degree to an operational depth scale for gravity signals. Previous studies have primarily examined the degree-depth relation for the gravity anomaly, the vertical component of the gravitational vector, and the gravity disturbance. However, degree-depth relations for other high-order radial disturbing potential gradients, such as the second- and third-order radial derivatives of the disturbing potential, remain unestablished. This study reviews existing degree-depth relations and their applications in modeling and spectral-scale interpretation of observed gravity signals. degree-depth relations are derived for the components of the second- and third-order radial derivatives of the disturbing potential. Furthermore, the general degree-depth relation for the sth-order ( s ≥ 1 ) radial disturbing potential gradients is established. Numerical results show that, for all degree-depth relations, operational depths decrease as spherical harmonic degrees increase, and vice versa. Results further indicate that distinct degree-depth relations should be applied to the corresponding orders of radial disturbing potential gradients. The derived degree-depth relations offer a self-consistent set of bounds for spectral-filtering choices when working with high-order radial gradients in geodesy, geophysics, and planetary sciences.
The Philippine Sea Plate (PSP) is one of the most important elements of plate tectonics in the western Pacific region. The most conspicuous feature of the PSP is that it is surrounded by subduction zones. Here, we review main geophysical studies in the past two decades on the evolution and general structure of the PSP and its surrounding subduction zones, as well as related seismic and volcanic activities. These studies revealed strong structural heterogeneities in all parts of the PSP and its surrounding subduction zones. Fluids from dehydration reactions of the subducting Pacific and Philippine Sea slabs cause active arc volcanism and affect the generation of large crustal earthquakes, megathrust earthquakes, and intraslab events. Tears and windows are revealed in the subducting Philippine Sea slab, which may be facilitated by subduction of oceanic ridges. There are interactions between the subducting Pacific and Philippine Sea slabs. Significant seismic anisotropy occurs in the mantle above and below the subducting slabs, which reflects mantle flows induced by the plate subductions. These studies shed new light on seismotectonics, volcanism, and geodynamics in the western Pacific and Southeast Asian regions, which are important for both scientific research and reduction of seismic, volcanic, and tsunami hazards.
Marine litter (ML) has attracted attention from international and national regulatory bodies because of its impact on biodiversity, water quality and the blue economy. Accordingly, ML is part of the United Nations (UN) Sustainable Development Goals, with quantitative monitoring descriptors proposed for the Goal 14 “Conserve and sustainably use the oceans, seas and marine resources for sustainable development” and the 14.1.1b sub-indicator “Plastic patches greater than 10 m”. Here, we focus our expert-driven evaluation on the prospects of monitoring the abundance of floating plastic ML in international waters from Earth observation (EO) as a complementary data source for deriving the 14.1.1b sub-indicator. The assessment we conducted, revealed the potential application of EO to enable global studies of general ML. There is significant progress in generating various ML indicators using moderate-to-medium pixel resolution (< 60 m/pixel) observations, primarily within the national waters of UN member states. Contrarily, the development of indicators in international waters has been lacking due to reduced resolution (> 100 m/pixel) of currently available EO data, the sparsity of in-situ validation observations and the limited size of the floating litter patches with plastics alone. Low-resolution EO sensors with high signal-to-noise could be leveraged, using knowledge gained from the wealth of evidence-based research in national waters. However, further research and development is essential in EO technologies to better monitor ML including investigating the potential synergy of multimodal remote sensing tools. Moreover, all EO tools must be complemented by modelling and field campaigns for a more holistic view of ML. Finally, the recommendation is to prioritise the monitoring of ML as an essential variable for future EO missions.
