Vertical deformations caused by non-tidal mass variations still remain in global navigation satellite system (GNSS) height time series, and can be computed from both Gravity Recovery and Climate Experiment (GRACE) and geophysical models. In this study, we provide a thorough evaluation of the relationships between these different techniques in the global scale by comparing non-tidal vertical deformations from IGS second reprocessing campaign (IG2), GRACE and Global Geophysical Fluid Center (GGFC) solutions, and investigate the noise properties of the GNSS corrected by GRACE solutions and GNSS corrected by GGFC solutions for global stations using optimal noise models. Our results demonstrate that the consistency between seasonal vertical deformations derived from GNSS, GRACE and GGFC is high. When correcting GNSS deformations with GRACE and GGFC solutions, 81% and 73% of the 186 stations have the weight root mean square ($WRMS$) reduction, respectively. The $WRMS$ variations averaged over all stations are −12.3% and −5.6%, respectively for GNSS corrected by GRACE and GNSS corrected by GGFC solutions. The obvious difference occurs in the GNSS corrected by GGFC solutions $WRMS$ increase, with the mean increase value up to 29%, mainly happening to stations located on islands or small peninsulas. In addition, noise properties of the GNSS corrected by GRACE solutions and GNSS corrected by GGFC solutions for global stations are investigated using optimal noise models. After correcting non-tidal loading effects, the solutions of GNSS corrected by GRACE solutions have the lowest noise level, and can occupy 5% of the noise behavior presenting in global stations, while the solutions of GNSS corrected by GGFC solutions can bring more than 5% of the noise into global stations, implying that GRACE correction solutions can present more favorable results when interpreting GNSS non-tidal loading deformations.

With rapid advancements in aerospace technology, research interest in the near-space atmospheric environment has surged. Active space release experiments, known for their high controllability and observational advantages, offer a well-established approach to investigating space physics, particularly in the ionosphere. Extending this technique to near-space is essential for deepening our understanding of its environmental properties and underlying physics. However, significant differences in pressure, chemical reactivity, and constituent distribution between near-space and the ionosphere introduce substantial complexity to active release experiments in this region. This study systematically evaluates the influence of the near-space environment on alkali metal releases. A kinetic model for such releases in near-space is developed, and the feasibility of their implementation is assessed. Numerical simulations demonstrate that releasing 10 kg of alkali metals at an altitude of 100 km can generate an artificial electron cloud that persists for over 30 min. The spatial scale and persistence time of the artificial electron cloud decrease markedly with decreasing release altitude. In the vicinity of an altitude of 70 km, intense recombination reactions rapidly deplete released material within seconds, preventing the formation of a stable electron cloud. This indicates a lower altitude limit for effective application of this technique. Single-point releases yield electron clouds with insufficient spatial extent and duration, employing multipoint release can effectively address this limitation. Ray-tracing simulations further indicate that electron clouds substantially alter radio wave propagation paths, creating a radio shadow region that impedes wave penetration. Crucially, these clouds also establish a new propagation path, forming an "air bridge" in near-space with the potential to enable autonomous, reliable long-distance (> 300 km) wireless communication. This work provides a new perspective and approach for near-space research, promising applications in technologies such as artificial communication channels and electromagnetic shielding. Graphical abstract

To overcome the limitations imposed by the natural ionosphere on high-frequency (HF) communication systems, the generation of artificial electron clouds through space-based release of ionizable materials offers a controllable means of constructing localized plasma environments. However, a systematic mapping between release parameters and radio wave propagation characteristics is still lacking, which restricts engineering applications. This paper establishes a full-chain simulation framework that links release parameters, cloud morphology, and propagation characteristics by combining a two-fluid hydrodynamic model with ray tracing. Results show that as release altitude rises from 150 km to 210 km, the cloud undergoes pronounced stretching along the magnetic field (the cloud scale grows from 17.28 km to over 80 km), resulting in a broader signal shadow zone (expands from 116 km to 170 km) and a marked increase in multipath delay spread. Increasing mass from 4 kg to 12 kg raises peak electron density from 7.416 × 10¹² to 2.154 × 10¹³ m⁻³ and widens the shadow zone from 144 km to 174 km. Raising the ionization rate from 20% to 80% broadens the enhancement zone but reduces the shadow zone. Higher altitudes favor broad shielding, larger masses enhance scattering strength and duration, while higher ionization rates accelerate cloud evolution for rapid response and lower rates provide stable coverage. These findings can provide theoretical guidance for the precise design of artificial electron clouds tailored to different application requirements.