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    Interhemispheric coupling study by observations and modelling (ICSOM)
    (Wiley, 2022-12-02)
    An international joint research project, entitled Interhemispheric Coupling Study by Observations and Modelling (ICSOM), is ongoing. In the late 2000s, an interesting form of interhemispheric coupling (IHC) was discovered: when warming occurs in the winter polar stratosphere, the upper mesosphere in the summer hemisphere also becomes warmer with a time lag of days. This IHC phenomenon is considered to be a coupling through processes in the middle atmosphere (i.e., stratosphere, mesosphere, and lower thermosphere). Several plausible mechanisms have been proposed so far, but they are still controversial. This is mainly because of the difficulty in observing and simulating gravity waves (GWs) at small scales, despite the important role they are known to play in middle atmosphere dynamics. In this project, by networking sparsely but globally distributed radars, mesospheric GWs have been simultaneously observed in seven boreal winters since 2015/16. We have succeeded in capturing five stratospheric sudden warming events and two polar vortex intensification events. This project also includes the development of a new data assimilation system to generate long-term reanalysis data for the whole middle atmosphere, and simulations by a state-of-art GW-permitting general circulation model using reanalysis data as initial values. By analyzing data from these observations, data assimilation, and model simulation, comprehensive studies to investigate the mechanism of IHC are planned. This paper provides an overview of ICSOM, but even initial results suggest that not only gravity waves but also large-scale waves are important for the mechanism of the IHC.
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    Measurement of a lithium plume from the uncontrolled re-entry of a Falcon 9 rocket
    (Nature Portfolio, 2026-12-01)
    A 10-fold enhancement of lithium atoms was detected at 96 km altitude by a resonance lidar at Kühlungsborn, Germany, approximately 20 hours after the uncontrolled re-entry of a Falcon 9 upper stage. The upper-atmospheric extension of the ICON general circulation model, nudged to ECMWF, was used to calculate winds. Backwards trajectories, including wind variability as measured by radar, traced air masses to the Falcon 9 re-entry path at 100 km altitude, west of Ireland. This study presents the first measurement of upper-atmospheric pollution resulting from space debris re-entry and the first observational evidence that the ablation of space debris can be detected by ground-based lidar. The analysis of geomagnetic conditions, atmospheric dynamics, and ionospheric measurements supports the claim that the enhancement was not of natural origin. Our findings demonstrate that identifying pollutants and tracing them to their sources is achievable, with significant implications for monitoring and mitigating space emissions in the atmosphere.
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    First Coincident Radar and Optical Observations of a Meteor Radio Afterglow
    (Wiley, 2026-03-01)
    It has been hypothesized that Meteor Radio Afterglows (MRAs) occur due to resonant transition radiation (RTR) where suprathermal electrons emit as they pass through electron density inhomogeneities in a turbulent plasma. Meteor trails are thought to produce suprathermal electrons through anion oxidation, which can be identified through meteor persistent trains. Meteor plasma turbulence can be identified through a non‐specular echo from a meteor radar. We present the first radar observations of a MRA that was also observed to produce a non‐specular echo and a persistent train, which indicate the presence of both plasma turbulence and anion oxidation. The observations were made using the Long Wavelength Array station at Sevilleta (LWA‐SV) and the Spread spectrum Interferometric Multi‐static Meteor radar Observing Network in New Mexico (SIMONe‐NM), the Widefield Persistent Train Camera version 2 (WiPT2) and the Global Meteor Network (GMN). Analysis reveals that while the MRA was spatially coincident a range‐spread, non‐specular echo, the brightest MRA emission came from a portion of the trail 8 km higher than the brightest radar scatter. We find that changes in the mean free path and collision frequency may be responsible for the higher altitude emission despite weaker plasma turbulence there. We also present evidence from the SIMONe‐NM head echo that the MRA and non‐specular echo were coincident with fragmentation of the meteoroid, which may have some role to play in both phenomena.
    Scopus© Citations 1  1