美国国家航空航天局

Cloud water serves as a chemical reactor where gases and particles undergo chemical transformations and thus is a key component in aerosol-cloud interactions. A total of 535 cloud water samples collected aboard the NASA ACTIVATE HU-25 Falcon (2020-2022) over the northwest Atlantic (U.S. East Coast to Bermuda) are analyzed, and a set of 31 dissolved species spanning major inorganic ions, selected organic acids, and trace elements are used here for source apportionment analysis. The EPA positive matrix factorization (PMF) 5.0 model yields a six-factor solution that explains considerable variability in dissolved solute mass (r = 0.77), with the factors being sea salt (81.3% of reconstructed mass), secondary aerosol (12.2%), traffic/combustion (5.2%), metal-enriched dust (0.9%), aged dust (0.3%), and an industrial/metallurgical factor (0.07%). Seasonal and spatial patterns showed strong sea salt mass contributions in all months, but especially in winter enhanced aged dust influence near Bermuda in June, and larger relative contributions of metal and traffic/combustion-related factors near the coast. Concentration-weighted trajectory maps link the dust factor to trans-Atlantic transport from North Africa and most other factors to export from the eastern United States. Overall, the results show that mass-based cloud water chemistry is strongly weighted toward larger, highly hygroscopic particles, while still retaining clear signatures of continental pollution and long-range dust transport.

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth's insolation) super-Earth GJ 486b (1.3 R$_{\oplus}$ and 3.0 M$_{\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 - 3.3 $\sigma$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$\sigma$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($\chi^2_\nu$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

Abstract Magnetotail current sheet (CS) flapping is a universal plasma phenomenon observed at multiple planets, yet its triggering mechanisms remain poorly understood outside of Earth. At Mars, single‐spacecraft observations have also reported tail flapping, but the processes responsible for its onset have never been identified. In this study, we investigate the potential correlation between magnetic reconnection and magnetotail flapping using multipoint measurements from Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen‐1 (TW‐1) missions. We analyze an example event in which MAVEN observed a reconnection‐associated CS crossing in the near tail while TW‐1 simultaneously detected CS flapping further downtail. A statistical survey of joint observations from November 2021 to February 2024 identifies that about two‐thirds of TW‐1 flapping events coincide with reconnection signatures observed by MAVEN. Multiple magnetic flux ropes were also detected before or during flapping intervals, similar to previous observations at Earth, suggesting that reconnection‐generated magnetic flux ropes may propagate tailward and drive plasma instabilities that trigger the tail flapping at Mars. These results provide the first multipoint evidence of a potential statistical correlation between magnetic reconnection and magnetotail flapping at Mars, enabling us to explore the potential triggering mechanism of magnetotail flapping. Our findings also offer new insights into Martian magnetotail dynamics and broaden the comparative understanding of this fundamental plasma process across planetary environments.

Abstract Surveys and observations of lightning on Jupiter prior to the NASA Juno mission used night‐side imaging approaches, and a common conclusion was that the optical energy was similar to the highest energy terrestrial lightning flashes, or superbolts. We use data from the Juno Microwave Radiometer (MWR) to measure the first radio pulse power distribution of Jovian lightning. The power distribution measurement was enabled by unique meteorological conditions in Jupiter's North Equatorial Belt (NEB) in 2021–2022, as the belt transitioned from an anomalously quiescent (non‐convective) state to its more typical configuration with small moist convective plumes scattered in longitude. During this transition, convective plumes in the NEB occurred only in isolated storms we label “stealth superstorms.” The isolated nature of these storms (as lightning sources) resolved the degeneracy between pulse location and pulse strength, allowing measurement of a pulse power distribution with statistical median values ranging from 27 to 214 W over the MWR bandpass, well within the observational sensitivity range. The MWR thus measures typical pulse power in the storms, rather than high‐power outliers. Pulse power in the stealth superstorms may be comparable to terrestrial lightning radio emission, or up to a million times more powerful, depending on uncertainties in unresolved pulse duration and lightning spectral energy distributions. Future studies may determine whether the lightning pulse power in stealth superstorm is typical or anomalous of Jupiter's lightning in general.

Proxy records of past climates have yielded powerful insights into regional hydroclimate dynamics. Novel insights may be gained by reconstructing spatiotemporal changes in precipitation isotopologues in past climate states that cannot be gleaned from individual site-level studies. In this paper, we ask whether latitudinal gradients in the stable hydrogen isotopic composition of precipitation, as inferred from sedimentary leaf wax biomarkers, reflect aspects of large-scale climate conditions in western North America (WNA). Modern coretop samples from offshore WNA show that leaf wax hydrogen isotopes broadly track the hydrogen isotopic composition of rainfall between 20 and 40N, but with an offset corresponding to a relatively constant "apparent fractionation" value. Poleward of 40N, the leaf wax signal may be complicated by fluvial transport of leaf waxes from the continental interior. Leaf wax-inferred precipitation hydrogen isotopes show a shift to more negative values between 30 and 40N. We use modern observational data to show that this latitudinal range marks a major transition between the subtropical arid zone and the location of the midlatitude storm tracks over the northeast Pacific. Nudged water isotope-enabled models capture the location of the arid to mesic climate transition with fidelity. This modern data set suggests that reconstructions of the latitudinal gradient of precipitation hydrogen isotopes can constrain the sensitivity of the storm tracks to shifts in climatic boundary conditions in past climate states. This approach can yield novel insights into past, present, and future hydroclimate variability in this arid region.