Geophysical Research Letters最新文献

Mangroves host many marine species and support fisheries in developing (sub)tropical countries. The suitability of mangrove habitats depends strongly thier the water chemistry. Here, we show how global warming and rising atmospheric CO₂ will reduce dissolved oxygen and increase CO₂ in mangrove waters. Observations from 23 mangrove-lined estuaries worldwide revealed that most sites already experience mild (34%–43% of the time) or severe (6%–32%) hypercapnic hypoxia, that is, high CO₂ and low oxygen conditions. Hypercapnic hypoxia mostly occurs during low tide, at low-salinity sites, and in warm tropical regions. Climate change will decrease oxygen concentrations by 5%–35% and increase CO₂ concentrations by 8%–60% in mangrove waters by 2100. Overall, hypercapnic hypoxia events will occur more frequently, last longer, and become more severe. These shifts will reduce mangrove biodiversity and deteriorate habitat quality for commercially valuable fish. The strongest impact is expected in tropical developing countries.

The sporadic E (Es) layer is a prominent ionospheric irregularity mainly driven by vertical wind shear at mid-latitudes. Hereby we statistically investigate for the first time Es responses to variations of the northern polar vortex (represented by NAM index) using long-term ionosonde observations over Japan (44 years) and Australia (34 years). The analysis reveals clear polar vortex modulation of Es, with increasing/decreasing foEs on low/high NAM days over Japan and decreasing foEs over Australia on low NAM days with a time lag of 5–7 days. This hemispheric asymmetry is largely attributed to nearly anti-phase wind shear responses in two hemispheres. Our results demonstrate the modulation of deep connection between stratosphere dynamics and ionospheric irregularities, emphasizing the importance atmosphere-ionosphere coupling. It suggests that the NAM index could be used to increase the accuracy of Es layer prediction and serve as indicator for assessing the risk of Es layer occurrence in advance. This has practical implications for fields such as radiocommunications and over-the-horizon radar.

Substorms are often described by a loading-unloading cycle, where onset follows gradual accumulation of solar wind magnetic flux in the magnetosphere. Yet observations indicate that intense substorms can also be directly driven, though the underlying mechanism remains unresolved. For the first time, global observations strongly indicate that substorm triggering is linked to enhanced dayside-driven convection and Region 1 FAC, supported by simulations. At 17:17UT during the May 2024 superstorm, a shock-compressed southward interplanetary magnetic field enhanced sunward convection and auroral currents. These rapidly extended to the nightside, initiating substorm expansion within 6 min. Simulations reproduce this response, revealing that dayside-driven convection of closed field lines depleted nightside flux and thinned the current sheet. This lowered onset threshold and triggered substorm expansion with negligible flux loading. Following onset, nightside flux loading became significant as a reconnection X-line formed near 10 Earth radii, extended azimuthally, and supported a global substorm current wedge.

Accurate forecasts of near-landfall TC characteristics (direction, translation speed, and intensity) are essential for timely disaster preparedness. Using best-track data (1951–2023), this study reveals a significant pre-landfall acceleration of TCs along the South China coast, with translation speed increasing by 35.5% and 16.4% during the 24 hr prior to landfall for eastbound and westbound cases, respectively. This acceleration is primarily contributed by the normal component of the translation vector. For westbound TCs, translation speed and its normal component increase with intensity, particularly at typhoon strength and above. Numerical simulations and diagnostic analyses attribute the acceleration to horizontal advection and diabatic heating, primarily driven by land-induced asymmetric flow and convection. These findings strengthen the current understanding of TC motion dynamics and support more effective disaster prevention and mitigation strategies as TCs approach coastal regions.