Geophysical Research Letters最新文献

Arctic Oscillation (AO) is the dominant mode of atmospheric circulation in the extratropical Northern Hemisphere regions. The spatial pattern of the AO Arctic center affects the extent of polar cold air outbreaks southward. However, the underlying nature and causes of its interdecadal variation remain unclear. Utilizing ERA5 reanalysis data, this study identifies two distinct spatial patterns of the wintertime AO Arctic center through the K-means clustering method, which alternate over different decade periods. The Double-trough pattern generates a tripolar temperature pattern of “cold Arctic-warm Eurasia-cold Tibetan Plateau” through a Rossby wave train during 1960–1997/2013–2024. While the Single-trough pattern leads to a dipolar temperature pattern in 1998–2012. Furthermore, interdecadal variations in North Atlantic sea surface temperature meridional gradient act as an influencing factor in shaping the spatial pattern of the AO Arctic center. This research aids the understanding and prediction of climate anomalies using AO signals within various decadal contexts.

Observations of Uranus in the near-infrared by ground-based telescopes from 1992 to 2018 have shown that the planet's upper atmosphere (thermosphere) steadily cooled from ∼700 to ∼450 K. We explain this cooling as due to the concurrent decline in the power of the solar wind incident on Uranus' magnetic field, which has dropped by ∼50% over the same period due to solar activity trends longer than the 11-year solar cycle. Uranus' thermosphere appears to be more strongly governed by the solar wind than any other planet where we have assessed this coupling so far. Uranus' total auroral power may also have declined, in contrast with the power of the radio aurora that we expect has been predominantly modulated by the solar cycle. In the absence of strong local driving, planets with sufficiently large magnetospheres may also have thermospheres predominantly governed by the stellar wind, rather than stellar radiation.

In this study, we used the coupled GITM (Global Ionosphere Thermosphere Model)-SAMI3 (Sami3 is Also a Model of the Ionosphere) model to simulate the response of the ionosphere-thermosphere system during the 7 September 2017 geomagnetic storm. In the simulation results, a super equatorial plasma bubble (SEPB) formed and rose to around $��40�°�$ magnetic latitude (MLAT). This is attributed to a penetration electric field (PEF) that enhances the growth rate of generalized Rayleigh-Taylor instability (GRTI), while traveling atmospheric/ionospheric disturbances act as a seeding mechanism.

The coast of Terra Nova Bay (TNB) is known as one of the intense katabatic wind confluence zones in Antarctica. Strong westerly winds with topography-specific foehn effects (foehn-like winds, FLWs) could have influenced surface temperatures in this area downwind of the Transantarctic Mountains, yet their impact remains unstudied. Jang Bogo Station (JBS) in TNB has weak winds year-round, with occasional strong winds causing significant winter temperature increases. This study aims to investigate the FLWs and their recent variability in occurrence at JBS in terms of surface temperature variability. During the strong wind events, the surface warms due to foehn effects such as adiabatic heating and vertical mixing. FLWs occur approximately 16% (10%) of the time in winter (annually). FLWs are caused by cyclones in the eastern Ross Sea. Meteorological records for 2015–2022 revealed an increased FLW frequency, particularly in winter, which has increased temperatures in recent years.

Paleoclimate data provide important information about the character of natural climate variability. However, records with sufficient length and resolution to resolve high-frequency (decadal-scale) variability across the Holocene are scarce. We present a 10,800-year reconstruction of spring and summer temperature at three-year resolution based on biochemical varves from Lake Żabińskie, Poland. The reconstruction is based on Ca/Ti ratio, which are significantly correlated with instrumental spring and summer temperature spanning 240 years. Major climate events of the Holocene period are represented in the reconstruction, including the Holocene Thermal Maximum, 8.2 ka Event, Medieval Climate Anomaly, and Little Ice Age. A low-frequency 8,000-year decreasing trend in warm-season temperatures is driven by declining summer insolation. Temperature variability is highest during the early Holocene, likely related to warmer and drier conditions. The rate of warming during the past 90 years is extremely unusual, if not unprecedented for the Holocene, based on our reconstruction.

Recent machine learning (ML)-based weather forecasting models have improved the accuracy and efficiency of forecasts while minimizing computational resources, yet still depend on traditional data assimilation (DA) systems to generate analysis fields. Four dimensional variational data assimilation (4DVar) enhances model states, relying on the prediction model to propagate observation to the initial field. Consequently, the initial fields from traditional DA are not optimal for ML-based models, necessitating a customized DA system. This paper introduces an ensemble 4DVar system integrated with the FuXi model (FuXi-En4DVar), which can independently generate accurate analysis fields. It utilizes automatic differentiation to compute gradients, and demonstrates the equivalence of these gradients with those derived from adjoint models. Experimental results indicate that this system preserves the physical balance of the analysis field and exhibits flow-dependent characteristics. These features enhance the propagation and assimilation of observation into the initial analysis field, thereby improving the accuracy of the analysis fields.

We investigated the effects of salt crystallization on the dynamics of saline water evaporation in porous media. Water mass loss rates from sand columns supplied with NaCl solutions at three concentrations were monitored under controlled ambient conditions. The formation and evolution of salt crystals over sand surfaces were synchronously imaged optically and thermally. Despite identical experimental and ambient conditions, we observed distinct crystallization dynamics that affected evaporative mass loss rates for similar salt concentrations, highlighting high variability of crystallization and its impact on evaporation. We observed the enhancement of maximum evaporation rates by factors of 3 to 14 under our experimental conditions and attributed this enhancement to the formation and evolution of porous crystalized salts at the surface. Additionally, visible intermittent temperature fluctuations of the salt crust were quantified using thermal imagery attributed to the dynamic processes of crystallization, dissolution and evaporation occurring simultaneously at the surface.

We estimate seismic azimuthal anisotropy for the Juan de Fuca - Gorda plates from inversion of a new 10–80 s period Rayleigh wave dataset, resulting in a two-layer model to 80 km depth. In the lithosphere, most anisotropy patterns reflect the kinematics of plate formation, as approximated from seafloor-age-based paleo-spreading, except for regions close to propagator wakes and near plate boundaries. In the asthenosphere, the fast propagation orientations align with convective shear as inferred from the NUVEL1A plate motion model, which is indicative of a ∼3 Myr average, rather than with the more recent, ∼0.8 Myr, motions inferred from MORVEL. Regional anisotropy of this young plate system thus records convection like older plates such as the Pacific. On smaller scales, anisotropy imaging provides insights into dynamics of plate generation and can further elucidate plate reorganizations and changes in boundary loading.

HCFC-22 is an ozone-depleting substance with a greenhouse effect. The atmospheric mole fractions of HCFC-22 have been increasing since the 1950s. Within the NDACC-IRWG network, HCFC-22 mol fractions can be retrieved from solar absorption spectra measured by ground-based FTIR. However, only a few sites have provided HCFC-22 data sets. Here, we demonstrate a harmonized FTIR HCFC-22 retrieval strategy and generate a new global NDACC-IRWG HCFC-22 data set at 16 FTIR sites. The systematic and random uncertainties are 5.3%–8.7% and 3.2%–8.0%, respectively. A maximum HCFC-22 column annual growth rate was observed in 2009 with a mean of 7.65 ± 1.39 ppt/year, and the HCFC-22 annual growth rate decreased to 3.57 ± 1.39 ppt/year (2016–2020) and 2.15 ± 2.09 ppt/year (2021–2023). The annual growth rates derived from the FTIR measurements are compared to the ones derived from NOAA surface flask samplings and ACE-FTS satellite measurements, and the three independent data sets show a good agreement.