Europa is characterized by a thin ice Ih shell overlying a subsurface ocean and a large solid core. Estimates of the outer ice shell’s thickness range from a few kilometers to several tens of kilometers, with strong implications for Europa’s thermal and geological history. Here, we model the thermal evolution of Europa’s ice shell using a parameterized convection approach that explicitly accounts for internal heat release. We explore changes in the thickness of this ice shell depending on several parameters, including the bulk ice viscosity, tidal heating, and ocean composition, and we further consider possible cyclical variations in tidal heating in response to changes in the eccentricity of Europa’s orbit. Our calculations show that ice shell thickness is mostly influenced by both the ice bulk viscosity and tidal heating. While significant in absence of tidal heating, the ocean composition has no or few influence when tidal heating is accounted for. Interestingly, for dissipated tidal heat and viscosity around 1 TW and 1014 Pa·s, respectively, which are within the expected range of values for these parameters, our calculations predict an ice shell thickness in the range 15-45 km and, at the top of this shell, a stagnant lid around 10 km in thickness, in agreement with recent estimates from impact basin morphology. Our calculations further indicate that a 10% change in orbital eccentricity may trigger variations in the ice shell thickness of approximately 15 km, which further helps to reconcile estimates based on geological features and modelled thermal history.

Detecting and attributing changes in mean precipitation is particularly challenging due to the strong influence of natural internal variability and poor performance of climate models in its simulations. There is still lack of research on human influence on mean precipitation in China. Here we use four observational datasets and CMIP6 simulations, with percentage precipitation anomaly (PPA) as a metric, to analyze precipitation changes in China and successfully detect human activity fingerprints based on the optimal fingerprinting method. Results show an increasing trend in annual mean precipitation across most regions since the 1960s, which CMIP6 models are generally able to reproduce. Human influence on China’s mean precipitation changes is detectable and separable from natural forcings. Across different regions, anthropogenic signals are detected in three sub-climatic regions: Northwest China, Northeast China, and Tibetan Plateau. Three-signal analysis further reveals that the increase in China’s mean precipitation is primarily driven by greenhouse gas forcing.

A document by Walter N Meier. Click on the document to view its contents.

In recent years, solar-induced chlorophyll fluorescence (SIF) has shown great potential for monitoring terrestrial photosynthesis, but existing SIF products retrieved from atmospheric sensors typically feature coarse spatial resolutions from several to hundreds of kilometers. Recently, the Chinese Terrestrial Ecosystem Carbon Inventory Satellite, Goumang, launched in August 2022, carries a unique SIF Imaging Spectrometer (SIFIS), the first spaceborne sensor specifically designed for global SIF retrieval. SIFIS provides a substantially improved spatial resolution (along track: 370 m; across track: 800 m) and high spectral resolution (0.24 nm, 664–786 nm), representing an important advance in SIF remote sensing capabilities and enabling accurate SIF retrieval using a data-driven approach. SIFIS SIF showed excellent spatial and temporal agreement with airborne AisaIBIS data and independent datasets (TROPOMI SIF, OCO-2 SIF, SMAP GPP). This new SIF product opens new avenues for studying fine-scale photosynthesis from space.

Geological, geodetic, and seismological observations show that large earthquakes damage the crust surrounding the main rupture and, sometimes, activate nearby, smaller, secondary faults. However, the long-term tectonic role of such secondary faults and their behavior in response to earthquakes or tectonic loading are unclear. We describe secondary faults activated by the Mw\,7.2, 2021 Haiti earthquake within the Enriquillo Plantain Garden Fault zone and show that they continued to slip for weeks after the main event, some of them slipping against the long-term tectonic stress. We model this time-dependent behavior as frictional slip in response to shear stress changes imparted by the earthquake. These faults, widely distributed in the hanging wall of the main rupture, are therefore very weak and capable of slipping under small stress changes. Therefore, they should also diffuse some of the tectonic load between large earthquakes, reducing the amount of stress that accumulates at shallow crustal depths.

Mangrove conservation and restoration has been increasingly recognized as cost-effective and sustainable strategies to mitigate the increasing coastal flood risks. As surge or tidal waves propagate through river deltas and estuaries, mangroves can lower peak water levels by exerting friction on the water flow, which results in within-wetland attenuation of high water levels, and by providing flood storage, resulting in along-channel attenuation. While the impact of channels and vegetation on the friction effect has been studied before, the impact on the storage effect is not. Here we present a hydrodynamic model in a tropical subestuary, calibrated and verified with field observations. Through a scenario analysis, we show that with a denser network of secondary subchannels and less dense vegetation, the storage effect becomes stronger, leading to higher along-channel attenuation. The opposite can be observed for the friction effect: we simulate lower within-wetland attenuation rates in case of higher channel density and lower vegetation density. If a wide 2 km mangrove band fringes the channels, we found the strongest along-channel attenuation in case of a dense network of secondary subchannels with low vegetation density. In contrast, when the mangrove extent is limited, for instance due the presence of aquaculture, a dense network of channels or sparse vegetation can result in the amplification of peak water levels. Future conservation and restoration efforts should consider this trade-off between within-wetland and along-channel attenuation in order for nature-based flood protection to safeguard both human settlements behind unchanneled wetlands and along deltaic channels fringed by mangroves.

Atmospheric surface pressure provides valuable information on the vertical dynamical structure of the atmosphere. Previous studies have reported that among the waves observed in surface pressure, semi-diurnal tides (SDTs) are significantly affected by the stratospheric quasi-biennial oscillation (QBO). Using historical surface-pressure observations and the Earth-system model MRI-ESM2.0, this study confirms that SDTs and the QBO are synchronized, such that SDT amplitude respectively increases or decreases at a rate of ~1 Pa per 20 ms−1 during westerly or easterly phases of the QBO at 30 hPa. Our numerical simulations and a linear analytical model support the QBO–SDT relationship being dynamically forced by background zonal winds rather than by anomalous ozone radiative heating. We also find that the QBO–SDT relationship was notably disturbed by the volcanic eruptions of Mount Agung in 1963 and Mount Pinatubo in 1991, during which increased shortwave radiative absorption caused by stratospheric aerosol enhanced the SDT amplitude. Short-lived El Nino events also occurred, moistening the upper troposphere to provide extra solar heating when volcanic aerosol was transported to higher latitudes. The influence of volcanic eruptions and El Nino events overlap with the QBO frequency band, jointly working as ‘noise’ in QBO–SDT synchronization.

The need is at peak for developing novel monitoring tools to accurately map Arctic permafrost landforms and thaw disturbances, track their changes over time, and to assess the economic impact on human-built infrastructure. The entire Arctic has been imaged by submeter resolution Maxar satellite sensors, multiple times during the last two decades.

Despite extensive implementation of best management practices to mitigate external nutrient runoff, numerous New Hampshire lakes are continuing to experience diminished water quality, likely due to internal phosphorus loading (IPL). This remobilization of legacy nutrients can lead to more frequent and prolonged cyanobacteria blooms and exacerbate the process of eutrophication. This is the case for Lake Kanasatka, Moultonborough, NH, where IPL contributes to nearly 25% of its total phosphorus budget, with that percentage increasing towards 50% by the end of summer as the hypolimnion reaches anoxia, accelerating dissolutive release. Cyanobacteria blooms at Lake Kanasatka have become more prevalent in recent years, heightened around fall turnover when bioavailable phosphate is upwelled into the epilimnion, with blooms lasting up to 83 days. With Lake Kanasatka receiving an aluminum sulfate treatment in early 2024, we are compiling a comprehensive biogeochemical profile of the water column from April to October with a focus on the fractionation of phosphorus into its organic, inorganic, and reactive forms to understand how treatment affects the different forms and bioavailability of this critical nutrient. In addition, we are conducting a comparison to the interconnected upstream waterbody, Wakondah Pond, to better understand the influence of IPL on the efficacy of treatment, and establish if Wakondah Pond is a possible source of external nutrients. Wakondah Pond has exhibited similar seasonal patterns and serves as a control to compare the Lake Kanasatka post-treatment results against. Evaluating both waterbodies will provide broader insight on the water quality and biogeochemical dynamics of the watershed and determine what future management and conservation efforts are needed. With only two other New Hampshire lakes receiving an aluminum sulfate treatment since 1984, it is important to analyze seasonal trends in nutrient loading along with consistent monitoring to better understand the longevity of treatment and its impact on water quality.

We present a statistical study of large magnetic field vector residuals between Swarm observations and the 13th generation International Geomagnetic Reference Field (IGRF-13) model under quiet to weakly disturbed geomagnetic conditions. Since the vast majority of data are taken during relatively quiet geomagnetic conditions, statistics of these large residuals are important for estimating potential errors for satellite operation when using IGRF-13 as reference, as well as for magnetosphere-ionosphere-thermosphere (MIT) studies. Residuals with magnitude of vector differences between Swarm observations and IGRF-13 estimations larger than 300 nT under Dst >-50 nT are studied from 2014 to 2020. All large residuals appear in the high-latitude auroral zone region peaking around 70° (-70°) magnetic latitude (MLAT) in the northern hemisphere (southern hemisphere) but there is also a secondary occurrence peak just below 80° (-80°) MLAT. However, the two hemispheres show clear asymmetries in the magnetic longitude (MLON) distribution where both hemispheres show high concentration of large residuals around the geographic poles. Since the two geographic poles are located at different geomagnetic locations and polar satellite’s orbits give rise to highly biased number of observations around the geographic poles, it results in high occurrence of large residuals around the geographic poles but a decrease in occurrence rate with respect to the total number of measurements. Identifying the interhemispheric asymmetries resulting from the asymmetry of the geographic poles with respect to the magnetic poles under relatively quiet geomagnetic conditions is helpful for a better understanding of interhemispheric asymmetry for the MIT system.

Understanding the impacts of high-resolution ocean model provides valuable insights for future research. However, the outcomes of sea surface state changes in both the tropics and mid-latitudes remain unclear, and initialized seasonal forecasts have not been studied extensively. This study investigates the impact of ocean model resolution with the first long-term hindcast experiment of an eddy-resolving (0.1°) ocean model used for global seasonal forecasting. We show that using the high-resolution ocean model significantly changes boreal winter jet streams in the atmosphere, based on the comparison of 30-year hindcasts with ocean resolutions ranging from 1° to 0.1° for the Japan Meteorological Agency/Meteorological Research Institute Coupled Prediction System version 3. In boreal winters, the cold sea surface bias in the equatorial Pacific is significantly reduced, leading to an equatorward shift in the intertropical convergence zone and enhanced convective activity in the western equatorial Pacific. The subtropical jet shifts southward due to the intertropical convergence zone shift and the weakening of equatorward propagation of mid-latitude atmospheric eddies. The enhanced convective activity in the tropics has a remote influence in the mid-latitudes, significantly reducing the upward eddy propagation of zonal wavenumber 1. Sea surface warm-up in the mid-latitudes partially cancels the reduction impact by enhancing the zonal wavenumber 2. Overall, the polar night jet accelerates due to the reduced supply of eddy forcing.

Using three-dimensional MHD simulations, we explore the stability of magnetotail configurations that include a local enhancement of $B_z$ (a “$B_z$ hump”). We focus on configurations that were previously found to be unstable in 2-D, neglecting cross-tail ($y$) variations as well as a cross-tail magnetic field component $B_y$.\, but approached final 2-D stable states. Not surprisingly, the 2-D unstable configurations were also found unstable in 3-D, developing 3-D structure after an initial rise as in 2-D. This is consistent with the fact that the selected $B_z$ hump configurations are characterized also by a local tailward decrease of field line entropy, which has been found to govern ballooning/interchange (B/I) instability \cite{schi04}. The evolution of the maximum electric field of the unstable 3-D modes showed an early exponential growth, which was only modestly faster than the 2-D mode. This might suggest that the unstable ballooning regime extends from $k_y \to \infty$ (proper ballooning modes) over finite $k_y$ even to $k_y \to 0$, at least for some equilibria. When the 3-D modes had evolved they grew significantly faster than the 2-D modes. This was associated with an evolution into several narrow beams. The 3-D modes did not approach stable final configurations. The final 2-D stable configurations approached from the unstable ones were found to be unstable in 3-D. These findings are again consistent with the fact that the 2-D evolution, governed by ideal MHD, did not alter the characteristics of the entropy function.

Nutrient runoff from different land management practices stimulates the growth of cyanobacteria and algae in surface water bodies. Excessive growth of algae in inland and coastal surface water bodies that release microcystins and other harmful algal contaminants are known as Harmful Algal Blooms (HABs). Monitoring HABs is important because they can cause negative health impacts to humans and create water quality issues such as depletion of dissolved oxygen in surface water bodies. Moreover, the increase in agricultural, industrial, and sewage effluents combined with frequent summer storms transports nutrients into water bodies and subsequently cause HABs. Therefore, implementing unmanned systems in monitoring HABs is useful because it reduces human contact with contaminated water and increases the spatial and temporal resolution of data collection. Recently unmanned aerial vehicles (UAVs) were used in monitoring surface water bodies for HABs because they are economical and collect data with high spatial resolution. However, in-situ monitoring combined with remote sensing enables in comparison of the two monitoring methods and evaluate the efficacy of remote sensing techniques to monitor HABs. Currently, monitoring is being conducted for HABs at the Grand Lake O' The Cherokees, OK, and Marion reservoir, KS using an unmanned surface vehicle (USV). Using the unmanned monitoring system, the chlorophyll and phycocyanin concentrations were estimated, and gridded estimates were plotted. Finally, the high spatial resolution data of chlorophyll, phycocyanin, and other water quality parameters by monitoring helps in calibrating statistical models to forecast HABs at Grand Lake and Marion reservoir. Methods and Results.