This study aims to quantify the impacts of ocean coupling on simulated and projected tropical cyclone (TC) precipitationin the Northern Hemisphere. We used global climate model (GCM) simulations over 1950-2050 from the High Resolution Model Intercomparison Project (HighResMIP) and compared its fully coupled atmosphere-ocean GCMs (AOGCMs) with atmosphere-only GCMs (AGCMs). We find that ocean coupling generally leads to decreased TC precipitation over ocean and land. Large-scale sea surface temperature (SST) biases are critical drivers of the precipitation difference, with secondary contributions from local TC-ocean feedbacks via SST cold wakes. The two driving factors, attributed to ocean coupling in the AOGCMs, influence TC precipitation in association with decreased TC intensity and specific humidity. The AOGCMs and AGCMs consistently project TC precipitation increases in 2015-2050 relative to 1950-2014 over ocean for all basins, and for landfalling TCs in the North Atlantic and western North Pacific.

Previous studies on future scenarios identified two key effects of increasing CO2 on the African summer monsoon (ASM): Rising CO2 leads to an enhancement in moisture supply, favoring an increase in ASM precipitation (the thermodynamic effect). However, it also results in a weakening in mean atmospheric flow, thus facilitating a dryness across the ASM region (the dynamic effect). Therefore, the ultimate change in ASM precipitation stems from the balance of both the thermodynamic and dynamic effects. This study further examines the impact of rising CO2 on ASM rainfall, by taking into account various climate states. Our results suggest that an increase in CO2 during warm interglacial periods has a stronger influence from thermodynamic factors than from dynamic factors, resulting in an enhancement in ASM rainfall. In contrast, if CO2 increases under cold glacial climate backgrounds, its dynamic impact dominates a reduction of rainfall in the ASM region.

River bifurcations are prevalent features in both gravel-bed and sand-bed fluvial systems, including braiding networks, anabranches and deltas. Therefore, gaining insight into their morphological evolution is important to understand the impact they have on the adjoining environment. While previous investigations have primarily focused on the influence on bifurcation morphodynamics by upstream channels, recent research has highlighted the importance of downstream controls, like branches length or tidal forcing. In particular, in the case of rivers, current linear stability analyses for a simple bifurcation are unable to capture the stabilizing effect of branches length unless a confluence is added downstream. In this work, we introduce a novel theoretical model that effectively accounts for the effects of downstream branch length in a single bifurcation. To substantiate our findings, a series of fully 2D numerical simulations are carried out to test different branches lengths and other potential sources of asymmetries at the node, such as different widths of the downstream channels. Results from linear stability analysis show that bifurcation stability increases as the branches length decreases. These results are confirmed by the numerical simulations, which also show that, as the branch length tends to vanish, bifurcations are invariably stable. Finally, our results interestingly show that, while in general, when a source of asymmetry is present at the node, the hydraulically favoured branch dominates, there are scenarios in which the less-favoured side becomes dominant.

The spectral-element method (SEM) for simulating wave propagation is widely used with adjoint methods for full-waveform inversion. Typically, SEM is used to compute forward and adjoint wavefields, which is then applied to evaluate the Fréchet derivatives for updating the seismic structural model. The Hessian is rarely computed as the high computational and storage costs, although it can improve the accuracy of the model update and model convergence. Instead the approximate Hessian is determined, which is obtained with less computational effort. We present a method for simultaneously constructing Fréchet and Hessian kernels on the fly, which we call Multi-solver spectral-element and adjoint methods (Multi-SEM). Rather than storing all the wavefields, Multi-SEM is computed on the fly and requires only about a 2-fold computational cost when compared to the computation of Fréchet kernels. Numerical examples demonstrate the functionality of the method and the computer codes are provided with this contribution.

Global warming is presently accelerating, raising the question whether all climate forcing and feedback mechanisms have been accounted for. Here a metabolic climate forcing and feedback mechanism is introduced, providing an explanation for the observed accelerated global warming. Based on more than 400,000 meteorological observations at various latitudes, it is shown that temperatures at the Earth's surface increasingly depart from thermodynamic equilibrium conditions towards warming at all examined geographical locations because of a long-lasting imbalance between the exothermic metabolic process of ecosystem respiration and the endothermic metabolic process of photosynthesis. Following the principles of the metabolic theory, metabolic imbalances are attributed to warmer temperatures stimulating ecosystem respiration at the same time as photosynthesis becomes light constrained. Since metabolic imbalances are expected to continue until ecosystem respiration becomes substrate limited, there is an urgent need to navigate climate mitigation towards measures that can slow down ecosystem respiration.

This study presents a novel approach to modeling the Earth’s geomagnetic field, which originates from electric currents approximately 2,900 km beneath the surface, crucial for understanding planetary dynamics. We introduce a method for inverting a planetary-scale equivalent magnetization source and develop a 3-D equivalent electric current circulation model from this source, enhancing understanding of these deep currents. This research signifies the first use of unstructured tetrahedral magnetization inversion technology for planet-scale magnetic data interpretation and equivalent source model construction. Validated through a synthetic case study, the method is applied to the International Geomagnetic Reference Field (IGRF) and SWARM satellite datasets, comprising 35,768 magnetic vectors from two orbital altitudes. Employing various mesh configurations, we construct and compare detailed current source models from these datasets. The effectiveness of our equivalent current sources is confirmed by comparison with dynamo research findings, demonstrating significant advancements in geomagnetic field modeling, particularly in interpretability, and providing novel insights into Earth’s magnetic phenomena.

A document by Kexin Liu. Click on the document to view its contents.

Detailed knowledge of fault geometry is important for accurate seismic hazard assessments. The Gulf of Aqaba, which corresponds to the southern termination of the 1200-km-long Dead Sea fault system, remains one of the least known parts of this plate boundary fault, in large part due to its location offshore. Classically, the Gulf of Aqaba has been described as a succession of three pull-apart basins. Here, building on a new multibeam bathymetric survey of the Gulf of Aqaba, we provide details about the geometry of the faults at the bottom of the gulf that controls its morphology. In particular, we identify a 50 km-long fault section that shows evidence of recent activation. We associate this fault section (Aragonese fault) with the section that ruptured during the 1995 magnitude Mw7.3 Nuweiba earthquake. In the southern part of the gulf, bathymetry emphasizes the strike-slip nature of the Arnona fault, while dip-slip motion seems to be accommodated mostly by faults located along the eastern edge of the gulf. Considering the simple linear geometry of the Arnona fault and the absence of any large earthquake for several centuries, despite an average slip-rate of ~5 mm/yr, this fault should be considered as a significant candidate for an earthquake rupture of magnitude 7 or above in the near future.

Clouds are one of the most critical yet uncertain aspects of weather and climate prediction. The complex nature of sub-grid scale cloud processes makes traceable simulation of clouds across scales difficult (or impossible). Often models and measurements are used to develop empirical relationships for large-scale models to be computationally efficient. Machine learning provides another potential tool to improve our empirical parameterizations of clouds. To explore these opportunities, we replace the warm rain formation process in a General Circulation Model (GCM) with a detailed treatment from a bin microphysical model that causes a 400\% slowdown in the GCM. We analyze the changes in climate that result from the use of the bin microphysical calculation and find improvements in the rain onset and frequency of light rain compared to detailed models and observations. We also find a resulting change in the cloud feedback response of the model to warming, which will significantly impact the climate sensitivity. We then emulate this process with an emulator consisting of multiple neural networks that predict whether specific tendencies will be nonzero and the magnitude of the nonzero tendencies. We describe the risks of over-fitting, extrapolation, and linearization of a non-linear problem by using perfect model experiments with and without the emulator and show we can recover the solutions with the emulators in almost all respects, and recover nearly all the speed to get simulations that perform as the detailed model, but with the computational cost of the control simulation.

Sedimentary specimens of the planktonic foraminifera Globorotalia inflata can provide much needed information on subsurface conditions of past oceans. However, interpretation of its geochemical signal is complicated by possible effects of cryptic diversity and encrustation. Here we address these issues using plankton tow and sediment samples from the western South Atlantic, where the two genotypes of G. inflata meet at the Brazil-Malvinas Confluence Zone. The 18O and δ13C of encrusted specimens from both genotypes from a core within the confluence zone are indistinguishable. However, we do find a large influence of encrustation on δ18O and Mg/Ca. Whereas crust Mg/Ca ratios are at all locations lower than lamellar calcite, the crust effect on δ18O is less consistent in space. Plankton tows show that encrusted specimens occur at any depth and that even close to the surface crust Mg/Ca ratios are lower than in lamellar calcite. This is inconsistent with formation of the crust at lower temperature at greater depth. Instead we suggest that the difference between the crust and lamellar calcite Mg/Ca ratio is temperature-independent and due to the presence of high Mg/Ca bands only in the lamellar calcite. The variable crust effect on δ18O is more difficult to explain, but the higher incidence of crust free specimens in warmer waters and the observation that a crust effect is clearest in the confluence zone, hint at the possibility that the difference reflects advective mixing of specimens from warmer and colder areas, rather than vertical migration.

We present, for the first time, a plasmaspheric hiss event observed by the Van Allen probes in response to two successive interplanetary shocks occurring within an interval of ~2 hours on December 19, 2015. The first shock arrived at 16:16 UT and caused disappearance of hiss for ~30 minutes. Significant Landau damping by suprathermal electrons followed by their gradual removal by magnetospheric compression opposed the generation of hiss causing the disappearance. Calculation of electron phase space density and linear wave growth rates showed that the shock did not change the growth rate of whistler mode waves within the core frequency range of plasmaspheric hiss (0.1 - 0.5 kHz) during this interval making conditions unfavorable for the generation of the waves. The recovery began at ~16:45 UT which is attributed to an enhancement in local plasma instability initiated by the first shock-induced substorm and additional possible contribution from chorus waves. This time, the wave growth rate peaked within the core frequency range (~350 Hz). The second shock arrived at 18:02 UT and generated patchy hiss persisting up to ~19:00 UT. It is shown that an enhanced growth rate and additional contribution from shock-induced poloidal Pc5 mode (periodicity ∼240 sec) ULF waves resulted in the excitation of hiss waves during this period. The hiss wave amplitudes were found to be additionally modulated by background plasma density and fluctuating plasmapause location. The investigation highlights the important roles of interplanetary shocks, substorms, ULF waves and background plasma density in the variability of plasmaspheric hiss.

Many indices have been defined to estimate the intensity of a heatwave. However, these indices are often used indiscriminately, without sufficient consideration of their possible different results and of the challenges that this poses to a proper characterization and comparison of events. This study, by comparing four different indices applied to reanalyses data, shows that the choice of heatwave intensity metrics has important effects on the detection of the most intense events for the period 1950-2021, with indices based on cumulative values of a target variable that must be preferred over the ones relying on temporal averages. Under these considerations, one of the given indices is additionally selected for the study of heatwaves of the period 1950-2021, showing that heatwaves that were unlikely before 1986 have become up to ten times more usual and up to three times more intense during recent times.

As there are strong crustal magnetic fields in some Martian concentrated regions. it has long been a goal of Martian science to understand how crustal magnetic field affects surrounding space environment. In the paper, using the data measured by MAVEN, the ratio of electron/CO2 density ( Ne/NCO2) in region with different levels of Martian ionospheric magnetic fields are studied. It seems that ratio of dayside Ne/NCO2 in region with stronger ionospheric magnetic field is larger while the altitude is more than 260 km. On the other hand, the effect of crustal magnetic field intensity on the nightside ratio of Ne/NCO2 is weak. Since the topological structure of magnetic field is very vulnerable to the solar wind, the correlation between Ne/NCO2 and solar wind parameters are analyzed. We find that there is obvious negative correlation between dayside ratio of Ne/NCO2 and solar wind dynamic pressure in the region with strong ionospheric magnetic field, which may imply that the ionospheric plasmas are significantly escaped in response to enhanced solar wind dynamic pressure pulses in the dayside region. However, the effect of solar wind on nightside ratio of Ne/NCO2 is very little. These results can be useful for understanding the dynamic process in the Martian ionosphere.

Arctic amplification is known to accelerate the hydrological cycle in high-latitude landmass, which eventually leads to increased river discharge into the Arctic Ocean. However, the majority of climate models in Coupled Model Intercomparison Project 5 (CMIP5) tend to underestimate Arctic river discharge. This study elucidates the role of additional Arctic river discharge for the phytoplankton responses in the present and future climate simulations. In the present climate simulation, the additional freshwater input showed a decrease in the phytoplankton in spring due to the increasing sea ice, and in summer, it showed an increase in phytoplankton due to the surplus nitrate leftover from spring and induced vertical mixing. Similar processes occurred in future climate simulations. However, in those simulations, the major response region of phytoplankton to additional freshwater input was altered from the Eurasian Basin to the Canadian Basin and the East-Siberian Sea. This is because the current marginal ice zone in the Barents-Kara Sea, where phytoplankton mainly responds, moves toward the East-Siberian-Chukchi Sea. We suggest that Arctic river discharge is potentially an important contributing factor for Arctic ecosystems in both present and future climate that controls sea ice and nutrient distribution.

There are different numerical models, such as the transmission-line matrix model or partially uniform knee model used to predict Schumann radiation. This report introduces a new idea, and reasoning to the previously stated idea of locating Schumann resonances on a single particle’s radiation pattern using a Golden ratio and their Octave, triad relationship. In addition, this different prediction method for Schumann resonances derived from the first principle fundamental physics combining both particle radiation patterns and the mathematical concept of the golden ratio spiral that expands at the rate of the golden ratio. The idea of golden ratio spiral allows locating Schumann resonant frequencies on particle’s radiation patterns. The Octaves allows us to predict the magnitude of other Schumann resonances on the radiation pattern of a single accelerated charged particle conveniently by knowing the value of the initial Schumann resonant frequency. In addition, it also allows us to find and match Schumann resonances that are on the same radiation lobe. Furthermore, it is important to find Schumann octaves as they propagate in the same direction and have a higher likelihood of wave interference. Method of Triads together with Octaves helps to predict magnitude and direction of Schumann resonant points without needing to refer to a radiation pattern plot. As the golden ratio seems to be part of the Schumann resonances, it is helpful in understanding to know why this is the case. The main method used in the reasoning of the existence of golden ratio in Schumann resonances is the eigenfrequency modes, $ \sqrt{n(n+1)} $ in the spherical harmonic model. It has been found that eigenfrequency modes have two a start off points, $ n_0 = 0 $ or $ n_0 = \frac{\sqrt{5}-1}{2} $ where the non-zero one is exactly the golden ratio. This allows to extend the existing eigenfrequency modes to $ \sqrt{(n_0+n)^2+(n_o+n)} $ in order to explain why golden ratio exist within Schumann resonances.

Since the 1970s, agricultural production in central Argentina has shifted away from perennial crops and grasses towards annual crops, largely soy. In this work we use observations and modeling to understand how this shift in land cover has affected the sub-surface, surface and atmospheric fluxes of moisture and energy in a flat agricultural area. We analyze the flux tower data from a paired site at Marcos Juarez in central Argentina during the period of the RELAMPAGO field campaign (2018-2019). When compared to perennial alfalfa, the observations over soy show lower evapotranspiration and specific humidity, higher sensible heat, higher outgoing shortwave radiation and soil temperature. Furthermore, water table depth is shallower below the soy than the alfalfa sites. To better understand the long-term temporal behavior from 1970s to present, the Noah-MP land surface model was calibrated at both soy and alfalfa sites based on RELAMPAGO data. Long-term simulation of the calibrated model suggests that ~95% of precipitation is evaporated in the alfalfa site with negligible recharge and runoff. In the case of soy, ET is about 68% of precipitation, leaving nearly 28% for recharge and 4% for runoff. Observed increases in streamflow and decreases in water table depth over time are likely linked to shifts in land cover. The changes in water table depth are enhanced in El Nino years. Furthermore, the partitioning of net radiation shifts from latent heat to sensible heat resulting in a 250% increase in Bowen ratio (from 0.2 to 0.7).

Using a three-dimensional coupled physical-biological model, this paper explores the creation of phytoplankton blooms around tropical islands in the presence of ambient currents and short-lived (~4 days) wind events. The ambient flow creates a retention zone of weak flows in the lee of the island, which is a typical feature of island wakes. Findings reveal that wind-induced upwelling effects are essential for the initial nutrient enrichment and phytoplankton growth that occur mainly in this retention zone. Oscillating flow, typical of island wakes, occasionally releases mesoscale patches of upwelled water and its phytoplankton load into the ambient ocean. The phytoplankton continues to grow within floating structures that are of up to 20 km in diameter. This mechanism complements the plankton growth associated with the formation of mesoscale eddies.

Elisa Romanelli 1, Julia Sweet 2,3, Sarah Lou Carolin Giering 4, David A. Siegel1, Uta Passow 2,51 Earth Research Institute, University of California, Santa Barbara, CA, United [email protected], [email protected] Marine Science Institute, University of California, Santa Barbara, CA, United States3 University of Louisiana at Lafayette, LA, United [email protected] National Oceanography Centre, Southampton, United [email protected] Memorial University, St John’s, [email protected]