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Abstract

Synthetic Aperture Radar (SAR) has emerged as a pivotal technology in geosciences, offering unparalleled insights into Earth's surface. Indeed, its ability to provide high-resolution, all-weather, and day-night imaging has revolutionized our understanding of various geophysical processes. Recent advancements in SAR technology, that is, developing new satellite missions, enhancing signal processing techniques, and integrating machine learning algorithms, have significantly broadened the scope and depth of geosciences. Therefore, it is essential to summarize SAR's comprehensive applications for geosciences, especially emphasizing recent advancements in SAR technologies and applications. Moreover, current SAR-related review papers have primarily focused on SAR technology or SAR imaging and data processing techniques. Hence, a review that integrates SAR technology with geophysical features is needed to highlight the significance of SAR in addressing challenges in geosciences, as well as to explore SAR's potential in solving complex geoscience problems. Spurred by these requirements, this review comprehensively and in-depth reviews SAR applications for geosciences, broadly including various aspects in air-sea dynamics, oceanography, geography, disaster and hazard monitoring, climate change, and geosciences data fusion. For each applied field, the scientific advancements produced because of SAR are demonstrated by combining the SAR techniques with characteristics of geophysical phenomena and processes. Further outlooks are also explored, such as integrating SAR data with other geophysical data and conducting interdisciplinary research to offer comprehensive insights into geosciences. With the support of deep learning, this synergy will enhance the capability to model, simulate, and forecast geophysical phenomena with greater accuracy and reliability.

Abstract

The parameterizations of air-sea turbulent heat flux are one of the major bottlenecks in atmosphere-ocean coupled model development, which play a crucial role in sea surface temperature (SST) prediction. Recently, neural networks start to be applied for the development of parameterizations of interface turbulent heat flux. However, these new parameterizations are primairily developed for specific regions and have not been tested in real atmosphere-ocean coupled models. In this study, we propose a new air-sea heat flux parameterization using a physical-informed neural network (PINN) based on multiple observational data sets worldwide. Evaluated with an independent observation data set, it is shown that the PINN can significantly reduce the RMSE of latent heat flux by at least about 48.6% compared to three traditional bulk formulas. Moreover, the PINN can be flexibly updated with new observational data by transfer learning. To test the performance of the new parameterization in realistic application, we implement the PINN into a global ocean-atmosphere coupled model and make seasonal forecasts for the first time. The PINN markedly reduce the errors of equatorial SST forecast, indicating a good performance of the PINN-based air-sea turbulent heat flux scheme. Noticeably, due to limited observational data, the NN-based parameterizations tend to underestimate heat flux at high wind speeds compared with bulk formula-based parameterizations. With more data available at extreme conditions, the PINN can be improved via transfer learning and need to be futher evaluated. This study suggests that PINN-based air-sea heat flux parameterization is promising to improve SST simulation.

Abstract

Arctic cyclones are key drivers of sea ice and ocean variability. During the 2019–2020 Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, joint observations of the coupled air-ice-ocean system were collected at multiple spatial scales. Here, we present observations of a strong mid-winter cyclone that impacted the MOSAiC site as it drifted in the central Arctic pack ice. The sea ice dynamical response showed spatial structure at the scale of the evolving and translating cyclonic wind field. Internal ice stress and ocean stress play significant roles, resulting in timing offsets between the atmospheric forcing and the ice response and post-cyclone inertial ringing in the ice and ocean. Ice motion in response to the wind field then forces the upper ocean currents through frictional drag. The strongest impacts to the sea ice and ocean from the passing cyclone occur as a result of the surface impacts of a strong atmospheric low-level jet (LLJ) behind the trailing cold front and changing wind directions between the warm-sector LLJ and post cold-frontal LLJ. Impacts of the cyclone are prolonged through the coupled ice-ocean inertial response. Local impacts of the approximately 120 km wide LLJ occur over a 12 hr period or less and at scales of a kilometer to a few tens of kilometers, meaning that these impacts occur at combined smaller spatial scales and faster time scales than most satellite observations and coupled Earth system models can resolve.

Abstract

Dry- and wet-bulb temperature (T d and T w ) are usually to define heatwaves (HWs) which have been enhanced under anthropogenic climate change (ACC) and urbanization. However, responses of various types of HWs (i.e., dry HWs, only high T d ; humid HWs, only high T w ; hybrid HWs, both high T d and T w ; total HWs, high T d or T w ), to ACC and urbanization remain unknown. In this study, both observations and simulations show significantly increasing occurrence probability of total HWs over China during 1971–2020, whereas this increase is mainly reflected in hybrid HWs, followed by dry HWs and humid HWs. 68.2%–93.0% of the observed increases in the above four types of HWs can be attributed to ACC; on the other hand, urbanization tends to suppress humid HWs but enhance dry HWs, as a result of contributing to the increase of hybrid HWs by 10.9%. Under future ACC, total HWs are projected to be more frequent as expected, which is mainly sourced from the increasing hybrid HWs because dry/humid HWs are projected to be steady/downward. As a consequence, urban population exposure to ACC-induced total HWs would remarkably increase to 83.55 billion person-days by the 2090s, 89.5% of which can be attributed to hybrid HWs. Urbanization would amplify this population exposure of ACC-induced hybrid HWs from 74.79 billion person-days to 110.9 billion person-days. Our results underscore the importance of improving understanding of hybrid HWs in urban areas and developing targeted adaptation planning on a warmer planet.

Abstract

As a significant macrophysical property, cloud horizontal scales play a role in cloud radiation, precipitation and vertical cloud overlap. Until now, however, the mechanisms behind the variations in cloud scale distribution have received far less attention. This study utilizes active satellite data from 2007 to 2016 to investigate the spatiotemporal distribution of cloud horizontal scales, and explains the variations through two meteorological factors: wind shear and atmospheric stability. Cloud scales exhibit a distinct power-law behavior when scale break is not considered, and the power-law exponent β is a characteristic measure of cloud scale distribution. A smaller power-law exponent β indicates a higher frequency of large clouds. During boreal summer season, the amount of large clouds is extremely large south of the 40°S but rather small between 10°S and 20°S. As wind shear decreases or atmospheric stability increases, more large clouds occur globally. The underlying mechanisms might be associated with cloud entrainment which can be promoted by wind shear but inhibited by atmospheric stability. However, our analysis of the impacts of these two factors on cloud scale distribution across different regions and heights reveals that both wind shear and atmospheric stability play dual roles on the values of the exponent β. The potential physical mechanisms, including the effects of precipitation, are further discussed. It is observed that precipitation also exerts a dual impact on the values of the exponent β. These findings underscore the significance of considering the impacts of meteorological factors on cloud scale distribution in numerical weather prediction models.

Implementing the iCORAL (version 1.0) coral reef CaCO3 production module in the iLOVECLIM climate model
Nathaelle Bouttes, Lester Kwiatkowski, Manon Berger, Victor Brovkin, and Guy Munhoven
Geosci. Model Dev., 17, 6513–6528, https://doi.org/10.5194/gmd-17-6513-2024, 2024
Coral reefs are crucial for biodiversity, but they also play a role in the carbon cycle on long time scales of a few thousand years. To better simulate the future and past evolution of coral reefs and their effect on the global carbon cycle, hence on atmospheric CO2 concentration, it is necessary to include coral reefs within a climate model. Here we describe the inclusion of coral reef carbonate production in a carbon–climate model and its validation in comparison to existing modern data.

OpenFOAM-avalanche 2312: depth-integrated models beyond dense-flow avalanches
Matthias Rauter and Julia Kowalski
Geosci. Model Dev., 17, 6545–6569, https://doi.org/10.5194/gmd-17-6545-2024, 2024
Snow avalanches can form large powder clouds that substantially exceed the velocity and reach of the dense core. Only a few complex models exist to simulate this phenomenon, and the respective hazard is hard to predict. This work provides a novel flow model that focuses on simple relations while still encapsulating the significant behaviour. The model is applied to reconstruct two catastrophic powder snow avalanche events in Austria.

Refactoring the elastic–viscous–plastic solver from the sea ice model CICE v6.5.1 for improved performance
Till Andreas Soya Rasmussen, Jacob Poulsen, Mads Hvid Ribergaard, Ruchira Sasanka, Anthony P. Craig, Elizabeth C. Hunke, and Stefan Rethmeier
Geosci. Model Dev., 17, 6529–6544, https://doi.org/10.5194/gmd-17-6529-2024, 2024
Earth system models (ESMs) today strive for better quality based on improved resolutions and improved physics. A limiting factor is the supercomputers at hand and how best to utilize them. This study focuses on the refactorization of one part of a sea ice model (CICE), namely the dynamics. It shows that the performance can be significantly improved, which means that one can either run the same simulations much cheaper or advance the system according to what is needed.

Abstract

Logjams create an upstream backwater of deepened, slower water, locally reducing bed shear stress. We compared hydraulic impact of logjam series across 37 geomorphically diverse reaches of mountain streams observed over 11 years in the US Southern Rockies. To enable reach-scale comparison of logjam structure and spacing, we identified the modeled best-fit effective resistance coefficient minimizing difference between outflow exiting a 1D channel with logjams present, and the same model channel with elevated channel resistance. Effective resistance increased with ratio of jam upstream depth to depth without a logjam, ratio of backwater length to average spacing, and decreased for randomly distributed jams due to close spacing, which reduced backwater impact. An analytic approximation and boundaries for region of relative spacing with steepest increase in effective resistance are provided. Our results can assist in targeting interventions to areas where hydraulic impact is greatest, providing value for money in nature-based solution design.

Abstract

Recent studies have suggested that the interplanetary magnetic field (IMF) By ${B}_{y}$ component modulates particle precipitation during solstices, or periods of high dipole tilt Ψ ${\Psi }$. So far this explicit IMF By ${B}_{y}$-effect has only been shown in statistical studies. Here we analyzed a sequence of high-speed stream (HSS) driven events of auroral (<30 ${< } 30$ keV) and medium energy (>30 ${ >} 30$ keV and >100 ${ >} 100$ keV) particle precipitation. We show that when HSSs are comparable in terms of IMF and solar wind parameters, they can lead to systematically stronger particle precipitation in individual events when the signs of By ${B}_{y}$ and Ψ ${\Psi }$ are opposite. We also perform a superposed epoch analysis of 485 HSSs giving further evidence that the By ${B}_{y}$-effect is especially significant during HSSs. This is likely due to the persistent IMF By ${B}_{y}$ polarity during HSSs. We show evidence that the By ${B}_{y}$ dependence in particle precipitation is caused by a similar By ${B}_{y}$ dependence in substorm occurrence.

Abstract

Magnetic reconnection is a fundamental process known to play a crucial role in electron acceleration and heating, however, the mechanism of electron energization during reconnection is still not fully understood. This study introduces a novel electron acceleration mechanism in which electrons can be accelerated by secondary reconnection in the separatrix region. The secondary reconnection occurs in a thin current sheet resulted from the shear of the out-of-plane Hall magnetic fields of the primary magnetopause reconnection. It results in the intense electron energy fluxes toward the primary X-line. This mechanism will likely be an important piece in the puzzle of particle acceleration by reconnection.

Abstract

Modeling radiative transfer in a 3D cloudy atmosphere is critical to climate projections. A recently developed fast 3D radiation parameterization scheme gains some success in quantifying horizontal radiative transfer through cloud sides using cloud area fraction. Based on 3D Monte Carlo simulations of radiative transfer through an idealized single-layer cloud with Koch-shaped fractal geometry edges, here we show that radiative energy transport through cloud sides correlates more significantly with cloud area fraction than with cloud perimeter length. The results exemplify the importance of accounting for the horizontal radiative energy exchanges between cloud-free and cloudy regions with cloud area fraction. Results from additional sensitivity simulations show that increased cloud vertical extent often enhances cloud-side sunlight leak more significantly than cloud-side sunlight interception. At low sun elevations, cloud-side sunlight interception is enhanced more than cloud-side sunlight leak does with the increase of cloud mass.

Abstract

Riverbeds often fine downstream, with a gravel-bedded reach, a relatively abrupt gravel-sand transition (GST), and a sand-bedded reach. Underlying this behavior, bed grain size distributions are often bimodal, with a relative paucity (gap) around the range 1–5 mm. There is no general morphodynamic model capable of producing the grain size gap and gravel-sand transition autogenically from a unimodal sediment supply. Here we use a one-dimensional morphodynamic model including size-specific bedload and suspended load transport, to show that bimodality readily evolves autogenically even under unimodal sediment feed. A GST forms when we include a floodplain width that abruptly increases at some point. Upstream of the transition, non-gap gravel ceases to move and gap sediment is preferentially transported. At the transition, non-gap sand rapidly deposits from suspension, enhancing gap sediment mobility and diluting its presence on the bed.

Abstract

We investigate whether geomorphic signatures of permafrost are embedded in planforms of river meanders, and we inquire as to how physical factors unique to permafrost environments are able to affect their dynamics. By exploiting satellite imagery, a data set of 19 freely-meandering Arctic rivers is compared against an independent data set of 23 freely-meandering streams flowing through temperate and tropical regions. Suitable dimensionless metrics are defined to characterize morphometric properties of meanders in terms of the spatio-temporal distribution of curvature and channel width. Results show the absence of marked contrasts in the amplitude of bend-curvature between the two data set. Differently, we find a permafrost signature in the channel width response, which manifests itself through larger values of the average bend-width and by peaks of width fluctuations. Field data suggest that permafrost meanders tend to widen for increasing bend sinuosity, likely promoting a shift of their morphodynamic regime as final cutoff is approached.

Abstract

The contradiction of high subducting plate rate (ranging from 4 to 9 cm/yr on Earth's surface) and low slab sinking rate (about 1 and 2 cm/yr in lower mantle) calls for significant slab deformation in the middle mantle. However, mechanisms that can account for both the deformation and the rate discrepancy have not been fully explored. Here, using 2-D numerical models that incorporate grain size evolution, we propose a new slab deformation mode, slab segmentation and stacking, to accommodate the differential slab sinking rates. Our results show that the segmented slab due to faulting and grain-size reduction may further break off and stack over itself as it encounters the high-viscosity lower mantle. Stacked slabs slowly sink in the lower mantle, while periodic slab tearing hinders upward stress transmission, allowing shallow plates to subduct at a higher rate. This discovered mode also provides an alternative explanation for slab thickening in the lower mantle.

Abstract

Based on two meteor radars in mid-latitudes of China, the mid-latitude lower thermospheric neutral wind responses to the 2015 St. Patrick's Day great storm are investigated. The AE and PCN indices presented the similar quasi-5-hour oscillations during the storm. Interestingly, the analogous and close-correlated storm-time quasi-5-hour oscillations were also observed in both the meridional wind differences at 90–102 km derived from meteor radars. The meridional wind disturbances in the lower thermosphere also showed the extension toward the lower latitudes. It has been found that the enhanced equatorward wind disturbances at 250 km estimated by the Horizontal Wind Model-14 and Fabry-Perot Interferometer (FPI) emerged accordingly with the increases of AE and PCN with a time delay. And the enhancements of equatorward (poleward) wind disturbances at 250 km were accompanied by the increments of equatorward (poleward) wind disturbances at 94 km with a time lag of a few hours. It is thus suggested that the multiple intensified Joule heating events with quasi-5-hour time intervals were triggered by the successive substorm expansions during the storm. Then the Joule heating events led to the vertical wind and temperature disturbances in the mid-latitude lower thermosphere via disturbing the thermospheric meridional circulation, which consequently induced the quasi-5-hour meridional wind disturbances therein.

Abstract

Joule heating is a major energy sink in the solar wind-magnetosphere-ionosphere system and modeling it is key to understanding the impact of space weather on the neutral atmosphere. Ion drifts and neutral wind velocities are key parameters when modeling Joule heating, however there is limited validation of the modeled ion and neutral velocities at mid-latitudes. We use the Blackstone Super Dual Auroral Radar Network radar and the Michigan North American Thermosphere Ionosphere Observing Network Fabry-Perot interferometer to obtain the local nightside ion and neutral velocities at ∼40° geographic latitude during the nighttime of 16 July 2014. Despite being a geomagnetically quiet period, we observe significant sub-auroral ion flows in excess of 200 ms−1. We calculate an enhancement to the local Joule heating rate due to these ion flows and find that the neutrals impart a significant increase or decrease to the total Joule heating rate of >75% depending on their direction. We compare our observations to outputs from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). At such a low geomagnetic activity however, TIEGCM was not able to model significant sub-auroral ion flows and any resulting Joule heating enhancements equivalent to our observations. We found that the neutral winds were the primary contributor to the Joule heating rates modeled by TIEGCM rather than the ions as suggested by our observations.

Abstract

During the last 20 kyr, the Etna volcano has been characterized by almost continuous summit eruptions and by less frequent—yet definitely more destructive—flank eruptions issuing at <1,000 m asl altitudes and reaching the Ionian Sea. The chronological framework of pre-historic (pre-2,750 yr BP) flank eruptions is supported only by few radiometric and paleomagnetic ages. Here we paleomagnetically investigated 15 Holocene lava flows from SE Etna lower slopes and dated 12 of them. Paleomagnetic dating at Etna relies on best method pre-requisites: European location where reference geomagnetic models are well defined, and detailed stratigraphic evidence is available. We sampled 45 sites (450 oriented cores) from lavas loosely constrained in the 19,000–2,000 yr BP age window. Ten eruptions yielded a minimum 40% refinement with respect to initial age constraints, with four lava flows achieving refinement up to 90%. We obtained 620–1,398 yr (998 yr on average) dating accuracy for three flows bracketed in relatively short (1,398–1,644 yr) independent age constraints. By contrast, five flows characterized by longer 6,567–7,439 yr initial age windows yielded multiple age solutions. Finally, four lava flows with 1,644–6,567 yr-long initial age windows were tightly dated with 120–680 yr age ranges. We conclude that at volcanoes where best paleomagnetic dating pre-requisite are fulfilled, singular solutions are expected for 30% of the analyzed flows and, significant refinements for the others. Seven kyr seems to represent an independent age window threshold length to get or not significant dating refinements.

Abstract

Prior to use in operational systems, it is essential to validate ionospheric models in a manner relevant to their intended application to ensure satisfactory performance. For Over-the-Horizon radars (OTHR) operating in the high-frequency (HF) band (3–30 MHz), the problem of model validation is severe when used in Coordinate Registration (CR) and Frequency Management Systems (FMS). It is imperative that the full error characteristics of models is well understood in these applications due to the critical relationship they impose on system performance. To better understand model performance in the context of OTHR, we introduce an ionospheric model validation technique using the oblique ground backscatter measurements in soundings from the Super Dual Auroral Radar Network (SuperDARN). Analysis is performed in terms of the F-region leading edge (LE) errors and assessment of range-elevation distributions using calibrated interferometer data. This technique is demonstrated by validating the International Reference Ionosphere (IRI) 2016 for January and June in both 2014 and 2018. LE RMS errors of 100–400 km and 400–800 km are observed for winter and summer months, respectively. Evening errors regularly exceeding 1,000 km across all months are identified. Ionosonde driven corrections to the IRI-2016 peak parameters provide improvements of 200–800 km to the LE, with the greatest improvements observed during the nighttime. Diagnostics of echo distributions indicate consistent underestimates in model NmF2 during the daytime hours of June 2014 due to offsets of −8° being observed in modeled elevation angles at 18:00 and 21:00 UT.

Abstract

Subauroral red (SAR) arcs are commonly observed ionospheric red line emissions. They are usually attributed to subauroral electron heating by inner magnetospheric heat flux (IMHF). However, the role of IMHF in changing the ionosphere-thermosphere (IT) still remains elusive. We conduct controlled numerical experiments with the Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM). Coulomb collisional heat flux derived with the Comprehensive Inner Magnetosphere Ionosphere (CIMI) model and empirical subauroral polarization streams (SAPS) are implemented in TIEGCM. The heat flux causes electron temperature enhancement, electron density depletion, and consequently SAR arcs formed in the dusk-to-midnight subauroral ionosphere region. SAPS cause more substantial plasma and neutral heating and plasma density variations in a broader region. The maximum enhancement of subauroral red line emission rate is comparable to that caused by the heat flux. However, the visibility of SAR arcs also depends on the relative enhancement to the background brightness.