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Abstract

As a practical reflection of the opportunity window of Madden-Julian Oscillation (MJO), there are intermittent periods of relatively high forecasting skills, namely the forecast skill windows. Robust forecast skill windows are identified based on the subseasonal-seasonal reforecast database, during which the majority of models show high forecast skills. A total of 15 MJO forecast skill windows during 1993–2020 have been identified. Most of the forecast skill windows are closely associated with active MJO events with high amplitude. Whether a high-skill forecast window appears significantly depends on the magnitude of MJO intensity during the same period. The maintenance of active strong MJO events is potentially related with the warmer surface sea temperature anomalies in the western Pacific. Further research into such processes may unveil the MJO development mechanism and improve the MJO forecast skill.

Partition between supercooled liquid droplets and ice crystals in mixed-phase clouds based on airborne in situ observations
Flor Vanessa Maciel, Minghui Diao, and Ching An Yang
Atmos. Meas. Tech., 17, 4843–4861, https://doi.org/10.5194/amt-17-4843-2024, 2024
The partition between supercooled liquid water and ice crystals in mixed-phase clouds is investigated using aircraft-based in situ observations over the Southern Ocean. A novel method is developed to define four phases of mixed-phase clouds. Relationships between cloud macrophysical and microphysical properties are quantified. Effects of aerosols and thermodynamic and dynamical conditions on ice nucleation and phase partitioning are examined.

Atmospheric H2 observations from the NOAA Cooperative Global Air Sampling Network
Gabrielle Pétron, Andrew M. Crotwell, John Mund, Molly Crotwell, Thomas Mefford, Kirk Thoning, Bradley Hall, Duane Kitzis, Monica Madronich, Eric Moglia, Donald Neff, Sonja Wolter, Armin Jordan, Paul Krummel, Ray Langenfelds, and John Patterson
Atmos. Meas. Tech., 17, 4803–4823, https://doi.org/10.5194/amt-17-4803-2024, 2024
Hydrogen (H2) is a gas in trace amounts in the Earth’s atmosphere with indirect impacts on climate and air quality. Renewed interest in H2 as a low- or zero-carbon source of energy may lead to increased production, uses, and supply chain emissions. NOAA measurements of weekly air samples collected between 2009 and 2021 at over 50 sites in mostly remote locations are now available, and they complement other datasets to study the H2 global budget.

Simulation and detection efficiency analysis for measurements of polar mesospheric clouds using a spaceborne wide-field-of-view ultraviolet imager
Ke Ren, Haiyang Gao, Shuqi Niu, Shaoyang Sun, Leilei Kou, Yanqing Xie, Liguo Zhang, and Lingbing Bu
Atmos. Meas. Tech., 17, 4825–4842, https://doi.org/10.5194/amt-17-4825-2024, 2024
Ultraviolet imaging technology has significantly advanced the research and development of polar mesospheric clouds (PMCs). In this study, we proposed the wide-field-of-view ultraviolet imager (WFUI) and built a forward model to evaluate the detection capability and efficiency. The results demonstrate that the WFUI performs well in PMC detection and has high detection efficiency. The relationship between ice water content and detection efficiency follows an exponential function distribution.

Abstract

This study analyzes hydrometeor evolution during rapid intensification (RI) and tropical cyclone (TC) intensity dependence using satellite data. Previous studies have suggested ice cloud water or non-convective precipitation as a predictor of RI from different perspectives. However, few studies have focused on the impact of TC intensity or comprehensive comparisons to identify better indicators. During RI, hydrometeor contents in weak TCs increase over the entire region, whereas they increase mainly in the inner-core region and decrease in advance in the outer-core region for strong TCs. Hydrometeor contents in the inner-core are higher in RI than in slow intensification, and their maxima location is related to TC intensity and intensification rate. Cloud water path (CWP) in the inner-core region is most correlated with the intensification rate, especially in weak TCs. Therefore, the CWP can serve as a predictor of RI and can be applied to all TC intensities.

Abstract

In this study, prominent dust source areas are identified along with their plume extent using high temporal frequency satellite observations. Hourly dust plume observations of the Dust Belt from geostationary-orbit satellites are analyzed for the 2017-12–2022-11 period. To identify dust source areas and their extents, we back-track plumes to their source, assessing source areas in terms of emission frequency, contribution, and plume extent patterns. This method advances over traditional source allocation techniques that rely on polar-orbiting satellites based on a few daily passes and meteorological wind fields for backtracking. Our findings indicate that Boreal summer is the most intense season for most sources, except in the Southern Sahara, which experiences winterly winds. Our analysis also reveals significant contributions from regions within the Sahara that experience expansive but infrequent dust storms, highlighting the importance of considering both frequency and magnitude in understanding dust emissions.

Abstract

Radio-echo sounding (RES) shows large-scale englacial stratigraphic folds are ubiquitous in Greenland's ice sheet. However, there is no consensus yet on how these folds form. Here, we use the full-Stokes code Underworld2 to simulate ice movements in three-dimensional convergent flow, mainly considering ice anisotropy due to a crystallographic preferred orientation, vertical viscosity and density gradients in ice layers, and bedrock topography. Our simulated folds show complex patterns and are classified into: large-scale folds (>100 m amplitude), small-scale folds (<<100 m) and basal-shear folds. The amplitudes of large-scale folds tend to be at their maximum in the middle of the ice column or just below, in accordance with observations in RES data. We conclude that ice anisotropy amplifies the perturbations in ice layers (mainly due to bedrock topography) into large-scale folds during flow. Density differences between the warm deep ice and cold ice above may enhance fold amplification.

Abstract

Ion-acoustic waves (IAWs) commonly occur near interplanetary (IP) shocks. These waves are important because of their potential role in the dissipation required for collisionless shocks to exist. We study IAW occurrence statistically at different heliocentric distances using Solar Orbiter to identify the processes responsible for IAW generation near IP shocks. We show that close to IP shocks the occurrence rate of IAW increases and peaks at the ramp. In the upstream region, the IAW activity is highly variable among different shocks and increases with decreasing distance from the Sun. We show that the observed currents near IP shocks are insufficient to reach the threshold for the current-driven instability. We argue that two-stream proton distributions and suprathermal electrons are likely sources of the waves.

Abstract

The Central Asian Orogenic Belt (CAOB) was formed by the aggregation and collage of numerous Paleozoic subduction-accretion assemblages and Precambrian microcontinental blocks. However, the tectonic nature of the southeastern CAOB remains controversial, which complicates the reconstruction of the Paleo-Asian Ocean. To address this issue, a deep seismic reflection survey was initiated across the southeastern CAOB and reveals broad gentle sub-horizontal reflectors in the middle-lower crust and a relatively transparent zone in the upper crust. Combining with the Precambrian geological outcrops and other geophysical features, we support a microcontinental block, the Xilinhot Block, existed in the Paleo-Asian domain. Thus, the Paleo-Asian Ocean was separated into two branches that underwent north-dipping and double-dipping oceanic plate subduction, respectively, to form the Hegenshan-Heihe and Solonker sutures. Multiple relics beneath Hegenshan-Heihe Suture indicate that multiple sets of unidirectional oceanic subduction-accretion and magmatism were important mechanisms of continental growth.

Abstract

Abduallah et al. (2024b, https://doi.org/10.1029/2023sw003824) proposed a novel approach using a deep neural network model, which includes a graph neural network and a bidirectional LSTM layer, named SYMHnet, to forecast the SYM-H index one and 2 hr in advance. Additionally, the network also provides an uncertainty quantification of the predictions. While the approach is innovative, there are some areas where the model's design and implementation may not align with best practices in uncertainty quantification and predictive modeling. We focus on discrepancies in the input and output of the model, which can limit the applicability in real-world forecasting scenarios. This comment aims to clarify these issues, offering detailed insights into how such discrepancies could compromise the model's interpretability and reliability, thereby contributing to the advancement of predictive modeling in space weather research.

Always on my mind: indications of post-traumatic stress disorder among those affected by the 2021 flood event in the Ahr valley, Germany
Marie-Luise Zenker, Philip Bubeck, and Annegret H. Thieken
Nat. Hazards Earth Syst. Sci., 24, 2837–2856, https://doi.org/10.5194/nhess-24-2837-2024, 2024
Despite the visible flood damage, mental health is a growing concern. Yet, there is limited data in Germany on mental health impacts after floods. A survey in a heavily affected region revealed that 28 % of respondents showed signs of post-traumatic stress disorder 1 year later. Risk factors include gender, serious injury or illness due to flooding, and feeling left alone to cope with impacts. The study highlights the need for tailored mental health support for flood-affected populations.

Abstract

This study presents an innovative approach to improving the accuracy and reducing the error convergence time of static Precise Point Positioning (PPP) in Global Positioning System (GPS) navigation. The research focuses on the impact of the high spatial and temporal resolution of a regional ionospheric data assimilation model on PPP over Taiwan. The study further evaluates the performance of both static PPP with the ionospheric information using commonly used models such as Klobuchar and International Reference Ionosphere (IRI), as well as a global ionospheric data assimilation model. Compared to the default IRI, the data assimilated IRI model can improve the overall ionospheric total electron content by approximately 83%. Additionally, it can significantly reduce horizontal positioning errors and shorten the error convergence time more than 52% for static PPP, even during geomagnetic storm events. The study concludes that the high resolution of a regional ionospheric data assimilation model can enhance the accuracy and reduce the error convergence time of PPP navigation and positioning. This research provides valuable insights for future studies in this field, especially in the development of more precise and efficient models for correcting ionospheric delay in GPS navigation.

Abstract

Fundamental processes in plasmas act to convert energies into different forms, for example, electromagnetic, kinetic and thermal. Direct derivation from the Vlasov-Maxwell equation yields sets of equations that describe the temporal evolution of magnetic, kinetic and internal energies in either the monofluid or multifluid frameworks. In this work, we focus on the main terms affecting the changes in kinetic energy. These are pressure-gradient-related terms and electromagnetic terms. The former account for plasma acceleration/deceleration from a pressure gradient, while the latter from an electric field. Although limited spatial and temporal deviations are expected, a statistical balance between these terms is fundamental to ensure the overall conservation of energy and momentum. We use in-situ observations from the Magnetospheric MultiScale (MMS) mission to study the relationship between these terms. We perform a statistical analysis of those parameters in the context of magnetic reconnection by focusing on small-scale Electron Diffusion Regions and large-scale Flux Transfer Events. The analysis reveals a correlation between the two terms in the monofluid force balance, and in the ion force and energy balance. However, the expected relationship cannot be verified from electron measurements. Generally, the pressure-gradient-related terms are smaller than their electromagnetic counterparts. We perform an error analysis to quantify the expected underestimation of gradient values as a function of the spacecraft separation compared to the gradient scale. Our findings highlight that MMS is capable of capturing energy and force balance for the ion fluid, but that care should be taken for energy conversion terms based on electron pressure gradients.

Abstract

Space weather forecasts are of utmost importance in safeguarding navigation, communication, and electric power system operations, satellites from orbital drag, and the astronauts in the International Space Station from hazardous space radiation during extreme space weather conditions. The finest space weather prediction requires a clear understanding of solar wind-magnetosphere coupling. The in-situ measurements of the solar wind properties give unique information about the Sun and its activity on smaller to longer timescales. The present work investigates the influence of solar activity on the coupling of solar wind and Earth's magnetosphere during 23–24 solar cycles. The geomagnetic storms with Symmetric H-component (SYMH) ≤ −85 nT during the 23–24 solar cycles are considered. We present the results of statistical analysis and relationships between the various solar wind parameters such as the total strength of interplanetary magnetic field (B) and its three-axis components (Bx, By, and Bz), solar wind proton density (Nsw), solar wind speed (Vsw), SYMH indices, the amplitude, duration, and profile of the geomagnetic storms. The integrated electric field and integrated SYMH index during storms show the highest correlation of 0.92, implying that integrated SYMH is a better proxy of the injected solar wind energy in the magnetosphere in the form of the ring current. Moreover, we do see the difference in the solar wind-magnetosphere coupling efficiency during the phases of 23–24 solar cycles which is intriguing.

Abstract

The North Pacific Meridional Mode (PMM) is the strongest interannual air-sea coupled system in the subtropical northeastern Pacific, which can significantly impact the development of El Niño and Southern Oscillation (ENSO). This study examines performance of the second version of the Chinese Academy of Sciences Earth System Model (CAS-ESM2), developed primarily at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP/CAS), in simulating the PMM, ENSO, and their relationship. It reveals that CAS-ESM2 can well reproduce the tropical climate mean states, including sea surface temperature (SST), surface winds, and precipitation. Furthermore, the model shows a good ability in reproducing the seasonal evolutions of the PMM and ENSO. Moreover, CAS-ESM2 effectively simulates the influence of the PMM on subsequent ENSO and the underlying physical mechanisms, including the wind-evaporation-SST feedback process, the trade wind charging mechanism and summer deep convection mechanism. However, some improvements are still needed, particularly in representing the periodicity of the PMM, an overestimation of the ENSO intensity and westward extension of ENSO-related SST anomalies in the tropical Pacific. The results obtained from the CAS-ESM2 showcase significant progress in understanding the interaction between air-sea interaction systems over the tropics and subtropics.

Abstract

The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign included deployment of a suite of atmospheric measurements in January–February 2022 with the goal of better understanding atmospheric processes and pollution under cold and dark conditions in Fairbanks, Alaska. We report on measurements of particle composition, particle size, ice nucleating particle (INP) composition, and INP size during an ice fog period (29 January–3 February). During this period, coarse particulate matter (PM10) concentrations increased by 150% in association with a decrease in air temperature, a stronger temperature inversion, and relatively stagnant conditions. Results also show a 18%–78% decrease in INPs during the ice fog period, indicating that particles had activated into the ice fog via nucleation. Peroxide and heat treatments performed on INPs indicated that, on average, the largest contributions to the INP population were heat-labile (potentially biological, 63%), organic (31%), then inorganic (likely dust, 6%). Measurements of levoglucosan and bulk and single-particle composition corroborate the presence of dust and aerosols from combustion sources. Heat-labile and organic INPs decreased during the peak period of the ice fog, indicating those were preferentially activated, while inorganic INPs increased, suggesting they remained as interstitial INPs. In general, INP concentrations were unexpectedly high in Fairbanks compared to other locations in the Arctic during winter. The fact that these INPs likely facilitated ice fog formation in Fairbanks has implications for other high latitude locations subject to the hazards associated with ice fog.

Abstract

We investigate the position and intensity changes of the Intertropical Convergence Zone (ITCZ) over Asia (50°E−135°E) relative to the preindustrial period annually and seasonally during the Last Interglacial (LIG), Last Glacial Maximum (LGM), and mid-Holocene (MH) using available models from phases 3 and 4 of the Paleoclimate Modeling Intercomparison Project. The multi-model mean shows that the June–July–August ITCZ variations generally dominate the annual changes. The Asian ITCZ shifts northward over western Asia and southward over the eastern side in both the LIG and MH, and the opposite occurs in the LGM. Its intensity varies with longitude similarly for the LIG and MH and generally weakens in the LGM. Precipitation changes associated directly with ITCZ indices are primarily caused by the dynamic term in the LIG and MH, while both dynamic and thermodynamic terms play roles in the LGM, with major contributions from the convergence components.

Abstract

This study investigates the background rotational influences on the secondary eyewall formation (SEF) in tropical cyclones (TCs) in quiescent f-plane environments. For given initial structures, simulated vortices tend to experience earlier SEF at lower latitudes. Yet the size of the secondary eyewall does not change monotonically with the latitudes. Specifically, ∼20°N provides the optimal amount of background rotation for the largest secondary eyewall size without considering other environmental forcings. Different background rotation rates affect SEF mainly by modulating the outer-core convection as well as the wind structures. Specifically, the lower rotation rate causes more outer-core surface fluxes, thus facilitating the outer rainbands (ORBs) at larger radii. Yet the secondary eyewall does not necessarily form at larger radii at lower latitudes since the transition from the ORBs to secondary eyewall is localized in a region of boundary layer (BL) convergence preceded by accelerated tangential winds. Budget analysis reveals that the differences in the acceleration of outer-core tangential winds among vortices at different latitudes are dominated by the radial flux of absolute vorticity. Due to the non-uniform influences of background rotation on the BL inflow and absolute vorticity, the most efficient spin-up of outer-core tangential winds is achieved at a medium latitude of 20°N, which leads up to SEF at the largest radii. By comparison, for TCs at lower (higher) latitudes, the lower outer-core absolute vorticity (radial inflow) limits the acceleration of outer-core tangential winds, thus placing SEF at smaller radii.

Abstract

In this study, based on solar energetic particle (SEP) events classification and a solution of the diffusion equation, we present an efficient system, HITSEP, to predict the intensities in different energy channels (P4 15.0–44.0 MeV, P5 40.0–80.0 MeV, and P6 80.0–165.0 MeV) of energetic proton events observed by GOES spacecraft. The system can predict the rising phase (especially the peak time and peak intensity) of the energetic proton events using only a small amount of data at the beginning of the solar energetic proton events. Among the events that meet the conditions for the use of our prediction system from 2003 to 2017, for P4, P5, and P6 channels, the median Warning Times are 3.70, 2.52, and 1.69 hr; the median Error of the Intensity for events are 0.43, 0.23, 0.34 orders of magnitude; the median Error of the Peak Time for events are 2.53, 0.55, 0.43 hr, respectively. Our system is based on physical mechanisms and has a high accuracy in forecasting the peak intensity with a strict definition of the error. The HITSEP system has huge potential to apply in the space weather forecast. The application of the HITSEP system in space weather forecasting is very promising.

Abstract

The Clarion–Clipperton Fracture Zone (CCFZ) in the eastern central Pacific Ocean is the world's largest area for potential deep-sea polymetallic nodule mining and is attracting increased scientific and commercial interest. Recent studies indicate that biogenic magnetite, generated intracellularly by magnetotactic bacteria (MTB), can carry a biogeochemical remanent magnetization in polymetallic nodules, although whether biogenic or physical-chemical processes are responsible for nodule formation remain poorly constrained. Here, we report a combination of magnetic, electron microscope and geochemical analyses on seafloor surface sediments from the eastern CCFZ to understand the spatial distribution of biogenic magnetite and possible relationships between MTB and polymetallic nodules. Experimental results indicate that sedimentary magnetic minerals from the northern and southern regions are dominated by detrital (eolian loess and volcanic material) and biogenic magnetic minerals (magnetosomes), respectively. Sediments from the intermediate region contain both detrital and biogenic magnetic minerals. Quantitative first-order reversal curve-principal component analysis indicates that biogenic magnetite has the highest concentration in the intermediate CCFZ region, coincident with the highest polymetallic nodule density. Combined with previous research, we speculate that MTB growth on the CCFZ seafloor is driven mainly by local redox conditions. Manganese nodule surfaces are rich in organic biofilms, which results in a relatively thick oxic-anoxic transition zone in high-abundance manganese nodule regions, which generates an optimal microenvironment for both MTB growth and magnetite biomineralization. This study provides new clues for understanding the ecological distribution of MTB and the biogeochemical remanent magnetization recorded by biogenic magnetite in deep-sea sediments.