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Abstract

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 (ITCZ) and enhanced convective activity in the western equatorial Pacific. The subtropical jet shifts equatorward due to the ITCZ 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.

Abstract

A cloud-resolved storm and chemistry simulation of a severe convective system in Oklahoma constrained by anvil aircraft observations of NO x was used to estimate the mean production of NO x per flash in this storm. An upward ice flux scheme was used to parameterize flash rates in the model. Model lightning was also constrained by observed lightning flash types and the altitude distribution of flash channel segments. The best estimate of mean NO x production by lightning in this storm was 80–110 mol per flash, which is smaller than many other literature estimates. This result is likely due to the storm having been a high flash rate event in which flash extents were relatively small. Over the evolution of this storm a moderate negative correlation was found between the total flash rate and flash extent and energy per flash. A longer-term simulation at 36-km horizontal resolution with parameterized convection was used to simulate the downwind transport and chemistry of the anvil outflow from the same storm. Convective transport of low-ozone air from the boundary layer decreased ozone in the anvil outflow by up to 20–40 ppbv compared with the initial conditions, which contained stratospheric influence. Photochemical ozone production in the lightning-NO x enhanced convective plume proceeded at a rate of 10–11 ppbv per day in the 9–11 km outflow layer over the 24-hr period of downwind transport to the Southern Appalachians. Photochemical production plays a large role in the restoration of upper tropospheric ozone following deep convection.

Abstract

Recent research has described a ‘moist margin’ in the tropics, defined through a total column water vapor (TCWV) value of 48 kg m−2, that encloses most of the rainfall over the tropical oceans. Diagnosing the moist margin in the ERA5 reanalysis reveals that it varies particularly on synoptic time scales, which this study aims to quantify. We define ‘wet and dry perturbation’ objects based on the margin's movement relative to its seasonal climatology. These perturbations are associated with a variety of synoptic weather systems. Wet (dry) perturbations produce substantially more (less) rainfall compared to the seasonal average, confirming the clear link between moisture and precipitation. On synoptic scales we suggest that mid-tropospheric humidity plays a key role in creating these perturbations, while sea surface temperatures (SSTs) are relatively unimportant.

Abstract

The present study investigates wavenumber-4 (wave-4) structure in the longitude variation of zonal and meridional winds observed by the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument onboard the Ionospheric Connection Explorer (ICON) satellite. The amplitude of the wave-4 pattern in meridional wind displays semi-annual variation with equinoctial maxima whereas its seasonal variation in zonal wind shows maxima during August–October at the equatorial and low latitudes. The wave-4 longitude variation maximizes at lower thermospheric heights (below 130 km) in zonal and meridional winds. It is considered primarily driven by the non-migrating eastward propagating diurnal tide with zonal wavenumber-3 (DE3) in the zonal wind. However, the amplitude of DE3 tide in the meridional wind does not show any enhancement during September–October. The seasonal variations of the wave-4 amplitude and the DE3 tide are not similar in the zonal and meridional winds. The migrating ter-diurnal tide (TW3) exhibits significant amplitudes during March–April and September–November in the meridional wind. In addition, the latitude variation of non-migrating TE1 tide shows maximum amplitude during September–October. These results suggest that the non-linear interaction between the TW3 and TE1 tides can serve as a potential source for the wave-4 longitude variation in the meridional wind at lower thermospheric altitudes.

Abstract

Studies commonly assumed that variations in ionospheric conductance were insignificant and proposed that vorticities can be a reliable proxy or diagnostic for ionospheric field-aligned currents (FACs). We propose a complete method for measuring FACs using data from the Super Dual Auroral Radar Network radar and the Defense Meteorological Satellite Program. In our method, the FACs are determined by three terms. The first term is referred to as magnetospheric-origin FACs, while the second and third terms are known as ionospheric-origin FACs. This method incorporates height-integrated conductances based on observational data, thereby addressing the limitation of assuming uniform conductances. Different from previous works, we can calculate FACs at a low altitude of 250 km and obtain high-resolution measurements within observable areas. Another advantage of this method lies in its ability to directly calculate and analyze the impact of ionospheric vorticity and conductance on FACs. We apply this method to obtain FACs in the Northern Hemisphere from 2010 to 2016 and analyze the distributions of height-integrated conductances and total FACs. Our analysis reveals that the average FACs clearly exhibit the large-scale R1 and R2 FAC systems. We conduct statistical analysis on magnetospheric-origin FACs and ionospheric-origin FACs. Our findings show that within the auroral oval, ionospheric-origin FACs reach a comparable level to magnetospheric-origin FACs. However, ionospheric-origin FACs are significantly minor and almost negligible in other regions. This implies that height-integrated conductance gradients and vorticities play equally significant roles within the auroral oval, whereas vorticities dominate in other regions.

Abstract

In this paper, the equatorial thermosphere anomaly (ETA) is investigated using accelerometer measurements to determine whether the feature is density-dominated, wind-dominated, or some combination of the two. An ascending-descending accelerometry (ADA) technique is introduced to address the density-wind ambiguity that appears when interpreting the ETA in atmospheric drag acceleration analyses. This technique separates ascending and descending acceleration measurements to determine if a wind's directionality influences the interpretation of the observed ETA feature. The ADA technique is applied to accelerometer measurements taken from the Challenging Minisatellite Payload mission and has revealed that the ETA is primarily density-dominated from 9:00 to 16:00 local time (LT) near 400 km altitude, with the acceleration perturbations behaving similarly between 2003 and 2004 across all seasons. This finding suggests that the perturbations in the acceleration due to in-track wind perturbations are small compared to the perturbations due to mass density, while indicating that the formation mechanisms across these local times are similar and persistent. The results also revealed that in the terminator region at 18:00 LT the acceleration perturbations deviate appreciably between ascending and descending passes, indicating different or multiple processes occurring at this local time compared to the 9:00–16:00 LT ascribed to the ETA. These results help constrain ETA formation theories to specific local times and thermospheric property responses without the use of supplemental wind measurements, while also indicating regions where in-track winds cannot always be neglected.

Abstract

We use seismic ambient noise recorded by dense ocean bottom nodes (OBNs) in the Gorgon gas field, Western Australia, to compute time-lapse seafloor models of shear-wave velocity. The extracted hourly cross-correlation (CC) functions in the frequency band 0.1–1 Hz contain mainly Scholte waves with very high signal-to-noise ratio. We observe temporal velocity variations (dv/v) at the order of 0.1% with a peak velocity change of 0.8% averaged from all station pairs, from the conventional time-lapse analysis with the assumption of a spatially homogeneous dv/v. With a high-resolution reference (baseline) model from full waveform inversion of Scholte waves, we present an elastic wave equation based double-difference inversion (EW-DD) method, using arrival time differences between the reference and time-lapsed Scholte waves, for mapping temporally varying dv/v in the heterogeneous subsurface. The time-lapse velocity models reveal increasing/decreasing patterns of shear-wave velocity in agreement with those from the conventional analysis. The velocity variation exhibits a ∼24-hr cycling pattern, which appears to be inversely correlated with the diurnal variations in sea level height, possibly associated with dilatant effects for porous, low-velocity shallow seafloor and rising pore pressure with higher sea level. This study demonstrates the feasibility of using dense passive seismic surveys and wave-equation time-lapse inversion for quantitative monitoring of subsurface property changes in the horizontal and depth domain.

Abstract

Antigorite is the high-temperature member of the serpentine group minerals and is broadly considered a primary carrier of water in the subducting oceanic lithosphere. It has a wavy crystal structure along its a-axis and several polysomes with different m-values (m = 13–24) have been identified in nature. The m-value is defined as the number of tetrahedra in one wavelength and is controlled by the misfit between the octahedral and tetrahedral layers. The degree of misfit primarily depends on the volumes of the MgO6 octehedra and SiO4 tetrahedra within the layers, which vary as a function of pressure and temperature. However, it is not well understood which m-values of antigorite are stable at different pressure and temperature conditions. To investigate the pressure dependence of the stability of different m-values in antigorite, we performed first-principles calculations for several polysomes (m = 14–19) at high pressure from 0 to 14 GPa and compared their enthalpies at static 0 K. We found that although the energy differences between polysomes are small, polysomes with larger m-values are more stable at ambient pressure, while polysomes with smaller m-values are more stable at elevated pressures. This suggests that the structure of antigorite in the oceanic lithosphere subducting into the deep Earth may gradually evolve into a different polysome structure than the antigorite samples observed at ambient or near-surface pressure conditions. These changes in the m-values are accompanied by a minor dehydration reaction. By modulating the available amount of free water in the system, antigorite polysomatism may influence the distribution of intermediate-depth seismicity, such as the observance of double seismic zones.

Abstract

Tectonic plate motions feed the earthquake cycle—a process whereby stress along crustal faults slowly increases over decade– or century–long periods, to then suddenly drop during earthquakes. Steadiness of plate motions during such cycles has long been a central tenet in models of earthquake genesis and of faults seismic potential, and can be tested against measurements of contemporary plate motions available from Global Navigation Satellite Systems (GNSS). Here we present analyses of GNSS data from Central and Northern Italy that illuminate the motion of the Adria microplate over a period of 6 years preceding the M W 6.3, 6 April 2009 L’Aquila (Italy) earthquake. We show that the motion of the whole Adria microplate changed before the 2009 earthquake, and slowed down by around 20%. We demonstrate with quantitative models that the torque required upon Adria in order to drive such a kinematic change is consistent with what is imparted to Adria by temporal stress variations occurring during the late interseismic phase of the 2009 L’Aquila earthquake cycle. The inference that plate motions can be influenced by, and thus sensitive to, earthquake cycles offers an additional perspective to assessing the seismic potential of tectonic margins.

Abstract

Scientists have observed the surface expression of creep events along the San Andreas Fault since the 1960s. However, the evolution of slip at depth has been examined relatively little. So here we probe that deep slip by analyzing strain observations just before and during hours- to day-long creep events at the northern end of the creeping section of the San Andreas Fault. We identify 71 strain offsets that are likely produced by few-hour bursts of slip at depth. Then, we grid search to determine the location, depth, and magnitude of these slip bursts. We find that the slip bursts occur at a range of along-strike locations, from 0 to 7 km away from the surface slip observations. Slip occurs at depths from 0 to 10 km; 42%–55% of the bursts are likely below 4 km depth. The bursts typically have moments equivalent to M w 3.2–4.1 earthquakes. These findings suggest that creep events are not just small shallow events; they are relatively large events that nucleate at significant depths and could play a prominent role in the slip dynamics of the creeping section.

Abstract

We validate the multiyear potential predictability of wintertime heavy precipitation potential in East Asia by combining initialized decadal hindcasts of the global climate model and large ensemble simulations from a high-resolution global atmospheric model. By analyzing a set of initialized hindcasts, the major predictive components of sea surface temperature (SST) variability beyond interannual timescales are identified as high-latitudes multidecadal variability and the so-called trans-basin variability (TBV). A set of 100 ensemble simulations using a high-resolution atmospheric model showed a significantly large signal-to-noise ratio for the wintertime heavy precipitation potential in East Asia, which is closely related to the TBV. When the SST around the maritime continent is higher, the anomalously low pressure in the northwestern Pacific enhances low-level cold air transport due to the winter monsoon. Consequently, the resultant weaker baroclinicity in the lower atmosphere reduces storm activity and wintertime heavy precipitation potential in East Asia.

Abstract

Reservoirs exert a profound influence on the cycling of dissolved organic matter (DOM) in inland waters by altering flow regimes. Biological incubations can help to disentangle the role that microbial processing plays in the DOM cycling within reservoirs. However, the complex DOM composition poses a great challenge to the analysis of such data. Here we tested if the interpretable machine learning (ML) methodologies can contribute to capturing the relationships between molecular reactivity and composition. We developed time-specific ML models based on 7-day and 30-day incubations to simulate the biogeochemical processes in the Three Gorges Reservoir over shorter and longer water retention periods, respectively. Results showed that the extended water retention time likely allows the successive microbial degradation of molecules, with stochasticity exerting a non-negligible effect on the molecular composition at the initial stage of the incubation. This study highlights the potential of ML in enhancing our interpretation of DOM dynamics over time.

Abstract

We study the sensitivity of South Asian Summer Monsoon (SASM) precipitation to Southern Hemisphere (SH) subtropical Absorbed Solar Radiation (ASR) changes using Community Earth System Model 2 simulations. Reducing positive ASR biases over the SH subtropics impacts SASM, and is sensitive to the ocean basin where changes are imposed. Radiation changes over the SH subtropical Indian Ocean (IO) shifts rainfall over the equatorial IO northward causing 1–2 mm/day drying south of equator, changes over the SH subtropical Pacific increases precipitation over northern continental regions by 1–2 mm/day, and changes over the SH subtropical Atlantic have little effect on SASM precipitation. Radiation changes over the subtropical Pacific impacts the SASM through zonal circulation changes, while changes over the IO modify meridional circulation to bring about changes in precipitation over northern IO. Our findings suggest that reducing SH subtropical radiation biases in climate models may also reduce SASM precipitation biases.

Statistical calibration of probabilistic medium-range fire weather index forecasts in Europe
Stephanie Bohlmann and Marko Laine
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-57,2024
Preprint under review for NHESS (discussion: open, 2 comments)
Probabilistic ensemble forecasts of the Canadian Forest Fire Weather Index (FWI) can be used to estimate the possible risk for wildfires but requires post-processing to provide accurate and reliable predictions. We present a calibration method using non-homogeneous Gaussian regression to statistical post-process FWI forecasts up to 15 days. Calibration improves the forecast especially at short lead times and in regions with elevated FWI values.

Evaluation of calibration performance of a low-cost particulate matter sensor using collocated and distant NO2
Kabseok Ko, Seokheon Cho, and Ramesh R. Rao
Atmos. Meas. Tech., 17, 3303–3322, https://doi.org/10.5194/amt-17-3303-2024, 2024
In our study, we examined how NO2, temperature, and relative humidity influence the calibration of PurpleAir PA-II sensors. We found that incorporating NO2 data from collocated reliable instruments enhances PM2.5 calibration performance. Due to the impracticality of collocating reliable NO2 instruments with sensors, we suggest using distant NO2 data for calibration. We demonstrated that performance improves when distant NO2 correlates highly with collocated NO2 measurements.

Identification of ice-over-water multilayer clouds using multispectral satellite data in an artificial neural network
Sunny Sun-Mack, Patrick Minnis, Yan Chen, Gang Hong, and William L. Smith Jr.
Atmos. Meas. Tech., 17, 3323–3346, https://doi.org/10.5194/amt-17-3323-2024, 2024
Multilayer clouds (MCs) affect the radiation budget differently than single-layer clouds (SCs) and need to be identified in satellite images. A neural network was trained to identify MCs by matching imagery with lidar/radar data. This method correctly identifies ~87 % SCs and MCs with a net accuracy gain of 7.5 % over snow-free surfaces. It is more accurate than most available methods and constitutes a first step in providing a reasonable 3-D characterization of the cloudy atmosphere.

Review article: Insuring the green economy against natural hazards – charting research frontiers in vulnerability assessment
Harikesan Baskaran, Ioanna Ioannou, Tiziana Rossetto, Jonas Cels, Mathis Joffrain, Nicolas Mortegoutte, Aurelie Fallon Saint-Lo, and Catalina Spataru
Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2024-82,2024
Preprint under review for NHESS (discussion: open, 0 comments)
There is a global need for insuring green economy assets against natural hazard events. But their complexity and low exposure history, means the data required for vulnerability evaluation by the insurance industry is scarce. A systematic literature review is conducted in this study, to determine the suitability of current, published literature for this purpose. Knowledge gaps are charted, and a representative asset-hazard taxonomy is proposed, to guide future, quantitative research.

Abstract

We study electromagnetic ion cyclotron (EMIC) waves based on observations from the ionosphere, magnetosphere, and ground during a geomagnetic storm recovery phase on 28 August 2018. In this case, multiple ducting EMIC waves in the ionosphere show higher frequencies in the post-midnight than those in the pre-midnight. Ionospheric EMIC wave frequency differences in magnetic local time (MLT) are consistent with MLT frequency differences in the equatorial magnetosphere, which are mainly caused by different background magnetic field at different L-shells. Moreover, we report the first observation of frequency range selections in ionospheric ducting EMIC waves and find that frequency selections depend on the magnetic field intensity in the main part of the ionospheric waveguide, with higher frequency corresponding to larger magnetic field. This study reveals the important role of background magnetic field in regulating ducting EMIC wave frequencies in the ionosphere.

In silico calculation of soil pH by SCEPTER v1.0
Yoshiki Kanzaki, Isabella Chiaravalloti, Shuang Zhang, Noah J. Planavsky, and Christopher T. Reinhard
Geosci. Model Dev., 17, 4515–4532, https://doi.org/10.5194/gmd-17-4515-2024, 2024
Soil pH is one of the most commonly measured agronomical and biogeochemical indices, mostly reflecting exchangeable acidity. Explicit simulation of both porewater and bulk soil pH is thus crucial to the accurate evaluation of alkalinity required to counteract soil acidification and the resulting capture of anthropogenic carbon dioxide through the enhanced weathering technique. This has been enabled by the updated reactive–transport SCEPTER code and newly developed framework to simulate soil pH.

Abstract

Bursty reconnection models predict that flux transfer events (FTEs) moving along the magnetopause launch fast mode compressional waves into the magnetosheath that push the bow shock outward. By contrast, increases in the solar wind density striking the bow shock should push that boundary inward and launch fast mode compressional waves that propagate across the magnetosheath, drive waves on the magnetopause, and generate transient events in the outer magnetosphere. Multipoint ACE, Wind, THEMIS, and GOES-11/12 solar wind, bow shock, and magnetospheric observations on 14 October 2008 provide direct evidence for solar wind pressure pulses producing a large amplitude indentation with crater FTE-like properties on the magnetopause.