It has been documented that significant amounts of tropical precipitation are concentrated in coastal areas, which is especially prominent over the western coast of Sumatra Island. We conducted 14-day-long numerical simulations, focusing on precipitation patterns around Sumatra Island. In the control experiment, the rainfall concentration was obscure, and dry biases were found. Based on the budget equation of the column-integrated frozen moist static energy (which is nearly equivalent to the column-integrated moisture under the weak temperature gradient assumption), we formulated 9 sensitivity experiments. When the terminal velocity and effective radius of ice clouds were reduced in addition to incorporating the warmer sea surface temperature (SST) around the coast, the model showed better rainfall peak fidelity. On the other hand, similar diurnal cycles of precipitation were simulated in the sensitivity tests without any conspicuous peaks in the coastal region, which indicated that the precipitation concentration fidelity was irrelevant to that of the diurnal cycle. An analysis in the time-mean fields demonstrated that inhibition of radiative cooling (associated with the upper-level ice clouds) and warmer SSTs induced anomalous updrafts, and thus, more moisture and precipitation were brought to the coast by enhancement of the vertical moisture advection. Comparing the simulation results with in situ observations, we speculated that together with the climatologically warmer SSTs, the SST diurnal cycle and lateral transport of ice clouds from inland convection, which was strictly regulated by solar insolation, significantly contributed to the precipitation concentration around the coastal region.

An along-isobath current in stratified waters leads to a bottom boundary layer. In models with no alongshore variation, cross-isobath density transport in this bottom boundary layer reduce the velocity in the bottom boundary layer via thermal wind, and thus the bottom friction experienced by the current above the boundary layer – this is bottom-boundary-layer arrest. If, however, alongshore variation of the flow is allowed, the bottom boundary layer is baroclinically unstable. We show with high resolution numerical models that these instabilities reduce this arrest and allow bottom friction to decelerate the flow above the bottom boundary layer when the flow is in the Kelvin wave direction (so that the bottom Ekman transport is downwelling). Both the arrest of the bottom boundary layer and the release from this arrest are asymmetric; the friction experienced by flows in the direction of Kelvin-wave propagation (downwave) is much greater than flows in the opposite direction. The strength of the near bottom currents, and thus the magnitude of bottom friction, is found to be governed by the destruction of potential vorticity near the bottom balanced by the offshore along-isopycnal transport of this anomalous potential vorticity. A simple model of this process is created and used to quantify the magnitude of this effect and the resulting reduction of arrest of the bottom boundary layer. It is shown that the instabilities allow along-isobath flows to spread across isobaths and move boluses of weakly stratified bottom water into the stratified interior.

Projecting the potential impacts of LULC (Land Use/Land Cover) change on watershed hydrological response is critical for water management decisions in a changing environment. An improved representation of vegetation dynamics is needed to improve the capability of several hydrological models to produce reliable projections of these impacts. Here we in troduce a modification in the plant growth module of SWAT (Soil Water Assessment Tool) to improve the representation of the bimodal seasonality of LAI (Leaf Area Index), which is particularly important for tropical watersheds with bimodal precipitation regimes. The new SWAT-Tb variant that we propose here reproduces not only observed streamflow, but also the bimodal seasonal pattern of LAI in a tropical mountain watershed of the Andes. In contrast, standard SWAT is inherently unable to reproduce this bimodality, although it can be calibrated to reproduce streamflow. Differences between models in the representation of LAI seasonality can lead to significantly different results about LULC change impacts on streamflow. SWAT-Tb results show that deforestation impacts on streamflow are more pronounced for seasonal than for annual streamflow, and indicate that forests can play a crucial role in enhancing water availability during dry seasons. The seasonality of streamflow anomalies is switched due to forest-to-pasture conversion, implying that while forest expansion increases water availability in dry seasons, forest conversion into pasture decreases it. Due to its poor representation of LAI seasonality, standard SWAT largely underestimates this role of forest, which can be misleading for decision making about water security and forest conservation

The control of land surface topography on the configuration of groundwater table has been recognized and well explored. However, the control of bedrock topography on water table is much less studied, potentially due to the limited observations of bedrock. This paper evaluates the controls of both surface and subsurface topography on the spatial distributions of steady-state water table and the corresponding water storage at the catchment scale based on numerical simulations. Numerical models with different topographic features are developed using MODFLOW (USG). When water table is shallow, the control on the spatial distributions of water table is dominated by land surface topography (i.e., water table is approximately parallel to land surface); with the increase of water table depth, the role of land surface topography decreases; when water table is deep and close to bedrock surface, the spatial distributions of water table is dominated by bedrock topography (i.e., water table is approximately parallel to bedrock surface). For land surface-dominated water table, storage capacity in unsaturated area is spatially uniform, which is the underlying assumption of TOPMODEL; however, for bedrock-dominated water table, water storage in unsaturated area is spatially uniform, which is the underlying assumption of VIC-type model. The systematical variations of the controls of surface and subsurface topography on water table configuration provide a framework to unify saturation excess runoff models by treating TOPMODEL and VIC-type model as two endmembers.

This paper presents a methodology to assess the influence of the correlation-covariance structure of measurement errors in online monitoring over the propagation of uncertainties, applied to wet-weather environmental indicators in Sustainable Urban Drainage Systems (SUDS). The effect of autocorrelated and heteroscedastic errors in measured time-series over the estimated Probability Density Function (PDF) of different environmental indicators is analyzed for a wide variety of possible error structures in the data. For this purpose, multiple correlation-covariance structures are randomly generated from exploring the parametric space of a Linear Exponent Autoregressive (LEAR) model, employing a Bayesian-based Markov Chain Monte Carlo sampling technique. Significant differences tests are proposed to identify the most correlated parameters of the correlation-covariance error model with statistics of the environmental indicators PDFs. The methodology is applied to Total Suspended Solids (TSS) and Chemical Oxygen Demand (COD) time-series recorded during 13 rainfall events at the inlet and outlet of a SUDS train (stormwater settling tank - horizontal constructed wetland). For this case, results showed that the total error in the estimation of the analyzed environmental indicators is mostly explained by standard uncertainties (flattening of the PDFs) rather than bias contributions (displacement of the PDFs). The correlation-covariance model parameters related to the temporal delimitation of hydrographs/pollutographs and the intensity of the autocorrelation showed to have the strongest influence in the propagation of measurement errors (flattening/displacement of the PDFs).

In this study, daily atmospheric radiation and temperature data at the surface were obtained from the archives of the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) for the period of 36 years (1980 – 2015) over West African geo-climatic regions. Analyses showed that the values of radiation balance in entire West Africa decreased from 140.37±2.11W/m2 in 1980 to 132.89±2.18 W/m2 in 2015. This shows that there is dominance of longwave radiation components in the radiation balance budget which determines the warming effect in the earth surface. Also, the magnitudes of ratio of change in surface temperature to change in radiation balance flux (radiative forcing) termed climate sensitivity ranged between 1.74±0.08 and 3.92±0.69 across the studied regions. These values fall within the threshold values of 1.5 and 4.5 proposed by the Intergovernmental Panel on Climate Change (IPCC) Assessment Report for the prevalence of surface warming. Meanwhile, the trend analyses of frequencies and intensities of warm nights and warm days whose maximum values were 35.52±0.77 oC and 42.34±0.73 oC showed predominant significant increasing trends respectively. Also, cross correlation analysis reveals strong significant relationships between radiation balance flux and temperature extreme events at short time-lags. Finally, it can be inferred from the results that the climate system of the West African Region is experiencing warming effects in which radiation balance contributed significantly. Consequently, this may result in more heat stress, drought, and flooding causing negative influences on agriculture, forestry, and entire ecosystems in this 21st century.

We modeled the bending deformation of the subducting plate at the southern Mariana using a 3-D elastic plate flexural model. Intraplate stresses were investigated, with the along-strike variable boundary loadings. In order to match the observed plate geometry, boundary vertical loading near the Challenger Deep had to be set twice of that in the region further east within our study area. By comparing results between 2-D and 3-D models, we found that the difference on estimating plate stress can exceed 20% when there is an along-strike variation in plate bending. Finally, we found that the sharp lateral variation in the σ and the σ corresponded to an outer-rise earthquake cluster at the southern Mariana subduction zone, indicating that along-strike variation in σ and σ may be a significant mechanism to cause non-uniform distribution of outer-rise earthquakes.

The diverse range of mechanisms driving the Arctic amplification are not completely understood and, moreover, the role of the greenhouse gas methane in Arctic warming remains unclear. Strong sources of methane at the ocean seabed in the Barents Sea and other polar regions are well documented. Nevertheless, those data suggest that negligible amounts of methane fluxed from the seabed enter the atmosphere, with roughly 90% of the methane consumed by bacteria. The observations are taken during summer, which is favorable for collecting data but also characterized by a strongly-stratified water column. In winter the stratification weakens and after a breakdown of the pycnocline, convection, storms, and turbulent diffusion can mix the full-depth water column in high latitudes.TheMixed Layer Depth (MLD) in the ice-free Central/Southern Barents Sea is deepening and the ocean-atmosphere methane exchange increases.. An additional barrier for the air-sea flux is seasonally and interannually variable sea-ice cover in partially ice-covered seas. We present Thermal IR space-based spectrometer data between 2002 and 2019 that shows increased methane concentration anomalies over the Barents and Kara seas in winter months. The seasonal methane cycle amplitude north of the Kara Sea has more than doubled since the beginning of the century; this may be interpreted as an effect of sea-ice decline and/or an evidence for growth of seabed emissions. A progressing degradation of Arctic sea-ice cover may lead to increased methane flux and, through a positive feedback loop, to further warming.

Ensemble predictions of the seasonal snowpack over Grand Mesa, CO were conducted for the hydrologic year 2016-2017 using a multilayer snow hydrology model. Ensembles were generated from gridded atmospheric reanalysis, model predictions were evaluated against SnowEx’17 measurements, and the signatures of the weather-dependent variability of snow physics in the behavior of multi-frequency microwave brightness temperatures and backscattering were examined through forward modeling. At sub-daily timescales , the ensemble standard deviation due to atmospheric forcing (i.e., mesoscale spatial variability of weather within the Grand Mesa) is < 3 dB for dry snow, and increases to 8-10 dB at midday when there is surficial melt that also explains the wide ensemble range (~20 dB). Further, the ensemble mean backscatter exhibits robust (R 2 > 0.95) time-varying, weather-dependent linear heuristic relationships with SWE (e.g., 5-6 cm/dB/month in January; 2-2.5 cm/dB/month in late February) as melt-refreeze cycles modify the microphysical structure in the top 50 cm of the snowpack. The nonlinear evolution of ensemble snow physics translates into seasonal hysteresis in the microwave behavior. The backscatter hysteretic offsets between accumulation and melt regimes are robust in the Land C-bands and collapse for wet shallow snow at Ku-band. The ensemble mean emissions behave as a limit-cycles with weak sensitivity in the accumulation regime, and hysteretic behavior during melt that is different for deep (winter-spring transition) and shallow snow (spring-summer) and offsets that increase with frequency. These findings suggest potential for multi-frequency active-passive remote-sensing of SWE conditional on snowpack regime, particularly suited for data-assimilation using coupled snow hydrology-microwave models.

In a recent study, Samset et al. reported that due to the imprint of natural variability, the effects of emission mitigation will only be perceived through global temperature with a multi-decadal delay. Their analysis, also including a decomposition into the effects of mitigating individual climate forcers, is highly relevant and timely, but does not fully substantiate all conclusions made by the authors. Here, we provide essential context around the findings by Samset et al. of multi-decadal delays of mitigation benefits. We also express concerns with their conceptual approach towards assessing a discernible warming response under different greenhouse gas concentration pathways. A broader debate on how to best assess and communicate emerging effects of climate mitigation in the light of natural variability seems warranted.

Body-to-surface wave scattering, originated from strong lateral heterogeneity, has been observed and modeled for decades. Compared to body waves, scattered surface waves propagate along the Earth’s surface with less energy loss and, thus, can be observed over a wider distance range. In this study, we utilize surface waves converted from teleseismic SH or Sdiff wave incidence to map strong lateral heterogeneities across the entire contiguous US. We apply array-based phase coherence analysis to broadband waveforms recorded by the USArray Transportable Array and other permanent/temporary networks to detect coherent signals that are associated with body-to-surface wave scattering. We then locate the source of the scattering by back-propagating the beamformed energy using both straight-ray and curved-ray approximations. Our results show that the distribution of scatterers correlates well with known geological features across the contiguous US. Topographic/bathymetric relief along the continental slope off the Pacific Border is the major source of scattering in the western US. On the other hand, sedimentary basins, especially their margins, are the dominant scatterers in the central US. Moho offsets, such as the one around the periphery of the Colorado Plateau, are also a strong contributor to scattering, but isolating their effect from that of other near-surface structures without any additional constraints can be complicated. Finally, we demonstrate the possibility of using scattered surface waves to constrain subsurface velocity structures, as complementary to conventional earthquake- or ambient-noise-based surface wave tomography.

The intense seismic scattering seen in Apollo lunar seismic data is one of the most characteristic features, making the seismic signals much different from those observed on the Earth. The scattering is considered to be attributed to subsurface heterogeneity. While the heterogeneous structure of the Moon reflects the past geological activities and evolution processes from the formation, the detailed description remains an open issue. Here we present a new model of the subsurface heterogeneity within the upper lunar crust derived through a full 3D seismic wave propagation simulation. Our simulation successfully reproduced the Apollo seismic observations, leading to a significant update of the scattering properties of the Moon. The results showed that the scattering intensity of the Moon is about ten times higher than that of the heterogeneous region on the Earth. The quantified scattering parameters could give us a constraint on the surface evolution process on the Moon and enable the comparative study for answering a fundamental question of why the seismological features are different on various planetary bodies.

An unusual devastating tsunami occurred on 28 September 2018 after a strike-slip faulting earthquake in Sulawesi, Indonesia. The induced tsunami struck Palu city with 4-m wave height and flow depth. We performed a two-step analysis to investigate the source of the tsunami. We first conducted the teleseismic source inversion and obtained the slip distribution of the strike-slip fault. Our tsunami simulation from the coseismic deformation of the seismically-estimated strike-slip faulting produced a tsunami comparable to the leading part of the observation at Pantoloan. We then jointly utilized the tsunami waveform and Synthetic Aperture Radar (SAR) data to reconstruct the detailed slip distribution on the fault plane. Because of the lack of SAR data in the bay, the tsunami data is necessary to constrain the offshore slip distribution, which directly induces the tsunami. The inverted source model shows a strike-slip fault which consists of three segments extending from the epicenter to the south of 1.4°S with two bends and two asperities around Palu city. The joint inversion model accurately reconstructs the observed surface displacements and the leading part of the tsunami waveform. Our result exhibits the significant contribution of the strike-slip faulting to the tsunami, but it also suggests additional tsunami sources, such as landslides, for the high inundations near Palu bay. The result also indicates that regional devastating tsunamis can result from an onshore strike-slip fault with localized large dip slip.

We present the characteristics of rotating convective updrafts in the 2021 version of GFDL’s Experimental System for High-resolution prediction on Earth-to-Local Domains (X-SHiELD), a kilometer scale global storm resolving model (GSRM). Rotation is quantified using 2–5 km Updraft Helicity (UH) in a year-long integration forced by analyzed SSTs. Updrafts with UH magnitudes above 50 m2/s2; are common over the mid-latitude continents, especially in the warm seasons where they are associated with severe weather but are also common over most tropical ocean basins. In nearly all areas cyclonically rotating convection dominates, with larger UH values increasingly preferring cyclonic rotation. The ratio of cyclonic to anticyclonic updrafts is largest in the subtropical and mid-latitude oceans and is slightly lower over mid-latitude continents. The ratio of cyclonic to anticyclonic updrafts can be substantively explained by the mean storm-relative helicity (SRH) in convective regions, indicating the importance for environmental controls on the sense of storm rotation, although internal storm dynamics also plays a role in the generation of anticyclonic updrafts.

The violent 2022 Tonga submarine volcanic eruption produced globally propagating atmospheric disturbance. The short explosive eruption generated a leading Lamb wave pulse that are recorded as a pressure pulse worldwide. A weather station network in Japan recorded the pressure pulse as well as temperature and winds during the passage of the Lamb pressure pulse. Individual temperature and wind records indicate little simultaneous change. However, after aligning temperature and wind records at the timing of pressure pulse arrivals and stacking, we obtain clear temperature and wind changes synchronized with the pressure change. By assuming Lamb wave propagation synthesized temperature and wind changes from the pressure record match well the observed waveforms. Observed wind speed and pressure change of the Lamb pulse directly yield the total energy transported by the pulse to be 4.2 x 1016 J.

The spectrum of slip modes on gouge-filled faults spans a continuum from fast ruptures to slow slip events. The nucleation of a certain slip mode is governed by the frictional heterogeneity of fault interface and the rheological fault stiffness. Though the pattern of mechanical parameter variation and dynamic stability loss during a seismic cycle is quite clear, it is important to have a unified seismic-acoustic signature of slow or fast slip event nucleation. We present laboratory acoustic emission (AE) experiments on a slider-model with a precise control of mechanical and AE parameters. A comprehensive analysis of AE activity points to the presence of two AE subpopulations. One of them manifests as pulses with harsh onsets. The second one exhibits a gradual amplitude rise and tremor-like signal. The second AE subpopulation shows a longer failure duration and increased energy dissipation. Regularities of changing the frequency-amplitude characteristics of AE subpopulations during a laboratory seismic cycle differ. The first AE subpopulation retains parameters of frequency-amplitude distribution, but the second one exhibits a pronounced cyclic recurrence of the b-value. The latter decreases before slip events and recovers after them. The detected features of AE subpopulations are common for the entire spectrum of slip modes. Findings reveal a coexistence of slow and fast modes at the same fault at the micro-scale and point to the unity of underlying physical mechanisms of different slip mode nucleation.

The week 3-6 averaged winter North Atlantic Oscillation (NAO) predictive skill in a state-of-the-art coupled climate prediction system is attributed to two principle sources: upper and lower boundary conditions linked to the stratosphere and El Niño-Southern Oscillation (ENSO), respectively. A 20-member ensemble of 45-day reforecasts over 1999-2015 is utilized, together with uninitialized simulations with the atmospheric component of the prediction system forced with observed radiative forcing and lower boundary conditions. NAO forecast skill for lead times out to six weeks is higher following extreme stratospheric polar vortex conditions (weak and strong vortex events) compared to neutral states. Enhanced week 3-6 NAO predictive skill for weak vortex events results primarily from stratospheric downward coupling to the troposphere, while enhanced skill for strong vortex events can be partly attributed to lower boundary forcing related to the ENSO phenomenon. Implications for forecast system development and improvement are discussed.

The inversion of Scholte wave dispersion curves is one of the most important methods employed in the detection of marine sedimentary structures. The measurement methods of Scholte wave dispersion are primarily developed from terrestrial geophysical exploration technologies. Unlike terrestrial seismic source excitation methods, marine exploration typically uses air guns to generate seismic waves in seawater, which will result in strongly dispersed Guided-P waves. We found that the Guided-P waves will truncate the higher-mode dispersive Scholte waves at their lower cutoff frequency. However, a simple individual preprocess of suppressing Guided-P procedure (SGP) before extracting dispersion curves can significantly increase the frequency band and image the full dispersive modes of Scholte waves. The wider frequency band and higher-mode Scholte wave dispersion curves can effectively improve the constraints on the submarine shear wave velocity structure. Based on this, we highly recommend adding this simple step to Scholte wave dispersion imaging.