The Ziway-Shala Lakes Basin is a structural depression found in the Main Ethiopian rift being associated with Cenozoic volcanism, faulting and sedimentation activities. The Aluto-Langano volcanic complex is one of the geothermal prospect sites found in this basin and is currently being exploited for geothermal power production. Although it contradicts with the previous research results, recent observations using magneto-telluric method reveal nonexistence of a heat source beneath the Aluto volcano. Instead existence of a strong conductor possibly a magmatic heat sources claimed to occur beneath the Silti Debre Zeyet Fault Zone that lays far NW of the Aluto volcanic complex. In this study, ground based magnetic survey is carried out to map magnetic anomaly patterns and structural features associated with the Aluto-Langano. The volcano-tectonic features are extracted from the differentially pole reduced total magnetic field anomaly map and its derivative maps compiled by applying upward continuation, first vertical derivative and tilt derivative filters. Interpretation of the complied anomaly maps reveal existence of a heat conduction structural path along a traverse running from the Aluto-Langano geothermal to the Silti Debre Zeyte Fault zone and laying between 1.5 km and 3 km depths. This result could be taken to prove the most likely heat source feeding the Aluto-Langano geothermal field is found at about the locality of the Silti Debre Zeyte Fault Zone. The research work also identified magnetic lineaments most of which oriented in the direction of pre-existing Mesozoic structures and in the direction of thermally altered structures.

We provide high-resolution maps of quasi-static Poynting flux (PF) in each hemisphere based on nine-satellite years of Defense Meteorological Satellite Program (DMSP) data. Conjugate comparisons from ~850 km reveal more quasi-static PF arriving in the northern hemisphere (NH) than the southern hemisphere (SH). This tendency is clear in the dawn-dusk sectors and during intervals when Kp < 3, which accounts for ~80% of the study interval. Summer-to-summer comparisons indicate this asymmetry is partially associated with more NH solar illumination, which supports stronger NH field-aligned currents (FAC). Differing hemispheric FAC configurations may also play a role. Our findings support and broaden earlier reports of similar NH preference for the deposition of Alfvenic PF. Regionally the NH has stronger dusk-region PF, while the SH has stronger mid-morning PF. We find PF deposition in the near-cusp regions that rivals and often exceeds the PF intensity in the auroral zones.

We discuss results on plasma density profile modifications in the F-region ionosphere caused by HF heating with the frequency f0 in the range [(-150 kHz)-(+75 kHz)] around the 4th electron gyroharmonic 4fc. The experiments were conducted at the HAARP facility on June 2014. The multi-frequency Doppler Sounder (MDS) which measures the phase and amplitude of reflected sounding radio waves complemented by the observations of the Stimulated Electromagnetic Emission (SEE) were used for the diagnostics of the plasma perturbations. We detected noticeable plasma expulsion from the reflection region of the pumping wave, and from the upper hybrid region, the expulsion from the latter one had been strongly suppressed for f0≈4fc. The plasma expulsion from the upper hybrid region was accompanied with the sounding wave’s anomalous absorption slower developing for f0≈4fc. Also, slower developing and weaker expulsion was detected for the height region between the pump wave reflection and upper hybrid altitudes.

We propose a numerical model of laboratory earthquake cycle inspired by a set of experiments performed on a triaxial apparatus on sawcut Carrara marble samples. The model couples two representations of rock matter: rock is essentially represented as an elastic continuum, except in the vicinity of the sliding interface, where a discrete representation is employed. This allows to simulate in a single framework the storage and release of strain energy in the bulk of the sample and in the loading system, the damage of rock due to sliding, and the progressive production of a granular gouge layer in the interface. After independent calibration, we find that the tribosystem spontaneously evolves towards a stick-slip sliding regime, mimicking in a satisfactory way the behaviour observed in the lab. The model offers insights on complex phenomena which are out of reach in experiments. This includes the variability in space and time of the fields of stress and effective friction along the fault, the progressive thickening of the damaged region of rock around the interface, and the build-up of a granular layer of gouge accommodating shear. We present in detail several typical sliding events, we illustrate the fault heterogeneity, and we analyse quantitatively the damage rate in the numerical samples. Some limitations of the model are pointed out, as well as ideas of future improvements, and several research directions are proposed in order to further explore the large numerical dataset produced by these simulations.

In 2020, global atmospheric methane (CH4) levels increased by 14.7 parts-per-billion (ppb) - the largest annual increase since atmospheric records began in 1983 (https://research.noaa.gov/article/ArtMID/587/ArticleID/2742/Despite-pandemic-shutdowns-carbon-dioxide-and-methane-surged-in-2020) continuing an upward trend since 2007. This is concerning since CH4 is the second most important long-lived greenhouse after CO2 and has global warming potential 28 times that of CO2 per unit mass on a 100-year time scale (Myhre et al. 2013). Moreover, pathways to limit global warming to 1.5°C, or even 2.0°C, require non-CO2 emissions and, in particular, CH4 emissions, to be reduced by 35% with respect to 2010 levels by 2050 (Forster et al. 2018).

High-resolution climate models (~28 km grid spacing) can permit realistic simulations of tropical cyclones (TCs), thus enabling their investigation in relation to the climate system. On the global scale, previous works have demonstrated that the Community Atmosphere Model (CAM) version 5 presents a reasonable TC climatology under prescribed present-day (1980-2005) forcing. However, for the Western North Pacific (WNP) region, known biases in simulated TC genesis frequency and location under-represent the basin’s dominant share in observation. This study addresses these model biases in WNP by evaluating WNP TCs in a decadal simulation, and exploring potential improvements through nudging experiments. Among the major environmental controls of TC genesis, the lack of mid-level moisture is identified as the leading cause of the deficit in simulated WNP TC genesis over the Pacific Warm Pool. Subsequent seasonal experiments explore the effect of constraining the large-scale environment on TC development by nudging WNP temperature field towards reanalysis at various strengths. Temperature nudging elicits significant response in TC genesis and intensity development, as well as in moisture and convection over the Warm Pool. These responses are sensitive to the choice of nudging timescale. Overall, the nudging experiments demonstrate that improvements in the large-scale environment can lead to improvements in simulated TCs. The verification of the environmental controls for simulated TC genesis suggests future model developments in relation to model physics. The potential improvements will contribute to the understanding of how the mean state of current or future climates may give rise to extremes such as TCs.

We have developed a model that simulates the power density profile of the Saskatoon Super Dual Auroral Radar Network (SuperDARN) radar at ionospheric altitudes. The model uses ray tracing software to project the radar system’s vacuum power profile to ionospheric altitudes, taking into account the influence of the ionospheric medium on the propagation characteristics of the High Frequency radio waves. Measurements of the radar’s transmissions by the Radio Receiver Instrument (RRI) in low-Earth orbit are used to validate the model during five experiments which occurred between August 4-8, 2017. Comparisons between simulated and measured RRI antenna voltages show good agreement, although there are clear instances in which the model underperforms. Nevertheless, the model demonstrates its utility as a tool for interpreting several RRI measurements of SuperDARN radars. The model also helps address a lack of knowledge of a SuperDARN radar’s power profile at ionospheric altitudes. In particular, we assess the assumption that SuperDARN’s scattering volume lies along the great-circle path of the transmitting beam’s bearing. Comparisons between the model and RRI’s measurements show that this assumption is reasonable for the five experiments investigated in this work. The model presents a new way of carrying out SuperDARN and HF radio science investigations.

We perform 3D simulations of seismic wavefields to clarify effects of strong reductions of shallow velocities on long-period seismic waves. The simulations use a reference community velocity model of Southern California and a modified version with strong velocity reductions in the top 500 m of the Los Angeles basin. Differences between wavefields generated by ten earthquakes in the reference and perturbed models are analyzed. Velocity changes are estimated by measuring relative time shifts between reference and perturbed seismograms using wavelet cross-correlation spectra. The results indicate that strong localized temporal velocity drops near the surface, such as those observed during strong ground motions, may generate regional perturbations of wavefields at periods up to 20 s. These perturbations may be misinterpreted as generated by temporal changes at seismogenic depths. The results also have important implications for waveform tomography studies.

India implemented stay-at-home order (i.e. lockdown) on 24 March 2020 to decrease the spread of novel COVID-19, which reduced air pollutant emissions in different sectors. The Weather Research and Forecasting model with Chemistry (WRF-Chem) was used to study the changes in air pollutants during the lockdown period in 2020 compared with similar period in 2019. We found that both meteorology and lockdown emissions contributed to daytime PM2.5 (-6% and -11%, respectively) and ozone (-6% and -8%, respectively) reduction averaged in April 2020 in the Indo-Gangetic Plain. However, the ozone concentration response to reductions in its precursors (i.e. NO2 and VOCs) due to the lockdown emissions was not constant over the domain. While ozone concentration decreased in most parts of the domain, it slightly increased in major cities like Delhi and in regions with many power plants. We utilized the reaction rates information in WRF-Chem to study the ozone chemistry. We found carbon monoxide, formaldehyde, isoprene, acetaldehyde, and ethylene as the major VOCs that contribute to the ozone formation in India. We used the ratio of chemical loss of radicals with radicals and NOx, and its corresponding formaldehyde to NO2 ratio (FNR) to find the ozone chemical regimes. Using the upper limit of FNR transition region (1.3), we found that most parts of India are within NOx-limited regime while urban regions and the regions with many power plants are in a VOC-limited regime. As a result, policy makers should study the characteristics of a region before implementing mitigation strategies.

Radiative skin temperature is often used to examine heat exposure in multi-city studies and for informing urban heat management efforts since urban air temperature is rarely measured at the appropriate scales. Cities also have lower relative humidity, which is not traditionally accounted for in large-scale observational urban heat risk assessments. Here using crowdsourced measurements from over 40,000 weather stations in ≈600 urban clusters in Europe, we show the moderating effect of this urbanization-induced humidity reduction on heat stress during the 2019 heatwave. We demonstrate that daytime differences in heat index between urban clusters and their surroundings are weak and associations of this urban-rural difference with background climate, generally examined from the skin temperature perspective, is diminished due to moisture feedback. We also examine the spatial variability of skin temperature, air temperature, and heat indices within these clusters, relevant for detecting hotspots and potential disparities in heat exposure, and find that skin temperature is a poor proxy for the intra-urban distribution of heat stress. Finally, urban vegetation shows much weaker (~1/6th as strong) associations with heat stress than with skin temperature, which has broad implications for optimizing urban heat mitigation strategies. Our results are valid for both operational metrics of heat stress (such as apparent temperature and Humidex) and for various empirical heat indices from epidemiological studies. This study provide large-scale empirical evidence that skin temperature, used due to the lack of better alternatives, is weakly suitable for informing heat mitigation strategies within and across cities, necessitating more urban meteorological observations.

Following sea-ice retreat, surface waters of Arctic marginal seas become nutrient-limited and subsurface chlorophyll maxima (SCM) develop below the pycnocline where nutrients and light conditions are favorable. The productivity associated with these “hidden” features has traditionally not been well constrained. Here, we use a unique combination of high-resolution biogeochemical and physical observations collected on the Chukchi shelf in 2017 to constrain the fine-scale structure of nutrients, O2, particles, SCM, and turbulence. We find large O2 excess at mid-depth, identified by positive saturation (∆O2) maxima of 15-20% that unambiguously indicate significant subsurface production. The ∆O2 maxima were situated immediately beneath the pycnocline and coincided with a complete depletion of inorganic nitrogen ([NO3-] + [NH4+]). The complete nutrient drawdown and O2 excess from this horizon is consistent with subsurface production that amounts to 1/3 to 1/2 the total regional primary production. Nitracline depths aligned with both the base of the mid-depth O2 maxima and with SCM depths, suggesting this horizon represents a compensation point for balanced growth and loss. Furthermore, SCM were also associated with turbulence minima and sat just above a high turbidity bottom layer where light attenuation increased significantly due to high particle loads. Spatially, the largest ∆O2 maxima were associated with high nutrient winter-origin water masses, under a shallower pycnocline associated with seasonal melt. These data implicate short-term and long-term control of SCM and associated productivity by stratification, turbulence, light, and seasonal water mass formation, with corresponding potential for climate-related sensitivities.

In winter, the Northwest Tropical Atlantic Ocean can be characterized by various regimes of interactions among ocean current, surface wind, and wind waves, which are critical for accurately describing surface wind stress. In this work, coupled wave-ocean-atmosphere model simulations are conducted using two different wave roughness parameterizations within COARE3.5, including one that relies solely on wind speed and another that uses wave age and wave slope as inputs. Comparisons with the directly measured momentum fluxes during the ATOMIC/EUREC4A experiments in winter 2020 show that, for sea states dominated by short wind waves under moderate to strong winds, the wave-based formulation increases the surface roughness length by 40\% compared to the wind-speed-based approach. For sea states dominated by remotely generated swells under moderate to strong wind intensity, the wave-based formulation predicts significantly lower roughness length and surface stress (~20%), resulting in increased near-surface wind speed above the constant flux layer (~5%). Further investigation of the mixed sea states in the model and data indicates that the impact of swell on wind stress is over-emphasized in the COARE3.5 wave-based formulation, especially under moderate wind regimes. Various approaches are explored to alleviate this deficiency by either introducing directional alignment between wind and waves or using the mean wave period instead of the wave period corresponding to the spectral peak to compute the wave age.

The growth of data recorded by dense seismic arrays has stimulated the development of new array-based receiver function (RF) imaging techniques. This study examines the feasibility and performance of the least-squares migration (LSM) method, a state-of-art technique used in exploration seismology, to lithospheric imaging using teleseismic RFs. Taking advantage of a pair of forward (de-migration) and adjoint (migration) operators, the LSM casts migration as a regularized least-squares optimization problem. We employ the Split-step Fourier method to design the two operators and conduct wavefield propagation in heterogeneous media. Synthetic tests with models containing various Moho geometries demonstrate that LSM enables resolving interfaces at a higher resolution than conventional migration. Then LSM is applied to teleseismic data recorded by the Hi-CLIMB array deployed on the Tibetan Plateau. Considering the irregular and noisy recordings from field acquisition, we adopt signal processing algorithms, including the Radon transform and Singular Spectrum Analysis filter, to regularize the wavefields and precondition the RFs. The proposed workflow produces a significantly improved subsurface image than conventional methods, revealing new observations of 1) two well-defined interfaces at the base of the crust and 2) gently dipping mantle discontinuities extending continuously from the Lhasa Block to the Qiangtang Block. These structures could represent the imbricated Indian and Tibetan crust underlain by the underthrusting Indian lithosphere, implying that the Indian collisional front extends as far north as the Bangong-Nujiang suture. Overall, our study offers a new high-resolution RF imaging tool and inspires the future development of advanced array processing workflows.

Water retention in soil exhibits diverse phenomena, including suction-saturation hysteresis, non-unique air entrapment at zero suction and negative suction under partial saturations. The constancy of suction after a long rest can be broken by relatively minor mechanical or hydraulic agitations such as low-amplitude wetting cycles -- this fact is here being related to metastable states that differ from the true equilibrium. The complete suction-saturation relationships are thus being recovered using non-equilibrium Landau's hydrodynamic theory and Onsager's reciprocity principles. Equilibrium suction does not pertain to hysteresis, yet can be approached through small amplitude agitations over long duration. Conditions for rate independence are being described, while rate-dependency are also accommodated and illustrated. Finally, it is shown that the new non-equilibrium theory retains the rigorously derived equilibrium result of the effective stress of partially saturated soils.

The 3rd-order upstream advection scheme for scalars on the Voronoi C-grid, once introduced by Skamarock and Gassmann (2011), is applied to horizontal momentum advection. A prerequisite is that the 2nd-order momentum advection is available in advection form for a trivariate coordinate system, so that the higher order terms can be formulated as an add-on. Three key ingredients for a successful application are (i) the determination of the advecting velocity, (ii) the determination of directional Laplacians of wind components and (iii) the determination of the upstream direction. The scheme is tested in two settings, a shallow water framework on the regular hexagonal mesh and the baroclinic wave test on the sphere, where the mesh is slightly deformed. In both cases, the trailing ripples and waves known to represent dispersion errors are impressively reduced. If they are not removed, they can lead to spurious excitation of gravity waves or wavy vorticity patterns. After upscale error growth, they can no longer be identified as a result of numerical errors. The effects of the 3rd-order upstream add-on and a Smagorinsky diffusion are compared. The Smagorinsky model reduces the amplitude of the mentioned waves, but does not erase them. With regard to the dissipation properties, the Smagorinsky diffusion is in accordance with the 2nd law of thermodynamics and dissipation is locally only positive. In contrast, dissipation can be locally negative in runs with the 3rd-order upstream add-on. Therefore, physical and numerical requirements cannot be fulfilled simultaneously.

The Mars Environmental Dynamics Analyzer (MEDA) on board Perseverance includes first-of-their-kind sensors measuring the incident and reflected solar flux, the downwelling atmospheric IR flux, and the upwelling IR flux emitted by the surface. We use these measurements for the first 350 sols of the Mars 2020 mission (Ls ~ 6-174 deg; in Martian Year 36) to determine the surface radiative budget on Mars, and to calculate the broadband albedo (0.3-3 μm) as a function of the illumination and viewing geometry. Together with MEDA measurements of ground temperature, we calculate the thermal inertia for homogeneous terrains without the need for numerical models. We found that: (1) the observed downwelling atmospheric IR flux is significantly lower than model predictions. This is likely caused by the strong diurnal variation in aerosol opacity measured by MEDA, which is not accounted for by numerical models. (2) The albedo presents a marked non-Lambertian behavior, with lowest values near noon and highest values corresponding to low phase angles (i.e., Sun behind the observer). (3) Thermal inertia values ranged between 180 (sand dune) and 605 (bedrock-dominated material) SI units. (4) Averages across Perseverance’ traverse of albedo and thermal inertia (spatial resolution of ~3-4 m2) are in very good agreement with collocated retrievals of thermal inertia from THEMIS (spatial resolution of 100 m per pixel) and of bolometric albedo in the 0.25-2.9 μm range from (spatial resolution of ~300 km2). The results presented here are important to validate model predictions and provide ground-truth to orbital measurements.

Predicting catchment stormflow responses after tropical deforestation remains difficult. We used five-minute rainfall and storm runoff data for 30 events to calibrate the Green–Ampt (GA) and the Spatially Variable Infiltration (SVI) model and predict runoff responses for a small, degraded grassland catchment on Leyte Island (the Philippines), where infiltration-excess overland flow is considered the dominant storm runoff generating process. SVI replicated individual stormflow hydrographs better than GA, particularly for events with a small runoff response or multiple peaks. Calibrated parameter values of the SVI model (i.e., spatially averaged maximum infiltration capacity, Im and initial abstraction, F0) varied markedly between events, but exhibited significant negative linear correlations with (mid-slope) soil water content at 10 cm (SWC10) – as did the ‘catchment effective’ hydraulic conductivity (Ke) of the GA model. SWC10-based values of F0 and Im in SVI resulted in satisfactory to good predictions (NSE > 0.50) for 18 out of 26 storms for which data on SWC10 were available, but failed to reproduce the hydrographs for six events (23%) with mostly small runoff responses. Median values of field-measured near-surface Ksat (~2–3 mm h-1, depending on method) were distinctly lower than the median Im (32 mm h-1) and, to a lesser extent, Ke (~8 mm h-1), confirming previously suspected under-estimation of field-measured Ksat. Using pre-storm topsoil moisture content and 5-min rainfall intensities as the driving variables to model infiltration with SVI gave more realistic results than the classic GA approach or the comparison of rainfall intensities with field-measured Ksat.

The correlation of global ocean surface temperatures with ocean heat content at interannual to decadal time scales shows wind-driven ocean circulation plays a fundamental role in the Earth’s energy balance. Wind-driven baroclinic Rossby waves contribute to the adjustment of the ocean circulation to the winds modulating ocean heat content at mid-latitudes. Here we use observational records, a reanalysis and a Rossby wave model to quantify the contribution of the waves to the variations in air-sea heat flux. We find that Rossby waves crossing the South Pacific at 35ºS can explain up to 70% of the interannual variance of the heat flux. The heat exchange attributed to the waves, ranging from -9 to 21 W m-2, has contributed to the multi-year increase in heat in the central Pacific. Heat fluxes due to Rossby waves could be forecast to provide predictability of this component of the heat exchange with the atmosphere.