The thermal response of the martian subsurface due to solar forcing lacks direct measurements. The InSight mission provides the best opportunity to detect the thermal behavior of the subsurface since it was equipped with both air temperature sensors and a subsurface heat flow probe. Here, we model heat conduction under the InSight landing site based on the measured subsurface thermal parameters and air temperature records, which provide insights into heat flow in the martian subsurface. Daily temperature variation over 1 K occurs only within 25 cm under the ground surface. The highest absolute rate of temperature change appears around sol 440, which coincides closely with the season of the dominant number of marsquakes observed around sunset. Thermal-mechanical finite-element method simulations indicate that more potential afternoon marsquakes might exist but be covered by the wind noise. Our results indicate that most high-frequency and low-magnitude marsquakes are likely thermal in origin.
Nudging is a ubiquitous capability of numerical weather and climate models that is widely used in a variety of applications (e.g. crude data assimilation, “intelligent’ interpolation between analysis times, constraining flow in tracer advection/diffusion simulations). Here, the focus is on the momentum nudging tendencies themselves, rather than the atmospheric state that results from application of the method. The initial intent was to interpret these tendencies as a quantitative estimation of model error (net parameterization error in particular). However, it was found that nudging tendencies depend strongly on the nudging time scale chosen, which is the primary result presented here. Reducing the nudging time scale reduces the difference between the model state and the target state, but much less so than the reduction in the nudging time scale, resulting in increased nudging tendencies. The dynamical core, in particular, appears to increasingly oppose nudging tendencies as the nudging time scale is reduced. These results suggest nudging tendencies cannot be quantitatively interpreted as model error. Still, nudging tendencies do contain some information on model errors and/or missing physical processes and still might be useful in model development and tuning, even if only qualitatively.
The sea surface salinity (SSS) maximum of the South Indian Ocean (the SISSS-max) is a high-salinity feature centered at 30°S, 90°E, near the center of the South Indian subtropical gyre. It is located poleward of a region of strong evaporation and weak precipitation. Using several different satellite and in situ datasets, we track changes in this feature since the early 2000’s. The centroid of the SISSS-max moves seasonally north and south, furthest north in late winter and farthest south in late summer. Interannually, the SISSS-max has moved on a northeast-southwest path about 1500 km in length. The size and maximum SSS of the feature vary in tandem with this motion. It gets larger (smaller) and saltier (fresher) as it moves to the northeast (southwest) closer to (further from) the area of strongest surface freshwater flux. The area of the SISSS-max almost doubles from its smallest to largest extent. It was maximum in area in 2006, decreased steadily until it reached a minimum in 2013, and then increased again. The seasonal variability of the SISSS-max is controlled by the changes that occur on its poleward, or southern, side, whereas intereannual variability is controlled by changes on its equatorward side. The variations in the SISSS-max are a complex dance between changes in evaporation, precipitation, wind forcing, gyre-scale ocean circulation and downward Ekman pumping. Its motion correlated with SSS changes throughout the South Indian Ocean and is a sensitive indicator of changes in the basin’s subtropical circulation.
A nearly pole-to-pole survey near 140°E longitude on Europa revealed many areas that exhibit past lateral surface motions, and these areas were examined to determine whether the motions can be described by systems of rigid plates moving across Europa’s surface. Three areas showing plate-like behavior were examined in detail to determine the sequence of events that deformed the surface. All three areas were reconstructed to reveal the original pre-plate motion surfaces by performing multi-stage rotations of plates in spherical coordinates. Several motions observed along single plate boundaries were also noted in previous works, but this work links together isolated observations of lateral offsets into integrated systems of moving plates. Not all of the surveyed surface could be described by systems of rigid plates. There is evidence that the plate motions did not all happen at the same time, and that they are not happening today. We conclude that plate tectonic-like behavior on Europa occurs episodically, in limited regions, with less than 100 km of lateral motion accommodated along any particular boundary before plate motions cease. Europa may represent a world perched on the theoretical boundary between stagnant and mobile lid convective behavior, or it may represent an additional example of the wide variations in possible planetary convective regimes. Differences in observed strike-slip sense and plate rotation directions between the northern and southern hemispheres indicate that tidal forces may influence plate motions.
The subpolar North Atlantic is a site of significant carbon dioxide, oxygen, and heat exchange with the atmosphere. This exchange, which regulates transient climate change and prevents large-scale hypoxia throughout the North Atlantic, is thought to be mediated by vertical mixing in the ocean's surface mixed layer. Here we present observational evidence that waters deeper than the conventionally defined mixed layer are affected directly by atmospheric forcing. When northerly winds blow along the Irminger Sea's western boundary current, the Ekman response pushes denser water over lighter water and triggers slantwise convection. We estimate that this down-front wind forcing is four times stronger than air--sea heat flux buoyancy forcing and can mix waters to several times the conventionally defined mixed layer depth. Slantwise convection is not included in most large-scale ocean models, which likely limits their ability to accurately represent subpolar water mass transformations and deep ocean ventilation.
Conceptual hydrological models are practical tools for estimating the performance of green roofs, with respect to stormwater management. Such models require calibration to obtain parameter values, which limits their use in cases when measured data are not available. One approach that has been thought to be useful is to transfer parameters from a gauged roof calibrated locally (i.e., single-site calibration) to a similar ungauged roof located in a different location. This study tested this approach by transferring calibrated parameters of a conceptual hydrological model between sixteen extensive green roofs located in four Norwegian cities with different climatic conditions. The approach was compared with a multi-site calibration scheme that explores trade-offs of model performances between the different sites. The results showed that single site calibration could yield optimal parameters for one site and perform poorly in other sites. In contrast, obtaining a common parameter set that yields satisfactory results (Kling Gupta Efficiency >0.5) for different sites, and roof properties could be achieved by multi-site calibration. The practical implications of multi-site calibration have been discussed in the context of stormwater management. The multi-site calibration scheme is recommended not only for transferability amongst roofs in different sites but also when applying conceptual models for evaluating climate change scenarios in which the climatic variables are significantly different from the ones used for calibration.
The orientation of faulting associated with volcano-tectonic earthquakes follows the stress field there, as with tectonic earthquakes. Therefore, stress changes associated with volcanic activity change fault orientations or focal mechanisms. Zhan et al. (2022) observed temporal changes of focal mechanisms associated with volcanic unrest. They decomposed the stress field into the ambient differential stress, volcano loading, and the stress change by the dike intrusion; they then evaluated their relative contributions to constrain the magnitude of the ambient differential stress that is consistent with the observation. This study indicates that focal mechanisms can be used to monitor the stress state of an active volcano. Combining focal mechanisms with other geophysical observables, such as seismic anisotropy and geodetic measurements, will give us more precise assessments of the stress state, leading to better forecasts of volcanic activity.
In winter 2013, a sea ice breakout in the Beaufort Sea produced extensive fracturing and contributed to record regional ice export. Rheinlænder et al. (2022) simulated this event using the neXtSIM sea ice model, reproducing a realistic progression of lead opening and ice drift following the track of an anticyclone. In their study, Rheinlænder et al. (2022) highlighted strong winds and thin ice as key factors for breakouts. We draw on observational records to provide additional context for the driving mechanisms of breakout events. We show that wind direction, rather than speed, was the primary control on patterns of lead opening and breakout timing in 2013. Records of similar events over previous decades demonstrate that breakouts are common under anticyclonic forcing, including during years when the ice was thicker. These additional events can be used to further validate models such as neXtSIM and improve predictive capabilities for future breakouts.
Wildfire smoke frequently blankets the U.S. throughout the agricultural growing season, and this will likely increase with climate change. Studies of smoke impacts have largely focused on air quality and human health; however, understanding smoke’s impact on photosynthetically active radiation (PAR) is essential for predicting how smoke affects plant growth. We compare surface shortwave irradiance and diffuse fraction (DF) on smoke-impacted and smoke-free days from 2006-2020 using data from multifilter rotating shadowband radiometers at ten U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Program stations and smoke plume locations from operational satellite products. On average, 20% of growing season days are smoke-impacted, but smoke prevalence increases over time (r = 0.60, p < 0.05). Smoke presence peaks in the mid- to late growing season (i.e., July, August), particularly over the northern Rocky Mountains, Great Plains, and Midwest. We find an increase in the distribution of PAR DF on smoke-impacted days, with larger increases at lower cloud fractions. On clear-sky days, daily average PAR DF increases by 10 percentage points when smoke is present. Spectral analysis of clear-sky days shows smoke increases DF (average: +45%) and decreases total irradiance (average: -6%) across all six wavelengths measured from 368-870 nm. Optical depth measurements from ground and satellite observations both indicate that spectral DF increases and total spectral irradiance decreases with increasing smoke plume optical depth (i.e., plume thickness). Our analysis provides a foundation for understanding smoke’s impact on PAR, which carries implications for agricultural crop productivity under a changing climate.
The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, USA is the largest instrumental event in the Mina deflection, an E-trending stepover zone of highly diffuse faulting within the Walker Lane. The MCRE mostly ruptured previously unmapped faults, motivating us to characterize the behaviour of an earthquake on a structurally-immature fault. We use Interferometric Synthetic Aperture Radar (InSAR) data and regional GNSS offsets to model the causative faulting. Our three fault model indicates almost pure left-lateral motion in the east and normal-sinistral slip in the west. Maximum slip of 1.1 m occurs at 8-10 km depth but less than 0.2 m of slip reaches the surface, yielding a pronounced shallow slip deficit (SSD) of 86%. Our calibrated relocated hypocenters and focal mechanisms indicate that the mainshock initiated at 9 km depth and aftershock focal depths range from 1 to 11 km, helping constrain the local seismogenic thickness. We further present new field observations of fracturing and pebble-clearing that shed light on the western MCRE kinematics, revealing a paired fault system below the spatial resolution of the InSAR model. The segmented fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic features, and an estimated cumulative offset of 600-700 m, are all characteristic of a structurally-immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (twenty-eight Mw≥6.4 strike-slip events) shows that SSDs are not correlated with structural maturity as previously suggested.
There has been increasing interest in quantifying methane emissions from a view towards mitigation. Accordingly, ground-based sampling of oil and gas production sites in the Permian Basin was carried out in January and October 2020. Ethane to methane ratios (EMRs) were quantified which may be used to distinguish emissions from particular sources, such as produced gas and oil tank flashing. The logarithmic mean EMR for 102 observations was 18 (±2)%, while source specific EMRs showed that sites where emissions were attributed to a tank produced much higher EMRs averaging 44%. Sites with other noticeable sources such as compressors, pneumatics, and separators had lower and less variable EMRs. Tanks displayed distinct behavior with EMRs between 10-21% producing CH4 emissions >30x higher than tanks with EMRs >21%. This observation supports the hypothesis that high emission rate tank sources are often caused by separator malfunctions that leak produced gas through liquids storage tanks.
This work presents a new approach to defining drought, establishing an empirical relationship between historical droughts (and wet spells) documented in impact reports, and a broad range of observed drought-related climate features. A Random Forest (RF) algorithm was trained to identify the particular combinations of predictors – such as precipitation, soil moisture and potential evapotranspiration – that led to categorical, documented drought or non-drought events. Unlike traditional drought definitions, the new RF drought indicator combines meteorological, hydrological, agricultural, and socioeconomic drought, providing drought information for all impacted sectors. The metric also quantifies the conditional probability of drought (rather than being threshold-based), considering multiple climate features and their interactive effect, and can be used for forecasting. The approach was validated out-of-sample across several random selections of training and testing datasets, and demonstrated better predictive capabilities than commonly used drought indicators in a range of performance metrics. Furthermore, it showed a comparable performance to the (expert elicitation-based) US Drought Monitor (USDM) which is the current state-of-the-art record of historical drought in the USA. As well as providing an alternative historical drought indicator to USDM, the RF approach offers additional advantages by being automated, by providing drought information at the grid-scale, and by having predictive capacity. As a proof-of-concept case, the RF drought indicator was trained on Texan climate data and droughts, and validated in all Texas ecoregions. However, the introduced approach can be easily implemented to develop a RF drought indicator for new regions if adequate information on historical droughts is available.
Previous studies have estimated that 25% to 35% of Amazonian precipitation comes from evapotranspiration (ET) within the basin. However, due to simplifying assumptions of traditional models, these studies primarily focus on large spatial and temporal scales. In this work we use the Weather Research and Forecast (WRF) regional climate model with the added capability of water vapor tracers to track the moisture from Amazonian ET at the native WRF resolution. The tracers reveal that the well-mixed assumption of simpler models does not hold, as local ET is more efficiently rained out of the atmospheric column than remote sources of moisture, particularly in the eastern part of the basin. Recycled precipitation shows a strong annual and semi-annual signal, associated with the passage of the Inter-Tropical Convergence Zone. The tracers also reveal a strong diurnal cycle of Amazonian water vapor related to the diurnal cycle of ET, convective precipitation and advected moisture. ET increases from early morning into the afternoon, some of this moisture is rained out through convective storms in the early evening, while later in the night strong winds associated with the South American Low Level Jet advect moisture downwind. Visualizing the Amazonian water vapor highlights its diurnal beating pattern and suggests that the Amazon has “younger” water than other regions in the globe, with very efficient recycling of local moisture.
Auroral brightness and color ratio imagery, captured using the Juno mission’s Ultraviolet Spectrograph, display intense emissions poleward of Jupiter’s northern main emission, and these are split into two distinctly different spectral or “color ratio” regimes. The most poleward region, designated the “swirl region” by Grodent et al. (2003), exhibits a high color ratio, while low color ratio emissions are found within the collar around the swirl region but still poleward of the main emission. We confirm the apparent strong magnetospheric local time control within the polar collar (Grodent et al., 2003), with the dusk side bright “active region” emissions extending from ~11 to 22 hr of magnetospheric local time. These bright emissions dim by at least an order of magnitude between ~0 and 11 hr magnetospheric local time, in the midnight to dawn side “dark region”. This magnetospheric local time structure holds true even when the entire northern oval is located on the night side of the planet (in ionospheric local time), a geometry unstudied prior to Juno, as it is unobservable from Earth. The swirl region brightens at ionospheric dawn (~5-7 ionospheric local time) and diminishes or completely disappears at ionospheric local times of ~20 to 22 hrs. Finally, the southern auroral polar emissions appear to share all of the local time dependencies of its northern counterpart, but at a reduced intensity.
Here, we extend the Fisher-Kolmogorov-Petrovsky-Piskunov equation to capture the interplay of multiscale and multiphysics coupled processes. We use a minimum of two coupled reaction-diffusion equations with additional nonlocal terms that describe the coupling between scales through mutual cross-diffusivities. This system of equations incorporates the physics of interaction of thermo-hydro-chemo-mechanical processes and can be used to understand a variety of localisation phenomena in nature. Applying bifurcation theory to the system of equations suggests that geological patterns can be interpreted as physical representation of three classes of well-known instabilities: Turing instability, Hopf bifurcation, and a chaotic regime of complex soliton-like waves. For specific parameters, the proposed system of equations predicts all three classes of instabilities encountered in nature. The third class appears for small fluid release reactions rates as a slow quasi-soliton wave for which our parametric diagram shows possible transition into the Hopf- or Turing-style instability upon dynamic evolution of coefficients.
The aquatic vegetation patch plays a significant role on sediment net deposition in the vegetated channels. Particularly, the flow is decelerated at the leading edge of a patch that tends to induce vertical updraft, that is, a diverging flow region, in which vegetation greatly affects the pattern of sediment net deposition. This study focuses on the simulation of the sediment net deposition in the whole vegetation patch region through an innovative random displacement model, a Lagrange method, with a probability-based boundary condition instead of the reflection or sorption boundary at the channel bottom. The probability model of deposition and resuspension is proposed according to the flow field characteristics in the different regions of the vegetation patch. The variation of the sediment deposition and resuspension with the turbulent kinetic energy is analyzed to illustrate the effect of the turbulence induced by vegetation, represented by the dimensionless turbulent kinetic energy (ψ), on the sediment deposition and resuspension. The sediment deposition predicted by the proposed model agrees well with the experimental measurements. Results show that the effect of vegetation on the sediment deposition and resuspension motions begins to prevail when the vegetation-induced ψ is larger than its threshold, ψ *. Although the experimental data are limited, the threshold of ψ is predicted to be within 6.8 to 10 according to the simulation results. As the turbulent kinetic energy increases, the deposition probability decreases continuously when ψ>ψ *.
We analyze two preindustrial experiments from the Community Earth System Model version 2 (CESM2) to characterize the impact of sea ice physics on regional differences in coastal sea ice production around Antarctica and the resulting impact on the ocean and atmosphere. The experiment in which sea ice is a “mushy” mixture of solid ice and brine has a substantial increase in coastal sea ice frazil and snow ice production that is accompanied by decreasing congelation growth and increasing bottom melt. With mushy ice physics, the subsurface ocean is denser and saltier, there is a statistically significant increase in Antarctic Bottom Water Formation by ~0.5 Sv, but differences in ocean biogeochemistry are minimal and only in regions where the summer ice state differs. While there are no significant changes in the atmospheric circulation, using “mushy” ice physics results in decreased turbulent heat flux, atmospheric convection, and low level cloud cover.
Intense snowfall sublimation was observed during a precipitation event over Davis in the Vestfold Hills, East Antarctica, from 08 to 10 January 2019. Radar observations and simulations from the Weather Research and Forecasting model revealed that orographic gravity waves (OGWs), generated by a north-easterly flow impinging on the ice ridge upstream of Davis, were responsible for snowfall sublimation through a Foehn effect. Despite the strong meridional moisture advection associated with an atmospheric river (AR) during this event, almost no precipitation reached the ground at Davis. We found that the direction of the synoptic flow with respect to the orography determined the intensity of OGWs over Davis, which in turn directly influenced the snowfall microphysics. Turbulence induced by the OGWs likely enhanced the aggregation process, as revealed by dual-polarization and dual-frequency radar observations. This study suggests that despite the intense AR, the precipitation distribution was determined by local processes tied to the orography. The mechanisms found in this case study could contribute to the extremely dry climate of the Vestfold Hills, one of the main Antarctic oasis.