Agricultural management strategies are crucial in regulating the soil-atmosphere interaction. The crop landscape is influenced by farmers through different field practices, and further impacts the variations of soil temperature, soil moisture, and field microclimate. To examine how different management strategies affect the soil properties and the aforementioned interaction, two observation systems were installed in an organic-certified (ORG) tea field and a conventional (CONV) tea field in northern Taiwan. The results show that the variation of canopy temperature was more significant in CONV while the difference in soil diurnal temperature range was minor. However, the daily loss rate of soil water content in ORG was two times faster than that in CONV (0.93% d−1 vs. 0.46% d−1). These findings suggest that the appropriate management strategies could assist farmers in adapting to environmental fluctuations and provide quantitative references for assessing soil characteristics under different agricultural applications and climatic conditions.
The region around the tip of the Antarctic Peninsula is one of the fastest warming regions of the world, a situation that will lead to widespread changes in permafrost state, local hydrological cycles and biological activity. Further, it is located in the path of the southern westerly winds, one of the poorest-understood components of the global climatic system. The sedimentary archives in the lakes from the ice-free regions on this region host a yet untapped wealth of information on the past changes and links between the regional climatic, hydrologic and biological systems. Especially important are the stable isotope compositions of these sediments, but to understand how they record these changes, an in-depth knowledge of their links to present-day conditions is required. We present here the first study of the stable isotope composition of the surface waters in the ice-free southern peninsulas of King George Island, Antarctica. Our results suggest that a clear separation of the various water bodies (permafrost, snow, meltwater, lakes) based on the stable isotope composition of the water is possible, allowing for future studies aiming to understand (changing) feeding behavior of terrestrial fauna. Further, water in lakes on a W-E transect have distinct stable isotope composition, leading to the possibility of studying the past changes in the strength and dynamics of the westerly winds in the region.
Floating communities exist throughout the world. Many live on water with a high pathogen load due to difficulties associated with sewage management. In Claverito, an informal floating community in Iquitos, Peru, we conducted a controlled experiment to test the ability of water hyacinth (Eichhornia crassipes) to remove Escherichia coli from water. When river E. coli concentrations were at or below ~1500 CFU 100 mL-1, water hyacinth reduced shallow concentrations (8-cm depth) down to levels deemed safe by U.S. EPA for recreational use. Above this threshold, plants were able to reduce E. coli levels within shallow water, but not down to “safe” levels. At deeper depths (>25 cm), there was evidence that plants increased E. coli concentrations. Water hyacinth removed E. coli from shallow water by providing a surface (i.e., submerged roots) onto which pathogens sorbed and by protecting organisms that consume E. coli. Unfortunately, because of root association, the total E. coli load within the water column was greater with water hyacinth present, and results hinted that the plants’ protective environment also harbored parasites. The use of water hyacinth to keep surface water around floating communities low in E. coli could be beneficial as this is the water layer with which people most likely interact. Aquatic vegetation naturally proliferates in and around Claverito. While this study was based on curating aquatic plants in order to achieve a water-quality outcome, it nonetheless supports concrete actions for Claverito residents under non-curated conditions, which are outlined at the end of the manuscript.
The quantitative and objective characterization of dissolution intensity in fossil planktonic foraminiferal shells could be used to reconstruct past changes in bottom water carbonate ion concentration. Among proxies measuring the degree of dissolution of planktonic foraminiferal shells, X-ray micro-Computed Tomography (CT) based characterization of apparent shell density appears to have good potential to facilitate quantitative reconstruction of carbonate chemistry. However, unlike the well-established benthic foraminiferal B/Ca ratio-based proxy, only a regional calibration of the CT-based proxy exists based on a limited number of data points covering mainly low-saturation state waters. Here we determined by CT-based proxy the shell dissolution intensity of planktonic foraminifera Globigerina bulloides, Globorotalia inflata, Globigerinoides ruber, and Trilobatus sacculifer from a collection of core top samples in the Southern Atlantic covering higher saturation states, and assessed the characteristics and reliability of CT-based proxy. We observed that the CT-based proxy is generally controlled by deep-water Δ[CO32–] like the B/Ca proxy, but its effective range of Δ[CO32–] is between –20 to 10 µmolkg–1. In this range, the CT-based proxy appears directly and strongly related to deep-water Δ[CO32–], whereas the B/Ca of benthic foraminifera appears to be affected by porewater saturation in carbonate-rich substrates. On the other hand, the CT-based proxy is affected by supralysoclinal dissolution in areas with high productivity. Like the B/Ca proxy, the CT-based proxy requires species-specific calibration, but the effect of species-specific shell difference in susceptibility to dissolution on the proxy is small.
The information on plasma pressures in the outer part of the inner magnetosphere is important for simulations of the inner magnetosphere and the better understanding of its dynamics. Based on 17-year observations from both CIS and RAPID instruments onboard the Cluster mission, we used machine- learning-based models to predict proton plasma pressures at energies from ~40eV to 4MeV in the outer part of the inner magnetosphere (L*=5-9). The location in the magnetosphere, and parameters of solar, solar wind, and geomagnetic activity from the OMNI database are used as predictors. We trained several different machine-learning-based models and compared their performances with observations. The results demonstrate that the Extra-Trees Regressor has the best predicting performance. The Spearman correlation between the observations and predictions by the model data is about 68%. The most important parameter for predicting proton pressures in our model is the L* value, which is related to the location. The most important predictor of solar and geomagnetic activity is the solar wind dynamic pressure. Based on the observations and predictions by our model, we find that no matter under quiet or disturbed geomagnetic conditions, both the dusk-dawn asymmetry at the dayside with higher pressures at the duskside and the day-night asymmetry with higher pressures at the nightside occur. Our results have direct practical applications, for instance, inputs for simulations of the inner magnetosphere or the reconstruction of the 3-D magnetospheric electric current system based on the magnetostatic equilibrium, and can also provide valuable guidance to the space weather forecast.
The Tropical cyclone (TC) forecast skill of the eight global medium-range forecast models which are participating in the DIMOSIC (DIfferent Models, Same Initial Conditions) project is investigated in this study. Each model was used to generate 10-day forecasts from the same initial conditions provided by the European Centre for Medium-Range Weather Forecasts. There are a total of 123 initial dates spanning in one year from June 2018 to June 2019 with a 3-day interval. The TC track and intensity forecasts are evaluated against the best track dataset. TC-related precipitation and tropical cyclogenesis forecasts are also compared to explore the differences and similarities of TC forecasts across the models. This comparison of TC forecasts allows model developers in different centers to benchmark their model against other models, with the impact of the initial condition quality removed. The verifications reveal that most models show slow-moving and right-of-track biases in their TC track forecasts. Also, a common dry bias in TC-related precipitation indicates a general deficiency in TC intensity and convection in the models which should be related to insufficient model resolution. These findings provide important references for future model developments.
Simulating whole atmosphere dynamics, chemistry, and physics is computationally expensive. It can require high vertical resolution throughout the middle and upper atmosphere, as well as a comprehensive chemistry and aerosol scheme coupled to radiation physics. An unintentional outcome of the development of one of the most sophisticated and hence computationally expensive model configurations is that it often excludes a broad community of users with limited computational resources. Here, we analyze two configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) with simplified “middle atmosphere” chemistry at nominal 1 and 2 degree horizontal resolutions. Using observations, a reanalysis, and direct model comparisons, we find that these configurations generally reproduce the climate, variability, and climate sensitivity of the 1 degree nominal horizontal resolution configuration with comprehensive chemistry. While the background stratospheric aerosol optical depth is elevated in the middle atmosphere configurations as compared to the comprehensive chemistry configuration, it is comparable between all configurations during volcanic eruptions. For any purposes other than those needing an accurate representation of tropospheric organic chemistry and secondary organic aerosols, these simplified chemistry configurations deliver reliable simulations of the whole atmosphere that require 35% to 86% fewer computational resources at nominal 1 and 2 degree horizontal resolution, respectively.
Groundwater depletion is a concern around the world with implications for food security, ecological resilience, and human conflict. Long-term perspectives provided by tree ring-based reconstructions can improve understanding of factors driving variability in groundwater elevations, but such reconstructions are rare to date. Here, we report a set of new 546-year tree-ring chronologies developed from living and remnant longleaf pine (Pinus palustris) trees that, when combined with existing bald cypress (Taxodium distichum) tree-ring chronologies, were used to create a set of nested reconstructions of mean annual groundwater elevation for North Central Florida that together explain 63% of the variance in instrumental measurements and span 1498–2015. Split calibration confirms the skill of the reconstructions, but coefficient of efficiency metrics and significant autocorrelation in the regression residuals indicate a weakening relationship between tree growth and groundwater elevation over recent decades. Comparison to data from a nearby groundwater well suggests extraction of groundwater is likely contributing to this weakening signal. Periodicity within the reconstruction and comparison with global sea surface temperatures highlight the role of El Niño-Southern Oscillation (ENSO) in driving groundwater elevations, but the strength of this role varies substantially over time. Atlantic and Pacific sea surface temperatures modulate ENSO influences, and comparisons to multiple proxy-based reconstructions indicate an inconsistent and weaker influence of ENSO prior to the 1800s. Our results highlight the dynamic influence of ocean-atmospheric phenomena on groundwater resources in North Central Florida and build on instrumental records to better depict the long-term range of groundwater elevations.
Sustainability of China’s numerous cities are threatened by both quantity- and quality-induced water scarcity, which can be measured by the water footprint from a consumption (WFcons) or production (WFprod) perspective. Although WFcons was widely assessed, the changes in WFprod of China’s cities were still unclear. Taking 31 major cities as examples, this study revealed the dynamics of urban WFprod in China from 2011 to 2016. First, the spatiotemporal patterns of WFprod and water deficit were evaluated and then the main reasons for the WFprod dynamics and its implications for urban sustainability were explored. A large-scale decrease in urban WFprod in China was found, with the average WFprod decreasing from 13.8 billion m³ to 10.3 billion m³ and the per capita WFprod decreasing from 1614.8 m³/person to 1184.0 m³/person (i.e., falling by more than a quarter in just six years). Such shrinkage was particularly evident in drylands, eliminating the water deficit in Xi’an and Xining. The reduction in grey WFprod caused by implementing water pollution prevention policies and other relevant measures played the most important role in the savings. In the future, the implementation of updated pollution discharge standards is projected to allow more cities to escape water deficits; however, the rapid growth of the domestic and ecological blue WFprod caused by urbanization and urban greening would destabilize this prospect. Thus, attention should be given to both water pollution prevention and domestic and ecological blue WFprod restriction to further alleviate urban water scarcity in China.
Sediment transport load monitoring is important in civil and environmental engineering fields. Monitoring the total load is difficult, especially because of the cost of the bed load transport measurement. This study proposes estimation models for the suspended load to total load ratio (Fsus) using dimensionless hydro-morphological variables. Two prominent variable combinations were identified using the recursive feature elimination procedure of support vector regression (SVR): (1) W/h, d*, Reh, Frd, and Rew and (2) Reh, Fr, and Frd. The explicit interactions between Fsus and the two combinations were revealed by two modern symbolic regression methods: multi-gene genetic programming and Operon. The five-variable SVR model showed the best performance (R2=0.7722). The target dataset was clustered by applying a self-organizing map and Gaussian mixture model. Through these steps, Reh and Frd are determined as the two most influential variables. Subsequently, the one-at-a-time sensitivity of the input variables of the empirical models was investigated. By referring to the clustering and sensitivity analyses, this study provides physical insights into Fsus controlling relationships. For example, Fsus is proportional to Reh and is inversely related to Frd. The empirical models developed in this study are applicable in practice and easy to implement in other real-time surrogate suspended-sediment monitoring methods, because they only require basic measurable hydro-morphological variables, such as velocity, depth, width, and mean bed material grain size.
This paper investigates the effects of geomagnetic storms of 25-27 September 2011, 16- 18 March 2013, and 6-8 September 2015 over five mid latitudes stations (Dourbes, Fairford, Moscow, Rome, and Roquetes) and performs a cross correlation analysis of ionospheric and solar parameters during these storms. We observed the highest fluctuations in ionospheric variables during the main phase of storms. In addition, there is strong evidence of pre-storm phenomenon occurring at least a few hours and more than 24 hours prior to the main phase of the geomagnetic storms. We found that the TEC and foF2 parameters have strong dependence with latitudes for the events with Sudden Storm Commencement(SSC) in mid latitude region. Relatively low TEC and foF2 can be observed in Moscow which is at the highest latitude among the five stations because of a decrease in the n(O)/n(N2) ratio through out the storm event. However, for the event with gradual storm commencement, there is no evidence of such dependence. The good correlation of Symmetric-H and Auroral Electrojet Indices with ionospheric parameters indicates that the coupling mechanism between magnetosphere and ionosphere produces intense electric field disturbances in the middle low latitudes.
Transionospheric radio signals might undergo random modulations of their amplitude and phase caused by scattering on irregular structures in the ionosphere. This phenomenon, known as scintillation, is governed by the space weather conditions, time of the day, season, local distribution of the geomagnetic field, etc. All these factors make ionospheric scintillation both highly variable in space and time. Moreover, scintillation are intrinsically anisotropic since the associated scattering irregularities tend to align and stretch along the geomagnetic field lines. Depending on the relative position of signal source, the receiving station, and the irregularity, the scintillation effect on the transmitted wave might be enhanced or reduced. This study is focused on the consistent accounting of this geometric effect in scintillation modeling with the emphasis on situations when the communication or sensing sender-receiver link is nearly horizontal. For this task the single phase screen model has been used to model the scattering of propagating radio signals on random ionospheric layer. The geometric enhancement effect of scintillation is demonstrated by considering communication links via a geostationary beacon satellite over the equator.
Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8000-9000 cm-2s-1 dominates atomic D loss under all solar conditions. The total fractionation factor, f, is 0.04–0.07, and integrated water loss is 147–158 m GEL. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.
The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally-driven diurnal surface displacements can constrain the mean ice shell thickness. Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite-element model of Enceladus to calculate diurnal tidal displacements for a range of mean crustal thickness values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing ---such as Tiger Stripes on Enceladus---their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of mean crustal thickness that assume spherical symmetry a priori can deviate from the true value by as much as ~41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneites near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ~41% range in estimates of mean crustal thickness from Love numbers is smaller than that found with approaches relying on static gravity and topography (~250%) or analyzing diurnal libration amplitudes (~ 85%) to infer mean crustal thickness at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.
Changes in vegetation in North America indicate Holocene shifts in the latitudinal temperature gradient along the western margin of the North Atlantic. The dynamics of tree taxa such as oak (Quercus) and hickory (Carya) showed opposing directions of change across different latitudes, consistent with changes in temperature gradients. Pollen-inferred temperatures from 34 sites quantify the changes and reconstruct a long-term southward shift of the sharpest temperature gradient in winter and a northward shift in summer. During the mid-Holocene, however, an oscillation in tree distributions interrupted the trends indicating that the steepest portion of the seasonal temperature gradients migrated rapidly northward at 5.8-3.2 ka. The shift produced an unusually late summer thermal maxima at 42-43.5°N where oak abundance peaked both in the early and mid-Holocene. The changes appear consistent with orbital and ice sheet forcing as well as millennial variability in the North Atlantic pressure field during the mid-Holocene.
Regions along the edges of the tropics host vast populations and ecosystems which are sensitive to climate change. Here we examine the extent of tropical climate land areas in the ERA5 and MERRA-2 reanalyses in high-emission scenarios of 45 models participating in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5/6). Based on the definition of tropical climate land areas as regions where the diurnal temperature range exceeds the seasonal temperature range, we find a net reduction of tropical land area with global warming. This change is primarily due to an increased seasonal temperature range, driven by enhanced summer warming. The reduction in tropical land area is consistent with the expansion of the subtropical descending zones and with the expansion of drylands with global warming. However, the particular contributions of dynamic and thermodynamic processes are not clear.
Based on reanalysis datasets and sea-ice sensitivity experiments, this study has pointed out that the autumn sea ice loss in East Siberian-Chukchi-Beaufort (EsCB) Seas significantly increases the frequency of winter extreme low temperature over western-central China. Autumn sea ice loss warms the troposphere and generates anticyclonic anomaly over the Arctic region one month later. Under the effects of synoptic eddy-mean flow interaction and anomalous upward propagated planetary wave 2, the Arctic anticyclonic anomaly strengthens and develops toward Greenland-Northern Europe, accompanied by a weakened stratospheric polar vortex. In winter, following intra-seasonal downward propagation of stratospheric anomalies, the Northern European positive geopotential anomalies enhance and expand downstream within 7 days, favoring Arctic cold air east of Novaya Zemlya southward (hyperpolar path) accumulating in Siberia around Lake of Baikal. In the subsequent 2~3 days, these cold anomalies rapidly intrude western-central China and induce abrupt sharp cooling, thus more frequent extreme low temperature there.
How are particles being energized by turbulent electromagnetic fields is an outstanding question in plasma physics and astrophysics. This paper investigates the electron acceleration mechanism in strong turbulence (δB/B0 ~ 1) in the Earth’s magnetosheath based on the novel observations of the Magnetospheric Multiscale (MMS) mission. We find that electrons are magnetized in turbulent fields for the majority of the time. By directly calculating the electron acceleration rate from Fermi, betatron mechanism, and parallel electric field, it is found that electrons are primarily accelerated by the parallel electric field within coherent structures. Moreover, the acceleration rate by parallel electric fields increases as the spatial scale reduces, with the most intense acceleration occurring over about one ion inertial length. This study is an important step towards fully understanding the turbulent energy dissipation in weakly collisional plasmas.