Seismic activity and deep conductivity structure of the Eastern Carpathians

We present results of a study of the seismicity and the geoelectric structure of the Eastern Carpathians. After the evaluation of the seismicity, new methods of processing and analyzing seismic data are developed, which allow constructing an averaged horizontal-layered velocity model of the crust in the Carpathian region of Ukraine, tracing the seismic active faults and localizing the seismic events both in horizontal and in vertical direction with a better precision. For the study of the conductivity structure beneath the Eastern Carpathians, the collected magnetovariation and magnetotelluric data are used. The depth of electrical conductivity anomalies are estimated and the resulting quasi-3D model of the conductivity structure beneath the Carpathians is compared with the seismicity in the depth range of 10 ± 2.5 km. The comparison suggests possible geological mechanisms: the seismic events occur mainly in resistive solid rock domains which surround aseismic high-conductivity zones, consisting of at least partially melted material. Aqueous fluids, or a joint effect of several mechanisms, may also play an active role in this distribution.     

The role of substrate characteristics in producing anomalously young crater retention ages in volcanic deposits on the Moon: Morphology,topography, subresolution roughness,and mode of emplacement of the Sosigenes lunar irregular mare patch

Lunar irregular mare patches (IMPs) comprise dozens of small, distinctive, and enigmatic lunar mare features. Characterized by their irregular shapes, well-preserved state of relief, apparent optical immaturity, and few superposed impact craters, IMPs are interpreted to have been formed or modified geologically very recently (<~100 Ma; Braden et al. 2014 ). However, their apparent relatively recent formation/modification dates and emplacement mechanisms are debated. We focus in detail on one of the major IMPs, Sosigenes, located in western Mare Tranquillitatis, and dated by Braden et al. ( 2014 ) at ~18 Ma. The Sosigenes IMP occurs on the floor of an elongate pit crater interpreted to represent the surface manifestation of magmatic dike propagation from the lunar mantle during the mare basalt emplacement era billions of years ago. The floor of the pit crater is characterized by three morphologic units typical of several other IMPs, i.e., (1) bulbous mounds 5–10 m higher than the adjacent floor units, with unusually young crater retention ages, meters thick regolith, and slightly smaller subresolution roughness than typical mature lunar regolith; (2) a lower hummocky unit mantled by a very thin regolith and significantly smaller subresolution roughness; and (3) a lower blocky unit composed of fresh boulder fields with individual meter-scale boulders and rough subresolution surface texture. Using new volcanological interpretations for the ascent and eruption of magma in dikes, and dike degassing and extrusion behavior in the final stages of dike closure, we interpret the three units to be related to the late-stage behavior of an ancient dike emplacement event. Following the initial dike emplacement and collapse of the pit crater, the floor of the pit crater was flooded by the latest-stage magma. The low rise rate of the magma in the terminal stages of the dike emplacement event favored flooding of the pit crater floor to form a lava lake, and CO gas bubble coalescence initiated a strombolian phase disrupting the cooling lava lake surface. This phase produced a very rough and highly porous (with both vesicularity and macroporosity) lava lake surface as the lake surface cooled. In the terminal stage of the eruption, dike closure with no addition of magma from depth caused the last magma reaching shallow levels to produce viscous magmatic foam due to H₂O gas exsolution. This magmatic foam was extruded through cracks in the lava lake crust to produce the bulbous mounds. We interpret all of these activities to have taken place in the terminal stages of the dike emplacement event billions of years ago. We attribute the unusual physical properties of the mounds and floor units (anomalously young ages, unusual morphology, relative immaturity, and blockiness) to be due to the unusual physical properties of the substrate produced during the waning stages of a dike emplacement event in a pit crater. The unique physical properties of the mounds (magmatic foams) and hummocky units (small vesicles and large void space) altered the nature of subsequent impact cratering, regolith development, and landscape evolution, inhibiting the typical formation and evolution of superposed impact craters, and maintaining the morphologic crispness and optical immaturity. Accounting for the effects of the reduced diameter of craters formed in magmatic foams results in a shift of the crater size–frequency distribution age from <100 Myr to billions of years, contemporaneous with the surrounding ancient mare basalts. We conclude that extremely young mare basalt eruptions, and resulting modification of lunar thermal evolution models to account for the apparent young ages of the IMPs, are not required. We suggest that other IMP occurrences, both those associated with pit craters atop dikes and those linked to fissure eruptions in the lunar maria, may have had similar ancient origins.     

Interdecadal variability of the Pacific Ocean: model response to observed heat flux and wind stress anomalies

Variability of the Pacific Ocean is examined in numerical simulations with an ocean general circulation model forced by observed anomalies of surface heat flux, wind stress and turbulent kinetic energy (TKE) over the period 1970-88. The model captures the 1976-77 winter time climate shift in sea surface temperature, as well as its monthly, seasonal and longer term variability as evidenced in regional time series and empirical orthogonal function analyses. Examination of the surface mixed-layer heat budget reveals that the 1976-77 shift was caused by a unique concurrance of sustained heat flux input anomalies and very strong horizontal advection anomalies during a multi-month period preceding the shift in both the central Pacific region (where cooling occurred) and the California coastal region (where warming occurred). In the central Pacific, the warm conditions preceding and the cold conditions following the shift tend to be maintained by anomalous vertical mixing due to increases in the atmospheric momentum flux (TKE input) into the mixed layer (which deepens in the model after the shift) from the early 1970s to the late 1970s and 1980s. Since the ocean model does not contain feedback to the atmosphere and it succeeds in capturing the major features of the 1976-77 shift, it appears that the midlatitude part of the shift was driven by the atmosphere, although effects of midlatitude ocean-atmosphere feedback are still possible. The surface mixed-layer heat budget also reveals that, in the central Pacific, the effects of heat flux input and vertical mixing anomalies are comparable in amplitude while horizontal advection anomalies are roughly half that size. In the California coastal region, in contrast, where wind variability is much weaker than in the central Pacific, horizontal advection and vertical mixing effects on the mixed layer heat budget are only one-quarter the size of typical heat flux input anomalies.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil     

High-Frequency and Low-Frequency Variability in Stochastic Daily Weather Generator and Its Effect on Agricultural and Hydrologic Modelling

The high-frequency and low-frequency variabilities, which are often misreproduced by the daily weather generators, have a significant effect on modelling weather-dependent processes. Three modifications are suggested to improve the reproduction of the both variabilities in a four-variate daily weather generator Met&Roll: (i) inclusion of the annual cycle of lag-0 and lag-1 correlations among solar radiation, maximum temperature and minimum temperature, (ii) use of the 3rd order Markov chain to model precipitation occurrence, (iii) applying the monthly generator (based on a first-order autoregressive model) to fit the low-frequency variability. The tests are made to examine the effects of the three new features on (i) a stochastic structure of the synthetic series, and on (ii) outputs from CERES-Wheat crop model (crop yields) and SAC-SMA rainfall-runoff model (monthly streamflow characteristics, distribution of 5-day streamflow) fed by the synthetic weather series. The results are compared with those obtained with the observed weather series.Results: (i) The inclusion of the annual cycle of the correlations has rather ambiguous effect on the temporal structure of the weather characteristics simulated by the generator and only insignificant effect on the output from either simulation model. (ii) Increased order of the Markov chain improves modelling of precipitation occurrence series (especially long dry spells), and correspondingly improves reliability of the output from either simulation model. (iii) Conditioning the daily generator on monthly generator has the most positive effect, especially on the output from the hydrological model: Variability of the monthly streamflow characteristics and the frequency of extreme streamflows are better simulated. (iv) Of the two simulation models, the improvements related to the three modifications are more pronounced in the hydrological simulations. This may be also due to the fact that the crop growth simulations were less affected by the imperfections of the unmodified version of Met&Roll.     

Vegetation impacts soil water content patterns by shaping canopy water fluxes and soil properties

Soil water content is a key variable for biogeochemical and atmospheric coupled processes. Its small‐scale heterogeneity impacts the partitioning of precipitation (e.g., deep percolation or transpiration) by triggering threshold processes and connecting flow paths. Forest hydrologists frequently hypothesized that throughfall and stemflow patterns induce soil water content heterogeneity, yet experimental validation is limited. Here, we pursued a pattern‐oriented approach to explore the relationship between net precipitation and soil water content. Both were measured in independent high‐resolution stratified random designs on a 1‐ha temperate mixed beech forest plot in Germany. We recorded throughfall (350 locations) and stemflow (65 trees) for 16 precipitation events in 2015. Soil water content was measured continuously in topsoil and subsoil (210 profiles). Soil wetting was only weakly related to net precipitation patterns. The precipitation‐induced pattern quickly dissipates and returns to a basic pattern, which is temporally stable. Instead, soil hydraulic properties (by the proxy of field capacity) were significantly correlated with this stable soil water content pattern, indicating that soil structure more than net precipitation drives soil water content heterogeneity. Also, both field capacity and soil water content were lower in the immediate vicinity of tree stems compared to further away at all times, including winter, despite stemflow occurrence. Thus, soil structure varies systematically according to vegetation in our site. We conclude that enhanced macroporosity increases gravity‐driven flow in stem proximal areas. Therefore, although soil water content patterns are little affected by net precipitation, the resulting soil water fluxes may strongly be affected. Specifically, this may further enhance the channelling of stemflow to greater depth and beyond the rooting zone.     

Surface currents in British Columbia coastal waters: Comparison of observations and model predictions

Abstract

Observations of the motion of ocean surface drifters are used to evaluate numerical simulations of surface currents in the region of Queen Charlotte Sound on the West Coast of Canada. More than 30 surface Argos drifters were deployed in the spring and summer of 1995, revealing daily average currents of 10 to 40 cm s^–1 near the coast of Vancouver Island in summer, and less than 10 cm s^–1 in mid‐sound. Wind observations in this region are provided by a network of weather buoys. Comparison of daily average drifter velocities and winds shows that the drifters moved at 2 to 3% of the wind speed, and at about 30 degrees to the right of the wind.

A complex transfer function is computed between daily wind and drifter vectors using least squares techniques. The ratio of variance in the least squares residual currents to the variance of observed drifter currents is denoted γ². A percent goodness‐of‐fit is defined as g(γ²) = 100(1 – γ²), and is 42% for the case of daily winds and drifter currents. Drifter‐measured currents are compared with two numerical simulations of surface currents: Fundy5, a steadystate baroclinic model based on historical water property measurements in summer, and the Princeton Ocean Model (POM), a prognostic, baroclinic model forced by the measured winds. Fundy5 by itself provides a goodness‐of‐fit of only 3%, whereas POM has g(γ²) = 42%. The combination of Fundy5 plus daily wind gives g(γ²) = 43%. Although the prognostic model performs only as well as the winds by themselves, it simulates the near shore currents more accurately and reproduces the speeds and veering in the surface Ekman layer on average without bias. Residual currents unexplained by POM are likely due to advection of water masses into this region and horizontal inhomogeneities in the density field that are not input to the model, as well as to Stokes drift of wind waves and to net Lagrangian tidal motion not represented by the model.     

Expected changes in agroclimatic conditions in Central Europe

During the past few decades, the basic assumption of agroclimatic zoning, i.e., that agroclimatic conditions remain relatively stable, has been shattered by ongoing climate change. The first aim of this study was to develop a tool that would allow for effective analysis of various agroclimatic indicators and their dynamics under climate change conditions for a particular region. The results of this effort were summarized in the AgriClim software package, which provides users with a wide range of parameters essential for the evaluation of climate-related stress factors in agricultural crop production. The software was then tested over an area of 114,000 km² in Central Europe. We have found that by 2020, the combination of increased air temperature and changes in the amount and distribution of precipitation will lead to a prolonged growing season and significant shifts in the agroclimatic zones in Central Europe; in particular, the areas that are currently most productive will be reduced and replaced by warmer but drier conditions in the same time the higher elevations will most likely experience improvement in their agroclimatic conditions. This positive effect might be short-lived, as by 2050, even these areas might experience much drier conditions than observed currently. Both the rate and the scale of the shift are amazing as by 2020 (assuming upper range of the climate change projections) only 20?C38% of agriculture land in the evaluated region will remain in the same agroclimatic and by 2050 it might be less than 2%. On the other hand farmers will be able to take advantage of an earlier start to the growing season, at least in the lowland areas, as the proportion of days suitable for sowing increases. As all of these changes might occur within less than four decades, these issues could pose serious adaptation challenges for farmers and governmental policies. The presented results also suggest that the rate of change might be so rapid that the concept of static agroclimatic zoning itself might lose relevance due to perpetual change.     

FFT-based high-performance spherical harmonic transformation

Spherical harmonic transformation is of practical interest in geodesy for transformation of globally distributed quantities such as gravity between space and frequency domains. The increasing spatial resolution of the latest and forthcoming gravitational models pose true computational challenges for classical algorithms since serious numerical instabilities arise during the computation of the respective base functions of the spherical harmonic expansion. A possible solution is the evaluation of the associated Legendre functions in the Fourier domain where numerical instabilities can be circumvented by an independent frequency-wise scaling of numerical coefficients into a numerically suitable double precision range. It is then rather straightforward to commit global fast data transformation into the Fourier domain and to evaluate subsequently spherical harmonic coefficients. For the inverse, the computation of respective Fourier coefficients from a given spherical harmonic model is performed as an inverse Fast Fourier Transform into globally distributed data points. The two-step formulation turns out to be stable even for very high resolutions as well as efficient when using state-of-the-art shared memory/multi-core architectures. In principle, any functional of the geopotential can be computed in this way. To give an example for the overall performance of the algorithm, we transformed an equiangular 1 arcmin grid of terrain elevation data corresponding to spherical harmonic degree and order 10800.