Seasonal redistribution of water in the surficial Martian regolith: Results from the <Emphasis Type="Italic">Mars Odyssey</Emphasis> high-energy neutron detector (HEND)

The seasonal variation of neutron emissions from Mars in different spectral intervals measured by the HEND neutron detector for the entire Martian year are analyzed. Based on these data, the spatial variations of the neutron emissions from the planet are globally mapped as a function of season, and the dynamics of seasonal variation of neutron fluxes with different energies is analyzed in detail. No differences were found between seasonal regimes of neutron fluxes in different energy ranges in the southern hemisphere of Mars, while the regime of fast neutrons (with higher energies) during the northern winter strongly differs from that during the southern winter. In winter (L _s = 270°–330°), the fast neutron fluxes are noticeably reduced in the northern hemisphere (along with the consecutive thickening of the seasonal cap of solid carbon dioxide). This provides evidence of a temporary increase in the water content in the effective layer of neutron generation. According to the obtained estimates, the observed reduction of the flux of fast neutrons in the effective layer corresponds to an increase in the water abundance of up to 5% in the seasonal polar cap (70°–90°N), about 3% at mid-latitudes, and from 1.5 to 2% at low latitudes. The freezing out of atmospheric water at the planetary surface (at middle and high latitudes) and the hydration of salt minerals composing the Martian soil are considered as the main processes responsible for the temporary increase in the water content in the soil and upper layer of the seasonal polar cap. The meridional atmospheric transport of water vapor from the summer southern to the winter northern hemisphere within the Hadley circulation cell is a basic process that delivers water to the subsurface soil layer and ensures the observed scale of the seasonal increase in water abundance. In the summer northern hemisphere, the similar Hadley circulation cell transports mainly dry air masses to the winter southern hemisphere. The point is that the water vapor becomes saturated at lower heights during aphelion, and the bulk of the atmospheric water mass is captured in the near-equatorial cloudy belt and, thus, is only weakly transferred to the southern hemisphere. This phenomenon, known as the Clancy effect, was suggested by Clancy et al. (1996) as a basic mechanism for the explanation of the interhemispheric asymmetry of water storage in permanent polar caps. The asymmetry of seasonal meridional circulation of the Martian atmosphere seems to be another factor determining the asymmetry of the seasonal water redistribution in the “atmosphere-regolith-seasonal polar caps” system, found in the peculiarities of the seasonal regime of the neutron emission of Mars.     

Simulation of the Ion Modification Processes in the Silicate Dust of Protoplanetary Disks

The modification of crystalline olivine under irradiation with 1.43-MeV deuterons was studied experimentally. For the first time, the partial destruction of olivine in the surface (100–200 nm) layer was found at a current density of 5–10 A/cm². This effect is caused by ionization and desorption of Mg and Fe atoms at deuteron fluences (3–8 × 10¹⁶cm^–2) which are substantially below the amorphization threshold. It was suggested that the negative charge of the anion group SiO₄ ^4–is neutralized by the interaction with the deuterium ions and Frenkel pairs. The mechanism of sputtering of the crystalline olivine surfaces under irradiation with H, D, He, and Ar ions was studied using of the TRIM 98 program.     

Algorithms of automatic calibration of multi-parameter models used in operational systems of flash flood forecasting

In the second article of the serie, new tools of fast and effective automatic calibration of multi-parameter hydrological models are presented. In particular, it is shown that the basic method, the Stepwise Line Search (SLS), two its modifications (SLS-F and SLS-2L) and their combination (SLS-2LF) can be used in automated systems of operational flash flood forecasting where computational efficiency is critical due to a great number of catchments that should be calibrated. Results of implementation of the SLS-based calibration procedures for parametrization of the Sacramento Soil Moisture Accounting Model, which demonstrate their high effectiveness and efficiency, are shown.     

Subarctic catchment water storage and carbon cycling – Leading the way for future studies using integrated datasets at Pallas,Finland

Subarctic ecohydrological processes are changing rapidly, but detailed and integrated ecohydrological investigations are not as widespread as necessary. We introduce an integrated research catchment site (Pallas) for atmosphere, ecosystems, and ecohydrology studies in subarctic conditions in Finland that can be used for a new set of comparative catchment investigations. The Pallas site provides unique observational data and high-intensity field measurement datasets over long periods. The infrastructure for atmosphere- to landscape-scale research in ecosystem processes in a subarctic landscape has recently been complemented with detailed ecohydrological measurements. We identify three dominant processes in subarctic ecohydrology: (a) strong seasonality drives ecohydrological regimes, (b) limited dynamic storage causes rapid stream response to water inputs (snowmelt and intensive storms), and (c) hydrological state of the system regulates catchment-scale dissolved carbon dynamics and greenhouse (GHG) fluxes. Surface water and groundwater interactions play an important role in regulating catchment-scale carbon balances and ecosystem respiration within subarctic peatlands, particularly their spatial variability in the landscape. Based on our observations from Pallas, we highlight key research gaps in subarctic ecohydrology and propose several ways forward. We also demonstrate that the Pallas catchment meets the need for sustaining and pushing the boundaries of critical long-term integrated ecohydrological research in high-latitude environments.     

Comparative Geochemical Characteristics and Genesis of Large Polyphase Plutons in the Cores and on the Periphery of the Mongol–Okhotsk Fold Belt Magmatic Areas of Different Ages

Doklady Earth Sciences - The early Mesozoic Baga-Khentei pluton is a part of the Daurian–Khentei batholite that was formed under the impact of the Mongolian plume on the lower horizons of the...     

The First Results of Tephrochronological Study of Late Pleistocene–Holocene Volcanic Eruptions in the Zhom–Bolok River Valley (Eastern Sayan)

Doklady Earth Sciences - The first results of tephrochronological studies of Late Pleistocene–Holocene volcanic eruptions in the Zhom-Bolok River valley (Eastern Sayan) are reported. Based on...     

On the radio emission of Callisto

A model of an icy surface and interior for Callisto gives a predicted thermal radio emission in good agreement with experimental radio astronomical data. The radio brightness temperature of an icy surface will not depend on wavelength. This may be a method to test icy surface hypotheses. The brightness temperatures of other satellites with icy surfaces will be equal to 200–220°K and will not depend on wavelength.     

Recent Geodynamics of Tensile Faults

The results of the analysis of extensive data about the local anomalies of recent surface displacements in the fault zones estimated from repeated geodetic observations in seismically active and weakly seismic (platform) regions are presented. It is shown that the local, symmetric sags of the Earth’s surface in the vicinity of the faults are the predominant type of anomalies. The simultaneous recording of the vertical and horizontal displacements shows that the local subsidence is accompanied by horizontal deformations of elongation along the lines that are orthogonal to the fault’s strike. Different kinematic types of faults are considered, and it is shown that the revealed anomalies correspond to the recent activation of the local joints within the fault zones resulting in the subsidence of the Earth’s surface. Three variants of the models describing the formation of the joint-type anomalies are considered: the block model, the dislocation model, and the parametric model. The comparison of the calculated distributions of the horizontal and vertical displacements in the vicinity of the fault with the observations shows that the parametric model fits the field data best. The parametric model describes a fault as a zone with varying internal parameters in two variants: as an inhomogeneity with a reduced stiffness or as an inclusion with anomalous strain according to the terminology of John D. Eshelby. By the example of regularly shaped objects, the equivalence of both approaches is demonstrated.     

Tectonic and Geodynamic Settings of Formation of the Mesozoic Cumulative Dunite–Wehrlite–Olivine Clinopyroxenite—Gabbro Massif in Eastern Chukotka

Geotectonics - The dunite–wehrlite–clinopyroxenite–gabbro massif in Eastern Chukotka, a key object for geodynamic reconstructions of the Vel’may terrane, which represents...