Spatial rainfall estimation by linear and non-linear co-kriging of radar-rainfall and raingage data

The feasibility of linear and nonlinear geostatistical estimation techniques for optimal merging of rainfall data from raingage and radar observations is investigated in this study by use of controlled numerical experiments. Synthetic radar and raingage data are generated with their hypothetical error structures that explicitly account for sampling characteristics of the two sensors. Numerically simulated rainfall fields considered to be ground-truth fields on 4×4 km grids are used in the generation of radar and raingage observations. Ground-truth rainfall fields consist of generated rainfall fields with various climatic characteristics that preserve the space-time covariance function of rainfall events in extratropical cyclonic storms. Optimal mean areal precipitation estimates are obtained based on the minimum variance, unbiased property of kriging techniques under the second order homogeneity assumption of rainfall fields. The evaluation of estimated rainfall fields is done based on the refinement of spatial predictability over what would be provided from each sensor individually. Attention is mainly given to removal of measurement error and bias that are synthetically introduced to radar measurements. The influence of raingage network density on estimated rainfall fields is also examined.     

Optimizing interpolation of shoot density data from a Posidonia oceanica seagrass bed

A case study on the optimization of Posidonia oceanica density interpolation, using a data set from a large meadow at Porto Conte Bay (NW Sardinia, Italy), is presented. Ordinary point kriging, cokriging and a weighted average based on inverse square distance were used to interpolate density data measured in 36 sampling stations. The results obtained from different methods were then compared by means of a leave‐one‐out cross‐validation procedure. The scale at which interpolation was carried out was defined on the basis of the Hausdorff dimension of the variogram. Optimizing spatial scale and data points search strategy allowed obtaining more accurate density estimates independently of the interpolation method.     

Controls on knickpoint migration in a drainage network of the moderately uplifted Ardennes Plateau,Western Europe

Much research has been devoted to the development of numerical models of river incision. In settings where bedrock channel erosion prevails, numerous studies have used field data to calibrate the widely acknowledged stream power model of incision and to discuss the impact of variables that do not appear explicitly in the model's simplest form. However, most studies have been conducted in areas of active tectonics, displaying a clear geomorphic response to the tectonic signal. Here, we analyze the traces left in the drainage network 0.7 My after the Ardennes region (western Europe) underwent a moderate 100–150 m uplift. We identify a set of knickpoints that have traveled far upstream in the Ourthe catchment, following this tectonic perturbation. Using a misfit function based on time residuals, our best fit of the stream power model parameters yields m = 0.75 and K = 4.63 × 10^‐8 m^‐0.5y^‐1. Linear regression of the model time residuals against quantitative expressions of bedrock resistance to erosion shows that this variable does not correlate significantly with the residuals. By contrast, proxies for position in the drainage system prove to be able to explain 76% of the residual variance. High time residuals correlate with knickpoint position in small tributaries located in the downstream part of the Ourthe catchment, where some threshold was reached very early in the catchment's incision history. Removing the knickpoints stopped at such thresholds from the data set, we calculate an improved m = 0.68 and derive a scaling exponent of channel width against drainage area of 0.32, consistent with the average value compiled by Lague for steady state incising bedrock rivers. Copyright © 2014 John Wiley & Sons, Ltd.     

A method for constructing high-order differential boundary conditions for solving external boundary value problems in geoelectromagnetism

A general approach to the construction of differential boundary conditions for vector fields satisfying the Helmholtz equation is proposed on the basis of the field expansion in multipole series and the application of annihilating operators to them. The resulting differential constraints can be used as boundary conditions in solving external boundary value problems. Examples of their application to the solution of forward geoelectric problems in three-dimensionally inhomogeneous media are examined. Their use at a finite distance from the source of an anomaly is shown to yield more accurate results than those obtained under the assumption that the anomalous field at this distance vanishes. Another effect of their application is a substantial decrease in the dimensions of the modeling domain and therefore in the time required to solve the forward problem. The “safe” distance for using the Dirichlet-type boundary conditions is estimated.     

Pulsar reflections within the Crab Nebula

Between 1997 August and October, the radio pulses from the Crab pulsar were followed by discrete moving echoes, which appear to be reflections from part of an ionized shell in the outer part of the Crab Nebula, crossing the line of sight to pulsar. Similar events have now been recognized in recordings from the past 30 yr, and it seems that the Nebula must contain a large number of ionized shell-like surfaces on a much finer scale than recognized hitherto.     

The almost constant-speed two-body problem with resistance

The almost constant-speed motion of a mass acted upon by a Newtonian attraction and a resisting force is treated. The equation of orbit is derived for a specific type of resistance which covers the familiar case of Danby's drag(=r ^–2) whilst the vector invariants are obtained by direct operation on the vector form of the equation of motion.     

Origin of a metamorphosed lithic clast in CM chondrite Grove Mountains 021536

Abstract– A metamorphosed lithic clast was discovered in the CM chondrite Grove Mountains 021536, which was collected in the Antarctica by the Chinese Antarctic Research Exploration team. The lithic clast is composed mainly of Fe‐rich olivine (Fo₆₂) with minor diopside (Fs_9.7–11.1Wo_48.3–51.6), plagioclase (An_43–46.5), nepheline, merrillite, Al‐rich chromite (21.8 wt% Al₂O₃; 4.43 wt% TiO₂), and pentlandite. Δ¹⁷O values of olivine in the lithic clast vary from ?3.9‰ to ?0.8‰. Mineral compositions and oxygen isotopic compositions of olivine suggest that the lithic clast has an exotic source different from the CM chondrite parent body. The clast could be derived from strong thermal metamorphism of pre‐existing chondrule that has experienced low‐temperature anhydrous alteration. The lithic clast is similar in mineral assemblage and chemistry to a few clasts observed in oxidized CV3 chondrites (Mokoia and Yamato‐86009) and might have been derived from the interior of the primitive CV asteroid. The apparent lack of hydration in the lithic clast indicates that the clast accreted into the CM chondrite after hydration of the CM components.     

Solar activity in the sixteenth and seventeenth centuries (a revision)

Maximum relative sunspot numbers for the 16th and 17th century were computed by means of the dependence of the maximum relative sunspot numbers on the solar cycle rise time and on the cycle asymmetry. In these dependencies four separate modes of relations, two for odd and two for even cycles, were identified. These modes are coupled two and two in even-odd cycle pairs. The rise times and the asymmetries of solar cycles in the 16th and 17th centuries were taken from cycle extreme estimates by Schove (1979), from auroral and telescopic sunspot observations during this period, but with some necessary corrections. Annual relative sunspot numbers and decade averages were estimated from the cycle maxima and the epochs of extremes. In addition, the efficiency of auroral records in latitudes lower than 55 deg was computed for the time interval 1500–1868. For this purpose the dependence of occurrence numbers of aurorae on the cycle and decade means of the relative sunspot numbers was derived.     

Hydrologic precursors to earthquakes: A review

This review summarizes reports of anomalous flow rates or pressures of groundwater, oil, or gas that have been interpreted as earthquake precursors. Both increases and decreases of pressure and flow rate have been observed, at distances up to several hundred kilometers from the earthquake epicenter, with precursor times ranging from less than one day to more than one year. Although information that might rule out nontectonic causes does not appear in many published accounts of hydrologic anomalies, several recent studies have critically evaluated the possible influences of barometric pressure, rainfall, and groundwater or oil exploitation. Anomalies preceding the 1976 Tangshan, China, and the 1978 Izu-Oshima-Kinkai, Japan, earthquakes are especially well-documented and worthy of further examination.Among hydrologic precursors, pressure head changes in confined subsurface reservoirs are those most amenable to quantitative interpretation in terms of crustal strain. The response of pressure head to earth tides determines coefficients of proportionality between pressure head and crustal strain. The same coefficients of proportionality should govern the fluid pressure response to any crustal strain field in which fluid flow in the reservoir is unimportant. Water level changes in response to independently recorded tectonic events, such as earthquakes and aseismic fault creep, provide evidence that a calibration based on response to earth tides may be applied to crustal strains of tectonic origin.Several models of earthquake generation predict accelerating stable slip on part of the future rupture plane. If precursory slip has moment less than or equal to that of the impending earthquake, then the coseismic volume strain is an upper bound for precursory volume strain. Although crustal strain can be only crudely estimated from most reported pressure head anomalies, the sizes of many anomalies within 150 kilometers of earthquake epicenters appear consistent with this upper bound. In contrast, water level anomalies at greater epicentral distances appear to be larger than this bound by several orders of magnitude.It is clear that water level monitoring can yield information about the earthquake generation process, but progress higes on better documentation of the data.     

Geomagnetic Field Variations during the Total Solar Eclipse of 2 July 2019 in La Serena,Chile

Geomagnetism and Aeronomy - The total solar eclipse on July 2, 2019, has been studied by using data of the La Serena ground magnetic station in Chile located in the path of the totality (at...