Similar Geophysical Conditions Research Articles

Mining-Induced Damage Characteristics of Floors during Fully Mechanized Caving Mining: A Case Study

To study the mining-induced damage characteristics of floors during fully mechanized mining, in situ measurements were performed using the hollow inclusion strain sensors in the No. 100502 (80 m, 180 m) mining face of the Yitang Coal Mine in the Huoxi coal field in the Shanxi Province of China. The in situ measurement results show that the failure depths of the floor rocks in the 100502 (80 m) and 100502 (180 m) mining faces were 12.50∼14.65 m and 17.50∼19.20 m, respectively. The longer the mining face was, the greater the failure depth and the more severe the deformation and damage of the floor rocks were. The failures of the damaged floor rocks can be divided into two types: pull-pressure strain mutations and abnormal mutations. With the advancement of the mining face, the strain increments of floor rocks at different buried depths showed obvious advanced and lagged responses. Specifically, the advanced response distance decreased with a negative exponential trend, while the lagged response distance generally first increased and then decreased as the depth increased. The results can not only provide important guidance to coal mining under water pressure, but also offer a key theoretical reference for failure depth control of floor rocks under similar geophysical conditions.

Statistical evaluation of GLONASS amplitude scintillation over low latitudes in the Brazilian territory

The ionospheric scintillation, generated by the ionospheric plasma irregularities, affects the radio signals that pass through it. Their effects are widely studied in the literature with two different approaches. The first one deals with the use of radio signals to study and understand the morphology of this phenomenon, while the second one seeks to understand and model how much this phenomenon interferes in the radio signals and consequently in the services to which these systems work. The interest of several areas, particularly to those that are life critical, has increased using the concept of satellite multi-constellation, which consists of receiving, processing and using data from different navigation and positioning systems. Although there is a vast literature analyzing the effects of ionospheric scintillation on satellite navigation systems, the number of studies using signals received from the Russian satellite positioning system (named GLONASS) is still very rare. This work presents for the first time in the Brazilian low-latitude sector a statistical analysis of ionospheric scintillation data for all levels of magnetic activities obtained by a set of scintillation monitors that receive signals from the GLONASS system. In this study, data collected from four stations were used in the analysis; Fortaleza, Presidente Prudente, São José dos Campos and Porto Alegre. The GLONASS L-band signals were analyzed for the period from December 21, 2012 to June 20, 2016, which includes the peak of the solar cycle 24 that occurred in 2014. The main characteristics of scintillation presented in this study include: (1) the statistical evaluation of seasonal and solar activity, showing the chances that an user on similar geophysical conditions may be susceptible to the effects of ionospheric scintillation; (2) a temporal analysis based on the local time distribution of scintillation at different seasons and intensity levels; and (3) the evaluation of number of simultaneously affected channels and its effects on the dilution of precision (DOP) for GNSS users are also presented in order to alert the timetables in which navigation will be most susceptible to such effects, as well as statistics on simultaneously affected channels. Relevant results about these statistical characteristics of scintillation are presented and analyzed providing relevant information about availability of a navigation system.

Solution uniquity of an inverse VLF problem: A case-study of the polar, ground-based, VLF radio signal disturbances caused by the ultra-energetic relativistic electron precipitations and of their southern boundaries

Here we present the results of a case study of the rare, abnormal, qualitatively specific behavior of Aldra (northern Norway) and GBR (UK) VLF transmitter signals (10–16kHz) received at Kola Peninsula. The abnormal amplitude and the phase disturbances of signals were used as a proxy for ultra-energetic relativistic (solar?) electron precipitation (URE, ∼100MeV) into the middle polar atmosphere. The disturbances have been observed under quiet or moderately disturbed geomagnetic activity. Based on bearing results, it was established that the abnormal variations of the electric conductivity of ionized middle atmosphere (of a sporadic Ds layer under the regular ionosphere D layer) were characterized by the following: (i) the time function of height h(t) of an effective spherical waveguide between the Earth surface and the sporadic Ds layer shows a minimum value equal to ∼30km and (ii) the reflection coefficient R(t) of radio wave with a grazing angle of incidence from a virtual boundary with height h(t) has a minimum value equal to ∼0.4. The southern boundaries of the ultra-energetic relativistic electron precipitations have been found as well. They turned out to be not southerly than 61 degree of magnetic latitude and similar to the ones obtained in our previous study of the events for other dates under the similar geophysical conditions although we do not know anything definite about the rigidity and density of the electron fluxes.A used calculation method of analysis is based on a necessary condition that a number n of input data should be greater than a number m of output parameter-functions. We have stated by numerical testing that a decrease of n from 6 to 4 generates a lack of uniqueness of an inverse VLF problem solution for m=2. It is important for future VLF ground-based monitoring of the URE precipitation events.

Vitamin D status during pregnancy: time for a more unified approach beyond borders?

Maternal hypovitaminosis D during pregnancy has been associated with a plethora of adverse health effects on the offspring. Maternal vitamin D status during pregnancy is affected by local climatic conditions. The aim of this article was to report on difficulties related to the heterogeneity of studies available in current literature on vitamin D status during pregnancy and discuss the incorporation of geophysical data in future studies, in an attempt to optimize their design and facilitate their interpretation. We focused on current vitamin D trials during pregnancy and their association with local regional climatic condition in geographical regions such as the Mediterranean basin based on our perspective on the field. Conduction of studies from areas with similar geophysical conditions is necessary, in order to extend our knowledge with respect to the question of which populations and under which circumstances would benefit most from vitamin D supplementation. Future vitamin D studies could benefit from the adoption of a unified concept minimizing these variations by selecting populations residing in areas with similar geophysical conditions adjusting also for their social and dietary habits.

Remote‐sensing measurements in the polar vortex: Comparison to in situ observations and implications for the simultaneous retrievals and analysis of the NO2 and OClO species

Nighttime remote‐sensing balloon observations conducted by the SALOMON instrument in the arctic polar vortex in January 2006 reveal high amounts of stratospheric NO2 in the lower stratosphere similarly to previously published profiles. NO2 concentration enhancements are also present in the vertical profiles observed by the GOMOS instrument on board the Envisat satellite and obtained coincidently to the balloon measurements. Such quantities are not present in in situ observations obtained by the SPIRALE instrument in similar geophysical conditions. While OClO amounts are acceptably reproduced by Chemistry Transport Model (CTM) calculations, NO2 simulated values are well below the observed quantities. The examination of the slant column densities of NO2 obtained at float altitude highlights unexpected strong enhancements with respect to the elevation angle and displacement of the balloon. It is shown that these fluctuations result from NO2 spatial inhomogeneities located above the balloon float altitude. Potential vorticity maps reveal the presence of midlatitude NO2‐rich air in the upper stratosphere or lower mesosphere as a result of the perturbed dynamical situation of the vortex. The presence of spatial inhomogeneities crossed by the lines of sight leads to artificial high concentration values of NO2 in the vertical profile retrieved from the slant column densities assuming spatial homogeneity. A direct implication is that the differences previously observed between measurements of NO2 and OClO and model results are probably mostly due to the improper inversion of NO2 in the presence of perturbed dynamical conditions or when mesospheric NOx production events occur. The dynamical situation will have to be systematically analyzed in future studies involving remote‐sensing observations.

The dayside high-latitude trough under quiet geomagnetic conditions: Radio tomography and the CTIP model

Abstract. The dayside high-latitude trough is a persistent feature of the post-noon wintertime auroral ionosphere. Radio tomography observations have been used to map its location and latitudinal structure under quiet geomagnetic conditions (Kp≤2) near winter solstice. The trough is also a clear feature in the ion density distribution of the Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP) under similar geophysical conditions. Comparisons of the measured and modelled distributions show that the plasma production equatorward of the trough is mainly controlled by solar radiation, but there are also other processes maintaining the equatorward trough-wall that are open to debate. The poleward trough-wall is produced by particle precipitation, but the densities are significantly overestimated by the model. At the trough minimum the observed densities are consistent with low nighttime densities convecting sunward to displace the higher daytime densities, but this is not borne out by the CTIP model. The study shows the potential of combining radio tomography and modelling to interpret the balance of the physical processes responsible for large-scale structuring of the high-latitude ionosphere, and highlights the role of tomographic imaging in validating and developing physical models.

Incoherent scatter radar observations of the F-region ionosphere at Arecibo during January 1993

Abstract We report incoherent scatter radar observation of the F-region ion drift, plasma density, and electron and ion temperatures during the January 1993 World Day 10-day campaign. Although the observed ion drift during the geomagnetically quiet period agrees with previous observation in the horizontal direction to a large extent for similar geophysical conditions, the vertical ion drift shows a very large downward component throughout the entire day, which averages at about 20m s −1 near the F-region peak. Such a large average downward plasma drift has not been reported before at low latitudes. The downward motion of the F-region plasma comes mainly from the component along the geomagnetic field line, which is chiefly controlled by the meridional wind during the day and ambipolar diffusion during the night. The E × B drift also contributes to the downward motion of the F-region plasma during the nighttime although it is in anti-correlation with the variation introduced by the ion motion along the field line. During the geomagnetically disturbed period on 25 January, the ion drifts showed large departure from the quiet period. The perturbed eastward ion drift was highly correlated with that along the magnetic field, which may be indicative of the presence of field-aligned current. Our observation shows that the daytime electron concentration and electron temperature have contrasting correlations at different altitude ranges in the F-region. They are positively correlated below 180 km, anti-correlated between 220–400 km, not well correlated between 440–620 km, and again positively correlated at 660 km. While the positive correlation at 220–400 km has been observed previously and is well understood, the positive correlations below 180 km and at 660 km are less known and have not been systematically studied. Using the electron energy balance equation, we show that the contrasting relationships between electron concentration and electron temperature depend on the ion composition at lower altitudes; and on how electron heating via photoionization compares with thermal conduction at higher altitudes. Our observation shows that plasma motion, electron concentration and the thermal characteristics of the F-region ionosphere are all interrelated. We also present the day-to-day variability of plasma drift, electron and ion temperatures as well as electron concentration.

Auroral ionospheric and thermospheric measurements using the incoherent scatter technique

The incoherent scatter technique has been applied since 1965 to study the ionosphere and thermosphere in different regions of the Earth. The analysis of the received signal gives access to several ionospheric parameters as a function of height: electron density, electron and ion temperatures and ion velocity. The derivation of these parameters is usually a complicated mathematical procedure that requires a non-linear regression program. A lot of research has been done in the ionospheric and atmospheric science using this technique. In this paper we describe how one derives the ion-neutral collision frequency and the ion composition parameters. It is usually difficult to retrieve these parameters with the incoherent scatter technique; as a result, in the standard data analysis procedure, an ionospheric model is used instead. However the numerical values chosen in the model have an influence on the other derived parameters. For instance the choice of a wrong ion composition leads to erroneous plasma temperatures. It is therefore important to assess by how much the standard procedure deviates from reality. For this reason we compare the ion composition and collision frequency retrieved from a sophisticated analysis scheme with the values that are derived from models under similar geophysical conditions. It also possible to derive from the observed ionospheric parameters the neutral concentrations, temperatures and winds, by using the energy and momentum equations for the ions and the neutrals. In this paper the different methods and the corresponding assumptions involved in the data analysis are discussed. We describe the influence of the frictional heating, of the vertical neutral wind and of the ionospheric perturbations on the derivation of the neutral atmospheric parameters. Our discussion of the processes involved are drawn from results obtained by Chatanika, Sondrestrom and EISCAT radars.

Observations of upper atmospheric weather during solar minimum winter

We report on a wide variety of thermospheric and ionospheric observations from three consecutive January World Day campaign periods. Despite remarkably similar geophysical conditions characterizing the in situ forcing of the upper atmosphere during these solar minimum campaigns, we find significant variability in the observations of the ionosphere and thermosphere particularly at low latitudes in the American sector. In addition, we present further observational evidence of the unexpected exospheric temperature suppression at low latitudes initially reported by Hagan and Salah (1988). We discuss the lower and upper atmospheric coupling mechanisms of plausible importance to the interpretation of the observed thermospheric weather patterns. We report evidence that lower thermospheric [NO] (nitric oxide number density) and upward propagating atmospheric tides affected the thermospheric energy and momentum budgets during the campaign periods.

Comparison of absolute photoelectron fluxes measured on AE-C and AE-E with theoretical fluxes and predicted and measured N 2 2PG 3371Å volume emission rates

As part of the continuing effort to improve the accuracy of the absolute measurements of the ambient photoelectron flux in the thermosphere from the Atmosphere Explorer Satellite Photoelectron Spectrometer experiments (PES), we present a detailed comparison of experimental photoelectron fluxes from AE-C and AE-E together with theoretical calculations of the ambient flux for the same geophysical conditions. As an additional check, the various experimental and theoretical fluxes are used to calculate the expected N 2 2PG (0, 0) volume emission rate expected at 3371Å and these results are compared to AE-C Visible Airglow Experimental (VAE) experimental results. The comparisons clearly show that because of spacecraft shielding of the sensor on AE-C, the agreement with AE-E spectra for similar geophysical conditions ranges from good when shielding is minimal to poor for severe shielding cases. The calculated fluxes are lower by approx. a factor of 1.5–2.0 in absolute magnitude than the AE-E or unshielded AE-C fluxes. The N 2 2PG volume emission rates calculated from the measured ambient electron fluxes overestimate the measured VAE volume emission rates by 20–30% while those calculated from the theoretical fluxes underestimate the measured emission rate by typically 30%. These data suggest therefore that the measured AE-E fluxes are 20–30% high.

The linkage between some climatic features of the antarctic and the external gravity field of the earth

Abstract It is suggested that the low‐pressure region around Antarctica is associated with a field of negative gravity anomalies. Similar geophysical conditions have been found to prevail in the Greenland region in the Northern Hemisphere, where a thick ice sheet has formed. It is therefore concluded that present geophysical factors are sufficient to explain the paleoclimate of Antarctica and that the Antarctic and Greenland ice sheets could have been formed under atmospheric circulation and climatic conditions similar to those now prevailing on earth.

Synoptic study of the attenuation coefficients for the cosmic-ray neutron monitors of the IGY network from 1957 to 1965

The solar-cycle variation of the attenuation coefficient of the intensity recorded by the IGY neutron monitors is synoptically studied by regression analysis on daily data of 21 stations using 3-month periods from 1957 to 1965. A combined technique of reducing and filtering the data is applied before performing the least-square analysis, in order to minimize the influence of primary and instrumental changes and to work towards optimal estimates. Values suitable for appropriate correction of the station data for pressure changes are generally found over the whole range of latitudes, altitudes and times. However, a quantitative estimate of the typical peak-to-peak amplitude of the solar-cycle change is reached only at high latitudes near sea level, where data from several stations under similar geophysical conditions are available and the effect is the largest. Here an average variation of about 4 percent is obtained, in agreement with an independent estimate of the effect.