Discovery of the pearl waves by Eyvind Sucksdorff

Eyvind Sucksdorff (1899–1955) was an enthusiastic scientist who was the director of Sodankylä Geophysical Observatory (SGO) from 1927 to 1945. He continued magnetic measurements, which were started in 1913 when SGO was established. Sucksdorff observed events with periodically modulated amplitude in the registration of the new La Cour quick-run magnetometers in 1932–35. He interpreted these events to be due to short-period oscillations and called them “rapid micropulsations” or “pearl necklace” due to the shape of the signal in the registration. From the “pearl necklaces” he estimated the upper bound of the oscillation to be 2–3 s. Sucksdorff did not know the accurate values of the eigenperiods of the systems (H, D and Z components of the magnetometer). Later measurements have shown that they were 2–3 s. Nowadays, the pearl pulsations discovered by Sucksdorff 70 years ago are known as a subgroup of Pc1 magnetic pulsations. Sucksdorff published his observations in 1936. He studied both the annual and diurnal distributions of the new pulsations. Comparisons of the records made in Stockholm, Copenhagen and Sodankylä revealed for the first time the global features of Pc1 pulsations. Sucksdorff did not present any explanation for the pearl pulsations he had observed. Leiv Harang from the Auroral Observatory at Tromsø, Norway, published his analysis of rapid registrations made in Tromsø in 1932–36 in the same issue of the Terrestrial Magnetism and Atmospheric Electricity. He used the name “vibrations” for his short-period oscillations.     

Reconciliation of sea-level observations in the Western North Atlantic during the last glacial cycle

A south to north gradient of increasing marine isotope substage (MIS) 5a (∼80 ka BP) sea level has been recorded across the Caribbean and surrounding region. Relative to present, MIS-5a sea levels range from −19 m to more than +3 m between Barbados, Haiti, the Bahamas, Florida, Bermuda and the US Atlantic Coast. In contrast, no gradient in sea level is observed for the last interglacial period MIS-5e (∼128–118 ka BP) at tectonically stable localities in the same region, with deposits generally lying several metres above present. We demonstrate here that these controversial observations are reconciled by taking into account the isostatic response of the Earth to glacial loading and unloading – a fundamental effect that is commonly overlooked in the interpretation of sea-level observations from different locations to define a ‘global sea-level curve’. Furthermore, the observed gradient can be used to place constraints on Earth rheology and is an important indicator of the behaviour of the North American ice sheets during the last glacial cycle.     

Reconnection driven lobe convection: Interball tail probe observations and global simulations

We present Interball Tail Probe observations from the high latitude mid-tail magnetopause which provide evidence of reconnection between the interplanetary magnetic field (IMF) and lobe field lines during a 6 h interval of stable northward and dawnward IMF on October 19, 1995. Results from a global magnetohydrodynamic simulation for this interval compare well with the Interball observations. With the simulations, we provide an extended global view of this event which gives us insight into the reconnection and convection dynamics of the magnetosphere. We find that reconnection occurs in a region of limited spatial extent near the terminator and where the IMF and the lobe field are anti-parallel. Reconnected IMF field lines drape over the dayside magnetosphere, convect along the flanks into the nightside, and enter the magnetotail through a small entry window that is located in the flank opposite to the reconnection site. Ionospheric convection is consistent with previous observations under similar IMF conditions and exhibits a two cell pattern with a dominant lobe cell over the pole. The magnetic mapping between the ionosphere and the lobe boundary is characterized by two singularities: the narrow entry window in the tail maps to a 6 h wide section of the ionospheric lobe cell. A singular mapping line cuts the lobe cell open and maps to almost the entire tail magnetopause. By this singularity the magnetosphere avoids having a stagnation point, i.e., the lobe cell center maps to a tailward convecting field line. The existence of singularities in the magnetic mapping between the ionosphere and the tail has important implications for the study of tail–ionosphere coupling via empirical magnetic field models. Because the lobe–IMF reconnection cuts away old lobe flux and replaces it with flux tubes of magnetosheath origin, solar wind plasma enters the lobes in a process that is similar to the one that operates during southward IMF.     

Numerical modeling of vibrations induced by railway traffic in tunnels: From the source to the nearby buildings

In this paper, a numerical approach for the prediction of vibrations induced in buildings due to railway traffic in tunnel is proposed. The numerical method is based on a sub-structuring approach, where the train is simulated by a multi-body model; the track–tunnel–ground system is modeled by a 2.5D FEM–PML approach; and the building by resource to a 3D FEM method. The coupling of the building to the ground is established taking into account the soil–structure-interaction (SSI). The methodology proposed allows dealing with the three-dimensional characteristics of the problem with a reasonable computational effort. Using the proposed model, a numerical study is developed in order to better discern the impact of the use of floating slabs systems for the isolation of vibrations in the tunnel on the dynamic response of a building located in the surrounding of the tunnel. The comparison between isolated and non-isolated scenarios allowed concluding that the mats stiffness is a key parameter on the efficiency of floating slab systems. Furthermore, it was found that the selection of the stiffness of the mats should be performed carefully in order to avoid amplification of vertical vibrations of the slabs of the building.     

On the dynamics and structure of Earth’s oscillations in December 2004 from seismic gravimeter observations in St. Petersburg

The paper describes phenomena of large-scale deformations, in particular, long-term deformation, observed on the planet during December 1–12, 2004, before a cycle of enhanced seismic activity. The spectrum of seismic vibrations with periods of 1 to 9 hr is calculated. A high correlation is established between the frequency distribution of significant vibrations recognizable in this spectrum and vibrations that should be excited most frequently in accordance with the statistical spectrum of the seismogravitational oscillations of the Earth.     

Prediction of ground motion due to the collapse of a large-scale cooling tower under strong earthquakes

The ground motion owing to the collapse of a large-scale cooling tower under strong earthquakes was appropriately predicted using a comprehensive approach. The predicted results can be used for the safety evaluation of nuclear-related facilities adjacent to the cooling tower as well as in the planning of nuclear power plant construction in China. In this study, a cooling tower–soil model was first developed based on a falling weight–soil model, which the authors verified by falling weight tests. Then the collapse process of a cooling tower was simulated, and the collapse-induced ground vibrations were assessed by using the proposed model. Finally, the ground motion, which was a combination of the earthquake-induced ground motion and the collapse-induced ground vibrations, was estimated based on the superposition principle of waves. It was found that the cooling tower may collapse under strong earthquakes with the peak ground accelerations (PGAs) in the range of 0.35–0.45 g in x (EW) and y (NS) directions, respectively. These PGAs are far beyond the PGA range of major earthquakes in the common seismic design in China. The types of the site geologies of towers can significantly affect the collapse-induced ground vibrations. For a typical hard soil consisting of strongly weathered sandy slate, moderate ground vibrations may occur in the considered region. The collapse-induced PGAs were in the range of 0.017–0.046 g for the observed points at distances of 350 m in radial direction. For a rock-like foundation, the collapse-induced radial PGAs may be as high as 0.08 g at distances of 350 m, indicating that the effect of the collapse-induced ground vibrations on the nuclear-related facilities should be seriously assessed in certain scenarios.     

Sea Surface Salinity Observations from Space with the SMOS Satellite: A New Means to Monitor the Marine Branch of the Water Cycle

While it is well known that the ocean is one of the most important component of the climate system, with a heat capacity 1,100 times greater than the atmosphere, the ocean is also the primary reservoir for freshwater transport to the atmosphere and largest component of the global water cycle. Two new satellite sensors, the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius SAC-D missions, are now providing the first space-borne measurements of the sea surface salinity (SSS). In this paper, we present examples demonstrating how SMOS-derived SSS data are being used to better characterize key land–ocean and atmosphere–ocean interaction processes that occur within the marine hydrological cycle. In particular, SMOS with its ocean mapping capability provides observations across the world’s largest tropical ocean fresh pool regions, and we discuss from intraseasonal to interannual precipitation impacts as well as large-scale river runoff from the Amazon–Orinoco and Congo rivers and its offshore advection. Synergistic multi-satellite analyses of these new surface salinity data sets combined with sea surface temperature, dynamical height and currents from altimetry, surface wind, ocean color, rainfall estimates, and in situ observations are shown to yield new freshwater budget insight. Finally, SSS observations from the SMOS and Aquarius/SAC-D sensors are combined to examine the response of the upper ocean to tropical cyclone passage including the potential role that a freshwater-induced upper ocean barrier layer may play in modulating surface cooling and enthalpy flux in tropical cyclone track regions.     

Seismic noise at the international gravity point in Prague-Ruzyně (Czechoslovakia)

Summary The vertical component of ground displacement was measured at the Prague - Ruzyn International Gravity Point in the frequency range of 1–300 Hz. The permanent noise, the vibrations caused by the observers during gravimetric observations and by the wind, as well as those due to normal operations at the airport, display maximum peak-to-peak amplitudes of 0.06 µm in the frequency range of 1–50 Hz; with a CG-2 gravimeter this is not detrimental to the accuracy of the observations. The taxiing of turbo-jet and jet aircraft and engine tests of aircraft generate vibrations in frequency ranges of 75–90 and 190–270 Hz. Their amplitudes, according to the results of laboratory tests published for various types of gravity meters (CG-2, GAK-PT, GVP-3, KVG), are of magnitudes which generate errors in tenths of mgl.     

Local and global shape functions in a boundary element formulation for the calculation of traffic induced vibrations

This paper compares the use of local and global shape functions in a boundary element method that is used in a prediction model for traffic induced vibrations. The boundary element formulation describes the interaction problem between a linear elastic layered half-space and a longitudinally invariant structure representing a road or a railway track. The boundary element formulation in the frequency–wavenumber domain is obtained by means of a weighted residual method. Constant element shape functions, as well as Legendre and Chebyshev shape functions are considered. Their effect on both accuracy and computational effort is investigated. The presence of a singularity in the Chebyshev based shape functions allows to obtain a better approximation for the soil tractions. The theory is applied to road traffic induced vibrations where the response is calculated in a large number of output points.     

Study of the train-induced vibration impact on a historic Bell Tower above two spatially overlapping metro lines

There is concern regarding the long-term vibration effects caused by metro trains on historic buildings. In this paper, the impact of metro train-induced vibrations on the Bell Tower in Xi’an above two spatially overlapping tunnels was studied.Metro Line 2 has been operational since 2011, and Line 6 is still under construction. To study and control the effect of micro vibrations on the Bell Tower, a metro train–track–tunnel–soil 3D dynamic FE model was developed. The vibration response generated by Line 2 was then predicted, and the influences of train speed on ground vibration were analysed. In addition, a detailed in situ measurement, which helped calibrate the numerical model and determine the dynamic behaviour of timber structures, was performed. Finally, the calibrated models and measured results were used to predict vibrations caused by road traffic and trains from two spatially overlapping metro lines. This was performed under different route schemes and train operation conditions.The results showed that installing steel spring floating slab tracks (FST) and decreasing train speeds had obvious effects on controlling the ground peak particle velocity (PPV). Simulated results from both the input impulse and output response generated by metro Line 2 matched well with actual measurements. If correct designs are employed, it is possible to resolve the vibration problem on historic buildings caused by metro trains.     

Physically Consistent Responses of the Global Atmospheric Hydrological Cycle in Models and Observations

Robust and physically understandable responses of the global atmospheric water cycle to a warming climate are presented. By considering interannual responses to changes in surface temperature (T), observations and AMIP5 simulations agree on an increase in column integrated water vapor at the rate 7 %/K (in line with the Clausius–Clapeyron equation) and of precipitation at the rate 2–3 %/K (in line with energetic constraints). Using simple and complex climate models, we demonstrate that radiative forcing by greenhouse gases is currently suppressing global precipitation (P) at ～?0.15 %/decade. Along with natural variability, this can explain why observed trends in global P over the period 1988?2008 are close to zero. Regional responses in the global water cycle are strongly constrained by changes in moisture fluxes. Model simulations show an increased moisture flux into the tropical wet region at 900 hPa and an enhanced outflow (of smaller magnitude) at around 600 hPa with warming. Moisture transport explains an increase in P in the wet tropical regions and small or negative changes in the dry regions of the subtropics in CMIP5 simulations of a warming climate. For AMIP5 simulations and satellite observations, the heaviest 5-day rainfall totals increase in intensity at ～15 %/K over the ocean with reductions at all percentiles over land. The climate change response in CMIP5 simulations shows consistent increases in P over ocean and land for the highest intensities, close to the Clausius?Clapeyron scaling of 7 %/K, while P declines for the lowest percentiles, indicating that interannual variability over land may not be a good proxy for climate change. The local changes in precipitation and its extremes are highly dependent upon small shifts in the large-scale atmospheric circulation and regional feedbacks.     

Seasonal and spatial variations of diurnal variations of the VLF pulsed flux of the natural electromagnetic field recorded in middle latitudes

A database of continuous measurements of the VLF pulsed flux of the natural electromagnetic field of the Earth (NEMFE) in southern Siberia during the period from March 31, 2008 to the present was created. Analysis of long-term continuous observations has shown that NEMFE diurnal variations have stable seasonal changes. A high interannual correlation coefficient of NEMFE diurnal variations for the same months in 2008–2014 was discovered. The analysis of data from spaced recorders has shown a high degree of spatial correlation, which indicates a single local mechanism of the NEMFE formation.     

Global distribution of energetic proton precipitations equatorward of the boundary of isotropic fluxes

Based on data of the NOAA POES satellite, the global distribution of the occurrence rate of precipitations of energetic protons (E > 30 keV) equatorward of the boundary of isotropic fluxes has been constructed for the first time. It has been shown that the occurrence rate of proton precipitations inside the zone of anisotropic fluxes is maximum in daytime hours (1100–1600 MLT) at latitudes L = 6–9 and decreases in evening and morning hours. Comparison of the obtained results about proton precipitations with the spatial distribution of the occurrence rate of electromagnetic ion–cyclotron (EMIC) waves in the equatorial magnetosphere according to results of satellite observations demonstrates a close relationship between them. This corroborates that precipitations of energetic protons equatorward of the boundary of isotropic fluxes are a consequence of the development of the ion–cyclotron instability in the equatorial magnetosphere.     

Conceptual study of lunar-based SAR for global change monitoring

As an active microwave remote sensing imaging sensor, Synthetic Aperture Radar (SAR) plays an important role in earth observation. Here we establish a SAR system based on the platform of the moon. This will aid large-scale, constant, and long-term dynamic Earth observations to better meet the needs of global change research and to complement the space borne and airborne earth observations. Lunar-based SAR systems have the characteristics of high resolution and wide swath width. The swath width could be thousands of kilometers in the stripe mode and it could cover 40% of earth’s surface with 10 meters or even higher spatial resolution in the scanning mode. Using the simplified observation model, here we quantitatively analyze the spatial resolution and coverage area of lunar-based SAR and simulate the observation on the Qinghai-Tibet plateau and the Amazon plain. The results show that this system could provide near 100% daily coverage of the Qinghai-Tibet plateau, whereas 40% to 70% daily coverage of the Amazon plain. Lunar-based SAR could provide large-scale, long-term and stable time series data in order to support future research of global change.     

Identifying induced variations in the seismic regime by the methods of nonlinear dynamics

The nonlinear analysis of the data on seismicity in the areas where the underground rocks were affected by the injection of fluids, blasting works, and vibrations shows that the technogenous impacts increase the regularity of the seismic regime. The effects of the man-made actions manifest themselves in the formation of stable states characterized by the finite fractal dimension of the attractor and the small dimension of the embedding space. In order to explain the increase in the regularity of the seismic process, we consider the model of motion in the fault zones which is described by the two-parameter friction law. The presence of the stable states paves the way for both forecasting the induced seismic activity and developing the technologies for the controlled forcing of the seismic regime.     

Time stability and variability of Electronically Scanned Thinned Array Radiometer soil moisture during Southern Great Plains hydrology experiments

Variability and time‐stability analysis for field‐scale (800 m) Electronically Scanned Thinned Array Radiometer soil moisture within a satellite scale footprint (∼ 50 km) were quantified using observations from the Southern Great Plains Hydrology Experiment 1997 and 1999 (SGP97 and SGP99). The pixels' time‐stability properties were examined with respect to soil, vegetation and topographic parameters in order to determine which physical parameters can be used to identify good candidate observation locations for validating soil moisture from satellite observations and global‐scale model output. The results show that the time‐stability concept remains valid at the satellite scale. The root mean square error values were 1·47, 1·51, 1·93 and 2·32% for the 1st, 2nd, 50th and 100th most stable fields, respectively. The most stable locations had sand and clay percentages consistent with sandy loam soils and moderate to high normalized difference vegetation index values. Neither land cover nor topography properties could be used to identify potentially stable fields in the study region. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of Weak Wind Stable Conditions from the Observations of the Land Surface Processes Experiment at Anand in India

The observations in weak wind stable conditions are scarce. The present study examines the observations from the Land Surface Processes Experiment (LASPEX) conducted at Anand, (Gujarat, India) during the year 1997–1998 to study the characteristics of surface layer under weak wind stable conditions. The observed surface fluxes are compared with those computed using Monin-Obukhov (M-O) similarity theory. The upper air observations and regional climatology are used to justify the persistence of weak wind conditions at Anand. The frequency of occurrence of weak wind stable conditions is observed to be around 67%. In 86% of the cases under weak wind conditions, bulk Richardson number (R_iB) is found to be larger than 0.2. The magnitude of surface fluxes computed from M-O similarity theory is shown to be smaller in comparison to those based on the observations in weak wind stable conditions. Surface fluxes computed using the empirical relations for the eddy diffusivities and drag and heat exchange coefficients are found to be comparable with those based on M-O similarity theory however these fluxes are under-predicted in comparison to the observations. The traditional M-O similarity theory is not able to simulate the observed fluxes well in weak wind stable conditions at Anand.     

Pc3 geomagnetic pulsations at near-equatorial latitudes at the initial phase of the magnetic storm of April 5, 2010

An analysis of sampled 1-s observational data on geomagnetic pulsations within the Pc3 range on the INTERMAGNET network of near-equatorial and low-latitude observatories spaced over longitude during the initial phase of a moderate magnetic storm (April 5–7, 2010) was carried out for the first time. The obtained results were compared with magnetic observations at the low-latitude Chambon-la-Foret (CLF) and subauroral Kerguelen (PAF) observatories, as well as with observations at six Australian observatories located at low and middle latitudes. Two time intervals were studied in detail: the sudden commencement (SC) of the storm and the onset of the great global substorm. In the first interval, maximal amplitudes of near-equatorial pulsations were observed in the near-noon sector; in the second interval, in the near-midnight sector. The dynamics of the spectral structure of Pc3 pulsations in the considered events was shown to be different in spite of the fact that in both cases an amplification of waves was observed in two close spectral bands of the Pc3 spectrum: ～20–30 and ～30–40 mHz. The considered Pc3 pulsations were characterized by very small azimuthal wavenumbers (0.5 and less). Possible generation mechanisms for the observed Pc3 pulsations are discussed.