Satellite Altimetry-Based Sea Level at Global and Regional Scales

Since the beginning of the 1990s, sea level is routinely measured using high-precision satellite altimetry. Over the past ~25 years, several groups worldwide involved in processing the satellite altimetry data regularly provide updates of sea level time series at global and regional scales. Here we present an ongoing effort supported by the European Space Agency (ESA) Climate Change Initiative Programme for improving the altimetry-based sea level products. Two main objectives characterize this enterprise: (1) to make use of ESA missions (ERS-1 and 2 and Envisat) in addition to the so-called ‘reference’ missions like TOPEX/Poseidon and the Jason series in the computation of the sea level time series, and (2) to improve all processing steps in order to meet the Global Climate Observing System (GCOS) accuracy requirements defined for a set of 50 Essential Climate Variables, sea level being one of them. We show that improved geophysical corrections, dedicated processing algorithms, reduction of instrumental bias and drifts, and careful linkage between missions led to improved sea level products. Regarding the long-term trend, the new global mean sea level record accuracy now approaches the GCOS requirements (of ~0.3 mm/year). Regional trend uncertainty has been reduced by a factor of ~2, but orbital and wet tropospheric corrections errors still prevent fully reaching the GCOS accuracy requirement. Similarly at the interannual time scale, the global mean sea level still displays 2–4 mm errors that are not yet fully understood. The recent launch of new altimetry missions (Sentinel-3, Jason-3) and the inclusion of data from currently flying missions (e.g., CryoSat, SARAL/AltiKa) may provide further improvements to this important climate record.     

Integrated Geophysical Studies in the East-Indian Geothermal Province

Integrated geophysical surveys using vertical electrical sounding (VES), very low frequency (VLF) EM, radiation counting, total magnetic field and self-potential (SP) measurements are carried out to characterize the geothermal area around a hot spring in the Nayagarh district, Orissa, India that lies in the East Indian geothermal province. The study was performed to delineate the fracture pattern, contaminated groundwater movement and possible heating source. VES interpretations suggest a three- to four-layer structure in the area. Resistivity survey near the hot spring suggests that weathered and fractured formations constitute the main aquifer system and extend to 60 m depth. Current flow measured at various electrode separations normalized by the applied voltage suggests that fractures extend to a greater depth. Detailed VLF study shows that fractures extend beyond 70 m depth. VLF anomaly has also very good correlation with the total magnetic field measured along the same profiles. Study results suggest that a gridded pattern of VLF survey could map the underground conductive fracture zones that can identify the movement of contaminated groundwater flow. Therefore, precautionary measures can be taken to check further contamination by delineating subsurface conducting structures. Self potential (SP) measured over the hot spring does not show a large anomaly in favor of the presence of a sulphide mineral body. A small positive (5–15mV) SP anomaly is measured which may be streaming potential due to subsurface fluid flow. A high radiation is measured about four kilometers from the hot spring, suggesting possible radiogenic heating. However, the exact nature of the heating source and its depth is not known in the area. Deep resistivity followed by a magneto-telluric survey could reveal the deeper structures.     

Iterative Spherical Downward Continuation Applied to Magnetic and Gravitational Data from Satellite

In the last few decades, satellites have acquired various potential data sets hundreds of kilometers above the Earth’s surface. Conventionally, these global magnetic and gravitational data sets are approximated by using spherical harmonics that allow straightforward work with both fields outside the Earth’s mass. In this article, we present an alternative approach for working with potential data in mass-free space given over a regular coordinate grid on a spherical surface. The algorithm is based on an iterative scheme and the Poisson integral equation for the sphere. With help from the Fourier transform, global potential (magnetic or gravitational) data can efficiently be continued from a mean orbital sphere down to a reference surface without using the spherical harmonics. This is illustrated both with simulated magnetic field data and with real data from the satellite gradiometry mission GOCE. In the case of simulated magnetic data and the downward continuation for 450 km, we have achieved a root mean square at the level of 0.05 nT, while it was <1 E (eotvos) for real GOCE data continued for 250 km. The crucial point is to apply the algorithm twice as a large part of noise can be removed from the input data.     

Geophysical and Hydrologic Studies of Lake Seepage Variability

Variations in lake seepage were studied along a 130 m shoreline of Mirror Lake NH. Seepage was downward from the lake to groundwater; rates measured from 28 seepage meters varied from 0 to ?282 cm/d. Causes of this variation were investigated using electrical resistivity surveys and lakebed sediment characterization. Two‐dimensional (2D) resistivity surveys showed a transition in lakebed sediments from outwash to till that correlated with high‐ and low‐seepage zones, respectively. However, the 2D survey was not able to predict smaller scale variations within these facies. In the outwash, fast seepage was associated with permeability variations in a thin (2 cm) layer of sediments at the top of the lakebed. In the till, where seepage was slower than that in the outwash, a three‐dimensional resistivity survey mapped a point of high seepage associated with heterogeneity (lower resistivity and likely higher permeability). Points of focused flow across the sediment–water interface are difficult to detect and can transmit a large percentage of total exchange. Using a series of electrical resistivity geophysical methods in combination with hydrologic data to locate heterogeneities that affect seepage rates can help guide seepage meter placement. Improving our understanding of the causes and types of heterogeneity in lake seepage will provide better data for lake budgets and prediction of mass transfer of solutes or contaminants between lakes and groundwater.     

天然气水合物的海洋地球物理研究进展

赋存于大陆边缘的天然气水合物是20世纪后期海洋地球物理的一个重要研究对象。本文从地震，测井，地热，岩石物性4个方面阐述天然气水合物的海洋地球物理研究现状，并展望其发展前景。     

Spherical Harmonic Analysis of Gravitational Curvatures and Its Implications for Future Satellite Missions

In this study we assume that a gravitational curvature tensor, i.e. a tensor of third-order directional derivatives of the Earth’s gravitational potential, is observable at satellite altitudes. Such a tensor is composed of ten different components, i.e. gravitational curvatures, which may be combined into vertical–vertical–vertical, vertical–vertical–horizontal, vertical–horizontal–horizontal and horizontal–horizontal-horizontal gravitational curvatures. Firstly, we study spectral properties of the gravitational curvatures. Secondly, we derive new quadrature formulas for the spherical harmonic analysis of the four gravitational curvatures and provide their corresponding analytical error models. Thirdly, requirements for an instrument that would eventually observe gravitational curvatures by differential accelerometry are investigated. The results reveal that measuring third-order directional derivatives of the gravitational potential imposes very high requirements on the accuracy of deployed accelerometers which are beyond the limits of currently available sensors. For example, for orbital parameters and performance similar to those of the GOCE mission, observing third-order directional derivatives requires accelerometers with the noise level of \({\sim}10^{-17}\,\hbox {m}\,\hbox {s}^{-2}\) Hz\(^{-1/2}\).     

Observations of a Unique Cusp Signature at Low and Mid Altitudes

Observations of a unique cusp feature at low and mid altitudes are reported. This feature has a consistent double-peaked or “V”-shaped structure at the equatorward edge of high-latitude particle precipitation flux, and is predominantly present for high IMF B_y conditions. The observations are consistent with the Crooker (‘A split separator line merging model of the dayside magnetopause’, J. Geophys. Res. 90 (1985) 12104, ‘Mapping the merging potential from the magnetopause to the ionosphere through the dayside cusp’, J. Geophys. Res. (1988) 93 7338.) antiparallel merging model, which predicts a narrow wedge-shaped cusp whose geometry depends greatly on the dawn/dusk component of the IMF. Various observations are presented at low altitudes (DE-2, Astrid-2, Munin, UARS, DMSP) and at mid altitudes (DE-1, Cluster) that suggest a highly coherent cusp feature that is consistent with the narrow, wedge-shaped cusp of Crooker (1988), and contains persistent wave signatures that are compatible with previously reported high-altitude measurements. A statistical survey of Astrid-2 and DMSP satellite data is also presented, which shows this feature to be persistent and dependent on the IMF angle at the magnetopause, as expected. Thus, the cusp signatures observed at a wide range of altitudes present a coherent picture that may be interpreted in terms of a footprint of the magnetopause current layer.     

高海拔地区颈动脉体瘤患者的CT能谱成像研究

目的：探讨CT能谱成像对颈动脉体瘤（CBT）的研究价值。方法：收集30例接受CT能谱检查并经手术确诊的CBT患者,通过GSI Viewer重建60 keV和40 keV单能量图像,对40 keV、60 keV单能量图像及120 kVp like三组图像的CBT供血动脉CT值、背景噪声（SD）、对比噪声比（CNR）、信噪比（SNR）及主观评分进行统计分析,分析CBT能谱参数及影像特征与手术结果的关系。结果：CBT动脉期及静脉期能谱参数与手术结果均无相关性;CBT横径、纵径、Shamblin分型与术中出血量呈强相关,供血动脉数量与术中出血量呈中度相关;横径、纵径、Shamblin分型与颅神经损伤呈中度相关,供血动脉数量与颅神经损伤呈强相关;40 keV是CBT供血动脉显示的最佳能级,CT值、SD、CNR及SNR均显著高于60 keV组及120 kVp like组,60 keV组CT值、噪声显著高于120 kVp like组,二者CNR及SNR差异无统计学意义;40 keV组主观评价分值最高,两位放射科医师主观评分一致性良好。结论：(1) CBT动脉期及静脉期能谱参数与GAPP评分无相关性;...     

Photochemistry of Ions at D-region Altitudes of the Ionosphere: A Review

The current state of knowledge of the D-region ion photochemistry is reviewed. Equations determining production rates of electrons and positive ions by photoionization of atmospheric neutral species are presented and briefly discussed. Considerable attention is given to the progress in the chemistry of O⁺(⁴S), O⁺(²D), O⁺(²P), N⁺, N₂ ⁺, O₂ ⁺, NO⁺, N₄ ⁺, O₄ ⁺, NO⁺(N₂), NO⁺(CO₂), NO⁺(CO₂)₂, NO⁺(H₂O) _n for n = 1–3, NO⁺(H₂O)(N₂), NO⁺(H₂O)₂(N₂), NO⁺(H₂O)(CO₂), NO⁺(H₂O)₂(CO₂), O₂ ⁺(H₂O), H₃O⁺(OH), H⁺(H₂O) _n for n = 1–8, O^?, O₂ ^?, O₃ ^?, O₄ ^?, OH^?, CO₃ ^?, CO₄ ^?, NO₂ ^?, NO₃ ^?, ONOO^?, Cl^?, Cl^?(H₂O), Cl^?(CO₂), HCO₃ ^?, CO₃ ^?(H₂O), CO₃ ^?(H₂O)₂, NO₃ ^?(H₂O), NO₃ ^?(H₂O)₂, OH^?(H₂O), and OH^?(H₂O)₂ ions. The analysis of the D-region rocket ion mass spectrometer measurements shows that, among these ions, O₂ ⁺, NO⁺, NO⁺(H₂O), and H⁺(H₂O) _n for n = 1–7 can make the main contribution to the total positive ion number density, and O^?, O₂ ^?, Cl^?, OH^?(H₂O), CO₃ ^?, HCO₃ ^?, NO₃ ^?, ONOO^?, CO₄ ^?, NO₃ ^?(H₂O), NO₃ ^?(H₂O)₂, and ³⁵Cl^?(CO₂) ions can be responsible for the main contribution to the total negative ion number density. Photodetachment of electrons from O^?, Cl^?, O₂ ^?, O₃ ^?, OH^?, NO₂ ^?, and NO₃ ^?, dissociative electron photodetachment of O₄ ^? and OH^?(H₂O), and photodissociation of O₃ ^?, O₄ ^?, CO₃ ^?, CO₄ ^?, ONOO^?, HCO₃ ^?, CO₃ ^?(H₂O), NO₃ ^?(H₂O), O₂ ⁺(H₂O), O₄ ⁺, N₄ ⁺, NO⁺(H₂O), NO⁺(H₂O)₂, H⁺(H₂O) _n for n = 2–4, NO⁺(N₂), and NO⁺(CO₂) are studied, and the photodetachment and photodissociation rate coefficients are calculated using the current state of knowledge on the cross sections of these processes and fluxes of solar radiation.     

Ion Chemistry of the Ionosphere at E- and F-Region Altitudes: A Review

The current state of knowledge of E- and F-region ion chemistry is reviewed. Considerable attention is given to the progress in the chemistry of unexcited N₂ ⁺, O₂ ⁺, NO⁺, O⁺(⁴S), N⁺, H⁺, He⁺, Fe⁺, Mg⁺, Na⁺, Ca⁺, and K⁺ ions and electronically excited O⁺(²D), O⁺(²P), O⁺(⁴P), and $ {\text{O}}^{ + } (^{2} {\text{P}}^{*} ) $ ions. Achievements in our understanding of the role of vibrationally excited N₂ ⁺, O₂ ⁺, and NO⁺ ions in the ionosphere are discussed.     

Possible Contribution of the Gravitational Influence of Jupiter and Saturn to the 60-Year Variation in Global Temperature

Geomagnetism and Aeronomy - The possible relationship between the 60-year variation in global temperature with an amplitude of 0.35°C and the corresponding cycle at the location of Jupiter and...     

Global Health Studies Based on Local Realities

A major new programme launched by the US Bureau of Educational and Cultural Affairs and the Council forInternational Exchange of Scholars will examine the "Challenges of Health in a Borderless World". The Fulbright New Century Scholars (NCS)Program is intended to build on the strengths of the traditional Fulbright ScholarProgram, which sponsors individual researchers to spend some time working in a country other than their own. The new programme aims to extend the idea of individual exchange, to provide a forum for international, interdiscipli-nary collaboration among groups of researchers.In choosing health as the subject for the first such collaboration, the Program recognises the key significance of the topic to developed and developing countries alike, as well as theneed for a coordinated global response to many of the health problems facing the world today.     

On Creating Global Gridded Terrestrial Water Budget Estimates from Satellite Remote Sensing

The increasing availability and reliability of satellite remote sensing products [e.g., precipitation (P), evapotranspiration (ET), and the total water storage change (TWSC)] make it feasible to estimate the global terrestrial water budget at fine spatial resolution. In this study, we start from a reference water budget dataset that combines all available data sources, including satellite remote sensing, land surface model (LSM) and reanalysis, and investigate the roles of different non-satellite remote sensing products in closing the terrestrial water budget through a sensitivity analysis by removing/replacing one or more categories of products during the budget estimation. We also study the differences made by various satellite products for the same budget variable. We find that the gradual removal of non-satellite data sources will generally worsen the closure errors in the budget estimates, and remote sensing retrievals of P, ET, and TWSC together with runoff (R) from LSM give the worst closure errors. The gauge-corrected satellite precipitation helps to improve the budget closure (4.2–9 % non-closure errors of annual mean precipitation) against using the non-gauge-corrected precipitation (7.6–10.4 % non-closure errors). At last, a data assimilation technique, the constrained Kalman filter, is applied to enforce the water balance, and it is found that the satellite remote sensing products, though with worst closure, yield comparable budget estimates in the constrained system to the reference data. Overall, this study provides a first comparison between the water budget closure using the satellite remote sensing products and a full combination of remote sensing, LSM, and reanalysis products on a quasi-global basis. This study showcases the capability and potential of the satellite remote sensing in closing the terrestrial water budget at fine spatial resolution if properly constrained.     

The lidar ratio derived from sun-photometer measurements at Belsk Geophysical Observatory

The lidar ratios at 500 and 1020 nm were derived from POM 01L sun-sky scanning photometer measurements taken at Belsk Geophysical Observatory (long. 20°47′, lat. 51°50′) in the period from 2002 to 2006. The most frequently occurring lidar ratio values for the study period are 50 sr and 30 sr at 500 nm and 1020 nm, respectively. Calculations of lidar ratios for summer and winter seasons have been made as well. Back trajectory analysis was also performed to final aerosol source of origin.     

Influence of Atmospheric Solar Radiation Absorption on Photodestruction of Ions at D-Region Altitudes of the Ionosphere

The influence of atmospheric solar radiation absorption on the photodetachment, dissociative photodetachment, and photodissociation rate coefficients (photodestruction rate coefficients) of O^?, Cl^?, O₂ ^?, O₃ ^?, OH^?, NO₂ ^?, NO₃ ^?, O₄ ^?, OH^?(H₂O), CO₃ ^?, CO₄ ^?, ONOO^?, HCO₃ ^?, CO₃ ^?(H₂O), NO₃ ^?(H₂O), O₂ ⁺(H₂O), O₄ ⁺, N₄ ⁺, NO⁺(H₂O), NO⁺(H₂O)₂, H⁺(H₂O) _n for n = 2–4, NO⁺(N₂), and NO⁺(CO₂) at D-region altitudes of the ionosphere is studied. A numerical one-dimensional time-dependent neutral atmospheric composition model has been developed to estimate this influence. The model simulations are carried out for the geomagnetically quiet time period of 15 October 1998 at moderate solar activity over the Boulder ozonesonde. If the solar zenith angle is not more than 90° then the strongest influence of atmospheric solar radiation absorption on photodestruction of ions is found for photodissociation of CO₄ ^? ions when CO₃ ^? ions are formed. It follows from the calculations that decreases in the photodestruction rate coefficients of ions under consideration caused by this influence are less than 2 % at 70 km altitude and above this altitude if the solar zenith angle does not exceed 90°.     

Geophysical imaging of a kaolinite deposit at Sylvan,Manitoba, Canada

A geophysical survey was performed at Sylvan, Manitoba, Canada (51°5′N, 97°22′W) to investigate a Lower Cretaceous kaolinite deposit. The deposit consists of zones of kaolinite, silica sand, and lignitic clay located in a series of channels formed during karsting of the underlying Palaeozoic bedrock and is covered by 3 to 5 m of glacial drift. The aim of the study was to identify cost-efficient electrical and electromagnetic (EM) geophysical methods for locating, mapping, and assessing this target. Methods applied included terrain conductivity (EM31), VLF-EM, time-domain electromagnetics (TEM), DC-resistivity, and shallow seismic refraction. The survey showed that EM methods offer a viable alternative to more expensive seismic reflection surveys in the investigation of small industrial mineral deposits. Comparison of the geophysical survey results with those of a drilling program indicated that VLF-EM and TEM were the best methods for delineating the kaolinite deposit. VLF-EM was the most cost-efficient method for delineating the kaolinite deposit over a ca. 10 ha area and for exploring for further deposits within several kilometers of the main site. Joint interpretation of the in-phase and quadrature response is required for increased reliability in identifying the major kaolinite-filled channels. The TEM method provided more detailed resolution of the deposit than VLF-EM and was the optimal method for assessing its thickness. However, TEM data acquisition is too slow and inefficient for reconnaissance mapping of 10 ha sites. EM31 surveying is useful for defining the palaeokarst surface and overburden thickness in areas surrounding the deposit but cannot be used reliably for mapping the kaolinite deposit itself. The combined geophysical survey results show the kaolinite deposit at Sylvan to be located in a channel which is 100 m wide and about 25 m deep. The deposit has a bulk electrical conductivity between 13 mS m⁻¹ and 25 mS m⁻¹ consistent with low cation exchange capacity values measured for the kaolinite. The palaeokarst surface surrounding the deposit contains a series of sinuous, discontinuous, depressions with a depth variations of several meters.     

Geophysical Signatures of Microbial Activity at Hydrocarbon Contaminated Sites: A Review

Microorganisms participate in a variety of geologic processes that alter the chemical and physical properties of their environment. Understanding the geophysical signatures of microbial activity in the environment has resulted in the development of a new sub-discipline in geophysics called “biogeophysics”. This review focuses primarily on literature pertaining to biogeophysical signatures of sites contaminated by light non-aqueous phase liquids (LNAPL), as these sites provide ideal laboratories for investigating microbial-geophysical relationships. We discuss the spatial distribution and partitioning of LNAPL into different phases because the physical, chemical, and biological alteration of LNAPL and the subsequent impact to the contaminated environment is in large part due to its distribution. We examine the geophysical responses at contaminated sites over short time frames of weeks to several years when the alteration of the LNAPL by microbial activity has not occurred to a significant extent, and over the long-term of several years to decades, when significant microbial degradation of the LNAPL has occurred. A review of the literature suggests that microbial processes profoundly alter the contaminated environment causing marked changes in the petrophysical properties, mineralogy, solute concentration of pore fluids, and temperature. A variety of geophysical techniques such as electrical resistivity, induced polarization, electromagnetic induction, ground penetrating radar, and self potential are capable of defining the contaminated zones because of the new physical properties imparted by microbial processes. The changes in the physical properties of the contaminated environment vary spatially because microbial processes are controlled by the spatial distribution of the contaminant. Geophysical studies must consider the spatial variations in the physical properties during survey design, data analysis, and interpretation. Geophysical data interpretation from surveys conducted at LNAPL-contaminated sites without a microbial and geochemical context may lead to ambiguous conclusions.     

Geophysical Survey and Archaeological Data at Masseria Grasso (Benevento,Italy)

The use of geophysical methods in metrology is a significant tool within the wide research topic of landscape archaeology context. Since 2011, the Ancient Appia Landscapes Project aims to recognize dynamics, shapes and layout of the ancient settlement located along the Appia road east of Benevento, and cyclical elements and human activities that influenced the choice of landscapes. The integration of geophysical data with an archaeological infra-site analysis allowed us to investigate the area of Masseria Grasso, about 6 km from Benevento (Campania region, Italy). In this framework, an archaeogeophysical approach (Geomagnetic and Ground Penetrating Radar) was adopted for detecting anomalies potentially correlated with buried archaeological evidences. The geomagnetic results have given a wide knowledge of buried features in a large survey highlighting significant anomalies associated with the presence of buildings, roads and open spaces. These geophysical results permitted us to define the first archaeological excavations and, successively, a detailed Ground Penetrating Radar approach has been provided highlighting the rooms and paved spaces. The overlap between archaeological dataset and geophysical surveys has also allowed recognizing the path of the ancient Appia road near the city of Benevento and hypothesize the settlement organization of the investigated area, which has been identified with the ancient Nuceriola.     

Radiating Vortices in Geophysical Fluid Dynamics

The dynamics of a single vortex on a beta-plane is discussed in this paper. A barotropic, an equivalent barotropic, one-and-a half and two-layer models are considered. The momentum and energy balances are used to describe the evolution of a vortex. A quasi-stationary balance of the Rossby, Zhukovsky-Kutta forces and the force induced by Rossby-wave radiation, describes the dynamics of the barotropic vortex. A net Coriolis force occurs if the fluid is stratified. The difference between the dynamics of cyclones and anticyclones results directly from the Coriolis force acting on a single vortex in a stratified fluid.All vortices radiate Rossby waves in the quasigeostrophic approximation but intense anticyclones propagate steadily in a one-and-a half layer model. A critical amplitude that bounds radiating and steadily propagating anticyclones is found. Steady propagation of anticyclones in general is impossible in a two-layer fluid due to the radiation of a barotropic Rossby-wave. Some solutions of solitary wave type which are known for a two-layer model, survive owing to wave interference.A single vortex can extract energy from a Rossby wave if synchronism conditions are satisfied. The wave interference again plays a crucial role in this case. The wave interference also determines the energy exchange of vortices located at larger distances. If the distance between the vortices is shorter than the length of the radiated waves, modon may be formed due to a small energy loss.The unbounded monotonic variation of the planetary vorticity is a characteristic feature of a beta-plane approximation. As a result, a single vortex propagates up to a 'rest latitude' where it disappears. The evolution of a single barotropic vortex over bottom topography provides another example of a background vorticity distribution with a local extremum above hills (valleys) or ridges (troughs). Physics of its movement differs from a beta-plane case, but if a vortex lies over broad topography, equations are similar and the evolution of a vortex manifests the same typical features. Particularly, a cyclonic vortex tends to drift to the top of a hill or a ridge. An anticyclonic vortex, on the contrary, slides to the bottom of a valley or a trough.An interaction of a barotropic vortex with a broad mean flow is tractable qualitatively on the basis of previous results. Numerical examples illustrating absorption of a small vortex by a larger one and a vortex movement across the flow, are direct analogies of the vortex evolution over a hill and a ridge, respectively. At the same time, strong influence of strain drastically changes the vortex structure.