Variation ofS q-ranges andL 2 (H) with the dip latitude in Indian region

Summary A modified method of computing theS _q -range in terms ofR _x inH, D andZ has been suggested. Mean quiet-day daily rangesR _x , have been computed for five Indian stations usingH, D andZ data for selected years. The seasonal and latitudinal variation ofR _x (H), R _x (Z) andR _x (D) are discusses. Thee-season maximum inR _x (H) andR _x (Z) is attributed to the decrease in the distance between the foci during equinoxes; the electrojet and theS _q -foci movement with seasons have little influence onS _q (D). It is inferred that the electrojet current is independent of the worldwideS _q current system and stands with its own return currents.The variation of lunar semi-diurnal tide inH[L ₂ (H)] with the dip latitude in Indian region shows a secondary peak at 9° N dip latitude. This secondary peak in theL ₂ (H) is termed as Lunar secondary electrojet, and it is suggested that this is possibly produced by magneto-acoustic oscillations due to the drift motion of the charged particles that produce the primary jet in a direct transverse to itself.     

Detection of the water level in fractured phreatic aquifers using nuclear magnetic resonance (NMR) geophysical measurements

Correlation of geophysical data collected using the NMR method in the Negev Desert, Israel, with hydrogeological data from nearby observation wells is presented. The experiment was conducted near Kibbutz Revivim in the Besor drainage system (Fig. 1). The objective of the survey was to detect groundwater layers in the Quaternary cover filling and Eocene fractured aquifers down to a depth of 100 m. The experiment was performed using a combination of two different geophysical techniques, namely the NMR and time domain electromagnetic (TDEM) methods. The geophysical results were verified by measuring the water level in three observation wells, two of which were drilled several months after the geophysical survey was carried out.The water level measured in these follow-up observation wells shortly after drilling did not coincide with the geophysical data. However, it settled over a period of time and finally stabilized at a depth very similar to that obtained from the NMR measurements. This phenomenon is caused by the fractured nature of the phreatic aquifer. Since the flow of water in such aquifers is confined by the fractures, the appearance of water in the well during or shortly after drilling is determined solely by the intersection of the well and the fracture. Our experiments showed that geophysical measurements in fractured phreatic aquifers may have a distinct advantage over direct borehole measurements, since the former average the depth to the water table over large areas (several thousand square meters) while the latter are limited by the area of the borehole cross-section (several tens of square centimeters).     

Superposition of different stress orientations in the western sector of the northern Apennines (Italy)

Previous studies of the stress regime in the northern Apennines report compression in the outer sector and extension in the inner sector. In this study we focus on the relationships between the two regimes and, by making use of 54 focal mechanism solutions, we try to shed some more light on a tectonic setting that appears more complex than the previous models. The focal mechanisms, computed using the first onset technique, are inverted for stress parameters. The method applied requires subdividing the volume to be investigated into homogeneous sectors: to comply with the complexity of the area under study, we included depth as a parameter for sub-zoning. Our results show that the shallow regime (0–10 km of depth) is transtensive even in the sector previously reported to be compressive. In fact, at a shallow depth, very few thrust focal solutions lie in a spatially limited sector in the eastern part of the area under study. Just below 10 km in depth, the stress regime converts to transpressional: stress axes are approximately inverted. Deeper than 45 km, thrust solutions are found. They are not numerous enough to perform an inversion but indicate the existence of a compressional regime at depth. It is worth noting that a gap of seismicity is observed in the layer 30–45 km.     

Latitudinal dependence of the seasonal variation of particulate extinction in the UTLS over the Indian longitude sector during volcanically quiescent period based on lidar and SAGE-II observations

The altitude profiles of particulate extinction in the upper troposphere and lower stratosphere (UTLS) obtained from SAGE-II in the latitude region 0–30°N over the Indian longitude sector (70–90°E) are used to study the latitudinal variation of its annual pattern in this region during the volcanically quiescent period of 1998–2003. The SAGE-II data is compared with the lidar measurements from Gadanki (13.5°N, 79.2°E) when the satellite had an overhead occultation pass over a small geographical grid centered at this location. The particulate optical depth (τ_p) in the UT region shows a general decrease with increase in latitude and a pronounced summer–winter contrast with relatively low values during winter and high values during summer. In general, these variations are in accordance with the latitudinal variation of convective available potential energy (CAPE) and thunderstorm activity, which are good representative indices of tropospheric convection. While the particulate extinction (and τ_p) in the 18–21 km (LS₁) region is relatively low in the equatorial region up to 15°N, it shows an increase in the off-equatorial region, beyond 15°N. While the annual variation of τ_p in the LS₁ region is almost insignificant near the equator, it is rather well pronounced in latitude region between 10 and 15°N with relatively high values during winter and low values during summer. Beyond 20°N, this shows a prominent peak during summer. At a higher altitude, the 21–30 km (LS₂) region, the latitude variation of τ_p shows a different pattern with high values near the equator and low values in the off-equatorial region confirming the existence of a stratospheric aerosol reservoir. Low values of τ_p at lower regime (LS₁) near the equator could be due to rapid transport of particulates from the near equatorial region to higher latitudes, while the equatorial high at upper regime (LS₂) could be due to lofting and subsequent accumulation.     

Hydrological conditions over the western Mediterranean basin during the deposition of the cold Sapropel 6 (ca. 175 kyr BP)

A new oxygen isotope record is reported from a stalagmite collected in the Argentarola Cave located on the Tyrrhenian coast of Italy. As shown from observations and numerical modeling of δ¹⁸O in modern precipitation, the recorded δ¹⁸O variability for this zone is dominated by the amount of precipitation (so-called ‘amount effect’). The δ¹⁸O profile measured in the stalagmite is characterized by a prominent negative excursion (ca. 2-3‰) between 180 and 170 kyr BP. This paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period, more precisely, during Marine Isotope Stage 6.5. This pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 (S6). Although this particular sapropel event occurred during a cold phase, the δ¹⁸O excursion is similar to those corresponding to other sapropels (S4, S3 and S2). The evidence for humid conditions during S6 in the western Mediterranean basin agrees with previous studies based on deep-sea sediment cores. Taken collectively, the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river Nile but was rather widespread over the entire Mediterranean Sea due to increased rainfall.     

Rock magnetic properties of the lake Pernatoe sediments (Paramushir Island) as an indicator of the changes in sedimentation conditions

Lake Pernatoe is located on Paramushir Island, Kuril Arc, in the area of sand dunes. The 7-m-thick sediments of this lake pertain to the Holocene and contain palustrine, marine, and lacustrine facies. The rock magnetic properties of the sediments are analyzed for tracking the changes in sedimentation conditions. Marine facies are noted with low content of magnetic minerals; their magnetization is dominated by the paramagnetic component; pseudo-single-domain particles of magnetic material and iron sulfides (pyrite) are present. Pyrite frequently occurs in diatoms in the form of chains, spherules, and crystals. The lacustrine facies show high values of the magnetic parameters; they contain multidomain particles, mostly titanomagnetite and magnetite. Sands and sandy silts have the maximum values of magnetic parameters and reflect the stages of aeolian activity, corresponding to climatic cooling and marine regressions. On the basis of magnetic properties, four stages of active aeolian sedimentation are identified in the Holocene.     

Unique variations of the total electron content in the preparation period of Haitian earthquake (M7.9) on January 12, 2010

Variations of the total electron content according to the index IONEX IGS in the period of preparation of the earthquake in Haiti (M7.9) on January 12, 2010, are considered. The situation is exceptional owing to the unique position of the island of Haiti relative to the structure of the ionosphere over the Caribbean Sea: the ionospheric region over Haiti is in the trough formed by the northern slope of the equatorial anomaly and additional maximum formed at latitudes of approximately 30° N within this longitudinal interval. Distortion of the shape of the equatorial anomaly, total decrease in the electron content in the equatorial anomaly a few days prior to the earthquake, increase in the electron concentration directly over the earthquake epicenter a few days prior to the earthquake, increase in the additional maximum at latitudes of ∼30° N, and formation of an additional maximum in the Southern Hemisphere in the region conjugated to the additional maximum in the Northern Hemisphere in the periods of its intensification are observed. The configuration of the equatorial anomaly is restored after the earthquake.     

Distribution and content of different artifical radio nuclides in the water of the North Sea during the years 1977 to 1981 (complemented with some results from 1982 to 1984)

Summary The measured concentrations of¹³⁷Cs in the water of the North Sea gained during the years 1977 to 1982 largely confirm the results found in the preceding years (Fig. 1). After a distinct maximum in 1978 — brought about by a particularly strong influx during 1977 — the total quantity of¹³⁷Cs present in the North Sea has reced, to around half of these peak values by the year 1982 (Table 1).On the way from the Sellafield Works near the Irish Sea as far as into the North Sea, a strong shift of the¹³⁷Cs:⁹⁰Sr ratio in favour of the⁹⁰Sr can be observed.By following the temporal course of that ratio at different measurement points, a transport time can be deduced of around 3 years between the Sellafield Works and the Pentland Firth; a further year would be needed to reach into the southeastern North Sea.The ratio Cs:Sr furthermore permits, in the southeastern North Sea, a good distinction between the watermasses comming from the north into the North Sea with respect to those that come through the Channel from the South. These masses practically flow side by side until about the entrance to the Skagerrak.The vertical distribution of the¹³⁷Cs shows, as is to be expected, seasonally conditioned differences. However, effects also occur, which — on the basis of the data available to date — do not yet permit a clear explanation.The⁹⁰Sr, as well as the^239+240Pu, present in the North Sea show an analogous distribution scheme compared with that of the¹³⁷Cs. Their concentrations lie far below that of the¹³⁷Cs (⁹⁰Sr 17.5%;^239+240Pu 0.03%).Tritium, on the other hand — with essentially higher concentrations — shows a completely different distribution, because it is principly introduced via the freshwater flowing in from the land.

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Verteilung und Gehalt verschiedener künstlicher Radionuklide im Wasser der Nordsee in den Jahren 1977 bis 1981 (ergänzt durch einige Ergebnisse von 1982 bis 1984)

Zusammenfassung Die in den Jahren 1977 bis 1982 gewonnenen Meßdaten der Aktivitätskonzentrationen von¹³⁷Cs im Wasser der Nordsee bestätigen weitgehend die in den vorhergehenden Jahren gefundenen Ergebnisse (Fig. 1) Nach einem deutlichen Maximum im Jahre 1978 — hervorgerufen durch eine besonders starke Zufuhr im Jahre 1977 —ist die in der Nordsee insgesamt vorhandene Menge an¹³⁷Cs bis zum Jahre 1982 wieder auf rund die Hälfte zurückgegangen (Tab. 1).Auf dem Weg von den Sellafield Works an der Irischen See bis in die Nordsee ist eine starke Verschiebung des¹³⁷Cs:⁹⁰Sr Verhältnisses zugunsten des⁹⁰Sr zu beobachten.Aus dem zeitlichen Verlauf dieses Verhältnisses an verschiedenen Meßpunkten ergeben sich Transportzeiten zwischen den Sellafield Works und dem Pentland Firth von rund 3 Jahren; bis in die südöstliche Nordsee wird ein weiteres Jahr benötigt.Das Verhältnis Cs:Sr erlaubt außerdem in der südöstlichen Nordsee eine gute Unterscheidung der aus der Nordsee bzw. durch den Kanal von Süden kommenden Wassermassen, die praktisch nebeneinander her bis etwa zum Beginn des Skagerraks fließen.Die Vertikalverteilung des¹³⁷Cs zeigt, wie zu erwarten ist, jahreszeitlich bedingte Unterschiede. Es treten aber auch Effekte auf, die sich anhand der bisher vorliegenden Daten noch nicht eindeutig erklären lassen.Das in der Nordsee vorhandene⁹⁰Sr sowie das^239+240Pu zeigen ein analoges Verteilungsschema verglichen mit dem des¹³⁷Cs. Ihre Konzentrationen liegen weit unter der des¹³⁷Cs (⁹⁰Sr 17,5%,^239+240Pu 0,03%).Das Tritium zeigt bei wesentlich höheren Konzentrationen dagegen eine völlig andere Verteilung, da seine Hauptzufuhr im wesentlichen über das von Land her zufließende Süßwasser erfolgt.

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Distribution et teneur de differents radionucleides artificiels, dans les eaux de la Mer du Nord entre les années 1977 et 1981 (completes par quelques résultats de 1982 à 1984)

Résumé Les mesures de concentration du Césium 137 dans les eaux de la Mer du Nord, acquises entre les années 1977 et 1982, confirment largement les résultats obtenus au cours des années précédentes. Après un net maximum en 1978 — occassionné par un apport particulièrement fort en 1977 — la quantité totale de Césium 137 présent en Mer du Nord a régressé,jusqu'en 1982, aux alentours de la moitié de ces valeurs maximales.Il a pu être observé une modification importante du rapport Césium 137/Strontium 90, en faveur du Strontium 90, sur le trajet de Sellafield Works prés de la Mer d'Irlande jusqu'à la Mer du Nord.En suivant l'évolution temporelle de la valuer de ce rapport en différents points de mesure, on peut en déduire une durée de transport d'environ 3 ans entre Sellafield Works et Pentland Firth; une année supplémentaire est ensuite nécessaire pour pénétrer en Mer du Nord Sud-orientale.En Mer du Nord Sud-orientale, le rapport Césium/Strontium permet en outre d'effectuer une nette distinction entre les masses d'eau pénétrant respectivement par le Nord dans la Mer du Nord et celles pénétrant par le Sud et venant de la Manche. Ces masses d'eau s'écoulent pratiquement côte à côte jusqu'à l'entrée du Skagerrak.Comme l'on pouvait s'y attendre, la distribution verticale du Césium est différente suivant les saisons. Cependant il apparaît également des effects qui, sur la base des données disponibles à ce jour, ne s'expliquent pas encore clairement.Le Strontium 90 aussi bien que le Plutonium 239+240 présent dans la Mer du Nord, montrent une distribution comparable, analogue à celle du Césium 137. Leurs concentrations sont bien inférieures à celle du Césium 137 (Strontium 90 17,5%; Plutonium 239+240 0,03%).Le tritium d'autre part, — avec des concentrations significativement plus fortes —montre une distribution complètement différente, due principalement au fait qu'il est introduit par l'intermédiaire de l'écoulement d'eau douce provenant de la terre.

     

2019年长宁M_S 6.0地震前后电离层垂直电子总含量（VTEC）异常扰动分析

2019长宁发生M_S 6.0地震,利用CODE全球电离层格网数据、中国地壳运动观测网络GPS数据、震中区域GPS数据,分别计算全球、中国区域垂直电子总含量(VTEC)异常分布及震中区域站点VTEC时间序列,揭示此次地震发生前后不同空间尺度电离层异常扰动变化。结果表明:地震发生前3天(6月14日),长宁震区上空出现连续电离层异常扰动现象,异常空间分布呈现向磁赤道偏移趋势。VTEC结果的时、空尺度变化反映,本次电离层扰动可能与长宁地震孕震过程有关,可为川滇区域临震电离层异常扰动监测及地震分析预报提供震例依据。     

Origin, enzymatic response and fate of dissolved organic matter during flood and non-flood conditions in a river-floodplain system of the Danube (Austria)

Spectroscopic techniques and extracellular enzyme activity measurements were combined with assessments of bacterial secondary production (BSP) to elucidate flood-pulse-linked differences in carbon (C) sources and related microbial processes in a river-floodplain system near Vienna (Austria). Surface connection with the main channel significantly influenced the quantity and quality of dissolved organic matter (DOM) in floodplain backwaters. The highest values of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) were observed during the peak of the flood, when DOC increased from 1.36 to 4.37 mg l^?1 and CDOM from 2.94 to 14.32 m^?1. The flood introduced DOC which consisted of more allochthonously-derived, aromatic compounds. Bacterial enzymatic activity, as a proxy to track the response to changes in DOM, indicated elevated utilization of imported allochthonous material. Based on the enzyme measurements, new parameters were calculated: metabolic effort and enzymatic indices (EEA 1 and EEA 2). During connection, bacterial glucosidase and protease activity were dominant, whereas during disconnected phases a switch to lignin degradation (phenol oxidase) occurred. The enzymatic activity analysis revealed that flooding mobilized reactive DOM, which then supported bacterial metabolism. No significant differences in overall BSP between the two phases were detected, indicating that heterogeneous sources of C sufficiently support BSP. The study demonstrates that floods are important for delivering DOM, which, despite its allochthonous origin, is reactive and can be effectively utilized by aquatic bacteria in this river-floodplain systems. The presence of active floodplains, characterized by hydrological connectivity with the main channel, creates the opportunity to process allochthonous DOC. This has potential consequences for carbon flux, enhancing C sequestration and mineralization processes in this river-floodplain system.     

四川及其三个分区的地震平静指标及其预测效能的研究--不同层次地震平静异常预测效能的研究之一

作为不同层次地震平静异常预测效能的研究之一,本文针对四川及其三个分区,利用过去积累的30多年地震资料,经过多种方案试算、评分检验,明确了平静指标和预测规则,找到了合适的研究平静预测的震级下限M0、预测震级M1、平静异常时间T1与预测时间T2等最佳参数组合,可以取T2等最佳参数组合,可以取得高于置信水平为97.5%的区别随机瞎报的阈值R0的R评分值。     

TEC variations over the Mediterranean before and during the strong earthquake (M = 6.5) of 12th October 2013 in Crete,Greece

In this paper, the total electron content (TEC) data from eight global positioning system (GPS) stations of the EUREF network, provided by IONOLAB (Turkey), were analyzed using discrete Fourier analysis to investigate the TEC variations over the Mediterranean before and during the strong earthquake of 12th October 2013, which occurred west of Crete, Greece. In accordance with the results of similar analyses in the area, the main conclusions of this study are the following: (a) TEC oscillations in a broad range of frequencies occur randomly over an area of several hundred km from the earthquake and (b) high frequency oscillations (f ⩾ 0.0003 Hz, periods T ⩽ 60 m) may point to the location of the earthquake with questionable accuracy. The fractal characteristics of the frequency distribution may point to the locus of the earthquake with higher accuracy. We conclude that the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanism through acoustic or gravity waves could explain this phenomenology.     

Precursory phenomena observed in the total electron content measurements before great Hokkaido earthquake of September 25, 2003 (<Emphasis Type="Italic">M</Emphasis> = 8.3)

In this paper the analysis of the ionospheric total electron content (TEC) variations obtained with using GPS measurements before the Hokkaido earthquake (M = 8.3) is presented. Anomalous behavior of TEC was detected within several days before the main event. Anomaly appeared as the local TEC enhancement situated in the vicinity of the forthcoming earthquake epicenter. These structures occurred during 5 days prior to the shock at the same interval of local time. At the process of the earthquake approach the amplitude of modification was increased, and it has reached the 85–90% level relative to the non-disturbed conditions 18 hours before the earthquake. The area of strong positive disturbance has extended over 1500 km in latitudes and 4000 km in longitudes. The analysis have shown that according to the series of characteristics (its locality, affinity with the epicenter, dome-shaped zone of manifestation, characteristic time of existence) the detected ionospheric anomaly may be associated to the precursors of seismic activity.     

Moisture transport and seasonal variations in the stable isotopic composition of rainfall in Central American and Andean Páramo during El Niño conditions (2015–2016)

High‐elevation tropical grassland systems, called Páramo, provide essential ecosystem services such as water storage and supply for surrounding and lowland areas. Páramo systems are threatened by climate and land use changes. Rainfall generation processes and moisture transport pathways influencing precipitation in the Páramo are poorly understood but needed to estimate the impact of these changes, particularly during El Niño conditions, which largely affect hydrometeorological conditions in tropical regions. To fill this knowledge gap, we present a stable isotope analysis of rainfall samples collected on a daily to weekly basis between January 2015 and May 2016 during the strongest El Niño event recorded in history (2014–2016) in two Páramo regions of Central America (Chirripó, Costa Rica) and the northern Andes (Cajas, south Ecuador). Isotopic compositions were used to identify how rainfall generation processes (convective and orographic) change seasonally at each study site. Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) air mass back trajectory analysis was used to identify preferential moisture transport pathways to each Páramo site. Our results show the strong influence of north‐east trade winds to transport moisture from the Caribbean Sea to Chirripó and the South American low‐level jet to transport moisture from the Amazon forest to Cajas. These moisture contributions were also related to the formation of convective rainfall associated with the passage of the Intertropical Convergence Zone over Costa Rica and Ecuador during the wetter seasons and to orographic precipitation during the transition and drier seasons. Our findings provide essential baseline information for further research applications of water stable isotopes as tracers of rainfall generation processes and transport in the Páramo and other montane ecosystems in the tropics.