Relationships between diurnal variations and mean daily concentrations of hydrochemical characteristics in a sea coastal zone

Data on Amur Bay (the Sea of Japan) are used to show the existence of a dependence between the diurnal variability and the mean daily concentrations of various hydrochemical characteristics, which can be approximated by power function. The formation mechanism of such dependences is considered. Relationships between the parameters of such functions and variability of water salinity are obtained. The possible variation limits of such parameters in a coastal tidal zone of a sea, subject to the effect of coastal runoff. In the frontal mouth zone, one of the parameter (the exponent) linearly increases toward the river, thus reflecting the increase in the contribution of water dynamics to the diurnal variability of characteristics. The notion of variability of characteristics “by salinity” is introduced.     

Diurnal Variations in the Hydrochemical Indices in Amur Bay

A study was conducted to assess the diurnal variations in water temperature, in-situ density, and salinity; major components of the salt composition; ion–chlorine relationships; elements of the carbonate system and their chlorine ratios; major nutrient compounds; total organic carbon content; suspended matter; dissolved oxygen and its percentage in the coastal waters of Amur Bay. The notions of zero, very small, small, medium, high, and very high relative variability are introduced.     

Seasonal and UT variations of the position of the auroral precipitation and polar cap boundaries

The data of the DMSP F7 spacecraft are used for studying the influence of the geomagnetic dipole tilt angle on the latitudinal position of auroral precipitation boundaries in the nighttime (2100–2400 MLT) and daytime (0900–1200 MLT) sectors. It is shown that, in the nighttime sector, the high-latitude zone of soft diffuse precipitation (SDP) and the boundary of the polar cap (PC) at all levels of geomagnetic activity are located at higher and lower latitudes relative to the equinox period in winter and summer, respectively. The position of boundaries of the diffuse auroral precipitation zone (DAZ) located equatorward from the auroral oval does not depend on the season. In the daytime sector, the inverse picture is observed: the SDP precipitation zone takes the most low-latitude and high-latitude positions in the winter and summer periods, respectively. The total value of the displacements from winter to summer of both the nighttime and daytime boundaries of the PC is ∼2.5°. A diurnal wave in the latitudinal position of the nighttime precipitation boundaries is detected. The wave is most pronounced in the periods of the winter and fall seasons, is much weaker in the spring period, and is almost absent in summer. The diurnal variations of the position of the boundaries are quasi-sinusoidal oscillations with the latitude maximum and minimum at 0300–0500 and 1700–2100 UT, respectively. The total value of the diurnal displacement of the boundaries is ∼2.5° of latitude. The results obtained show that, undergoing seasonal and diurnal variations, the polar cap is shifted as a whole in the direction opposite to the changes in the tilt angle of the geomagnetic dipole. The seasonal displacements of the polar cap and its diurnal variations in the winter period occur without any substantial changes in its area.     

Influence of variable salinity conditions in a tidal creek on riparian groundwater flow and salinity dynamics

While recent studies have revealed that tidal fluctuations in an estuary significantly affect groundwater flows and salt transport in the riparian zone, only seawater salinity in the estuary has been considered. A numerical study is conducted to investigate the influence of estuarine salinity variations on the groundwater flow and salt dynamics in the adjacent aquifer to extend our understanding of these complex and dynamic systems. Tidal salinity fluctuations (synchronous with estuary stage) were found to alter the magnitude and distribution of groundwater discharge to the estuary, which subsequently impacted on groundwater salinity patterns and residence times, especially in the riparian zone. The effects of salinity fluctuations were not fully captured by adopting a constant, time-averaged estuarine salinity. The modelling analysis also included an assessment of the impact of a seasonal freshwater flush in the estuary, similar to that expected in tropical climates (e.g. mean estuary level during flood significantly greater than average), on adjacent groundwater flow and salinity conditions. The three-month freshwater flushing event temporarily disrupted the salt distribution and re-circulation patterns predicted to occur under conditions of constant salinity and tidal water level fluctuations in the estuary. The results indicate that the salinity variations in tidal estuaries impact significantly on estuary–aquifer interaction and need to be accounted for to properly assess salinity and flow dynamics and groundwater residence times of riparian zones.     

Preliminary Observation of Complex Salt‐Fresh Water Mixing in a Beach Aquifer

Continuous observations of beach groundwater salinity over a 35‐d period from a monitoring well established in the intertidal zone of a coastal harbor provided intriguing data on the interaction in the intertidal zone between the salt and fresh groundwater. During the monitoring period of the study, both semidiurnal variations and longer temporal trends in groundwater salinity were observed. The semidiurnal salinity variations were observed to occur nearly synchronously, but inconsistently with the tides. However, the salinity relationship with the tides was more complex, switching back and forth from being in‐sync (higher salinities at high tide) to out‐of‐sync (higher salinities at low tide) a total of four times during the 35‐d test period. The longer temporal trends showed chloride concentration (representing salinity) varying from as low as 50 mg/L to as high as 3600 mg/L over a period of between 9 to 12 d. The observations from the monitoring well reveal a complex pattern likely resulting from a combination of tidal pumping, density‐induced convection, and changes in the terrestrial hydraulic gradient. However, these observations are based upon data from only one monitoring well, and are speculative at this point. A more thorough study of the complex fresh water‐saline water relationship in the intertidal zone seems to have merit.     

Variations in Methane Concentrations in the Water of the Don River and Taganrog Bay under the Effect of Natural Factors

Seasonal and diurnal variations in CH₄ concentration in the water of the Don River and Taganrog Bay are examined, and two maximums are recognized in the seasonal variations. The diurnal variations are shown to be affected by the meteorological conditions.     

Locating the zone of saline intrusion in a coastal karst aquifer using springflow data

Coastal fresh water aquifers are an increasingly desirable resource. In a karstic aquifer, sea water intrusion occurs as a salt water wedge, like in porous media. However, preferential flow conduits may alter the spatial and temporal distribution of the salt water. This is typically the case when the outlet of the aquifer is a brackish spring. This paper shows that salinity and flow rate variations at a spring, where salinity is inversely proportional to discharge, can help to understand the hydrodynamic functioning of the aquifer and to locate the fresh water-sea water mixing zone deep inside the aquifer. The volume of water-filled conduit between the sea water intrusion zone and the spring outlet is calculated by the integral over time of the flow rate during the time lag between the flow rate increase and the salinity decrease as measured at the spring. In the example of the spring at Almyros of Heraklio (Crete, Greece), this time lag is variable, depending on the discharge, but the volume of water-filled conduit appears to be constant, which shows that the processes of salt water intrusion and mixing in the conduit are constant throughout the year. The distance between the spring and the zone where sea water enters the conduit is estimated and provides an indication of the position where only fresh water is present in the conduit.     

Diurnal dynamics of streamflow in an upland forested micro‐watershed during short precipitation‐free periods is altered by tree sap flow

Diurnal variations in streamflow are becoming acknowledged as a way of analysing how changing climatic conditions and land use affects watersheds but also as a way to understand watersheds as a whole. Yet not many studies from uplands below 900 mm mean annual precipitation zone are available from European countries. During the 2012 growing season, a sampling campaign took place in an upland forested micro‐watershed, Czech Republic (65 ha). Tree sap flow, rainfall and temperature were measured continuously, while streamflow at the discharge point and soil moisture were estimated from short‐term measurements. Short precipitation‐free periods lasting several days were identified for evaluation of trends in diurnal dynamics of both sap flow and streamflow. The results demonstrated that during these periods, the main factor altering streamflow was almost exclusively tree sap flow. A decrease in streamflow was observed during the day and an increase at night. The decline in sap flow after sunset was accompanied by a continuous increase in streamflow throughout the night up to its initial maximum in the morning. The amplitude in diurnal variations reached 18%. The observed time lag between the diurnal variations of sap flow and streamflow was approximately 2 h. Relatively low changes in diurnal dynamics of streamflow pointed out a strong regulatory role of the forest in buffering water discharge from the catchment. Copyright © 2015 John Wiley & Sons, Ltd.     

Diurnal variation in the effect of the weekend in global seismic activity

The influence of the earthquake probability diurnal variation on specific features in the weekend effect in global seismic activity is revealed. The dependence of the global earthquake number on the local time and its possible relation to a quiet solar diurnal variation (Sq) in the geomagnetic field have been considered in detail. It has been indicated that a stable diurnal effect, which has a maximum near midnight and a minimum near local noon, exists in the global seismicity of the Earth. The diurnal variation amplitude changes insignificantly during days of week and substantially decreases (by a factor of almost 3) on Saturday and Sunday. The weekend effect is not revealed during “local nights.” Since the daily effect of a quiet solar diurnal variation (Sq) should not depend on days of week, we arrive at the conclusion that the diurnal variation in global seismicity evidently contains the anthropogenic activity product. The Sunday effect in the earthquake number decreases over the course of time and is most probably real but weak and not stationary since weekly variations occur against a background (or under the action) of stronger variations, i.e., an increase in the earthquake number and diurnal variations.     

Assessing the spatial and temporal variability of dissolved organic matter in Liverpool Bay using excitation–emission matrix fluorescence and parallel factor analysis

The spatial and diurnal tidal variability of dissolved organic carbon (DOC) concentrations and the composition of dissolved organic matter (DOM), as evaluated by high-temperature catalytic oxidation and excitation–emission matrix combined with parallel factor analysis (EEM–PARAFAC), respectively, were determined in Liverpool Bay. EEM–PARAFAC modeling resulted in six fluorescent components characterized as terrestrial humic-like (two), microbial humic-like (two), and protein-like (two). The spatial distributions of DOC and the four humic-like components were negatively correlated with salinity in the high-salinity waters observed in this study (30.41–33.75), suggesting that terrestrial DOM was conservatively distributed. The spatial patterns of protein-like components were largely different from those of DOC, humic-like components, and chlorophyll a, suggesting that these distributions were the combined result of production and degradation in the bay in addition to river inputs. These findings suggest that the DOM dynamics in Liverpool Bay are strongly controlled by river-dominated allochthonous DOM inputs with some less significant contributions of autochthonous DOM within the bay. In addition, the temporal variations of DOM associated with the diurnal tidal cycles were determined at one inshore (31.34–32.24 salinity) and one offshore (33.64–33.75 salinity) station in the bay. Negative linear relationships between salinity and DOM characteristics, i.e., DOC, humic-like, and protein-like components, were observed at the inshore station. In contrast, no relationship was observed at the offshore station, suggesting that the export of DOM through rivers and possibly tidal flats have a noticeable influence on DOM concentration and composition up to a relatively elevated salinity of around 33 in Liverpool Bay.     

Long-term temperature monitoring in a borehole drilled into the Nojima Fault, southwest Japan

Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m².     

Meteorological features in Adélie Land during the austral summer season

Intensive meteorological observations were carried out at three sites along the slope of Adélie Land, Antarctica, with the goal of documenting summertime meteorological features of the katabatic zone. Three observational sites were placed at 5 km (D10), 110 km (D47), and 210 km (D57) from the coast, and frequency distributions of meteorological parameters were obtained at each site. Some meteorological features at D47 and D57 (interior sites) were different than at D10 (the coastal site); namely, mean air temperatures averaged for the whole observational period showed more pronounced diurnal variations at the interior sites than at the coastal site. These variations could be represented by sinusoidal curves. Wind speeds also showed diurnal variations, whose extremes appeared several hours later than the temperature extremes. The prevailing wind direction for all sites was southerly, about 30° east of the fall line, with small variations in wind direction. The strength and the height of temperature inversions were examined in two different layers (0 to 50 m, 50 to 300 m) at D47. A strong, shallow inversion layer formed at night, however, completely vanished during the day. On the other hand, an upper level inversion whose strength was weak persisted. The katabatic characteristics of the surface wind found at D47 in summer could be due to this upper level temperature inversion.A contribution to I.A.G.O. (Interaction-Atmosphere-Glace-Ocean).     

Impacts of blending on dilution of negatively buoyant brine discharge in a shallow tidal sea

A fine-resolution three-dimensional hydrodynamic model is applied to study the dilution of desalination brine discharged into a tidal sea. Based on given inflow rate and salinity excess of discharge brine, this study explores variations in mid-field dilutions when other low-salinity wastewater is added to the discharge. Findings reveal that this blending leads to a decrease in dilution in the mixing zone and therefore to higher levels of pollutants in this zone, while, on the other hand, the mixing zone occupies a smaller area. The reason is that the discharge of brine creates a density-driven flow that operates to partially remove effluent from the discharge location. This removal is less efficient for the decrease in density excess of the discharge. Hence, in an ambient sea of moderate mixing, blending can be expected to increase the risk of marine pollution in the mixing zone.     

Influence of Seasonal Variations in Sea Level on the Salinity Regime of a Coastal Groundwater–Fed Wetland

Seasonal variations in sea level are often neglected in studies of coastal aquifers; however, they may have important controls on processes such as submarine groundwater discharge, sea water intrusion, and groundwater discharge to coastal springs and wetlands. We investigated seasonal variations in salinity in a groundwater‐fed coastal wetland (the RAMSAR listed Piccaninnie Ponds in South Australia) and found that salinity peaked during winter, coincident with seasonal sea level peaks. Closer examination of salinity variations revealed a relationship between changes in sea level and changes in salinity, indicating that sea level–driven movement of the fresh water‐sea water interface influences the salinity of discharging groundwater in the wetland. Moreover, the seasonal control of sea level on wetland salinity seems to override the influence of seasonal recharge. A two‐dimensional variable density model helped validate this conceptual model of coastal groundwater discharge by showing that fluctuations in groundwater salinity in a coastal aquifer can be driven by a seasonal coastal boundary condition in spite of seasonal recharge/discharge dynamics. Because seasonal variations in sea level and coastal wetlands are ubiquitous throughout the world, these findings have important implications for monitoring and management of coastal groundwater–dependent ecosystems.     

Dependence of magnetic activity on the plasma sheet location relative to the geomagnetic equator

Geomagnetic activity variations depending on the angle between the planes of geomagnetic equator and plasma sheet of the magnetosphere are considered on the basis of data of midlatitude stations. The dependences of diurnal variations proceeding in the universal time with opposite phases in winter and summer months, as well as the well-known semiannual variations in magnetic activity, on this angle are established. The amplitude of the diurnal wave displays substantial semiannual variations with maximums in the periods of solstices.     

Diurnal periodicity of the representative earthquakes in Greece

The diurnal periodicity of seismic events of different energy from the Greece earthquake catalog was studied. Earthquake samplings of different energy with a known level of magnitude of completeness were compiled. Parameters of the diurnal periodicity of earthquakes in different time and magnitude intervals were analyzed. Significant diurnal periodicity of earthquakes with M ≤ 4.1 was revealed. The most important result of the paper is the discovery of the diurnal periodicity of the representative earthquakes with M = 3.2–4.1. The diurnal periodicity of representative earthquakes cannot be explained at the base of the prevailing hypothesis considering the diurnal periodicity of earthquakes as an apparent phenomenon resulting from diurnal changes in the real sensitivity of the seismic network due to diurnal variations of seismic noise.     

Strong tidal currents over two shallow banks in the western subarctic Pacific

The south-flowing waters of the Kamchatka and Oyashio currents are key components of the western subarctic Pacific gyre. The dissipation of tidal energy in shallow and coastal regions of these currents and the attendant mixing are the important processes that affect the upper layer temperature and salinity. Examples of the impact of tidal currents on water temperature and salinity are the persistent tide-driven mixing around the Kashevarov and Kruzenshtern banks. The Kruzenshtern Bank is a shallow submarine bank stretching along the eastern continental slope of the Kuril Islands with the minimum depth of 86 m. Surface drifters observations are used to determine the characteristics of tidal currents and the circulation over these banks. New software that allows more versatility in the harmonic analysis is used for drifter’s data. The two banks have similar features. The variations in current velocities are dominated by the diurnal signals. The K₁ and O₁ tidal ellipses over the banks are the largest and clockwise. The enhanced tidal currents suggest that the formation of cold and saline water in summer is due to mixing of water column over the banks with intermediate waters. Variations of tidal ellipses over the bank may explain the formation of polynya at the western end of the Kashevarov Bank. We found that the 18.6-year lunar nodal cycle is a significant characteristic of salinity variation at the temperature minimum in the eddies eastward of the Boussole Strait over the period 1990–2015.     

Diurnal variations of the total electron content under quiet helio-geomagnetic conditions

The morphology of averaged diurnal variations of total electron content (TEC) under quiet helio-geomagnetic conditions for all latitudinal bands and various longitudes has been studied using Global Ionospheric Maps (GIMs) datasets. The diurnal TEC variation maximum is generally registered at 14–15 LT. The maximum is 38±5, 14±2, 10±2 TECU (TECU is generally accepted TEC unit) at the equatorial, middle and high latitudes. The nighttime TEC minimum is within 5–7 TECU regardless of a season, latitude and longitude. At the equatorial latitudes TEC exhibits the most significant daily/season variations and the asymmetry of its behavior in the hemispheres near the equinox. Abnormal diurnal TEC variations (evening maximum, near-noon minimum) are observed at middle and high latitudes in summer due to atmospheric wind effects. The comparison of the averaged diurnal TEC variations with the behavior of the ionospheric F2-layer critical frequency indicated that GIMs describe daily/annual TEC variations reasonably well.     

Morphology and causes of the Weddell Sea anomaly

The zone of anomalous diurnal variations in foF2, which is characterized by an excess of nighttime foF2 values over daytime ones, has been distinguished in the Southern Hemisphere based on the Intercosmos-19 satellite data. In English literature, this zone is usually defined as the Weddell Sea anomaly (WSA). The anomaly occupies the longitudes of 180°–360° E in the Western Hemisphere and the latitudes of 40°–80° S, and the effect is maximal (up to ∼5 MHz) at longitudes of 255°–315° E and latitudes of 60°–70° S (50°–55° ILAT). The anomaly is observed at all levels of solar activity. The anomaly formation causes have been considered based on calculations and qualitative analysis. For this purpose, the longitudinal variations in the ionospheric and thermospheric parameters in the Southern Hemisphere have been analyzed in detail for near-noon and near-midnight conditions. The analysis shows that the daytime foF2 values are much smaller in the Western Hemisphere than in the Eastern one, and, on the contrary, the nighttime values are much larger, as a result of which the foF2 diurnal variations are anomalous. Such a character of the longitudinal effect mainly depends on the vertical plasma drift under the action of the neutral wind and ionization by solar radiation. Other causes have also been considered: the composition and temperature of the atmosphere, plasma flows from the plasmasphere, electric fields, particle precipitation, and the relationship to the equatorial anomaly and the main ionospheric trough.     

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.