Accurate analytical representation of Pluto modern ephemeris

An accurate development of the latest JPL’s numerical ephemeris of Pluto, DE421, to compact analytical series is done. Rectangular barycentric ICRF coordinates of Pluto from DE421 are approximated by compact Fourier series with a maximum error of 1.3 km over 1900–2050 (the entire time interval covered by the ephemeris). To calculate Pluto positions relative to the Sun, a development of rectangular heliocentric ICRF coordinates of the Solar System barycenter to Poisson series is additionally made. As a result, DE421 Pluto heliocentric positions by the new analytical series are represented to an accuracy of better than 5 km over 1900–2050.     

Geophysical Hazard for Human Health in the Circumpolar Auroral Belt: Evidence of a Relationship between Heart Rate Variation and Electromagnetic Disturbances

Geomagnetic storms are a natural hazard tohuman health in the Auroral Belt of the Circumpolar.Geomagnetic disturbances in space, and the associated short-term variations in the atmosphere and the geophysical environment,provoke a disturbance of nervous and cardiovascular systems in the human body. The Heart Rate Variability (HRV) method providesa momentary response of human organisms toshort-term geophysical perturbations related to the Polar Aurora. A pilot project was performed in the Murmansk region in 1997–1999 with a contemporaneous series of records for both HRV in a test group of local inhabitants and the variations of natural geomagnetic fields.A correlation between geomagnetic disturbances and heart rate was calculated and different reactions of people on geophysical impact were shown. The special group of `Aurora Disturbance Sensitive People' (ADSP) was revealed. Aninternational study, aimed atevaluation of the impact on human health due to exposure of northern populations to the geophysical risk factor (GRF) in the Circumpolar areas located under the Aurora Belt, is needed.     

Statistical description of the Black Sea near-surface circulation using drifters in 1999–2003

The near-surface circulation in the Black Sea is studied with the data of 54 satellite-tracked drifters in the period 1999–2003. The drifter trajectories confirm the prevalence of the Rim Current trapped on the continental slope (between water depths of 400 and 1800 m) along the periphery of the basin where sub-inertial speeds can reach 1 m/s. Some drifters were found to complete an entire basin loop with the Rim Current in 90–180 days. Meanders and loops in the tracks prove the existence of mostly anticyclonic circulation features inshore of the Rim Current, including strong signatures of the Batumi and Sevastopol eddies. They also reveal the presence of cyclonic and anticyclonic currents in most areas of the Black Sea. Pseudo-Eulerian statistics (averaged in 50-km bins), that is, mean currents and the corresponding velocity variances, show a strong and highly fluctuating signature of the Rim Current and the enhanced variability associated with the Batumi and Sevastopol eddies. The latter is also collocated with the branching of the Rim Current southwest of the Crimean Peninsula. It is shown that the kinetic energy is mainly in the mean for the Rim Current and in the velocity fluctuations elsewhere. Seasonal variability is also explored. The Rim Current tends to form a stronger single loop trapped on the continental slope in winter/spring, whereas in summer/fall the mean circulation is more meandering, recirculation cells appear in the central areas and the bifurcation southwest of Crimea is enhanced. There is some evidence of the reversal of sense of rotation of the currents in the Batumi Eddy region, changing from mainly anticyclonic in summer/fall to cyclonic in winter/spring. Mean residence times were calculated in the 50-km bins, with values ranging from a few days in the central basin to 8 days in the northwestern coastal area. Globally, the kinetic energy levels were found higher in winter–spring and lower in summer–fall, with a significant maximum in March. Single-particle Lagrangian statistics were computed for the entire basin, for the two extended seasons, and in selected local areas. Velocity variance, diffusivity and Lagrangian integral time scales are generally larger in the zonal direction. Globally, the velocity variance is 174 and 127 cm²/s² in the zonal and meridional directions, respectively, after the removal of the pseudo-Eulerian mean circulation. For the zonal direction, a diffusivity value of 4.5×10⁷ cm²/s and Lagrangian integral time and space scales of 3 days and 34 km were found. For the meridional direction, these statistics amount to 4.5×10⁷ cm²/s, 1.2 days and 12.2 km. Seasonal and geographical variations of these Lagrangian statistics were also assessed, showing variations between 1.9 (0.9) 10⁷ and 8.3 (2.0) 10⁷ cm²/s for the diffusivity in the zonal (meridional) direction. Integral time and space scales vary between 1 and 4.7 days, and 8.8 and 58 km, respectively. Seasonal differences are significant only in the zonal direction, where the diffusivity increases from 3.1×10⁷ to 5.9×10⁷ cm²/s and the integral scales vary from 2.1 days (24 km) to 3.8 days (44 km) from summer/fall to winter/spring.     

Impact of spatial resolution on simulated surface water mass transformations in the Atlantic

We analyze the water mass transformation in coarse (1°) and high (1/6°) resolution ocean simulations with the identical configuration of the CLIPPER model and interannual ERA15 forcing function. Climatological characteristics of surface water mass transformation in the two experiments are quite different. The high resolution experiment exhibits a stronger surface transformation in equatorial and tropical regions, in the Gulf Stream area and in the location of the formation of Subtropical Mode Water (STMW), associated with high levels of eddy kinetic energy. The coarse resolution experiment shows a better representation of the transformation rates corresponding to the densest subpolar mode waters and Labrador Sea Water (LSW). This is explained by the differences in lateral mixing procedures between high and coarse resolution experiments. The high resolution 1/6° run is eddy-resolving only in the tropics and mid-latitudes. In these areas eddies are found to enhance the process of water mass transformation compared to the isopycnal diffusion used to parameterized the eddies in the 1° model. Despite its 1/6° resolution, the high resolution model does not adequately represent eddies in the subpolar gyre and Labrador Sea. In these areas the high resolution model fails to correctly simulate water mass transformation because the lateral mixing (provided through the bi-harmonic sub-gridscale parameterization) of newly ventilated waters with surrounding waters is not efficient enough. In contrast in the coarse 1° resolution model, the strong lateral mixing and the unrealistically broad boundary currents imposed by the high diffusivity required for numerical stability mixes newly formed LSW waters with the warmer and saltier waters of the rim current. Finally, it results in a more effective representation of the surface water mass transformation in high latitudes in the 1° model. A possible impact of the increased lateral diffusion in high resolution experiment on the representation of re-stratification in the Labrador Sea was studied in sensitivity experiments with different lateral diffusion coefficients compared to the regional eddy-resolving 1/15° simulation in the subpolar North Atlantic. If the eddies are not resolved in subpolar latitudes (as in the case of 1/6° model), the GM90 parameterization with the coefficient close to 800 m² s⁻¹ provides the closest agreement with the solution of eddy-resolving 1/15° model.     

Morphotectonics, Volcanism and Hydrothermal Activity on the East Pacific Rise between 21°12′ S and 22°40′ S

The morphotectonic setting of the East Pacific Rise (EPR) between21°12 and 22°40 S and its recent and past hydrothermalactivity were the focus of the Russian R/V Geolog Fersmans expeditionin 1987–1988.The EPR axial zone in the study area is comprised of three segmentsseparated by overlapping spreading centers (OSCs) near 21°44 and22°08 S. The northern segment is the shallowest of three and hasa distinct massive axial ridge, trapeziodal in cross-section, toppedby a very wide flat summit surface and cut by a well-developedcentral graben. These features testify to intense magmatism and to avoluminous crustal magmatic chamber underlying the whole segment.Fine-scale segmentation is most clearly revealed in the structure ofthe central graben within which several 4th-order segments can bedistinguished. This scale of segmentation is also reflected on flanks of theaxis by variations in the character and intensity of faulting.According to structural and petrologic data, the magmatism is mostintense in the central part of the segment which is probably locateddirectly over a magmatic diapir supplying the melt to the whole segment.Magma migration at the subcrustal level from the center towards the ends ofthe segment with discrete injection into the crustal magmatic chamber ispresumed.The central segment is broken into two morphologically distinct partsseparated by a deval. In the subsided northern part, the wide summit of theaxial ridge is cut by a well-developed, intensely fractured axialgraben. In the southern part, the axial ridge is relatively elevated, butnarrow with an ephemeral graben along its crest. The character and intensityof faulting on the axial flanks are also considerably different in thenorthern and southern parts of the segment. Thus, the magmatic supply tothese two parts is thought to originate from two different sources. If so,then at present the magma chamber underlying the southern part of thesegment is probably at the stage of replenishment, while in the north it isat the stage of deep cooling.The southern segment is structurally similar to the central one. Howeverthere is considerably less intensive magmatic activity in this region,especially south of 22°30 S where the axial ridge is narrow, andtriangular in cross-section.Both OSCs studied are marked by abrupt narrowing and sharp subsidence ofthe tips of axial ridges within the northern limbs. The southern OSC limbsare morphologically similar to normal sections of axial ridges. In bothcases the flanks are structurally and morphologically disrupted adjacent tothe OSCs and oblique structures can be traced far southward of the OSCflanks. Due to the spatial position of oblique structures on the the flanksit is presumed that the OSC near 22°07 S is migrating northward.The 21°44 S OSC zone has apparently undergone small spatialoscillations. In spite of the small amplitude of lateral displacement, thiszone is marked by prominent bathymetric anomalies.Numerous massive sulfide deposits were discovered atop the axial ridgealong the entire length of the uplifted and hydrothermally active northernsegment. Ore metal concentrations in near-bottom waters are maximumover the southern part of the northern segment, while maximum concentrationsof the same metals in surficial sediments are confined to the central partof the same segment. We surmise that there has been a recentalong-axis shift of the zone of maximum hydrothermal activity fromthe middle of the segment to its present position in the southern part ofthe segment. Considering sedimentation rates, the age of this shift can beapproximately estimated to be 5 to 10 thousand years before the present.The relatively Mg-enriched basalts of the middle part of thenorthern segment represent a tike of a more primitive pattern, while therelatively Fe-rich rocks of its southern part probably reflect alarge degree of fractionation at shallow crustal levels. Considering thistrend, in addition to morphotectonic data we presume that subaxial magmaflow from the middle to the southern part of the segment is responsible forthe along-axis shift of hydrothermal activity.In the central segment of the study area, massive sulfides have only beendiscovered south of the 21°55 S deval, where the axial ridgeshoals and where the existence of a subjacent magma chamber is presumed.The very weak manifestations of recent volcanism within the southernsegment explain the absence of hydrothermal activity and sulfide depositswithin this segment.     

The fifth-order analytical solution of the equations of motion of a satellite in orbit around a non-spherical planet

A high-precise analytical theory of a satellite in orbit around a non-spherical planet has been developed. The Poisson's small parameter method has been used. All secular and short-periodic perturbations proportional up to and including a product of five arbitrary harmonic coefficients of the planetary potential expansion are calculated. Long-periodic perturbations are derived with the accuracy of up to the fourth-order, inclusive. The influence of the high-order perturbations on the motion of ETALON-1 satellite has been investigated. The results of comparison of the numerical and analytical integration of the equations of its motion over a five year interval are as follows:

On anelliptic approximations for qP velocities in VTI media

A unified approach to approximating phase and group velocities of qP seismic waves in a transversely isotropic medium with vertical axis of symmetry (VTI) is developed. While the exact phase‐velocity expressions involve four independent parameters to characterize the elastic medium, the proposed approximate expressions use only three parameters. This makes them more convenient for use in surface seismic experiments, where the estimation of all four parameters is problematic. The three‐parameter phase‐velocity approximation coincides with the previously published ‘acoustic’ approximation of Alkhalifah. The group‐velocity approximation is new and noticeably more accurate than some of the previously published approximations. An application of the group‐velocity approximation for finite‐difference computation of traveltimes is shown.     

Precursors of Copepod Abundance in the Gulf of Maine in Atmospheric Centers of Action and Sea Surface Temperature

Interannual variations of total copepod abundance in the Gulf of Maine (1961-1991) are analyzed and related to the semi-permanent atmospheric pressure systems: Icelandic Low (IL) and the Azores High (AH). These centers of action dominate atmospheric and oceanic circulation in the North Atlantic. Cross-correlation analysis of zooplankton, sea surface temperature (SST) and the atmospheric characteristics have revealed different (from one to three years) time lags between the above characteristics. A multiple stepwise regression analysis gave a correlation value of 0.7 between observed and predicted interannual changes of total copepod abundance. A discussion is included of possible mechanisms that may contribute to the dynamic links that transfer atmospheric variation into observed changes in zooplankton abundance.