Variations In Inclination Research Articles

Paleosecular variations 12–20 Kyr as recorded by sediments from Lake Moreno (Southern Argentina)

We present results of paleomagnetic and sedimentological studies carried out on three cores Lmor1, Lmo98-1, Lmor98-2 from bottom sediments of Lake Moreno (south-western Argentina), and integrate them with data from our previous studies. Measurements of directions (declination D and inclination I) and mass specific intensity of natural remanent magnetization (NRM intensity), magnetic susceptibility (specific, χ and volumetric, κ), isothermal remanent magnetization (IRM), saturation of isothermal remanent magnetization (SIRM), and back field remanent coercivity (B0CR) were performed. The stability of the NRM was investigated using alternating-field demagnetization. The results show that these sediments meet the criteria required to construct a reliable paleomagnetic record. The cores were correlated very well based on magnetic parameters, such as χ and NRM intensity, as well as with lithological features. Tephra layers were identified from the lithological profiles and magnetic susceptibility logs. We obtained the D and I logs of the characteristic remanent magnetization for the cores as a function of shortened depth. The data from the three cores were combined to form a composite record using the Fisher method. A comparison between stacked inclination and declination records of Lake Moreno and those obtained in previous works on Lake Escondido and Lake El Trebol shows good agreement. This agreement made it possible to transform the stacked curves into time series spanning the interval 12–20 kyr. The results obtained improved our knowledge of SV and the behaviour of the geomagnetic field and also allowed us to determine the range of past inclination variations from −70° to −45° for the southern hemisphere, where data are scarce.

A ~5 M ⊕ Super-Earth Orbiting GJ 436? The Power of Near-Grazing Transits

Most of the presently identified exoplanets have masses similar to that of Jupiter and therefore are assumed to be gaseous objects. With the ever-increasing interest in discovering lower mass planets, several of the so-called super-Earths (1 M? < M < 10 M?), which are predicted to be rocky, have already been found. Here we report the possible discovery of a planet around the M-type star GJ 436 with a minimum mass of 4.7 ? 0.6 M? and a true mass of ~5 M?, which would make it the least massive planet around a main-sequence star found to date. The planet is identified from its perturbations on an inner Neptune-mass transiting planet (GJ 436b), by pumping eccentricity and producing variations in the orbital inclination. Analysis of published radial velocity measurements indeed reveals a significant signal corresponding to an orbital period that is very close to the 2:1 mean motion resonance with the inner planet. The near-grazing nature of the transit makes it extremely sensitive to small changes in the inclination.

High resolution radiant distribution and orbits of sporadic radar meteoroids

Five years of meteor orbit data from CMOR (the Canadian Meteor Orbit Radar) are used to study the high-resolution orbital structure of the sporadic meteoroid complex. The large number of high quality orbits (2.35 million) allows the orbital characteristics of meteoroids to be studied not only in the five sporadic sources accessible from the latitude of London, Ontario, Canada, but at a resolution of 2 degrees. The radiant distribution of sporadic meteors is investigated, applying corrections for observing biases, and weighting to a constant limiting mass, and to a constant limiting energy. The orbital distribution of the sporadic sources is compared to other studies. The variation of average geocentric speed, semimajor axis, eccentricity, inclination and perihelion distance with meteoroid radiant is investigated. The source of a ring depleted in meteor radiants at 55 degrees from the apex is attributed to shorter collisional lifetimes inside the ring, due to a higher probability of catastrophic collisions with particles in the zodiacal cloud for the predominantly retrograde meteoroids inside the ring.

Coulomb-type solutions for passive earth pressure with steady seepage

Present paper deals with the computing of passive earth pressure acting on the vertical rigid retaining wall supporting the soil mass subjected to water seepage. The basic assumptions of Coulomb’s theory and the 2-dimensional steady flow function are used. Three Coulomb-type solutions for the passive earth pressures are presented for the walls provided with three different drainage systems respectively. Based on the general solutions, the variations of the critical inclination of the failure surface and the coefficient of passive earth pressure with increasing the effective friction angle of the soil mass, the soil/structure friction angle, and the water/soil unit weight ratio are discussed. Two tables with values of the coefficients of passive earth pressure for Cases 1 and 3 respectively are also presented.

Relative paleointensity record during the last 800 ka from the equatorial Indian Ocean: Implication for relationship between inclination and intensity variations

Paleomagnetic and rock magnetic investigations were carried out on three sediment cores taken from the Ninetyeast Ridge, the eastern equatorial Indian Ocean. The cores are 4.1–10.2 m long and cover the last 270–790 ka with average sedimentation rates of 1.3–1.9 cm/ka. Generally stable demagnetization behaviors and relatively uniform rock magnetic characteristics allowed us to reconstruct relative paleointensity records (NRM30mT/IRM30mT) for each core. The relative paleointensity records showed a beneficial agreement with each other except for the uppermost parts of the cores, and patterns similar to the Sint‐800 paleointensity stack and other relative paleointensity records. Spectral analyses of the relative paleointensity records revealed a dominant periodicity at about 100 ka, but not for the normalizer and other rock magnetic proxies. These results suggested that the 100 ka periodicity in the paleointensity records during the Brunhes Chron would not be caused by sedimentological effects. The mean inclination values of the three cores were close to the expected hypothetical geocentric axial dipole (GAD) direction, which implies that ∼5–10° of negative inclination anomaly (ΔI) is centered at the western equatorial Pacific Ocean, and not extended to the eastern equatorial Indian Ocean. A comparison between the relative paleointensity variation and ΔI amplitude between the eastern equatorial Indian Ocean and the western equatorial Pacific Ocean suggests that changes of the GAD intensity control the relative contribution of the persistent nondipole components and produces the inclination variation.

The Effect of Free Surface on the Vortex Shedding From Inclined Circular Cylinders

Spectral analysis of laser Doppler velocimetry measurements and flow visualization are employed to study the wake of inclined cylinders piercing a free surface. The results indicate that the free surface affects vortex shedding almost two to three cylinder diameters below the free surface. Variation of the vortex axis inclination and cells of shedding were visually observed. These effects induce a phase difference in the vortex-shedding mechanism. Streamwise vortical structures are formed along the primary vortex axis. Furthermore, for the case of the highest Froude number, evidence is provided that vortex shedding is suppressed in the region near the free surface.

Geomagnetic field behavior at high latitudes from a paleomagnetic record from Eltanin core 27–21 in the Ross Sea sector, Antarctica

We present a high-resolution paleomagnetic record from 682 discrete samples from Eltanin 27–21 (69.03°S 179.83°E), a 16-meter long piston core recovered in 1968 at a water depth of 3456 m by the USNS Eltanin as part of Operation Deep Freeze. After removal of a low-coercivity overprint, most samples yield stable characteristic remanent magnetization directions. The downhole variation in the magnetic inclination provides a well-resolved magnetostratigraphy from the Brunhes Chron (0–0.781 Ma), through the Reunion Subchron (2.128–2.148 Ma), and into Chron C2r.2r. The sedimentation rates are sufficiently high that even short-term geomagnetic features, like the Cobb Mountain excursion, are resolved. The record from Eltanin 27–21 provides new insights into the behavior of the geomagnetic field at high latitudes, about which very little is currently known. Using the variability in the inclinations during stable polarity intervals, we estimate that the dispersion in the paleomagnetic pole position over the past ~ 2 Myr is 30.3° ± 4.3°, which is significantly greater than observed at low to mid latitude sites. The higher dispersion observed at Eltanin 27–21 is consistent with numerical modeling of the geodynamo. That modeling has shown that polar vortices can develop in the Earth's core within the tangent cylinder, defined as the cylinder coaxial with the Earth's rotation axis and tangent to the inner core/outer core boundary. The polar vortices produce vigorous fluid motion in the core, which creates greater geomagnetic field variability above the tangent cylinder at the surface of the Earth. The tangent cylinder intersects the Earth's surface in the polar regions at 79.1° latitude, which is relatively close to the latitude of Eltanin 27–21.

Manifestation of the Gothenburg geomagnetic field excursion in the Barents Sea bottom sediments

An analysis of the paleomagnetic characteristics of the bottom sediments taken in 2000 in the northern Barents Sea for the first time revealed the Gothenburg geomagnetic field excursion (13 000–12 000 years ago) at the time boundary of the transition from the glacial period to the recent warm epoch (the Holocene). The obtained data confirm the excursion complex structure: the presence of two successive time intervals of variations in the geomagnetic field inclination. An increase in the magnetic susceptibility and natural remanent magnetization of the samples at the above boundary and about 15 000 years ago indicates that the magnetic parameters of the sediments respond to climate changes in the environment in this time interval.

The geomagnetic field recorded in sediments of the Tuzla section (the Krasnodar Territory, Russia) over the time interval 120–70 ka

Petro-and paleomagnetic methods are applied to the study of the lower part of the Early Pleistocene Tuzla section on the Black Sea coast of the Taman Peninsula, This part of the section is composed of marine and lagoonal sediments deposited over the time interval 120–70 ka. The measured curves of the variation in the geomagnetic field inclination reveal an anomalous direction dated at ∼110 ka that coincides with a similar anomalous direction in the Eltigen section (Ukraine) correlating with the Blake paleomagnetic event. The significant correlation between the time series NRM0.015/SIRM0.015 (Tuzla section) and the world composite Sint-800 curve indicates that the curve NRM0.015/SIRM0.015 in the interval 110–70 ka actually reflects the variation in the relative paleointensity of the geomagnetic field.

The Palaeomagnetic Studies of Varved Clays from Warsaw Basin

Summary The palaeomagnetism of varved clays from Mochty and Plecewice which were deposited in the Warsaw Basin during the Middle Polish glaciation has been studied. Magnetite was identified as a main carrier of remanence. The discussion of palaeomagnetic directions and the secular variations of magnetic declination and inclination during an interval of 250 yr about 150 000 yr ago are described.

Discrimination of density flow deposits using elemental geochemistry—Implications for subtle provenance differentiation in a narrow submarine canyon, Palaeogene, Danish North Sea

Elemental geochemistry of 1131 sandstone samples has been used to characterise five Palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon, Danish North Sea. Diagenetic overprinting has complicated the use of most main and trace elements, but a group of “heavy mineral bound” elements with low mobility (Ti, Y, Zr, Nb and Th) has proved highly potential for correlation. The individual sandstone members exhibit very consistent relations between the “heavy mineral elements” along the canyon and, based on Zr/Ti plots, two families of sandstone members can be distinguished. The families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance/source area. The inclination is believed to be controlled by the detrital heavy mineral (HM) suite and composition, whereas the intersections are controlled by the background contribution, such as HM inclusions in detrital rock forming minerals, e.g. quartz and/or feldspar, as well as substituted and/or adhered elements in glauconite. The correlation pattern has been used to suggest a re-interpretation of the stratigraphic relation of some of the sands.

Holocene paleosecular variation from dated lava flows on Maui (Hawaii)

Low inclination and low secular variation seem to be present for at least the past 5 Myear in central Pacific. The period covering the past 10 kyear is crucial to the study of the field variability and to fill the gap between historical field measurements and long-term paleomagnetic records. We have conducted a paleomagnetic study of 13 sites of basaltic lava flows from Maui island with 14C ages between 10.3 and 0.2 ka. Two other sites dated at 45 and 730 ka were also sampled. Eight to 10 samples from each site were demagnetized using thermal treatment and companion specimens from the same samples were demagnetized by alternating fields (af). Thermomagnetic and hysteresis measurements indicated that magnetite (575 °C) in fine grains was the dominant magnetic carrier, although in many cases we also observed a low-temperature phase which is likely carried by titanomagnetite with low titanium content. The existence of relatively high coercivities associated with these two mineralogical phases generated overlapping components which could not be properly isolated using af demagnetization. Successful results were obtained after thermal demagnetization for 13 sites with a mean inclination of 36.9 ± 4°. The mean inclination (inc. = 36.3°) of the eleven sites younger than 10.5 ka is also very close to the value (37°) of the geocentric axial dipole (GAD) at the site latitude, but the angular dispersion of the virtual geomagnetic poles (VGPs) about the spin axis (9° with N = 13 and 6.7° with N = 11) is significantly lower than the predictions of the models of paleosecular variation at this latitude. The inclination variations for the past 10 kyear are in excellent agreement with the very detailed dataset which has previously been obtained from the big island of Hawaii. The mean inclination of all volcanic records ( N = 132) is 1.8° lower than expected, but this is likely caused by the lack of records between 5 and 7 ka B.P. We note also that the inclinations from Lake Waiau sediments (big island) are shallower than those of the volcanic records (Mauna Kea, Hawaii) and were thus probably affected by compaction. We infer that there is no striking evidence for an inclination anomaly under Hawaii during this period, being aware of the need for additional records covering at least the 5–7 ka B.P. time interval. The absence of a systematic deviation going beyond the dispersion of the inclinations obtained for the past millions of years neither pleads for a significant long-term persistent anomaly. However, all studies report a low dispersion of the VGPs which must reflect low secular variation.

Solar Variability and Climate Impact on Terrestrial Planets

Some possible factors of climate changes and of long term climate evolution are discussed with regard of the three terrestrial planets, Earth, Venus and Mars. Two positive feedback mechanisms involving liquid water, i.e., the albedo mechanism and the greenhouse effect of water vapour, are described. These feedback mechanisms respond to small external forcings, such as resulting from solar or astronomical constants variability, which might thus result in large influences on climatic changes on Earth. On Venus, reactions of the atmosphere with surface minerals play an important role in the climate system, but the involved time scales are much larger. On Mars, climate is changing through variations of the polar axis inclination over time scales of ∼105–106 years. Growing evidence also exists that a major climatic change happened on Mars some 3.5 to 3.8 Gigayears ago, leading to the disappearance of liquid water on the planet surface by eliminating most of the CO2 atmosphere greenhouse power. This change might be due to a large surge of the solar wind, or to atmospheric erosion by large bodies impacts. Indeed, except for their thermospheric temperature response, there is currently little evidence for an effect of long-term solar variability on the climate of Venus and Mars. This fact is possibly due to the absence of liquid water on these terrestrial planets.

CHAMP and GRACE resonances, and the gravity field of the Earth

Using orbital data far more precise than existed a quarter of a century ago, we have derived values for lumped geopotential harmonic coefficients from the passage of the satellites CHAMP (Challenging Minisatellite Payload) and GRACE (Gravity Recovery And Climate Experiment) through particular resonances. Due to orbit decay, CHAMP first passed through the 46/3 resonance (orbit repeating after 46 revolutions over three days) and then, in due course, 77/5, 31/2 and 47/3; indeed it passed through 31/2 three times, following orbit raises to extend the satellite’s useful lifetime. The orbit data we used for CHAMP came from the retrospectively computed and highly accurate state vectors, but for GRACE (both satellites) only the routine (less accurate) TLEs (Two-Line mean Elements) have so far been available, being used for 61/4 analysis. Values for the lumped harmonics come from analysis of the large variation in the orbital inclination (and to a lesser degree the nodal right ascension) that they cause. Our main success has been for the 31/2 resonance, including the implicit 62/4, but in all cases our lumped values agree well with values based on the complete CHAMP and GRACE high-degree global gravity models (Eigen-3p and Eigen-Grace02s, respectively), though essentially independent of them. This confirms both the validity of our method and the high quality of the new global models.

An analytical study of the powered swing-by to perform orbital maneuvers

In the present paper, we present an analytical description of the powered swing-by maneuver in the three-dimensional space. To perform this task, new analytical equations are derived for the three-dimensional unpowered swing-by, including the variation in velocity, angular momentum, energy and inclination of the spacecraft due to the maneuver. This is done based on the patched-conics approximation. From those general three-dimensional equations, it is possible to confirm some well-known analytical results for the planar case. The equations developed here are verified by numerical integrations, using the restricted problem of three bodies, showing an agreement better than 1%. After that, based on those equations, some new analytical results are obtained for the situation when an impulse is applied to the spacecraft during the close approach. Those new equations are based in the assumption that the impulse applied is small compared to the velocity of the spacecraft, and they allow the calculation of the same variations cited above. Those equations can be simplified for specific cases, and it can generate some conclusions about the direction to apply the impulse to attend specific goals. A study is also executed to investigate in which cases the impulse is more efficient when applied at the periapsis of the swing-by hyperbola or at points far way from the swing-by body.

Obtaining of information about the IMF evolution from an analysis of the geomagnetic field data

A comparison of the time variations in the geomagnetic field characteristics (the u and aa indices of geomagnetic activity) with the variation in the solar magnetic dipole inclination shows close agreement between these variations. The linear correlation coefficients between the u and aa indices, the u index and solar magnetic dipole inclination, and the aa index and solar magnetic dipole inclination are 0.93, 0.45, and 0.49, respectively. This makes it possible to extend studying the IMF evolution in the 11-year cycle of solar activity to the 170-year period beginning from 1835. It has been indicated that the time variation in the heliospheric current sheet (HCS) surface deviation from the solar magnetic equator plane, calculated based on the actual HCS configuration, is in good agreement with the time variation in the amplitude of the Fourier series second harmonics in a harmonic analysis of the series of daily data on the IMF sign in the vicinity of the Earth. The linear correlation coefficient is 0.9 in this case.

Fore-and-aft transmissibility of backrests: Effect of backrest inclination, seat-pan inclination, and measurement location

Car seats have inclined backrests and inclined seat-pans, but there has been little study of how the inclinations of the surfaces of a seat influence the transmission of fore-and-aft vibration through the backrest. The effects of backrest inclination and seat-pan inclination on the fore-and-aft transmissibilities of two seats (a car seat and a rigid seat with solid foam backrest) have been investigated in the laboratory. With 12 subjects, each seat was exposed to random fore-and-aft vibration in the frequency range 0.25–20 Hz with a vibration magnitude of 0.4 ms −2 rms. At six vertical locations on each backrest, the fore-and-aft transmissibilities of the backrests were measured with four backrest inclinations (90° (i.e. vertical), 105°, 100°, and 105°) and up to four seat-pan inclinations (0° (i.e. horizontal), 5°, 10°, and 15°). At all six measurement locations, there was a resonance of both backrests at about 4 Hz, which increased in frequency with increasing backrest inclination for the car seat but showed little change with inclination for the foam backrest. The inclination of the backrest had more influence at the bottom that at the top of the backrest of the car seat, but showed little variation with position on the foam backrest. Variations in seat-pan inclination had little influence on the resonance frequencies of either backrest at any location. Inclining the backrest and the seat-pan increased the transmissibility at resonance with the car seat, but produced little change with the foam backrest. It is concluded that both the backrest inclination and the seat inclination can affect the fore-and-aft transmissibility of backrests but, with moderate changes of inclination, the effects are not large.

Magnetostatic penumbra models with field-free gaps

We present numerical 2D magnetostatic models for sunspot penumbrae consisting of radially aligned field-free gaps in a potential magnetic field, as proposed by Spruit and Scharmer (2006). The shape of the gaps and the field configurations around them are computed consistently from the condition of magnetostatic pressure balance between the gap and the magnetic field. The results show that field-free gaps in the {\it inner} penumbra are cusp-shaped and bounded by a magnetic field inclined by about $70^\circ$ from the vertical. Here, the magnetic component has a Wilson depression on the order 200--300 km relative to the top of the field-free gap; the gaps should thus appear as noticeably elevated features. This structure explains the large variations in field strength in the inner penumbra inferred from magnetograms and two-component inversions, and the varying appearance of the inner penumbra with viewing angle. In the {\it outer} penumbra, on the other hand, the gaps are flat-topped with a horizontal magnetic field above the middle of the gap. The magnetic field has large inclination variations horizontally, but only small fluctuations in field strength, in agreement with observations.

Study of slow n = 1, m = 1 reconnection in JET discharges with low central magnetic shear

Experiments designed for the attainment of the hybrid advanced mode of operation in JET revealed the existence of a new form of reconnecting modes with toroidal number n = 1 and poloidal number m = 1, which have the same radial structure as sawtooth precursors but are characterized by small growth rate and low saturation amplitude. These modes develop in repetitive cycles with typical growth times of 100 ms. Temperature perturbations are not in the form of sawteeth; in fact, there is slow and mild erosion of the central temperature without any crash. Comparison with theory of m = 1 modes indicates that the slow growth observed in the hybrid regime is caused by low magnetic shear (a measure of the radial variation of field line inclination) and possibly by diamagnetic effects in the plasma core.

Stem Phototropism of Trees: A Possible Significant Factor in Determining Stem Inclination on Forest Slopes

The main stems of trees on forest slopes incline down the slope to various extents that are characteristic of the species. The inclination has been explained as an active response to a horizontally asymmetrical light environment, but the contributing physiological mechanisms are unknown. The present study tested the hypothesis that stem phototropism, gravitropism, or a combination of the two determines the inclination of tree stems on forest slopes. Cryptomeria japonica, Pinus densiflora, Quercus myrsinaefolia and Q. serrata were studied. Measurements were made of stem inclination of mature trees on forest slopes in uniform plantations of each species, and changes in stem inclination of potted seedlings in response to illumination treatments (unilateral or overhead) and inclination treatments (artificially inclined or erect). Indices of phototropic and gravitropic responsiveness were evaluated for each species, calculated from the change in stem inclination in response to artificial inclination with unilateral or overhead illumination. Stem inclination on forest slopes varied significantly among species: Q. serrata inclined most in the down-slope direction, C. japonica inclined the least, and P. densiflora and Q. myrsinaefolia were intermediate. The change in stem inclination of seedlings in each treatment varied significantly among species. One-year-old stems of Q. serrata and 2-year-old stems of Q. myrsinaefolia bent toward the light source. Interspecific variation in the change in stem inclination in response to the unilateral illumination or that in the index of phototropic responsiveness was strongly correlated with the variation in stem inclination on forest slopes. The orientation of woody stems that have finished elongation can be actively controlled by phototropism. Interspecific variation in phototropic responsiveness of trees is a possible significant determinant of interspecific variation in stem inclination on forest slopes.