Investigation of some of the principal geometric effects on planetary polarization

Three major geometric factors which are likely to influence theoretical interpretation of planetary polarization measurements, viz., observer—planet distance, horizontal inhomogeneity of planetary disk, and deviation from a spherical body, are investigated.The distance effect is examined for regional as well as global polarizations. For convenience of analysis, the expressions for zenith and azimuth angles of incident and emergent light appropriate for a snap-shot observation are derived as explicit functions of distance between observer and planet. Sample computations for Venus indicate that regional polarization near the planetary limb is significantly affected by the observer's distance. This effect should be particularly noticeable when an observation is made at a phase angle around which the single scattering polarization of atmospheric scattering agents exhibits a steep variation. The global polarization at large phase angles (measured at disk-center) is gradually moved toward smaller phase angles, as the observer approaches the planet. Any narrow polarization features such as rainbow and glory at small phase angles are heavily smoothed out.The effects of horizontal inhomogeneity are investigated with a planetary disk having highly polarizing regions at high latitudes. Comparison of theoretical global polarization computed for such a disk with the Pioneer Venus OCPP measurements shows a possible change in cloud-haze stratification approximately at 50° latitude, consistent with other imaging observations. An approximate analytical representation of residual polarization at zero phase angle is then derived to compare to the numerical results for Venus. An attempt is also made to explain the relatively large magnitude of residual polarization observed on Jupiter.Finally, to study the effects of nonsphericity of planetary body, the global polarizations are computed for a spheroidal planet. The global polarization tends to increase as the planet's oblateness increases. However, for Jupiter and Saturn, such effect may be of secondary importance.     

Electrical Structure in Marine Tectonic Settings

This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations, (2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle. The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab) are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent. Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity patterns in the depth range of 60–200 km.     

The 1998 Hida Mountain, Central Honshu, Japan, earthquake swarm: Double-difference event relocation, frequency–magnitude distribution and Coulomb stress changes

By using the double-difference relocation technique, we have determined the fine structure of seismicity during the 1998 Hida Mountain earthquake swarm. The distribution of seismic activity defines two main directions (N–S and E–W) that probably correspond to the regional stress pattern. The detailed structure of seismicity reveals intense spatio-temporal clustering and earthquake lineations. Each cluster of events contains a mainshock and subsequent aftershock activity that decays according to the Omori law. The seismicity and the b-value temporal and spatial patterns reflect the evolution of the static stress changes during the earthquake swarm. About 80% of the swarm's best-relocated events occur in regions of increased ΔCFF. The smaller value of b found in the northern part of the swarm region and a larger b-value observed to the south, for the same period of time, could be well explained by the static stress changes caused by the larger events of the sequence. We argue that the state of stress in the crust is the main factor that controls the variation of b-value.     

Atmospheric radiative equilibria in a simple column model

 An analytic radiative-equilibrium model is formulated where both short- and longwave radiation are treated as two-stream (down- and upward) fluxes. An equilibrium state is defined in the model by the vertical temperature profile. The sensitivity of any such state to the model atmosphere’s optical properties is formulated analytically. As an example, this general formulation is applied to a single-column 11-layer model, and the model’s optical parameters are obtained from a detailed radiative parametrization of a general circulation model. The resulting simple column model is then used to study changes in the Earth-atmosphere system’s radiative equilibrium and, in particular, to infer the role of greenhouse trace gases, water vapor and aerosols in modifying the vertical temperature profile. Multiple equilibria appear when a positive surface-albedo feedback is introduced, and their stability is studied. The vertical structure of the radiative fluxes (both short- and longwave) is substantially modified as the temperature profile changes from one equilibrium to another. These equilibria and their stability are compared to those that appear in energy-balance models, which heretofore have ignored the details of the vertical temperature and radiation profiles. Received: 22 December 1995/Accepted: 17 January 1997     

Variation of the partial pressure of CO2 in surface water from Kuroshio to Oyashio and the relation between environmental factors and the partial pressure at 144°E off Sanriku, northwestern North Pacific in May, 1997

Partial pressure of CO₂ in surface sea water (pCO₂) was measured continuously off Sanriku in May, 1997 by a new pCO₂ measurement system. We have examined the relation of pCO₂ to physical factors such as temperature, salinity and density, chemical and biological factors such as nutrients and carbonate system and chlorophylla. In the Kuroshio region pCO₂ was not correlated to physical, chemical and biological factors in the range of 260 to 290 μatom. In transition water (Tr1) between Kuroshio and the Oyashio second branch, pCO₂ was weakly correlated to physical factors and strongly correlated to nutrients. In transition water (Tr2) between the Oyashio first and second branches, pCO₂ was highly correlated to temperature (SD: 10.9 μatom) and salinity (SD: 8.6 μatom) and also to nutrients. In transition water (Tr1+Tr2), pCO₂ was highly multivariately correlated to temperature (T), salinity (S), chlorophylla (CH) (or nitrate+nitrite (N)) as follows, pCO₂(μatom)= 10.8×T(°C)+27.7×S+2.57CH(μg/1) −769, R²= 0.86, SD = 20.9, or pCO₂(μatom)= 3.9×T(°C)+25.5×S+16.0NO₃(μM) −686, R²= 0.99, SD = 6.4. Moreover, pCO₂ was predicted by only two factors, one physical (S) and the other chemical/biological (N) as follows: pCO₂ (μatom)=32.8×S+19.4N−908, R²=0.97, SD=8.4. The pH measured at 25°C was well correlated with normalized pCO₂ at a fixed temperature. In the Oyashio region pCO₂ was decreased to 160 μatom, probably because of spring bloom, but was not correlated linearly to chlorophylla. The results obtained showed the possibility of estimating pCO₂ of the Oyashio and transition regions in May by satellite remote sensing of SST, but the problem of estimation of pCO₂ in Kuroshio water remains to be solved.     

A design for digital signal processing in a large field radio patrol camera

An FFT processor is being developed for the present pilot system of the large field radio patrol camera. A design of the processor is discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Observation of the S-component of the solar radio emission by an eight element grating interferometer at 17 Gc/s

The slowly varying components (S-components) of the solar radio emission were observed by a 17 Gc/s grating interferometer. In combination with 4 Gc/s data, it is deduced that the source of the 17 Gc/s S-component is optically thin.     

Spectroscopic Studies of the Solar Corona – V. Physical Properties of Coronal Structures

Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec^–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec^–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures.