Regional Seas and Sustainable Development Results of an International Workshop

Reports

Regional Seas and Sustainable Development Results of an International Workshop     

Sedimentary Features of Shallow Ancient River Channels on the Northern Shelf of the South China Sea

Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand -body types, and discusses thei     

Energy release in a prominence-loaded flaring loop

Zaitsev and Stepanov (1991, 1992) proposed a mechanism for energy release in solar flares that involves the intrusion of dense prominence material into a coronal loop. The resulting non-steady state conditions are claimed to increase the resistance of the loop by 8–10 orders of magnitude. It is shown here that the dramatic increase in resistance calculated by Zaitsev and Stepanov depends on a gross overestimate of the of the magnitude of the magnetic force in the loop prior to the flare trigger. A more realistic estimate of the increase due to the mechanism suggests that it is by no more than about four orders of magnitude. As a consequence, the prominence-loading mechanism does not provide a tenable flare model.     

An examination of directional discontinuities and magnetic polarity changes around interplanetary sector boundaries usingE > 2 keV electrons

Past studies of interplanetary magnetic sector boundaries have been based on the assumption that one can determine the field polarities by comparing the field directions with those of the nominal Parker spiral angles. Previous investigators have found evidence for decreases of B, the magnitude of the magnetic fieldB, and increases of , the angle betweenB and the ecliptic plane, at sector boundaries. Others have argued that the characteristic thickness of sector boundaries exceeds that of tangential discontinuities, making sector boundaries a separate class of structures.We use a simple technique for inferring the polarities of interplanetary magnetic fields based on the assumption thatE > 2 keV electrons are always flowing along the magnetic field away from the Sun. Electron data from the UC Berkeley experiment on the ISEE-3 spacecraft are used to examine periods around several apparent sector boundaries in 1978 and 1979. We compare properties of (a) boundaries with field polarity changes and (b) large-angle ( > 60°) directional discontinuities with no field polarity changes. We find no significant differences between the sector boundaries and the directional discontinuities in terms of associated decreases in B or of values of . These results suggest no significant difference between sector boundaries and directional discontinuities other than the change in field polarities. Within limited statistics we find that about half the polarity changes would not have been identified using a requirement that > 90° and that half of the > 120° discontinuities would have been misidentified as polarity changes.     

Doppler velocity measurements made with a scanning photoelectric magnetograph

We discuss the problems connected with the measurements and evaluation of line-of-sight velocities, obtained with a scanning photoelectric magnetograph using a line-shifter with enhanced sensitivity. We bring arguments for the validity of the results of our photoelectric Doppler velocity recordings. We have found a network of cellularly shaped patterns in the distribution of photo-electrically measured line-of-sight motions, upflowing in the magnetically quiet (blue-shifted) and downflowing in magnetically active (red-shifted) areas of the photosphere, if the mean velocity level is estimated for a sufficiently large measured area. The features of both directions are mutually complementary. We demonstrate the effect of the shift of the reference zero velocity level on the topology of the line-of-sight velocity maps, and the dependence of this level on the size of the area from which it is estimated.     

Capture of dust grains in exterior resonances with planets

The temporary capture of the dust grains in the exterior resonances with planets is studied in the frames of the planar circular three-body problem with Poynting-Robertson (PR) drag. For the Earth and particles ~ 10 m the resonances 4/5, 5/6, 6/7, 7/8 are shown to be most effective. The capture is only temporary (of order 10⁵ years) and the position of resonance may be calculated from semi-analytical model using averaged disturbing function. These semi-analytical results are confirmed by numerical integration. For various planet this picture changes as with increasing planetary mass the more exterior resonances become more important. We showed that for Jupiter (at least in the space between Jupiter and Saturn) the resonance 1/2 plays the dominant role. The capture time is here several myr but again eccentricity is evolving to eccentricity e ₀ ~ 0.48 of libration point for this resonance.     

Solar flare activity and the structure of the coronal neutral line

In this study we analyse the positions of major flares from 1978 and 1979, with respect to the magnetic structure of the solar corona, as described by a potential field model. We find that major flares exhibit no strong association with the neutral line at the chromospheric level. However, when we calculate the neutral line's position at higher and higher altitudes in the corona, we find that major flares show an increasing tendency to be found close to these high-altitude coronal neutral lines. The correlation between flares and higher-altitude coronal neutral lines reaches a maximum at an altitude of 0.35R , and thereafter decreases as the neutral line is moved out to the source surface at an altitude of 1.50R . This indicates that major flares are strongly associated with coronal structure at the 0.35R level ( 250 000 km) - an altitude surprisingly high in the corona. This reinforces the idea that flares are associated with large-scale coronal magnetic fields and also indicates that the region of coronal magnetic topology important to solar flare processes may be larger than previously thought.     

The role of flares, CMEs and CME shocks in the generation of solar energetic proton events

We examined solar energetic proton (SEP) events associated with intense H flares. We located these flares on the solar disk and obtained their distribution in heliographic longitude as well as their angular distance distribution with respect to the neutral lines corresponding to the heliospheric current sheet at 2.5R. We found that the SEP-associated H flares tend to occur in active regions at the feet of those helmet streamers which form the heliomagnetic equator and are related to coronal mass ejections (CMEs) and CME shocks. We discuss the possible role of flares, CMEs and CME shocks in generating SEPs.     

Dynamical evolution of comets and the problem of cometary fading

Possibilities to explain the observed 1/a-distribution are discussed in the light of improved understanding of the dynamical evolution of long-period comets. It appears that the fading problem applies both to single-injection and continuous-injection models. Although uncertainties due to nongravitational effects do not allow detailed results to be drawn from the observed 1/a-distribution at small perihelion distance q, that for q 1.5 AU shows that a constant fading probability cannot explain all the features of the observed distribution. Assuming that comets can reappear following a period of fading, values for the assumed constant fading and renewal probabilities, and the total cometary flux have been estimated for q > 1.5 AU.