Solar constant and sunspots

Summary The relationship, already found by the authors, between sunspot numbers and the solar constant, as deduced from the highest global irradiance values at noon, is here reexamined and confirmed. Some attempts at explanation and further inferences are presented.     

The composition and vertical structure of the lower cloud deck on Venus

The opportunity to determine the planetwide temperature and cloud structure of Venus using radio occultation techniques arose with Pioneer Venus. Amplitude and Doppler data provided by the radio occultation experiment offered a unique and powerful means of examining the atmospheric properties in the lower cloud region.Absorption due to gaseous components of the atmosphere was subtracted from the measured absorption coefficient profiles before they were used to compute cloud mass contents. This absorption was found to represent a small part of the total absorption, depending on the latitude. In the main cloud deck, gaseous absorption contributes 10 to 20%, however, at the bottom of the detected absorption layer the sulfuric acid vapor contributes up to 100% due to increased vapor pressures. The clouds are the primary contributing absorbers in the 1- to 3-bar level of the Venus atmosphere. Below about 3 bars, depending on the latitude, absorption due to sulfuric acid vapor dominates.If a cloud particle model consisting of a solid nonabsorbing dielectric sphere with a concentric liquid sulfuric acid coating is invoked, the absorptivity of the particles increases from that of a pure sulfuric acid liquid sphere, and the mass content derived from the absorption coefficient profiles decreases. As the ratio of the core radius to the total radius (q) increases, absorption increases by more than a factor of 10 for high values of q. In the case of pure sulfuric acid droplets, the conductivity is sufficiently high that some of the field is excluded from the interior of the droplet thereby reducing the absorption. When a dielectric core of nonabsorbing material is introduced, the surface charge density is reduced and the absorption increases.The mass contents for all orbits in the equatorial region of Venus were calculated using values of q from 0 to 1. The resulting profiles match the probe mass content profiles at similar locations when a q of 0.97 is chosen.The wavelength dependence of the absorption for the spherical shell model varies with q from 1/λ² for pure liquid to λ^0.2 for a large core. A q of from 0.96 to 0.98 results in a wavelength dependence of 1/λ^1.0 to 1/λ^1.4 which matches the radio occultation absorption wavelength dependence and the microwave opacity wavelength dependence.Mass content profiles using a q of 0.97 were determined for occultations in the polar, collar, midlatitudinal, and equatorial regions assuming q remains constant over the planet. The results show considerable variability in both the level and the magnitude of the lower cloud deck. The cloud layer is lowest in altitude in the polar region. This might be expected as the temperature profile is cooler in the polar region than over the rest of the planet. The mass content is greatest in the polar and collar regions; however, many of the collar profiles were cut off due to fluctuations resulting from increased turbulence in the collar region. The mass contents are least dense in the midlatitude regions. There is a sharp lower boundary at about 1.5 bars in the equatorial and midlatitude regions and at about 2.5 bars in the polar region. Measurements made by the Particle Size Spectrometer and nephelometers also showed sharp lower cloud boundaries at this level.     

An instrument to measure solar magnetic fields by an atomic-beam method

Using the atomic-beam technique in absorption, a new kind of very narrow-passband filter is obtained, which may also be used as a high-resolution spectrograph and as a Babcock window for detecting solar magnetic fields without a spectrograph.     

Some developments of the magnetic beam absorption filter

In the present paper some experimental arrangements are shown which utilize the magnetic filter described by Cimino et al. (1968). For a single cell we have elaborated an elementary theory in the following cases: (i) absorption by an atomic beam in a uniform magnetic field (i.e. pure damping profile); (ii) atomic beam in a non-uniform magnetic field; (iii) vapours in a uniform magnetic field (i.e. gaussian distribution); (iv) vapours in a non-uniform magnetic field.     

Liquid content of the lower clouds of venus as determined from mariner 10 radio occultation

S-band (13.06-cm) and X-band (3.56-cm) radio occulation data obtained during the flyby of Venus by Mariner 10 on February 5, 1974 were analyzed to obtain the effects of dispersive microwave absorption by the clouds of Venus. The received power profiles were first corrected for the effects of refraction in the atmosphere of Venus, programmed changes in the pointing direction of the high-gain antenna, and limit-cycle motion of the spacecraft attitude control system. The resulting excess attenuation profiles presumbaly due to cloud absorption have been inverted discretely to obtain profiles of absorption coefficient at the two wavelenghts. The ratios of the absorptivities are consistent with a sulfuric acid-water mixture as the constituent of the absorbing clouds, having a sulfuric acid concentration of 75 ± 25%. Three absorption peaks are evident in the profiles at altitudes of 68, 60, and 48 km. With a sulfuric acid concentration of 75%, the upper cloud has a peak liquid content of 0.08 g/m³, and an integrated content of 0.024 g/cm², which corresponds roughly to terrestrial stratus or altostratus clouds. The major absorption layer has a peak of 1.1 g/m³ at an altitude of 48 km, with an integrated content of 0.5 g/cm², similar to that of terrestrial cumulus and cumulonimbus clouds. The absorption ratios for the middle cloud at 60 km are not consistent with a sulfuric acid-water mixture.     

A multi-disciplinary study of the 2002–03 Etna eruption: insights into a complex plumbing system

The 2002–03 Mt Etna flank eruption began on 26 October 2002 and finished on 28 January 2003, after three months of continuous explosive activity and discontinuous lava flow output. The eruption involved the opening of eruptive fissures on the NE and S flanks of the volcano, with lava flow output and fire fountaining until 5 November. After this date, the eruption continued exclusively on the S flank, with continuous explosive activity and lava flows active between 13 November and 28 January 2003. Multi-disciplinary data collected during the eruption (petrology, analyses of ash components, gas geochemistry, field surveys, thermal mapping and structural surveys) allowed us to analyse the dynamics of the eruption. The eruption was triggered either by (i) accumulation and eventual ascent of magma from depth or (ii) depressurisation of the edifice due to spreading of the eastern flank of the volcano. The extraordinary explosivity makes the 2002–03 eruption a unique event in the last 300 years, comparable only with La Montagnola 1763 and the 2001 Lower Vents eruptions. A notable feature of the eruption was also the simultaneous effusion of lavas with different composition and emplacement features. Magma erupted from the NE fissure represented the partially degassed magma fraction normally residing within the central conduits and the shallow plumbing system. The magma that erupted from the S fissure was the relatively undegassed, volatile-rich, buoyant fraction which drained the deep feeding system, bypassing the central conduits. This is typical of most Etnean eccentric eruptions. We believe that there is a high probability that Mount Etna has entered a new eruptive phase, with magma being supplied to a deep reservoir independent from the central conduit, that could periodically produce sufficient overpressure to propagate a dyke to the surface and generate further flank eruptions.Editorial responsibility: J. Donnelly-Nolan     

Globalisation and regional integration: the case of the Italian urban system

A recent study on the European integration of the Italian urban system shows that globalisation processes do not necessarily separate cities from their regional networks. The most successful cases of recent urban development in Italy are associated with the formation of metropolitan networked regions in which a major metropolitan centre is linked with cities of a lower level by hierarchical, complementary and synergetic relations. The paper examines the result of an analysis carried out on 148 major Italian daily urban systems. It takes into account two sets of indicators: one referring to the supraregional network interactions, measuring the degree of globalisation, and one referring to the proximity interactions inside the regional networks, measuring the degree of regional cohesion. They allow the definition of typologies of urban systems founded on a (normally positive) correlation between supraregional functional openness and regional integration.