F.—PERSONALIA

Abstract

Hydrometeorological investigations are being carried out by the Meteorological Service of the German Democratic Republic in four experimental basins with different altitudes, surface areas and physico-geographical features. This research work predominantly aims at the exploration of the water balance of the respective area, including the possibilities of extending the results by way of extrapolation to larger areas; the setting up, verification and improvement of methods designed for determining the individual components of the water balance, especially the precipitation and evapotranspiration in the respective areas; as well as for obtaining increased knowledge with regard to the heat and water balance of the snow cover. In the following, some of the hitherto achieved results of this complex research activity will be presented.     

On the mode theory of V. L. F. ionospheric propagation

Summary The space between the earth and the ionosphere is considered as a wave-guide with sharply bounded walls. Employing a representation in terms of spherical wave functions of complex order, the field of a vertical dipole source is calculated for very low frequencies. It is shown that the dominant mode for 16 kc is of order one and not zero as has been commonly supposed. Good agreement is obtained with the experimental results ofJ. Heritage.Paper presented at «Colloque International sur la propagation des Ondes Radio électriques» Paris, September 1956.     

Multiple reflections between the earth and the ionosphere in V.L.F. propagation

Summary Treating the ionosphere as a sharply bounded ionized medium, sky wave field intensities are calculated by geometrical-optical methods for very low radio frequencies. The reflection coefficients are discussed in some detail and the numerical data are compared with experiment.     

Annual and semiannual variations in the ionospheric F2-layer. I. Modelling

Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al.     

Comments on “Evolution of Eolian arc volcanism (Southern Tyrrhenian Sea)” by F. Barberi,G. Ferrara,F. Innocenti,J. Keller and L. Villari

Sr-isotopic measurements were performed on samples of each main stage of eruption of the various Eolian islands, coupled with REE and Rb, Sr, U, Th, Hf and Sc determinations.A subcrustal origin is invoked for the older calc-alkaline series related to the subduction zone of the Eolian arc confirming the view of Barberi et al. (1974). A different explanation is given for the shoshonitic association which shows higher⁸⁷Sr/⁸⁶Sr values and different REE concentrations, making a direct derivation from the mantle doubtful. Contamination by crustal material or anatexis of the lower crust are considered as possible mechanisms. Finally the significance of a shoshonitic series is questionned.