Geomagnetic secular acceleration

Summary. A spherical harmonic model of the second time-derivative of the geomagnetic field is determined, for the first time, directly from measures of the secular acceleration based on observatory annual mean data. The data span the interval 1964.5–1975.5, and 165 observatories are included. The model comprises the 32 coefficients of degree and order up to 6 that are significant at the 5 per cent level. Its primary purpose is to aid in the reduction of data to epoch for the 1980 series of navigational charts. The model is compared with earlier estimates of secular acceleration, derived by less direct methods.     

Main problems of water use and transfer of technology

Man and water are closely related in a dualistic manner: on one hand water has great influence on man's welfare and social development, on the other man's activities greatly affect water as such. Comparing the present and future water needs with water availability, the author concludes that some world regions should be considered as truly water scarce at least during the next generation. Man's activities create water problems which tend to change with time and exhibit a regional pattern. Many problems can be avoided if advance impact studies were made more regularly for planned water-related activities and projects. The author ends by stressing that differences in climate, hydrology, culture and dominating water problems tend to complicate the important process of transfer of knowledge between temperate and tropical countries.     

The Sq current system during the International Geophysical Year

Summary. The daily variation for the mean of the eight most quiet days of the IGY is represented as a function of latitude, longitude and UT by means of a spherical harmonic model. The most appropriate choice of Sq baseline is investigated, on the assumption that the external electric currents deduced from the model should be negligible at local midnight. The properties of the final model are discussed, particularly with regard to the external current foci, and are compared with those of previous models.     

Climate, weather, and north polar observations from the Mars Reconnaissance Orbiter Mars Color Imager

The Mars Reconnaissance Orbiter observes Mars from a nearly circular, polar orbit. From this vantage point, the Mars Color Imager extends the ∼5 Mars years record of Mars Global Surveyor global, visible-wavelength multi-color observations of meteorological events and adds measurements at three additional visible and two ultraviolet wavelengths. Observations of the global distribution of ozone (which anti-correlates with water vapor) and water ice and dust clouds allow tracking of atmospheric circulation. Regional and local observations emphasize smaller scale atmospheric dynamics, especially those related to dust lifting and subsequent motion. Polar observations detail variations related to the polar heat budget, including changes in polar frosts and ices, and storms generated at high thermal contrast boundaries.     

Encounters with an unearthly mudstone: Understanding the first mudstone found on Mars

The Sheepbed mudstone forms the base of the strata examined by the Curiosity rover in Gale Crater on Mars, and is the first bona fide mudstone known on another planet. From images and associated data, this contribution proposes a holistic interpretation of depositional regime, diagenesis and burial history. A lake basin probably received sediment pulses from alluvial fans. Bed cross‐sections show millimetre to centimetre‐scale layering due to distal pulses of fluvial sediment injections (fine‐grained hyperpycnites), fall‐out from river plumes, and some aeolian supply. Diagenetic features include mineralized synaeresis cracks and millimetre‐scale nodules, as well as stratiform cementation. Clay minerals were initially considered due to in situ alteration, but bulk rock chemistry and mineralogy suggests that sediments were derived from variably weathered source rocks that probably contained pre‐existing clay minerals. X‐ray diffraction analyses show contrasting clay mineralogy in closely spaced samples, consistent with at least partial detrital supply of clay minerals. A significant (ca 30 wt%) amorphous component is consistent with little post‐depositional alteration. Theoretical modelling of diagenetic reactions, as well as kinetic considerations, suggest that the bulk of diagenetic clay mineral formation occurred comparatively late in diagenesis. Diagenetic features (synaeresis cracks and nodules) were previously thought to reflect early diagenetic gas formation, but an alternative scenario of synaeresis crack formation via fabric collapse of flocculated clays appears more likely. The observed diagenetic features, such as solid nodules, hollow nodules, matrix cement and ‘raised ridges’ (synaeresis cracks) can be explained with progressive alteration of olivine/glass in conjunction with centrifugal and counter diffusion of reactive species. Anhydrite‐filled fractures in the Sheepbed mudstone occurred late in diagenesis when fluid pressures built up to exceed lithostatic pressure. Generating fluid overpressure by burial to facilitate hydraulic fracturing suggests a burial depth of at least 1000 m for the underlying strata that supplied these fluids.