Total ozone variations in the tropical belt: An application for quality of ground based measurements

Summary The study of the regime of ozone variations in the huge tropical belt (25° S to 25° N), which are, in general, very small and zonally nearly symmetric, permits to establish a statistical model for estimating the ozone deviations using Total Ozone Mapping Spectrometer (TOMS) data. The equatorial stratospheric winds at 25 and 50hPa and the solar flux at 10.7 cm are used as major predictors and the linear trend was also estimated. The 10m/sec stratospheric wind change is related to1.2% ozone change at the equator, to practically no change in the 8–15° belts and up to 1.4% change with opposite phase over the tropics in spring but nearly zero change in fall. The solar cycle related amplitude is about 1.4% per 100 units of 10.7 cm solar flux. The ozone trends are negative: not significant over the equator and about –2% per decade (significant at 95% level) over the tropics. The latter could have been enforced by the 2 to 4% lower ozone values during 1991–1993, part of which might be related to the effects of the Mt. Pinatubo eruption, but might also be due to the strong QBO. The estimated deviations are verified versus reliable observations and the very good agreement permits applying the model for quantitative quality control of the reported ozone data from previous years. The standard deviation of the difference between observed ozone deviations and those estimated from the model is only 0.9–1.6% for yearly mean, that means instruments used for total ozone observations in the tropical belt should have systematic error of less than 1%. Cases when the discrepancies between the model and reported observations at a given station exceed 2–3% for time interval of 2 or more years should be verified.With 17 Figures     

Design of land-air parameterization scheme (LAPS) for modelling boundary layer surface processes

Summary A land-air parametrization scheme (LAPS) describes mass, energy and momentum transfer between the land surface and the atmosphere. The scheme is designed as a software package which can be run as part of an atmospheric model or a stand-alone scheme. A single layer approach is chosen for the physical and biophysical scheme background. The scheme has six prognostic variables: two temperatures (one for the canopy vegetation and one for soil surface), one interception storage, and three soil moisture storage variables. The scheme's upper boundary conditions are: air temperature, water vapour pressure, wind speed, radiation and precipitation at some reference level within the atmospheric boundary layer. The sensible and latent heat are calculated using resistance representation. The evaporation from the bare soil is parametrized using the scheme. The soil part is designed as a three-layer model which is used to describe the vertical transfer of water in the soil.The performances of the LAPS scheme were tested using the results of meteorological measurements over a maize field at the experimental site De Sinderhoeve (The Netherlands). The predicted partitioning of the absorbed radiation into sensible and latent heat fluxes is in good agreement with observations. Also, the predicted leaf temperature agrees quite well with the observed values.With 9 Figures     

Quantification of the effects of secondary matrix on the analysis of sandstone composition, and a petrographic-chemical technique for retrieving original framework grain modes of altered sandstones

Most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine-grained breakdown products of labile mineral grains and rock fragments, usually termed secondary matrix or pseudomatrix. However, the data presented here demonstrate that, when the proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic analysis can lead to incorrect provenance interpretation. Petrographic schemes for provenance analysis such as QFL and QFR should not therefore be applied to sandstones containing more than 10% secondary matrix. Pseudomatrix is commonly abundant in sandstones, and this is therefore a problem for provenance analysis. The difficulty can be alleviated by the use of whole-rock chemistry in addition to petrographic analysis. Combination of chemical and point-count data permits the construction of normative compositions that approximate original framework grain compositions. Provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport. Many sandstones, particularly shallow marine deposits, have undergone vigorous reworking, which may destroy unstable mineral grains and rock fragments. In such cases it may not be possible to retrieve provenance information by either petrographic or chemical means. Because of this, pseudomatrix-rich sandstones should be routinely included in chemical-petrological provenance analysis. Because of the many factors, both pre- and post-depositional, that operate to increase the compositional maturity of sandstones, petrologic studies must include a complete inventory of matrix proportions, grain size and sorting parameters, and an assessment of depositional setting.     

Revised chemical models of ζ Oph based on HST data

Hubble Space Telescope observations by Savage, Cardelli and Sofia (1992) and Cardelliet al. (1993) have led to improved gas phase abundances for many elements in the diffuse cloud towards the star Oph. Most remarkably, it was found that oxygen is much more strongly depleted than previousCopernicus observations indicated. As a consequence, chemical models of the Oph cloud are severely affected by the drop in the observed oxygen abundance by almost a factor of two; some previous model calculations for the Oph cloud failed to reproduce-even approximately-the observed high CO column density. The model calculations for the Oph cloud developed by Wagenblast (1992) in which the abundance of all observed neutral molecules could be reproduced have been revised and it is found that oxygen and nitrogen hydrides are required to be formed efficiently on the surface of grains; further, there are indications for a high cosmic ray ionization rate of the order 10^–16 s^–1.     

Wound magnetostatics and flaring

We discuss the winding of a force-free axisymmetric magnetic field rooted on a heavy conductor onz=0. In quadrupolar symmetry the field expands in the half-spacez>0 and the toroidal flux concentrates on a conical surface. After a mean twist of 208°, the conical layer hosts large toroidal current loops with reversal of the magnetic flux on either side. The evolution of the field structure is described by scale-free static solutionsBr ^–(p+2), withp taking values between 0 and 2. The large expansion factor of the field structure is suggestive of flaring originating on the solar photosphere.     

Surface renewal analysis for sensible and latent heat flux density

High frequency temperature measurements were recorded at five heights and surface renewal (SR) analysis was used to estimate sensible heat flux density (H) over 0.1 m tall grass. Traces of the temperature data showed ramp-like structures, and the mean amplitude and duration of these ramps were used to calculate H using structure functions. Data were compared with H values measured with a sonic anemometer. Latent heat flux density (E) was calculated using an energy balance and the results were compared with E computed from the sonic anemometer data. SR analysis provided good estimates of H for data recorded at all heights but the canopy top and at the highest measurement level, which was above the fully adjusted boundary layer.     

The Taconite Inlet Lakes Project: a systems approach to paleoclimatic reconstruction

A comprehensive study of meteorological, hydrological, limnological and sedimentological conditions in the watersheds of density-stratified (meromictic) lakes around Taconite Inlet, Northern Ellesmere Island, N.W.T., Canada was carried out from 1990–1992. Lakes C1 and C2 contain seawater trapped by isostatic uplift as the former embayments became isolated from the sea. These lakes, and Lake C3, contain varved sediments which provide an annually resolvable paleoclimatic record. By studing the major systems influencing sedimentation in one of these lakes (Lake C2) a better understanding of the climatic controls on varve formation, and hence on the paleoclimatic signal in the varved sediment record, was obtained. The varves of Lake C2 provide a proxy record of summer temperature for the region.This is the first in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

The spatial mobility of two generations of young adults in Norway

"This article presents results from a longitudinal study using data from the Norwegian population register, combined with data from the 1970 and 1980 censuses. For two generations, those born in 1948 and 1958, successive migrations are considered and the effects of various sociodemographic characteristics on migratory behaviour are explored....Event-history analysis is used to examine the duration of stay at the place reached at age 22, and the effects of individual characteristics on this duration. Since a distinction is made between intra- and inter-regional migration, it has been possible to show that these effects vary significantly depending on whether we are dealing with short- or long-distance migration."     

Rupture process of large earthquakes in the northern Mexico subduction zone

The Cocos plate subducts beneath North America at the Mexico trench. The northernmost segment of this trench, between the Orozco and Rivera fracture zones, has ruptured in a sequence of five large earthquakes from 1973 to 1985; the Jan. 30, 1973 Colima event (M _s 7.5) at the northern end of the segment near Rivera fracture zone; the Mar. 14, 1979 Petatlan event (M _s 7.6) at the southern end of the segment on the Orozco fracture zone; the Oct. 25, 1981 Playa Azul event (M _s 7.3) in the middle of the Michoacan gap; the Sept. 19, 1985 Michoacan mainshock (M _s 8.1); and the Sept. 21, 1985 Michoacan aftershock (M _s 7.6) that reruptured part of the Petatlan zone. Body wave inversion for the rupture process of these earthquakes finds the best: earthquake depth; focal mechanism; overall source time function; and seismic moment, for each earthquake. In addition, we have determined spatial concentrations of seismic moment release for the Colima earthquake, and the Michoacan mainshock and aftershock. These spatial concentrations of slip are interpreted as asperities; and the resultant asperity distribution for Mexico is compared to other subduction zones. The body wave inversion technique also determines theMoment Tensor Rate Functions; but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes. An appendix describes theMoment Tensor Rate Functions methodology in detail.The systematic bias between global and regional determinations of epicentral locations in Mexico must be resolved to enable plotting of asperities with aftershocks and geographic features. We have spatially shifted all of our results to regional determinations of epicenters. The best point source depths for the five earthquakes are all above 30 km, consistent with the idea that the down-dip edge of the seismogenic plate interface in Mexico is shallow compared to other subduction zones. Consideration of uncertainties in the focal mechanisms allows us to state that all five earthquakes occurred on fault planes with the same strike (N65°W to N70°W) and dip (15±3°), except for the smaller Playa Azul event at the down-dip edge which has a steeper dip angle of 20 to 25°. However, the Petatlan earthquake does prefer a fault plane that is rotated to a more east-west orientation—one explanation may be that this earthquake is located near the crest of the subducting Orozco fracture zone. The slip vectors of all five earthquakes are similar and generally consistent with the NUVEL-predicted Cocos-North America convergence direction of N33°E for this segment. The most important deviation is the more northerly slip direction for the Petatlan earthquake. Also, the slip vectors from the Harvard CMT solutions for large and small events in this segment prefer an overall convergence direction of about N20°E to N25°E.All five earthquakes share a common feature in the rupture process: each earthquake has a small initial precursory arrival followed by a large pulse of moment release with a distinct onset. The delay time varies from 4 s for the Playa Azul event to 8 s for the Colima event. While there is some evidence of spatial concentration of moment release for each event, our overall asperity distribution for the northern Mexico segment consists of one clear asperity, in the epicentral region of the 1973 Colima earthquake, and then a scattering of diffuse and overlapping regions of high moment release for the remainder of the segment. This character is directly displayed in the overlapping of rupture zones between the 1979 Petatlan event and the 1985 Michoacan aftershock. This character of the asperity distribution is in contrast to the widely spaced distinct asperities in the northern Japan-Kuriles Islands subduction zone, but is somewhat similar to the asperity distributions found in the central Peru and Santa Cruz Islands subduction zones. Subduction of the Orozco fracture zone may strongly affect the seismogenic character as the overlapping rupture zones are located on the crest of the subducted fracture zone. There is also a distinct change in the physiography of the upper plate that coincides with the subducting fracture zone, and the Guerrero seismic gap to the south of the Petatlan earthquake is in the wake of the Orozco fracture zone. At the northern end, the Rivera fracture zone in the subducting plate and the Colima graben in the upper plate coincide with the northernmost extent of the Colima rupture zone.     

Radiocarbon redating of contaminated samples from a tropical volcano: the Mansion ‘Series’ of St Kitts,West Indies

Heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits, in addition to easy contamination of this wood by root systems and soluble humic material. Because the physical nature of the charcoal varies, some samples are more prone to contamination. Two independent studies of the same volcano, Mt Liamuiga on St Kitts in the Lesser Antilles, sometimes using samples from the same carbonized tree, yielded a systematic difference in radiocarbon ages. An exchange of samples and a re-investigation of three physically distinct types of charcoal yielded the following results. Rare, hard, dense charcoal, lacking contamination, which had yielded a spurious age of 2860 years bp, was redated at 1845±58 years bp. Common soft, friable charcoal with good cellular structure proved to be susceptible to contamination. A field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre-treatment was used, indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets. A previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the Mansion Series contradicted ages older than 41000 years bp from common friable charcoal in the lower Mansion Series. The soft powdery charcoal was re-investigated using a sample collected a few centimeters from the original, although field decontamination of this sample was not possible, more extensive laboratory treatment yielded an age of ca. 43000 years bp, again proving that routine laboratory pretreatments are inadequate. A revised geochronology for the Mansion Series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits.