Polarization features of type IV bursts

Using both the polarization records of our institute at seven different frequencies and polarization records from other stations, the spectral diagrams of some important type IV bursts are completed by polarization diagrams. Combining both types of diagrams and adding the results of optical observations and X-ray data it is possible to come to a deeper understanding of the processes taking place during strong solar radio bursts.     

Anisotropy in the continental upper mantle: possible evidence from explosion seismology

Summary. Peculiarities of propagation in the upper mantle of western Europe are documented by profiles of stations recording body waves generated by explosions. Azimuthal variations of travel times and amplitudes of P waves and possible birefringence of S waves may be associated with an anisotropic layer at depths where the lithosphere-asthenosphere transition is supposed to be.     

Analysis and simulation of namurian sediments in central Scotland using a Markov-process model

Many difficulties inherent in analyzing cyclical successions in terms of an idealized cycle and, to a lesser extent, in terms of the modal cycle and composite sequence can be overcome by structuring data in terms of probabilities of upward transitions from one lithology to another. This enables a finite Markov-process model to be used. Transition probability matrices have been constructed from two versions of the same borehole section through paralic Namurian (Pendleian Stage, E ₁ ) sediments east of Stirling. The first version does not allow, but the second allows, adjacent items to be of the same lithology. The matrix derived from the first version indicates the following preferred upward succession of lithologies: coal, mudstone, siltstone, sandstone, seatclay, silty and sandy rooty beds, coal. A version of the Chi-square test strongly rejects the hypothesis that the lithologies were deposited in random order. The second matrix is used as computer input forTestmark, Stochex, andMarchain programs, the last of which stimulates a realistic vertical succession. The transition probability data fit readily into the broad framework of deltaic cycles.Published with permission of the Director, Institute of Geological Sciences.     

350 ka Organic δ13C record of the monsoon variability on the Oman continental margin, Arabian Sea

The stable isotope compositions of sedimentary organic carbon and content of organic carbon for sediment cores recovered at two sites (sites 724C and 725C) during Ocean Drilling Program (ODP) Leg. 117 on the Oman continental margin are used to document variability of the monsoon winds for the past 350 ka. Although both sites have a mean δ¹³C value of -20.1‰, three zones depleted in¹³C are observable at site 724C during isotope stages 3, 8 and 10, while only one zone is recognizable at site 725C. Increased coastal upwelling during isotope stage 3 owing to intense SW monsoon winds resulted in higher concentration of CO₂ in the water column causing the formation of organic matter that was depleted in¹³C. The other two zones deposited during oxygen isotope stages 8 and 10, which are also characterized by low values of organic carbon, nitrogen and C/N ratios, could be attributed to the dilution by terrestrial material derived from paleosol by transported by northwester lies. Because of utilization of¹³C enriched dissolved CO₂ during the last glacial maximum Holocene sedimentary organic materials are depleted in¹³C relative to the the fomer. The content of residues organic carbon (ROC) is higher at site 724C (with an average of 2.3 ± 1.2%) relative to site 725C, which averages to 0.9 ± 0.4% probably because of differences in the degree of preservation. Organic material deposited at site 725C has undergone more degradation relative to site 724C as reflected by a systematic downcore decrease in¹³C resulting from a loss of¹³C enriched organic compounds. Owing to lack of good chronology at site 725C, a zone that is characterized by low δ¹³C values it could not be correlated with the other three zones observed at Site 724C.     

Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes

Petrological and isotopic investigations were undertaken on high pressure granulites of granitic to mafic composition from the Prachatice and Blansky les granulite complexes of southern Bohemia, Czech Republic. The predominant felsic granulites are quartz + ternary feldspar (now mesoperthite)-rich rocks containing minor garnet, kyanite and rutile, and most show a characteristic mylonitic fabric formed during retrogression along the exhumation path. Three high temperature reaction stages at distinctly different pressures are recognized. Rare layers of intermediate to mafic composition, containing clinopyroxene, best record a primary high pressure–high temperature stage (>15 kbar, >900 °C), and a well-defined overprint at medium pressure granulite facies conditions (6–8 kbar, 700–800 °C) during which orthopyroxene (+plagioclase) formed from garnet and clinopyroxene. A further high temperature overprint at lower pressure (ca. 4 kbar) is reflected in the development of cordierite- and/or andalusite-bearing partial-melt patches in some felsic granulites. Conventionally separated zircons from the granulites were measured on a SHRIMP II ion microprobe. Near-spherical, multifaceted grains interpreted to be metamorphic, and short prismatic grains from the cordierite-bearing melt patch, are all concordant and yielded indistinguishable results producing an average age, for 83 individual grain spots, of 339.8 ± 2.6 Ma (2σ). Metamorphic grains from a meta-granodiorite associated with the granulites gave the same age (339.6 ± 3.1 Ma, mean of 9), whereas inherited magmatic grains of the same sample yielded 367.8 ± 1.4 Ma. A mean age of 469.3 ± 3.8 Ma was obtained for two short prismatic concordant grains in one of the granulites, whereas several of the rounded grains with ca. 340 Ma metamorphic zircon overgrowths had much older (²⁰⁷Pb/²⁰⁶Pb minimum ages up to 1771 Ma) discordant cores. In addition to analysis of conventionally separated grains, ion-microprobe measurements were also made on zircons extracted from thin sections (drilled-out, mounted and repolished) such that a direct relationship between the dated zircons and petrographic position could be made. Identical results were obtained from both preparation methods, thus showing that the considerable advantage in petrological control is not offset by any appreciable lack of precision when compared to conventionally prepared ion-microprobe samples. All these isotopic results are identical to those previously obtained by conventional multigrain and single-grain evaporation techniques, but rather than allowing a greater resolution of the age of the petrographically obvious different metamorphic stages the results document, for the first time, the apparent short time scale for high, medium and low pressure metamorphism in the granulites. The short time period between the 340 Ma age for the high pressure granulites, as derived here and from studies of similar rocks elsewhere in the European Variscides, and the 320–330 Ma ages for regional low pressure–high temperature metamorphism, migmatization and granite magmatism, strongly suggests an important link between these two high temperature processes. Received: 25 February 1999 / Accepted: 27 September 1999     

Large-scale motion of solar filaments

Precise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.     

Spatio-temporal regression kriging for modelling urban NO2 concentrations

ABSTRACT

Recently developed urban air quality sensor networks are used to monitor air pollutant concentrations at a fine spatial and temporal resolution. The measurements are however limited to point support. To obtain areal coverage in space and time, interpolation is required. A spatio-temporal regression kriging approach was applied to predict nitrogen dioxide (NO₂) concentrations at unobserved space-time locations in the city of Eindhoven, the Netherlands. Prediction maps were created at 25 m spatial resolution and hourly temporal resolution. In regression kriging, the trend is separately modelled from autocorrelation in the residuals. The trend part of the model, consisting of a set of spatial and temporal covariates, was able to explain 49.2% of the spatio-temporal variability in NO₂ concentrations in Eindhoven in November 2016. Spatio-temporal autocorrelation in the residuals was modelled by fitting a sum-metric spatio-temporal variogram model, adding smoothness to the prediction maps. The accuracy of the predictions was assessed using leave-one-out cross-validation, resulting in a Root Mean Square Error of 9.91 μg m^?3, a Mean Error of ?0.03 μg m^?3 and a Mean Absolute Error of 7.29 μg m^?3. The method allows for easy prediction and visualization of air pollutant concentrations and can be extended to a near real-time procedure.     

Markov-random-field-based super-resolution mapping for identification of urban trees in VHR images

Identification of tree crowns from remote sensing requires detailed spectral information and submeter spatial resolution imagery. Traditional pixel-based classification techniques do not fully exploit the spatial and spectral characteristics of remote sensing datasets. We propose a contextual and probabilistic method for detection of tree crowns in urban areas using a Markov random field based super resolution mapping (SRM) approach in very high resolution images. Our method defines an objective energy function in terms of the conditional probabilities of panchromatic and multispectral images and it locally optimizes the labeling of tree crown pixels. Energy and model parameter values are estimated from multiple implementations of SRM in tuning areas and the method is applied in QuickBird images to produce a 0.6 m tree crown map in a city of The Netherlands. The SRM output shows an identification rate of 66% and commission and omission errors in small trees and shrub areas. The method outperforms tree crown identification results obtained with maximum likelihood, support vector machines and SRM at nominal resolution (2.4 m) approaches.     

A new assessment of the mid-1970s abrupt atmospheric temperature change in the NCEP/NCAR reanalysis and associated solar forcing implications

Based on the reanalysis data from the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP?CNCAR) and solar radio irradiance (SRI) at 10.7?cm wavelength obtained from the National Oceanic and Atmospheric Administration??s Space Weather Prediction center, the abrupt temperature change in the mid-1970s and its possible association with solar irradiance variability have been investigated. The results show that a discontinuous abrupt change in the mid-1970s in the NCEP?CNCAR reanalysis was observed in the tropical lower and middle stratospheric temperature. The shift in temperature and its timing agrees well with the climate regime shift discovered in the radiosonde observations (HadAT), European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), and many previous studies and manifests a statistically significant change at the 95% confidence level. A corresponding change of the SRI was identified in the mid 1970s although the statistical t test value is not very high. The running correlation with a 21-year moving time window exhibits a strong positive correlation between the solar cycle and atmospheric temperature in the tropical stratosphere during the period of 1948?C2007. However, the positive correlation was broken at the time of the mid-1970s abrupt change and two peak positive correlation points were observed in 1972 and 1982, respectively.     

Possible solar forcing of interannual and decadal stratospheric planetary wave variability in the northern hemisphere: An observational study

The variability of stratospheric planetary waves and their possible connection with the 11-year solar cycle forcing have been investigated using annual-mean temperatures for the period of 1958–2001 derived from two reanalysis data sets. The significant planetary waves (wavenumbers 1–3) can be identified in the northern mid-high latitudes (55–75°N) in the stratosphere using this data. Comparisons with satellite-retrieved products from the Microwave Sounding Unit (MSU) confirm the significant planetary wave variability seen in the reanalyses. A planetary wave amplitude index (PWAI) is defined to indicate the strength of the stratospheric planetary waves. The PWAI is derived from Fourier analysis of the temperature field for wavenumbers 1–3 and averaged over 55–75°N latitude and the 70–20 hPa layers. The results include two meaningful inter-annual oscillations (2- and 8-year) and one decadal trend (16-year) that was derived from wavelet analysis. The stratospheric temperature structure of the wave amplitudes appear associated with the Arctic Oscillation (AO) which explicitly changed with the PWAI. The temperature gradients between the polar and mid-high latitudes show opposite tendencies between the top-10 strong and weak wave regimes.The variation of the planetary wave amplitude appears closely related to the solar forcing during the recent four solar cycles (20–23). The peak of the 2-year oscillation occurs synchronously with solar minimum, and is consistent with the negative correlation between the PWAI and the observed solar UV irradiance. The UV changes between the maxima and minima of the 11-year solar cycle impact the temperature structure in the middle-lower stratosphere in the mid-high latitudes and hence influence the planetary waves. During solar maximum, the dominant influence appears to be exerted through changes in static stability, leading to a reduction in planetary wave amplitude. During solar minimum, the dominant influence appears to be exerted through changes in the meridional temperature gradient and vertical wind shear, leading to an enhancement of planetary wave amplitude.