Risk occurrences of damaging frosts during the growing season of vegetables in the Elbe River lowland,the Czech Republic

This study has, for the first time, analysed in detail the risk occurrences of the last spring frost, first fall frost and the length of the frost-free period during the growing season of vegetable crops at a high horizontal resolution of 10 km in the Elbe River lowland in the Czech Republic. The daily minimum air temperature from 116 grid points throughout the studied area for the period 1961–2011 was used. The daily values of minimum air temperature ranges of 0 to ?1.1 °C, ?1.2 to ?2.2 °C and below ?2.2 °C were considered to constitute mild, moderate and severe frost intensities, respectively. Firstly, the spatiotemporal variability of the date of the last spring frost, the date of the first fall frost and the length of the frost-free period in the Elbe River lowland is provided. Secondly, the estimation of the probability of a later date in the spring and an earlier date in the fall for various severe frost events and the length of the frost-free period is determined. Third, the changes in the timing of the last and first frosts of the three severities, as well as the length of the frost-free period, are evaluated. From 1961 to 2011, the Elbe River lowland has experienced a decrease in the number of frost days, while the length of the frost-free period between the last spring frost and the first fall frost has increased. The temporal evolution of the frost-free period anomalies displays two distinct periods: a shortening of the frost-free period in the 1960s and an intensified lengthening of the frost-free period since the 1980s. Whereas the latest spring frost has ended on an earlier date across the Elbe River lowland, the first frost date in the fall has generally been delayed to a later date. The dates of the last spring frost have advanced by ?0.21 days per year on average. The fall dates are delayed up to 0.18 days per year, whereas the frost-free period is lengthening by up to 0.39 days per year on average. However, regional frost series suggests that the frost-free period exhibits a large amount of inter-annual variability. In terms of the growth of field vegetables, a late spring frost remains a risk factor, but the degree of risk has decreased. There is a 25 % chance of the occurrence of dangerous spring frosts during the planting of field vegetables after 3rd May, but after 15th May, the risk is only 10 %.     

The Little Ice Age signature and subsequent warming seen in borehole temperature logs versus solar forcing model

The ‘low’ in the transient temperature versus depth borehole profiles around 120 m seen from deep temperature logs in the Canadian Prairies (southern Alberta–southern Saskatchewan), as well as in some of the European data, has been interpreted to be related to the Little Ice Age (LIA). Data point to the lowest ground surface and subsurface temperatures occurring in the very late eighteenth to nineteenth centuries. Inversion of these logs shows that surface temperature lows were followed by a recent warming period. Further, the synthetic profiles built on the basis of solar forcing history, stretching as far back as the beginning of the seventeenth century, suggest that the LIA signatures interpreted from the inversion of the borehole temperature logs would be difficult to be explained by known published models of past solar irradiation despite large range of assumed sensitivities for the couplings assumed, and that further forcing needs to be considered.     

Isotope geochemistry and modelling of the multi-aquifer system in the eastern part of Lithuania

A steady-state groundwater flow model of three Quaternary intertill aquifers in the eastern part of Lithuania has been compiled. The distinction of separate modelled layers is based on hydraulic and isotope-hydrochemistry data criteria. ³H data were used to estimate the corrected groundwater age and were coupled with a groundwater-flow-dynamics model of the Quaternary aquifer system along a cross-section flow pathway from the Baltic Upland recharge area in eastern Lithuania towards the discharge area in the lowlands near the city of Kaunas in central Lithuania. The bicarbonate content in groundwater (214–462 mg/l) increases downgradient towards the lowland area. The other major constituents and total dissolved solids (TDS) have a trend analogous to the bicarbonate. The ¹⁴C activity of dissolved inorganic carbon (DIC) in the groundwater ranges from 41.4 to 85.7 pMC. With aquifer-system depth, active precipitation of aqueous solution takes place by dissolving minerals of calcite and dolomite and leakage of “old” groundwater from lower aquifers; the process is also traced by lower ¹⁴C and ³H activities and by more positive δ¹⁸O values in lowland areas.     

The relation between the long-term X-ray and optical activity of the polar AM Her (RX J1816.2 + 4952)

We analyze the relation between the long-term (1996–2009) activity of the polar AM Her in the optical and hard X-ray spectral regions. We investigate the mean values of the intensities in the individual high-state episodes. We made use of the ASM/RXTE observations for a time-series analysis of the long-term variations in the 1.5–12 keV band. The optical data came from the AFOEV database. We reveal a complicated relation between the optical (I_O) and hard X-ray intensity (I_X). We argue that our observations cannot be explained by the variations of the orbital modulation in the high-state. Also, the precession of the spin axis of the white dwarf or asynchronous rotation of this object are unlikely in our case. We show that the basic properties of the emitting region (s) is (are) established in the early phase (several days long) of the high-state episode but they are not reproduced for every episode. The increase of the mass transfer rate from the donor that switches the polar from the low to the high-state also establishes a division of the emission released during the accretion process into various spectral regions that is valid only for a given episode. These results enable us a better understanding of the multifrequency behavior of polars on long time-scales.     

An Interpretation of the Coronal Holes’ Visibility in the Millimeter Wavelength Range

Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsähovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 10⁶ K). This can explain both the LTRs and HTRs associated with coronal holes.     

Dioritic intrusions of the Slavkovský les (Kaiserwald), Western Bohemia: their origin and significance in late Variscan granitoid magmatism

Mafic and intermediate intrusions occur in the Slavkovsky les as dykes, sills and minor tabular bodies emplaced in metamorphic rocks or enclosed in late Variscan granites near the SW contact of the Western Krušné hory/Erzgebirge granite pluton. They are similar in composition and textures to the redwitzites defined in NE Bavaria. Single zircon Pb-evaporation analyses constrain the age of a quartz monzodiorite at 323.4 ± 4.4 Ma and of a granodiorite at 326.1 ± 5.6 Ma. The P–T range of magma crystallization is estimated at ~1.4–2.2 kbar and ~730–870°C and it accords with a shallow intrusion level of late Variscan granites but provides lower crystallization temperatures compared to the Bavarian redwitzites. We explain the heterogeneous composition of dioritic intrusions in the Slavkovsky les by mixing between mafic and felsic magmas with a minor effect of fractional crystallization. Increased K, Ba, Rb, Sr and REE contents compared to tholeiitic basalts suggest that the parental mafic magma was probably produced by melting of a metasomatised mantle, the melts being close to lamprophyre or alkali basalt composition. Diorites and granodiorites originated from mixed magmas derived by addition of about 25–35 and 50 vol.%, respectively, of the acid end-member (granite) to lamprophyre or alkali-basalt magma. Our data stress an important role of mafic magmas in the origin of late Variscan granitoids in NW Bohemian Massif and emphasize the effect of mantle metasomatism on the origin of K-rich mafic igneous rocks.     

P–T–t–D records of Early Palaeozoic Andean-type shortening of a hot active margin: The Dunhuang block in NW China

High-pressure (HP) granulites form either in the domain of the subducted plate during continental collision or in supra-subduction systems where the thermally softened upper plate is shortened and thickened. Such a discrepancy in tectonic setting can be evaluated by metamorphic pressure–temperature–time-deformation (P–T–t–D) paths. In the current study, P–T–t–D paths of Early Palaeozoic HP granulite facies rocks, in the form of metabasic lenses enclosed in migmatitic metapelite, from the Dunhuang block, NW China, are investigated in order to constrain the nature of the HP rocks and shed light on the geodynamic evolution of a modern hot orogenic system in an active margin setting. The rocks show a polyphase evolution characterized by (1) relics of horizontal or gently dipping fabric (S1) preserved in cores of granulite lenses and in garnet porphyroblasts, (2) a N-S trending sub-vertical fabric (S2) preserved in low-strain domains and (3) upright folds (F3) associated with a ubiquitous steep E-W striking axial planar foliation (S3). Garnet in the granulites preserves relics of a prograde mineral assemblage M1a equilibrated at ~11.5 kbar and ~770–780°C, whereas the matrix granulite assemblage (M1b) from the S1 fabric attained peak pressure at ~13.5 kbar and ~850°C. The granulites were overprinted at ~8–11 kbar and ~850–900°C during crustal melting (M2) followed by partial re-equilibration (M3) at ~8 kbar and ~625°C. A garnet Lu–Hf age of 421.6 ± 1.2 Ma dates metamorphism M1, while a garnet Sm–Nd age of 385.3 ± 4.0 Ma reflects M3 cooling of the granulites. The mineral assemblage, M1, of the host migmatitic metapelite formed at ~9–12.5 kbar and ~760–810°C, partial melting and migmatization (M2) occurred at ~7 kbar and ~760°C and re-equilibration (M3) at ~5–6 kbar and ~675°C. A garnet Lu–Hf age of 409.7 ± 2.3 Ma dates thermal climax (M2) and a garnet Sm–Nd age of 356 ± 11 Ma constrains M3 for the migmatitic metapelites. The timing of this late phase is also bracketed by an emplacement age of syntectonic granite dated at c. 360 Ma. Decoupling of M1 and M2 P–T evolutions between the mafic granulites and migmatitic metapelites indicates their different positions in the crustal column, while the shared pressure–temperature (P–T) evolution M3 suggests formation of a mélange-like association during the late stages of orogeny. The high-pressure event D1-M1 is interpreted as a result of Late Silurian–Early Devonian moderate crustal thickening of a thermally softened and thinned pre-orogenic crust. The high-temperature (HT) re-equilibration D2-M2 is interpreted as a result of Mid-Devonian shortening of the previously thickened crust, possibly due to ‘Andean-type’ underthrusting. The D3-M3 event reflects Late Devonian supra-subduction shortening and continuous erosion of the sub-crustal lithosphere. This tectono-metamorphic sequence of events is explained by polyphased Andean-type deformation of a ‘Cascadia-type’ active margin, which corresponds to a supra-subduction tectonic switching paradigm.