Some Aspects of Meteoric Head Echo Velocity Determination

Velocity determination of 131 head echoes recorded during Perseid meteor shower observations by the Canadian 2 MW radar, has been performed under the assumption of either their constant velocity or of its linear change with time. Even though the constant velocities concentrated at 60 km s-1 generally accepted for the Perseids, a substantial number of echoes had velocities either lower than 60 km s-1 or greater than this value. The inclusion of variable velocity into considerations led to surprising result that a great portion of the head echoes accelerated (3 possibly decelerating echoes in comparison with 33 accelerating cases on the level of relative standard deviations of output parameters not exceeding 10%). It seems that the allocation of the ionization responsible for the head echo is not entirely identical with the instantaneous meteoroid position. As a consequence, the velocity derived from the measured head echo coordinates can differ from the velocity of parent body. We are not able to explain this finding at present. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radar Observations of Taurid Complex Meteor Showers in 2003: Activity and Mass Distribution

Results of Ondřejov radar observation of Taurid complex meteor showers, i.e. ζ Perseids, β Taurids, S and N Taurids, performed in 2003, are presented. We have found some mass segregation within ζ Perseid, β Taurid and S Taurid showers. We have also established conspicuous lack of long duration echoes (with T ⩾ 3 s resp. T ⩾ 5 s) in S and N Taurid showers. The lack within remaining showers is not so pronounced but still persists.     

Constraining genesis and geotectonic setting of metavolcanic complexes: a multidisciplinary study of the Devonian Vrbno Group (Hrubý Jeseník Mts., Czech Republic)

The low-grade metavolcanic/volcanosedimentary complex of the Devonian Vrbno Group (Silesicum, NE Bohemian Massif, Czech Republic) occurs in two ~NE–SW trending belts, separated by tectonic slices of Cadomian metagranitic paraautochton. (1) The basic–intermediate lavas of the calc-alkaline Western Volcanic Belt came from a moderately depleted mantle $ \left( {\varepsilon_{\text{Nd}}^{370} \sim + 3} \right) $ . Rare rhyolites (374.0 ± 1.7 Ma: 2σ, LA–ICP–MS U–Pb Zrn) were derived most likely from immature crust or by extensive fractionation of primary basaltic melts. The rock association is interpreted as a vestige of a deeply dissected continental arc. (2) The Eastern Volcanic Belt consists mainly of (nearly) contemporaneous (371.0 ± 1.4 Ma) felsic alkaline lavas with high HFSE contents, as well as high Ga/Al and Fe/Mg ratios, typical of within-plate igneous setting. The petrology and Nd–Sr isotopic data point to a high-T anatexis of a young metagranitic crust, resembling the Cadomian (Brunovistulian) basement, in a back-arc setting. The attenuated Brunovistulian lithosphere could have partially melted by the heat provided by the upwelling asthenosphere and/or underplating basic magma. (3) Finally, the region was penetrated by numerous subalkaline, MORB/EMORB-like dolerite sheets—a hallmark of the considerable crustal thinning.     

Magmatic history of granite-derived mylonites from the southern Desná Unit (Silesicum, Czech Republic)

Summary In the southern part of the Hruby Jeseník Mts. (Silesicum, Bohemian Massif) granitic orthogneisses and quartz-feldspars mylonites occur that were variously deformed, metamorphosed and imbricated with the overlaying Devonian volcano-sedimentary complex during the Variscan orogeny. Based on combined mapping, petrologic and geochemical studies, three main rock groups are distinguished. The fairly primitive nature of the tonalite suite is shown by low ⁸⁷Sr/⁸⁶Sr₅₅₀ ratios (0.7034–0.7038) and positive ε _Nd ⁵⁵⁰ values (+3.8 and +3.1). Isotopic composition of the metagranite suite is similar (ε _Nd ⁵⁵⁰ = +1.9 to +2.9). Both suites probably belong to a single Cadomian calc-alkaline tonalite–granite association, which can be correlated with acid-intermediate plutonic rocks of the eastern Brunovistulicum (Slavkov Terrane). All these units are interpreted as representing dismembered fragments of the same continental margin magmatic arc system. The leucogranite suite is most likely early Variscan in age. The initial Nd isotopic composition (ε _Nd ³³⁰ = +0.8 and +2.3) is consistent with its formation by a Variscan remelting of the metaigneous Cadomian crust represented by the rocks of the tonalite–granite association. The within-plate granite affinity of the leucogranite suite is most likely related to the break-up of the Brunovistulicum during the Variscan orogeny.     

Application of the self-calibrated palmer drought severity index and standardized precipitation index for estimation of drought impact on maize grain yield in Pannonian part of Croatia

Recent global warming and more frequent droughts are causing significant damage to maize production. A reliable estimate of drought intensity and duration is essential for testing maize hybrids to drought tolerance. For this purpose, the self-calibrating 10-day palmer drought severity index (scPDSI) and standardized precipitation index (SPI) for 1, 2, 3, 6, 9, 18, 27, and 36 10-day scales were used to estimate the effects of drought on grain yield of 32 maize hybrids evaluated in 2017 and 2018 at eight experimental locations in the Pannonian part of Croatia. Time series of observed 10-day mean air temperature, relative humidity, and precipitation totals for a set of “reference” weather stations of the croatian meteorological and hydrological service (DHMZ) for the period 1981–2018 were used to calculate the scPDSI and SPI indices. According to the 10-day scPDSI and SPI for different time scales, 2018 proved to be a “normal year,” while 2017 experienced a “mild to moderate drought,” which resulted in a 13% reduction in maize grain yield at eight experimental locations compared to 2018. The correlation between grain yield and drought indices for summer months was the highest for the 10-day scPDSI. To some extent, correlations between summer months’ SPI for the 3 10-day time scale and maize grain yield were comparable to the corresponding correlations for the 10-day scPDSI. However, for other SPI time scales considered, the corresponding correlations were weaker and less informative. The dependence of grain yield on scPDSI values was not the same for all hybrids, indicating their different tolerance to drought. The reduction in grain yield due to drought was primarily caused by insufficient grain filling (lower 1000-grain weight) and, to some extent, by a reduction in the number of grains. In this study, application of 10-day scPDSI data proved to be more relevant in detecting effects of drought on agronomic traits than application of SPI data for the most time scales.

     

Radar sporadic meteor rates and solar activity

The correlation of sporadic meteor rates from radar observations in January, August, and December non-show-er periods in 1958–2000, and relevant solar activity represented by the solar relative number, R, is investigated. Similar analysis of the December sporadic period was already presented by Simek 1999, and Pecina. Complete analysis indicates high correlation of both phenomena with sporadic meteor counts curve following that of solar activity after 1.5–2 years in the mean eleven year solar cycle with the correlation index exceeding 70%. This result supports the large volume of observing material of the Ondřejov meteor radar in the above mentioned span covering almost four solar cycles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Construction of remains of small-scale mining activities as a possible innovative way how to prevent desertification

Initial mapping of secondary succession in places disturbed by mining of the Khan Khentii Strictly Protected Area in Mongolia shows a possible innovative direction taken by afforestation in order to prevent further expansion of the Gobi Desert in northern Mongolia. The study results from the knowledge of secondary succession of mined areas, which are classified as the remains and consequences of prospecting and mining work dated to the Soviet times. Ongoing succession on sites affected by mining is very slow. In quarry dumps and canavas, herb layer has not been recovered despite the fact that the prospecting and mining activities had finished more than 30 years ago. Herbs biodiversity is very poor in these areas. Conversely, representatives of the tree layer, especially Larix sibirica and Populus tremula, are found far from the continuous forest; they colonized sites located within the aridized steppe. We assume that the main factor of successful tree growth on the mining activities remains consists in the humidity condensation due to and caused by the specific shape of the canavas and dumps. Trees prosperity on these extreme habitats can be ensured particularly in the early stages of growth when the tree roots are unable to reach the groundwater table. Detail mapping of quantitative and qualitative parameters of trees shows that the dump is an ideal shape of self-watering condensation mound for forest growth and can prevent the desertification as well.     

Perseid meteor stream as observed in 1993

Presented are results of Perseid 1993 meteor shower from radar observation at Ondejov observatory. Investigation of the shower activity profiles in four echo duration intervals proved the position of dominant peak at solar longitude L = 138.°8±0.°05 (epoch 1950.0) followed by series of secondary maxima positions of which depend on examined echo duration class. Extremely low value of the mass distribution indexs = 1.27 ± 0.01 near the maximum activity peak associated with high proportion of fragmenting particles leads to the suggestion that meteor particles concentrated in this filament are younger than those which form the other parts of the stream.