The chemical composition of the halo and evolutionary problems

The chemical composition of the Milky-Way halo is studied on the basis of a sample of metal-poor (logarithmic metallicity less than –1) globular clusters. The histogram obtained may be interpreted in the terms of the classical galaxy formation theory of Eggen, Lynden-Bell and Sandage. Interestingly enough, this is in a rough agreement with the data on metallicity of high-redshift damped Ly-alpha and Ly-alpha forest systems. This may serve the important purpose of constraining the nature and the formation timescale of MACHOs discovered through gravitational microlensing experiments. This revised version was published online in August 2006 with corrections to the Cover Date.     

An inadvertent transport of the seeding material as a result of cloud modification

Successful seeding of clouds in weather modification experiments essentially depends on the seeding time and dynamics, amount of seeding material and location of the initial seeding area. In the present study, we focus on the influence of the initial seeding zone location on the transport of seeding agent material into the target cloud. In addition, the inadvertent transport of seeding material is analysed. During weather modification activities, a lot of seeding material can be transferred far from the seeding zone in a downwind direction. The primary motivation for this research was to prove this statement. We use a three-dimensional, mesoscale cloud-resolving model to achieve our goal. We performed sensitivity tests with respect to the distance between the mass centres of the initial seeding area and the cloud. Different seeding scenarios are analysed. Our principal findings are as follows: (1) For distances between the mass centres of the initial seeding area and the cloud below 2.5 km, all seeding agent material would be activated after a short time. For distances above 10 km, most of the seeding agent would remain inactivated, because horizontal transport of the seeding agent becomes more important than transport induced by the main updraft. For these scenarios, the seeding agent is injected in the cold peripheral part of the cloud. (2) Sensitivity tests show that the inactivated seeding agent would remain close to the seeding area if the seeding is performed below cloud base. This effect occurs even for large distances between the seeding area and the target cloud (>20 km) due to low-level convergence. Thus, this seeding method suppresses the inert seeding material from being transferred far from the seeding zone. (3) The complete seeding material stays inactivated if the seeding is performed between the ?8 and ?12°C isotherms in front of the increased reflectivity zone. As a consequence, it would be transferred far from its initial area. The cloud would not be able to capture the seeding agent even during its greatest lateral extent.     

Seasonal and interannual variations in pigments in the Adriatic Sea

Spatial and temporal variability of pigments was studied from the CZCS satellite data and fromin situ chlorophyll and transparency for the period 1979-1985. The three Adriatic sites, Northern, Middle, and Southern Adriatic are differently influenced by meteorological, hydrological and oceanographic parameters. The differences between seasonalin situ chlorophyll and remotely sensed pigment concentrations (from CZCS satellite data) from the Adriatic are large in winter. Through the correlation analysis, pigments were compared to meteo-oceanographic and hydrological parameters from different Adriatic sites. The PCA (principal component analysis) was applied to the pigment data series and significant components were compared. Different correlations are obtained for warm and cold periods of the year pointing to seasonal differences in the underlying mechanism of pigment variability. The first PC is influenced mainly by temperature. In the warm period more parameters seem to influence the pigment field, than in the cold period. The pigments in the Adriatic are in good correlation to a number of hydrologic and meteo-oceanographic factors.     

Numerical modeling of thunderstorm

Summary A brief review of numerical models of thunderstorms is presented. The attempts of modeling these clouds have to deal with an extremely broad range of microphysical and dynamic processes. Basic concepts of thunderstorm modeling, 1-D, 2-D and 3-D models are considered. Particular attention is given to the basic equations and to the capability of these models to predict characteristics of the tunderstorms. A brief treatment is also given of hail growth in thunderstorm models.

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Zusammenfassung Im folgenden wird eine knappe Übersicht numerischer Gewittermodelle präsentiert. Bei der Modellierung von Gewitterwolken muß ein ausgesprochen weiter Bereich von mikrophysikalischen und dynamischen Prozessen beachtet werden. Grundkonzepte der Gewittermodellierung, 1-D-, 2-D- und 3-D-Modelle werden hierzu herangezogen. Besondere Aufmerksamkeit gilt dabei den Ausgangsgleichungen sowie den potentiellen Möglichkeiten dieser Modelle, Charakteristika der Gewitter vorherzusagen. Weiters wird auch das Hagelwachstum in Gewittermodellen kurz behandelt.

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With 8 Figures     

Modification of the degree-day formula for diurnal meltwater generation and refreezing

Theoretical and Applied Climatology - The standard degree-day, temperature-index approach to calculating snowmelt generation and refreezing (the SDD method) is convenient and popularly used but...     

Intergalactic Pressure and the Maximal Extent of Gaseous Haloes of Field Galaxies

The problem of influence of the ambiental intergalactic pressure on extended gas associated with normal field galaxies is briefly discussed. An empirically established characteristic radius of absorption can not be explained in the context of simple two-phase halo model as a consequence of pressure equilibrium of the hot halo with the smooth intergalactic medium. This conclusion is based upon the stringent constraints on the temperature and density of the intergalactic plasma obtained through the CMBR measurements. On the other hand, ram-pressure stripping caused by peculiar motions of galaxies does present a viable alternative for the hot halo truncation. It is shown that for a particular set of chosen parameters, a simple model is capable of producing the absolute upper limit on the extent of gas associated with the galaxy. The values obtained are compatible with the results of the recent QSO absorption-line studies, and are significantly higher than the radius at which the cooling timescale of the halo gas equates the dynamical timescale.     

Wave height statistics for seakeeping assessment of ships in the Adriatic Sea

The paper presents methodology and results of the development of sea states statistics for the Adriatic Sea. Such statistics is still lacking despite a need of the shipping industry. The presented study is based on the Atlas of Climatology containing statistics of sea states observations in the Adriatic Sea made by merchant ships during the period of 15 years. The results, presented in the Atlas in the form of “wave roses”, are digitalized and empirical frequencies of sea state occurrences are obtained. The 3-parametric Weibull distribution is then fitted through empirical data points enabling the “smoothening” of the histogram. The resulting histogram is compared with other studies for the long-term prediction of the sea states in the Adriatic Sea. The paper concludes with the discussion on the accuracy and applicability of the results.     

Chronology and sources of lunar impact bombardment

The Moon has suffered intense impact bombardment ending at 3.9 Gyr ago, and this bombardment probably affected all of the inner Solar System. Basin magnetization signatures and lunar crater size-distributions indicate that the last episode of bombardment at about 3.85 Gyr ago was less extensive than previously thought. We explore the contribution of the primordial Mars-crosser population to early lunar bombardment. We find that Mars-crosser population initially decays with a 80-Myr half-life, with the long tail of survivors clustering on temporarily non-Mars-crossing orbits between 1.8 and 2 AU. These survivors decay with half-life of about 600 Myr and are progenitors of the extant Hungaria asteroid group in the same region. We estimate the primordial Mars-crosser population contained about 0.01–0.02 Earth masses. Such initial population is consistent with no lunar basins forming after 3.8 Gya and the amount of mass in the Hungaria group. As they survive longer and in greater numbers than other primordial populations, Mars-crossers are the best candidate for forming the majority of lunar craters and basins, including most of the Nectarian system. However, this remnant population cannot produce Imbrium and Orientale basins, which formed too late and are too large to be part of a smooth bombardment. We propose that the Imbrian basins and craters formed in a discrete event, consistent with the basin magnetization signatures and crater size-distributions. This late “impactor shower” would be triggered by a collisional disruption of a Vesta-sized body from this primordial Mars-crossing population (Wetherill, G.W. [1975]. Proc. Lunar Sci. Conf. 6, 1539–1561) that was still comparable to the present-day asteroid belt a 3.9 Gya. This tidal disruption lead to a short-lived spike in bombardment by non-chondritic impactors with a non-asteroidal size–frequency distribution, in agreement with available evidence. This body (“Wetherill’s object”) also uniquely matches the constraints for the parent body of mesosiderite meteorites. We propose that the present-day sources of mesosiderites are multi-km-sized asteroids residing in the Hungaria group, that have been implanted there soon after the original disruption of their parent 3.9 Gyr ago.     

Graupel growth and trajectories in a shallow cb cloud determined by a forced 1‐D model

Abstract

A kinematic model is applied to graupel growth. The vertical velocity and ther‐modynamic field data are taken from the forced 1‐D time‐dependent model of Cb cloud developed by Curie and Jane (1988). The graupel embryo pocket was released at the height of the — 10°C isotherm. The influence of the forced lifting on further graupel growth and its trajectory is analysed by sensitivity experiments based on the amplitude of the forced lifting, and initial graupel radius, density and cloud droplet concentration for the forced lifting initiation time derived from the model and the forced lifting duration time that agreed with observations. In particular, the sensitivity analysis was carried out for the forced lifting initiation and duration times.

It is shown that for large values of the forced lifting amplitudes, the residence time of the graupel within cloud and the final graupel radius may be significantly larger compared with those in the non‐forced case. The residence time in a cloud can also be significantly larger for the smallest amplitude, whereas the final radius is rather insensitive owing to oscillations around the melting level. For some cases the forced lifting causes recycling inside the updraft, contrary to the results of previous non‐forced numerical models. The recycling mechanism is sensitive to the forced lifting duration time and the time interval between the graupel pocket injection in cloud and the initiation of the forced lifting. Initially the observed recycling mechanism is a consequence of the periodic forced lifting mechanism, but then combines with recycling of the Pflaum type (1980).     

New Cretaceous paleomagnetic results from the foreland of the Southern Alps and the refined apparent polar wander path for stable Adria

The central-western and the eastern Southern Alps are separated by the triangular shaped Adige embayment, which belongs to stable Adria and was the site of pelagic sedimentation from the Tithonian through Maastrichtian. The first part of this study presents paleomagnetic results from the Tithonian–Cenomanian Biancone and Turonian–Maastrichtian Scaglia Rossa formations sampled at 33 geographically distributed and biostratigraphically dated localities.The new and high quality paleomagnetic results from the Adige embayment are then combined with coeval paleomagnetic directions from autochthonous Istria (Márton et al., 2008), which also belongs to stable Adria. The combined data set (which for the Late Albian–Maastrichtian time period is constructed similarly to the synthetic African curve by Besse and Courtillot, 2002, 2003) reveals an important tectonic event (Late Aptian–Early Albian) characterized by 20° CCW rotation and sedimentary hiatus.Comparison between paleomagnetic declinations/inclinations expected in an African framework (i.e. with the assumption that Adria is still an African promontory) leads to the following conclusions. The time-distributed Tithonian and Berriasian (150–135 Ma) paleomagnetic directions exhibit the “African hairpin” with an inclination minimum and a sudden change from CW to CCW rotation at 145 Ma. Concerning the younger ages, the declinations for Adria continue to follow the African trend of CCW rotation till the end of Cretaceous. However, the Tithonian–Maastrichtian declination curve for stable Adria is displaced by 10° from the “African” curve as a result of two rotations. The first, an about 20° CW rotation of Adria with respect to Africa took place between the Maastrichtian and the mid-Eocene. During this time the orientation of Adria remained the same, while Africa continued its CCW rotation. The younger rotation (30°CCW) changed the orientation of Adria relative to Africa as well as to the present North.