Modeling of type III bursts dynamic spectra

The one-dimensional process of spatially limited electron stream propagation in the solar corona is simulated. It is shown that the beam instability development results either in strong relaxation in velocity space and inhibition of spatial diffusion (high-stream density) or in velocity space relaxation decrease and simultaneous growth of spatial stream length (low-stream density). Assuming a profile of background plasma density to be exponential, dynamic spectra of type III bursts are modeled, which shows that the emission source velocity is constant, and a duration of the burst emission at a given frequency reduces for high-stream densities.     

Caledonian Low-Temperature Granulite-Facies Metamorphism in the West Kunlun Orogenic Belt—SHRIMP Chronological Evidence from Zircon

The West Kunlun orogenic belt is located at the conjunction of the paleo-Asian tectonic system and the Tethys tectonic system. Petrological and mineralogical studies of the Early Cambrian metamorphic surface crust in this region have shown that in case the metamorphism reached low-temperature granulate facies, the typical mineral assemblage is biotite-garnet-silimanite-K feldspar-plagioclase-quartz. The peak metamorphic temperatures are within the range of 720–740°C and the pressure is 0.6 GPa ±. Three types of metamorphic zircon have been detected in the metamorphic rocks: the complex inclusion-bearing type ; the early relic zircon inclusion-bearing type; and the inclusion-free type. SHRIMP age determination of these three types of metamorphic zircon have revealed that these zircons were formed principally during 400–460 Ma, indicating that pre-Cambrian metamorphic surface crust rocks underwent low-temperature granulite facies metamorphism during the Caledonian. In combination with the geological characteristics of this region, it is considered that when the oceanic basin was closed, there occurred intense intracontinental subduction (type A), bringing part of the Early Cambrian metamorphic basement in this region downwards to the lower crust. Meanwhile, there were accompanied with tectonic deformation at deep levels and medium- to high-grade metamorphism. This study provided important chronological and mineralogical evidence for the exploration of the evolutionary mechanism and process of the West Kunlun Early Paleozoic. Part of the results from the research project “ Research on the West Kunlun pre-Cambrian tectonic events” under the program “ Research on the important geological problems of China’ s pre-Cambrian” (No. 200113900070) sponsored by the China National Geological Surveying Bureau.     

Long Term Evolution of Solar Meridional Circulation and Phase Synchronization Viewed Through a Symmetrical Kuramoto Model

The solar-cycle oscillations of the toroidal and poloidal components of the solar magnetic field in the northern solar hemisphere have a persistent phase difference of about \(\pi \). We propose a symmetrical Kuramoto model with three coupled oscillators as a simple way to understand this anti-synchronization. We solve an inverse problem and reconstruct natural frequencies of the top and bottom oscillators under the conditions of a constant coupling strength and a non-delayed coupling. These natural frequencies are associated with angular velocities of the meridional flow circulation near the solar surface and in the deep layer of the solar convection zone. A relationship between our reconstructions of the shallow and the deep meridional flow speed during recent Solar Cycles 21?–?23 is in agreement with estimates obtained in helioseismology and flux-transport dynamo modeling. The reconstructed top oscillator speed presents significant solar-cycle like variations that agree with recent helioseismical reconstructions. The evolution of reconstructed natural frequencies strongly depends on the coupling strength. We find two stable regimes in the case of strong coupling with a change of regime during anomalous solar cycles. We see the onset of a new transition in Solar Cycle 24. We estimate the admitted range of coupling values and find evidence of cross-equatorial coupling between solar hemispheres not accounted for by the model.     

Hα Dimming Associated With the Eruption of a Coronal Sigmoid in the Quiet Sun

We report on the occurrence of Hα dimming associated with a sigmoid eruption in a quiet-sun region on 14 August 2001. The coronal sigmoid in soft X-ray images from the Yohkoh Soft X-ray Telescope was located over an Hα filament channel. Its eruption was accompanied by a flare of GOES X-ray class C2.3 and possibly associated with a halo coronal mass ejection (CME) observed with the Large Angle and Spectroscopic Coronagraphs (LASCO) on board the Solar and Heliospheric Observatory (SOHO). During the eruption, coronal bipolar double dimming took place at the regions with opposite magnetic polarities around the two sigmoid ends, but the underlying chromospheric channel did not show observable changes corresponding to the coronal eruption. Different from the erupting coronal sigmoid itself, however, the coronal dimming had a detectable chromosphere counterpart, i.e., Hα dimming. By regarding the sigmoid as a coronal sign for a flux rope, these observations are explained in the framework of the flux rope model of CMEs. The flux rope is possibly deeply rooted in the chromosphere, and the coronal and Hα dimming regions mark its evacuated feet, through which the material is possibly fed to the halo CME.     

Tectonics of southwestern Mexico,isotopic evidence,nuclear Central America,Late Cretaceous break up

In the paleogeographic reconstruction of Mexico and northern Central America, an ever-increasing amount of evidence shows that the entire region is a collage of suspect terranes transported from abroad, whose timing and sense of motion are now beginning to be understood. Among these, the Chortis block (nuclear Central America) and the Baja California Peninsula have been proposed as pieces of continent separated from the Pacific coast of southwestern Mexico, that have moved either southeastward by the Farallon plate or northwestward by the Kula plate. Previous studies mainly confined to the northern margin of the Chortis block, confirmed a left-lateral displacement of 130 km in Neogene time. Further studies made northwestward along the Mexican coast provided a better understanding of magmatic and metamorphic processes in the area, and suggested times of detachment increased to 30 Ma, 40 Ma, and 66 Ma. The pre-detachment westernmost position of the block has changed, depending on the model chosen, from Puerto Vallarta and beyond, to the current position. Here we show that the isotopic mineral ages from coastal granites along the coast from Puerto Vallarta, Jalisco (80 Ma) to Puerto Angel, Oaxaca (11 Ma) record systematic decrease of cooling ages from NW to SE. This pattern is interpreted to result from the progressive uplift of rocks exposed at the present-day coast in that direction, such uplift occurred in response to the development of the Middle America Trench at the newly formed continental margin when the Chortis block was sliding at an average rate of 1.5 cm/year in a sinistral sense to its present position. Our results also constrain the position of the Kula-Farallon spreading axis north of Puerto Vallarta. These observations led us to conclude that several indicators point to this time and region for the onset of strike-slip drifting of the Chortis block toward its current position. Here, we also present several view points in terms of other possilble interpretations to different tectonic, geologic and isotopic data sets published recently by different authors.     

Integration of reflection seismic and sediment grain-size data from Lake Khubsugul (Northern Mongolia): a reply to Prokopenko and Kendall

Prokopenko and Kendall (J Paleolimnol doi:, 2008) criticise the work presented in Fedotov et al. (J Paleolimnol 39:335–348, 2008), and instead propose an alternative interpretation for the grain-size evolution recorded in the KDP-01 core, retrieved from the central part of Lake Khubsugul. Their interpretation is based (i) on a seismic-stratigraphic re-interpretation of sparker seismic profile khub012 (which they copied from Fedotov et al. (EOS Trans 87:246–250, 2006)), (ii) on the presupposition that changes in lake level are the dominant control on facies distribution in Lake Khubsugul, and (iii) on the invalidation of our age-depth model. In this reply to their comment, we demonstrate that they interpreted seismic artefacts and geometries caused by changes in profile orientation as true stratigraphic features and that the lake-level reconstruction they derive from this interpretation is therefore incorrect. We also demonstrate that their grain-size predictions, which they consider to be predominantly driven by changes in lake level, are inconsistent with the measured sulphate concentration, which is a demonstrated proxy of lake level in Lake Khubsugul, and with the measured grain-size record. Finally, we point out that even if there would be a problem with the age-depth model, this problem would not affect the part of the sedimentary sequence discussed in Fedotov et al. (J Paleolimnol 39:335–348, 2008).     

Estimating Solar Flux Density at Low Radio Frequencies Using a Sky Brightness Model

Sky models have been used in the past to calibrate individual low radio frequency telescopes. In this article we generalize this approach from a single antenna to a two element interferometer, and formulate the problem in a way that allows us to estimate the flux density of the Sun using the normalized cross-correlations (visibilities) measured on a low resolution interferometric baseline. For wide field-of-view instruments, typically the case at low radio frequencies, this approach can provide robust absolute solar flux calibration for well characterized antennas and receiver systems. It can provide a reliable and computationally lean method for extracting parameters of physical interest using a small fraction of the voluminous interferometric data, which can be computationally prohibitively expensive to calibrate and image using conventional approaches. We demonstrate this technique by applying it to data from the Murchison Widefield Array and assess its reliability.     

Facies Structure and Quantitative Parameters of Pleistocene Sediments of the Bering Sea

Lithofacies zoning is described for the first time for the Neo- and Eopleistocene of the Bering Sea. Four lithofacies sedimentation zones are distinguished: (I) terrigenous; (II) siliceous–terrigenous; (III) siliceous, and (IV) volcanoterrigenous ones. Corresponding maps were treated using Ronov volumetric method to quantify sedimentation parameters for distinguished lithofacies zones (subzones) and types of Pleistocene sediments. It was revealed that terrigenous sediments predominate over other sediments. Accumulation of the terrigenous sediments was more intense (by 1.4 times) in the Neopleistocene than in the Eopleistocene. The sedimentation rate of siliceous sediments of the Bowers Ridge in the Eopleistocene was two times higher than in the Neopleistocene.     

The Dergaon (H5) chondrite: Fall,classification, petrological and chemical characteristics,cosmogenic effects,and noble gas records

Abstract— A multiple fall of a stony meteorite occurred near the town of Dergaon in Assam, India, on March 2, 2001. Several fragments weighing <2 kg and a single large fragment weighing ～10 kg were recovered from the strewn field, which extended over several tens of square kilometers. Chemical, petrographic, and oxygen isotopic studies indicate it to be, in most aspects, a typical H5 chondrite, except the unusually low K content of ～340 ppm. A cosmic ray exposure of 9.7 Ma is inferred from the cosmogenic noble gas records. Activities of eleven cosmogenic radionuclides were measured. ²⁶Al and ²²Na activities as well as the ²²Na/²⁶Al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays. The low ⁶⁰Co activity (<1 dpm/kg) is indicative of a small preatmospheric size of the meteorite. Cosmic ray heavy nuclei track densities in olivine grains range from ～106 cm^?2 in samples from the largest fragment to approximately (4–9) × 105 cm^?2 in one of the smaller fragments. The combined track, radionuclide, and noble gas data suggest a preatmospheric radius of ～20 cm for the Dergaon meteorite.     

On the instability of weakly radially anisotropic star clusters

We discuss contradictions existing in the literature in the problem on the stability of collisionless spherical stellar systems, which are the simplest anisotropic generalization of the well-known polytropic models. On the one hand, calculations of the growth rates within the framework of a linear stability theory and N-body simulations suggest that these systems should become stable when the parameter s characterizing the degree of anisotropy of the stellar velocity distribution becomes lower than some critical value s _crit > 0. On the other hand, according to Palmer and Papaloizou, the growth rate should be nonzero up to the isotropic limit s = 0. Using our method of determining the eigenmodes of stellar systems, we show that even though the mode growth rates in weakly radially anisotropic systems of this type are nonzero, they are exponentially small, i.e., decrease as γ ∝ exp(−a/s) when s → 0. For slightly radially anisotropic systems with a finite lifetime, this actually implies stability.