Refine
Has Fulltext
- no (16) (remove)
Document Type
- Article (15)
- Monograph/Edited Volume (1)
Language
- English (16)
Is part of the Bibliography
- yes (16)
Keywords
- Sun: flares (4)
- Sun: filaments, prominences (3)
- Sun: coronal mass ejections (CMEs) (2)
- Clock tree (1)
- High rate GPS (1)
- Modeling (1)
- OsDUR3 (1)
- Real time (1)
- Reference station (1)
- Rover station (1)
Force-free equilibria containing two vertically arranged magnetic flux ropes of like chirality and current direction are considered as a model for split filaments/prominences and filament-sigmoid systems. Such equilibria are constructed analytically through an extension of the methods developed in Titov & Demoulin and numerically through an evolutionary sequence including shear flows, flux emergence, and flux cancellation in the photospheric boundary. It is demonstrated that the analytical equilibria are stable if an external toroidal (shear) field component exceeding a threshold value is included. If this component decreases sufficiently, then both flux ropes turn unstable for conditions typical of solar active regions, with the lower rope typically becoming unstable first. Either both flux ropes erupt upward, or only the upper rope erupts while the lower rope reconnects with the ambient flux low in the corona and is destroyed. However, for shear field strengths staying somewhat above the threshold value, the configuration also admits evolutions which lead to partial eruptions with only the upper flux rope becoming unstable and the lower one remaining in place. This can be triggered by a transfer of flux and current from the lower to the upper rope, as suggested by the observations of a split filament in Paper I. It can also result from tether-cutting reconnection with the ambient flux at the X-type structure between the flux ropes, which similarly influences their stability properties in opposite ways. This is demonstrated for the numerically constructed equilibrium.
The Relative Pollen Productivities (RPPs) of common steppe species are estimated using Extended R-value (ERV) model based on pollen analysis and vegetation survey of 30 surface soil samples from typical steppe area of northern China. Artemisia, Chenopodiaceae, Poaceae, Cyperaceae, and Asteraceae are the dominant pollen types in pollen assemblages, reflecting the typical steppe communities well. The five dominant pollen types and six common types (Thalictrum, Iridaceae, Potentilla, Ephedra, Brassicaceae, and Ulmus) have strong wind transport abilities; the estimated Relevant Source Area of Pollen (RSAP) is ca. 1000 m when the sediment basin radius is set at 0.5 m. Ulmus, Artemisia, Brassicaceae, Chenopodiaceae, and Thalictrum have relative high RPPs; Poaceae, Cyperaceae, Potentilla, and Ephedra pollen have moderate RPPs; Asteraceae and Iridaceae have low RPPs. The reliability test of RPPs revealed that most of the RPPs are reliable in past vegetation reconstruction. However, the RPPs of Asteraceae and Iridaceae are obviously underestimated, and those of Poaceae, Chenopodiaceae, and Ephedra are either slightly underestimated or slightly overestimated, suggesting that those RPPs should be considered with caution. These RPPs were applied to estimating plant abundances for two fossil pollen spectra (from the Lake Bayanchagan and Lake Haoluku) covering the Holocene in typical steppe area, using the "Regional Estimates of Vegetation Abundance from Large Sites" (REVEALS) model. The RPPs-based vegetation reconstruction revealed that meadow-steppe dominated by Poaceae, Cyperaceae, and Artemisia plants flourished in this area before 6500-5600 cal yr BP, and then was replaced by present typical steppe.
Using Big Bear Solar Observatory film data recently digitized at NJIT, we investigate a Moreton wave associated with an X9 flare on 1990 May 24, as well as its interactions with four filaments F1-F4 located close to the flaring region. The interaction yields interesting insight into physical properties of both the wave and the filaments. The first clear Moreton wavefront appears at the flaring-region periphery at approximately the same time as the peak of a microwave burst and the first of two gamma-ray peaks. The wavefront propagates at different speeds ranging from 1500-2600 km s(-1) in different directions, reaching as far as 600 Mm away from the flaring site. Sequential chromospheric brightenings are observed ahead of the Moreton wavefront. A slower diffuse front at 300-600 km s(-1) is observed to trail the fast Moreton wavefront about one minute after the onset. The Moreton wave decelerates to similar to 550 km s(-1) as it sweeps through F1. The wave passage results in F1's oscillation which is featured by similar to 1 mHz signals with coherent Fourier phases over the filament, the activation of F3 and F4 followed by gradual recovery, but no disturbance in F2. Different height and magnetic environment together may account for the distinct responses of the filaments to the wave passage. The wavefront bulges at F4, whose spine is oriented perpendicular to the upcoming wavefront. The deformation of the wavefront is suggested to be due to both the forward inclination of the wavefront and the enhancement of the local Alfven speed within the filament channel.
Slow rise and partial eruption of a double-decker filament. I. observations and interpretation
(2012)
We study an active-region dextral filament that was composed of two branches separated in height by about 13 Mm, as inferred from three-dimensional reconstruction by combining SDO and STEREO-B observations. This "double-decker" configuration sustained for days before the upper branch erupted with a GOES-class M1.0 flare on 2010 August 7. Analyzing this evolution, we obtain the following main results. (1) During the hours before the eruption, filament threads within the lower branch were observed to intermittently brighten up, lift upward, and then merge with the upper branch. The merging process contributed magnetic flux and current to the upper branch, resulting in its quasi-static ascent. (2) This transfer might serve as the key mechanism for the upper branch to lose equilibrium by reaching the limiting flux that can be stably held down by the overlying field or by reaching the threshold of the torus instability. (3) The erupting branch first straightened from a reverse S shape that followed the polarity inversion line and then writhed into a forward S shape. This shows a transfer of left-handed helicity in a sequence of writhe-twist-writhe. The fact that the initial writhe is converted into the twist of the flux rope excludes the helical kink instability as the trigger process of the eruption, but supports the occurrence of the instability in the main phase, which is indeed indicated by the very strong writhing motion. (4) A hard X-ray sigmoid, likely of coronal origin, formed in the gap between the two original filament branches in the impulsive phase of the associated flare. This supports a model of transient sigmoids forming in the vertical flare current sheet. (5) Left-handed magnetic helicity is inferred for both branches of the dextral filament. (6) Two types of force-free magnetic configurations are compatible with the data, a double flux rope equilibrium and a single flux rope situated above a loop arcade.
Despite the great agricultural and ecological importance of efficient use of urea-containing nitrogen fertilizers by crops, molecular and physiological identities of urea transport in higher plants have been investigated only in Arabidopsis. We performed short-time urea-influx assays which have identified a low-affinity and high-affinity (Km of 7.55 mu M) transport system for urea-uptake by rice roots (Oryza sativa). A high-affinity urea transporter OsDUR3 from rice was functionally characterized here for the first time among crops. OsDUR3 encodes an integral membrane-protein with 721 amino acid residues and 15 predicted transmembrane domains. Heterologous expression demonstrated that OsDUR3 restored yeast dur3-mutant growth on urea and facilitated urea import with a Km of c. 10 mu M in Xenopus oocytes. Quantitative reverse-transcription polymerase chain reaction (qPCR) analysis revealed upregulation of OsDUR3 in rice roots under nitrogen-deficiency and urea-resupply after nitrogen-starvation. Importantly, overexpression of OsDUR3 complemented the Arabidopsis atdur3-1 mutant, improving growth on low urea and increasing root urea-uptake markedly. Together with its plasma membrane localization detected by green fluorescent protein (GFP)-tagging and with findings that disruption of OsDUR3 by T-DNA reduces rice growth on urea and urea uptake, we suggest that OsDUR3 is an active urea transporter that plays a significant role in effective urea acquisition and utilisation in rice.
Oases is a special ecosystem formed in arid climate and hungriness environment, in which resident, water and soil are the principal factor and exchanges of materials, energy and information are the main functional characteristics. The oases regions in central Asia are not only the basilic cradle of civilization of human beings, but also the important strategic places in world growing awareness of the potential benefits. We choose Keriya River Basin oases in south of Xinjiang as a case to study critical controlling of Oases Evolution, Based on the theories and methods used for environmental geology, physical geography, land resource research, and oases ecology. This study try to indicate the essential factors driving the oases ecosystem and the interactional dynamic mechanism in different scales and levels, confirm the optimal equilibrium aggregate of harmonious development between Population, Resources, Environment and Development, and establish the critical controlling pattern of sustainable development. We advance the indicator system to research the evolution of the PRED System of oases in Keriya River valley oases, in basis of the information derived from the field investigation and local materials. According to inquisitional result based on technical support of Geographic Information System (GIS) and Remote Sense (RS), the comparisons and analyses are carried out in land use at the upper reaches, vegetation change in the middle reaches, and desertification at the lower reaches, which narrates the regulations of Keriya River Valley oases land cover dynamic change. The main land cover types represent distinct characteristics of the local place. On the basis of field survey and statistical data, we use ARCINFO software to preprocess these data and the 2 TM satellite images. Through analyzing these images resulting from post- classification compare, we sums up the concrete quantificational dynamic distributed data of 13 land types covering a span of 15 years and regulation of the local ecological environment system. It finally points out that the trend of Keriya River Valley oases desertification expansion is mainly related to two important reasons: impact of natural environment and impact of human activities.