Hasil untuk "physics.space-ph"

R. Bates

M. Wachstein, E. Meisel

D. Brookins

A. Gourine, V. Kasymov, N. Marina et al.

M. Wedborg, D. Turner, L. Anderson et al.

A. Savina, C. Jancic, S. Hugues et al.

Sung-Ching Chen, Yung-Chih Wu, F. Mi et al.

Y. Ohno, K. Maehashi, Y. Yamashiro et al.

M. Chesler

Y. Urano, D. Asanuma, Y. Hama et al.

C. Shih, Shangchao Lin, Richa Sharma et al.

J. Xiong, Yongqin Liu, Xiangui Lin et al.

Continent-scale biogeography has been extensively studied in soils and marine systems, but little is known about biogeographical patterns in non-marine sediments. We used barcode pyrosequencing to quantify the effects of local geochemical properties and geographic distance for bacterial community structure and membership, using sediment samples from 15 lakes on the Tibetan Plateau (4–1670 km apart). Bacterial communities were surprisingly diverse, and distinct from soil communities. Four of 26 phyla detected were dominant: Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria, albeit 20.2% of sequences were unclassified at the phylum level. As previously observed in acidic soil, pH was the dominant factor influencing alkaline sediment community structure, phylotype richness and phylogenetic diversity. In contrast, archaeal communities were less affected by pH. More geographically distant sites had more dissimilar communities (r = 0.443, P = 0.030). Variance partitioning analysis showed that geographic distance (historical contingencies) contributed more to bacterial community variation (12.2%) than any other factor, although the environmental factors explained more variance when combined (28.9%). Together, our results show that pH is the best predictor of bacterial community structure in alkaline sediments, and confirm that both geographic distance and chemical factors govern bacterial biogeography in lake sediments.

G. Jeppu, T. Clement

Lenox Helene Baloglou, Parneet Gill, Tonatiuh Sánchez-Vizuet

Lambert's problem is a classical boundary value problem in analytical mechanics. It arises when trying to determine the energy required to place a particle, subject to a central gravitational potential, in a "free fall" trajectory connecting two given points on a desired travel time. Due to its mathematical beauty and its relevance in aerospace engineering, it has been and remains the object of attention of countless engineers, mathematicians (pure and applied), and physicists seeking to produce efficient solution algorithms. In this expository article, didactic in nature, we present a unified and comprehensive derivation that assumes only a minimal background in physics and mathematics. We focus on the simplest unperturbed case and carefully develop the argument for elliptical trajectories. The goal is to provide a single reference that can serve as an accelerated introduction for students and researchers interested in a quick introduction to the subject.

Xi Lu, Xiao-Jia Zhang, Anton V. Artemyev et al.

Electromagnetic whistler-mode waves play a crucial role in the acceleration and precipitation of radiation belt electrons. Statistical surveys of wave characteristics suggest that these waves should preferentially scatter and precipitate relativistic electrons on the day side. However, the night-side region is expected to be primarily associated with electron acceleration. The recent low-altitude observations reveal relativistic electron precipitation in the night-side region. In this paper, we present statistical surveys of night-side relativistic electron losses due to intense precipitation bursts. We demonstrate that such bursts are associated with storm time substorm injections and are likely related to relativistic electron scattering by ducted whistler-mode waves. We also speculate on the role of injections in creating conditions favorable for relativistic electron precipitation.

Alexander Lukin, Zhifang Guo, Yu Lin et al.

Magnetic reconnection is one of the most universal processes in space plasma that is responsible for charged particle acceleration, mixing and heating of plasma populations. In this paper we consider a triggering process of reconnection that is driven by interaction of two discontinuities: solar wind rotational discontinuity and tangential discontinuity at the Earth's magnetospheric boundary, magnetopause. Combining the multispacecraft measurements and global hybrid simulations, we show that solar wind discontinuities may drive the magnetopause reconnection and cause the mixing of the solar wind and magnetosphere plasmas around the magnetopause, well downstream of the solar wind flow. Since large-amplitude discontinuities are frequently observed in the solar wind and predicted for various stellar winds, our results of reconnection driven by the discontinuity-discontinuity interaction may have a broad application beyond the magnetosphere.

A. Hu, E. Camporeale, B. Swiger

The Disturbance storm time (Dst) index has been widely used as a proxy for the ring current intensity, and therefore as a measure of geomagnetic activity. It is derived by measurements from four ground magnetometers in the geomagnetic equatorial regions. We present a new model for predicting $Dst$ with a lead time between 1 and 6 hours. The model is first developed using a Gated Recurrent Unit (GRU) network that is trained using solar wind parameters. The uncertainty of the $Dst$ model is then estimated by using the ACCRUE method [Camporeale et al. 2021]. Finally, a multi-fidelity boosting method is developed in order to enhance the accuracy of the model and reduce its associated uncertainty. It is shown that the developed model can predict $Dst$ 6 hours ahead with a root-mean-square-error (RMSE) of 13.54 $\mathrm{nT}$. This is significantly better than the persistence model and a simple GRU model.

M. Nakanotani, G. P. Zank, L. -L. Zhao

We investigate particle acceleration in an MHD-scale system of multiple current sheets by performing 2D and 3D MHD simulations combined with a test particle simulation. The system is unstable for the tearing-mode instability, and magnetic islands are produced by magnetic reconnection. Due to the interaction of magnetic islands, the system turns into a turbulent state. The 2D (3D) case yields both $-5/3$ ($-11/3$ and $-7/3$) power-law spacetra for magnetic and velocity fluctuations. Particles are efficiently energized by the generated turbulence, and it forms a power-law tail with an index of $-2.2$ and $-4.2$ in the energy distribution function for the 2D and 3D case, respectively. We find more energetic particles outside magnetic islands rather than inside. We observe super-diffusion in the 2D ($\sim t^{2.27}$) and 3D ($\sim t^{1.2}$) case in the energy space of energetic particles.

A. Bandodkar, V. Hung, W. Jia et al.

C. Larrodera, L. Nikitina, C. Cid

This research provides an analysis of extreme events in the solar wind and in the magnetosphere due to disturbances of the solar wind. Extreme value theory has been applied to a 20 year data set from the Advanced Composition Explorer (ACE) spacecraft for the period 1998-2017. The solar proton speed, solar proton temperature, solar proton density and magnetic field have been analyzed to characterize extreme events in the solar wind. The solar wind electric field, vB$_{z}$ has been analyzed to characterize the impact from extreme disturbances in the solar wind to the magnetosphere. These extreme values were estimated for one-in-40 and one-in-80 years events, which represent two and four times the range of the original data set. The estimated values were verified by comparison with measured values of extreme events recorded in previous years. Finally, our research also suggests the presence of an upper boundary in the magnitudes under study.