Search for: All records

Abstract Ultraviolet images of Earth's polar regions obtained by high altitude spacecraft have proved to be immensely useful for documenting numerous features of the aurora and understanding the coupling between Earth's magnetosphere and ionosphere. In this study we have examined images obtained by the far ultraviolet Spectrographic Imager camera on the IMAGE satellite during the first three years of its mission (2000–2002) for comparison with observations of large geomagnetic disturbances (GMDs) by ground‐based magnetometers in eastern Arctic Canada. To our knowledge, this is the first study to investigate the use of high‐altitude imager data to identify the global context of GMDs. We found that rapid auroral motions or localized intensifications visible in these images coincide with regions of largedB/dtas well as localized and closely spaced up/down vertical currents and increased equivalent ionospheric currents, but one of the two events presented did not appear to be related to substorm processes. These magnetic perturbations and currents can appear or disappear in a few tens of seconds, thus highlighting the importance of images with a high cadence. 

Abstract Following the auroral substorm onset, the active aurora undergoes expansion, which can vary in spatial and temporal extent. The spatiotemporal development of the expansion phase active aurora is controlled by new auroral intensifications that often follow the initial onset. Using seven examples, we investigate the nature of these new auroral intensifications and address a question: are they new auroral onsets, that is, “successive onsets” or poleward‐boundary intensifications (PBIs) and ensuing auroral streamers? We observed events that included both types of auroral features—successive onsets and PBIs—and their combinations. For multiple‐onset substorms, successive onsets may occur eastward, westward, and poleward of the initial onset, resulting in a diverse range of expansion phase spatial extent and durations. Single‐onset substorms show only one auroral onset, but their spatiotemporal development can resemble that of multiple‐onset substorms. However, the additional activations are mainly PBIs and subsequent streamers. In some cases, PBIs undergo explosion, leading to a rapid poleward and azimuthal expansion of the aurora, resembling the auroral substorm onset. A prolonged sequence of PBIs and its longitudinal extension can contribute significantly to the spatiotemporal development of substorms expansion phase. Results suggest that post‐onset flow channels drive the spatiotemporal development of the substorm expansion phase by (a) triggering successive onsets and (b) inducing bursts of PBIs and their prolonged sequence. We speculate that post‐onset flow channels likely originate from the polar cap, but more evaluation is required. Our findings highlight the significance of examining imager data before solely relying on magnetometers to identify substorm onsets. 

Abstract Dawnside auroral polarization streams (DAPS) are fast eastward flows in the dawn convection cell of Earth's ionosphere. With a steep flow gradient near the interface between Region 1 and 2 currents and a peak poleward of it, DAPS were suggested to be responsible for instabilities and dramatic events in the magnetosphere‐ionosphere (M‐I) system. To predict these events, it is important to investigate when and where DAPS prefer to occur and how they are related to other M‐I phenomena. We conduct this investigation statistically using 10 years of Swarm data and find that DAPS under sunlit and dark ionospheric conditions exhibit different dependencies on magnetic local times and geomagnetic activities, reflecting a complicated interplay between magnetotail dynamics and ionospheric conductance. The statistical results also reveal a strong correlation between DAPS and embedded Region 2 currents. These findings provide new insights into the DAPS generation mechanism. 

Introduction: Magnetopause reconnection is known to impact the dayside ionosphere by driving fast ionospheric flows, auroral transients, and high-density plasma structures named polar cap patches. However, most of the observed reconnection impact is limited to one hemisphere, and a question arises as to how symmetric the impact is between hemispheres. Methods: We address the question using interhemispheric observations of poleward moving radar auroral forms (PMRAFs), which are a “fossil” signature of magnetopause reconnection, during a geomagnetic storm. We are particularly interested in the temporal repetition and spatial structure of PMRAFs, which are directly affected by the temporal and spatial variation of magnetopause reconnection. PMRAFs are detected and traced using SuperDARN complemented by DMSP, Swarm, and GPS TEC measurements. Results: The results show that PMRAFs occurred repetitively on time scales of about 10 min. They were one-to-one related to pulsed ionospheric flows, and were collocated with polar cap patches embedded in a Tongue of Ionization. The temporal repetition of PMRAFs exhibited a remarkably high degree of correlation between hemispheres, indicating that PMRAFs were produced at a similar rate, or even in close synchronization, in the two hemispheres. However, the spatial structure exhibited significant hemispherical asymmetry. In the Northern Hemisphere, PMRAFs/patches had a dawn-dusk elongated cigar shape that extended >1,000 km, at times reaching >2,000 km, whereas in the Southern Hemisphere, PMRAFs/patches were 2–3 times shorter. Conclusion: The interesting symmetry and asymmetry of PMRAFs suggests that both magnetopause reconnection and local ionospheric conditions play important roles in determining the degree of symmetry of PMRAFs/patches. 

Error-bounded lossy compression is a state-of-the-art data reduction technique for HPC applications because it not only significantly reduces storage overhead but also can retain high fidelity for postanalysis. Because supercomputers and HPC applications are becoming heterogeneous using accelerator-based architectures, in particular GPUs, several development teams have recently released GPU versions of their lossy compressors. However, existing state-of-the-art GPU-based lossy compressors suffer from either low compression and decompression throughput or low compression quality. In this paper, we present an optimized GPU version, cuSZ, for one of the best error-bounded lossy compressors-SZ. To the best of our knowledge, cuSZ is the first error-bounded lossy compressor on GPUs for scientific data. Our contributions are fourfold. (1) We propose a dual-quantization scheme to entirely remove the data dependency in the prediction step of SZ such that this step can be performed very efficiently on GPUs. (2) We develop an efficient customized Huffman coding for the SZ compressor on GPUs. (3) We implement cuSZ using CUDA and optimize its performance by improving the utilization of GPU memory bandwidth. (4) We evaluate our cuSZ on five real-world HPC application datasets from the Scientific Data Reduction Benchmarks and compare it with other state-of-the-art methods on both CPUs and GPUs. Experiments show that our cuSZ improves SZ's compression throughput by up to 370.1x and 13.1x, respectively, over the production version running on single and multiple CPU cores, respectively, while getting the same quality of 

Abstract The Poynting vector (Poynting flux) from Earth's magnetosphere downward toward its ionosphere carries the energy that powers the Joule heating in the ionosphere and thermosphere. The Joule heating controls fundamental ionospheric properties affecting the entire magnetosphere‐ionosphere‐thermosphere system, so it is necessary to understand when and where the Poynting flux is significant. Taking advantage of new data sets generated from DMSP (Defense Meteorological Satellite Program) observations, we investigate the Poynting flux distribution within and around the auroral zone, where most magnetosphere‐ionosphere (M‐I) dynamics and thus Joule heating occurs. We find that the Poynting flux, which is generally larger under more active conditions, is concentrated in the sunlit cusp and near the interface between Region 1 and 2 currents. The former concentration suggests voltage generators drive the cusp dynamics. The latter concentration shows asymmetries with respect to the interface between the Region 1 and 2 currents. We show that these reflect the controlling impact of subauroral polarization streams and dawnside auroral polarization streams on the Poynting flux.