An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field‐aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). ...However, the transient (<∼1 min) response of the ionosphere‐thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using ∼6 s resolution Super Dual Auroral Radar Network ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only ∼1 min before moving upward. By contrast, the post‐midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed E⃗×B⃗ $\vec{E}\times \vec{B}$ vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.
Plain Language Summary
It is well‐known that a shock wave can suddenly compress objects they directly interact with. In this study, we report a special case in the geospace environment in which an interplanetary shock produced a concussion‐like response in the ionosphere that was tens of thousands of kilometers away from the location where the shock first impacted. The ionized part of the atmosphere, or the ionosphere, was remotely connected to the magnetosphere‐the region of geospace dominated by the Earth's magnetic field‐via electric currents. When the magnetosphere was abruptly compressed after the shock arrival, a pair of electric currents flowing along the geomagnetic field lines was generated in the dayside mid‐latitudes. The newly generated currents flipped the dayside ionospheric electric field from eastward to westward, leading to a downward motion of dayside ionospheric charged particles. Within 1 minute, the vertical motion and zonal electric field flipped again to the direction before the compression due to the generation of another pair of electric currents with an opposite sense to the first pair. This study depicts a global picture of the transient ionospheric response using multi‐point high‐resolution measurements and simulations with a state‐of‐the‐art fully coupled geospace model.
Key Points
Dayside ionospheric plasma undergoes a transient motion from downward to upward during a sudden commencement (SC)
Both observations and simulations show that the reversed vertical drift is a global response of the ionosphere to the SC
The transient response is caused by a reversal of induced zonal electric field during the SC
Concept drift is a phenomenon that commonly happened in data streams and need to be detected, because it means the statistical properties of a target variable, which the model is trying to predict, ...change over time in an unseen way. Most current detection methods are based on a hypothesis test framework. As a result, in these detection methods, a hypothesis test is need to be set, and more importantly, cannot obtain the type of drift. The setting of a hypothesis test requires an understanding of data streams, and cannot obtain the type of concept drift results in the loss of drift information. Hence, in this paper, to get rid of the setting of hypothesis test, and obtain the type of concept drift, we propose Active Drift Detection based on Meta learning (Meta-ADD), a novel framework that learns to classify concept drift by offline pre-training a model on data stream with known drifts, then online fine-tuning model to improve detection accuracy. Specifically, in the pre-trained phase, we extract meta-features based on the error rates of various concept drift, after which a pre-trained model called meta-detector is developed via a prototypical neural network by representing various concept drift classes as corresponding prototypes. In the detection phase, the meta-detector is fine-tuned to adapt to the real data stream via a simple stream-based active learning. Hence, Meta-ADD does not need a hypothesis test to detect concept drifts and identify their types automatically, which can directly support drift understand. The experiment results verify the effectiveness of Meta-ADD.
Transition disks with large inner dust cavities are thought to host massive companions. However, the disk structure inside the companion orbit and how material flows toward an actively accreting star ...remain unclear. We present a high-resolution continuum study of inner disks in the cavities of 38 transition disks. Measurements of the dust mass from archival Atacama Large Millimeter/Submillimeter Array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. An inner dust disk is detected in 18 of 38 disks in our sample. Of the 14 resolved disks, 8 are significantly misaligned with the outer disk. The near-infrared excess is uncorrelated with the mm-dust mass of the inner disk. The size-luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. The inner disks are depleted in dust relative to the outer disk, and their dust mass is uncorrelated with the accretion rates. This is interpreted as the result of radial drift and trapping by planets in a low (∼10−3) disk, or a failure of the -disk model to describe angular momentum transport and accretion. The only disk in our sample with confirmed planets in the gap, PDS 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. We hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets.
The field‐aligned plasma drift in the equatorial ionosphere drives the interhemispheric transport of the ionospheric F region plasma between the Northern and Southern Hemispheres. We use the ...Communication/Navigation Outage Forecasting System satellite measurements, for the first time, to present the responses of the equatorial field‐aligned drift during the 2009 sudden stratosphere warming (SSW). The observations show that the equatorial field‐aligned drift presents a southward disturbance in the morning sector and a large northward disturbance in the afternoon sector and gradually shifts to later local time during the SSW. Further, this new finding of semidiurnal disturbance in field‐aligned drift can well explain the hemispheric differences of the responses of the total electron content to the SSW. Based on the whole atmosphere model Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy, it is suggested that the meridional wind can contribute to the disturbance field‐aligned drift. Our results give a new perspective for understanding the ionospheric perturbations during SSWs.
Key Points
The responses of the equatorial ionospheric field‐aligned drift during 2009 SSW are reported
The field‐aligned drift shows a southward disturbance in the morning and a northward disturbance in the afternoon
This disturbance field‐aligned drift can well explain the hemispheric differences of the total electron content responses to SSW
With the current research impetus on neuromorphic computing hardware, realizing efficient drift and diffusive memristors are considered critical milestones for the implementation of readout layers, ...selectors, and frameworks in deep learning and reservoir computing networks. Current demonstrations are predominantly limited to oxide insulators with a soft breakdown behavior. While organic ionotronic electrochemical materials offer an attractive alternative, their implementations thus far have been limited to features exploiting ionic drift a.k.a. drift memristor technology. Development of diffusive memristors with organic electrochemical materials is still at an early stage, and modulation of their switching dynamics remains unexplored. Here, halide perovskite (HP) memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift are proposed and experimentally demonstrated. An ion permissive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate interface that promotes diffusive kinetics and an ion source nickel oxide (NiOx) interface that supports drift kinetics are identified to design diffusive and drift memristors, respectively, with methylammonuim lead bromide (CH3NH3PbBr3) as the switching matrix. In line with the recent interest on developing artificial afferent nerves as information channels bridging sensors and artificial neural networks, these HP memristive barristors are fashioned as nociceptive and synaptic emulators for neuromorphic sensory signal computing.
Halide perovskite memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift as nociceptive and synaptic emulators for neuromorphic sensory signal computing are experimentally demonstrated. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate interfaces promote diffusive kinetics while NiOx interfaces support drift kinetics with CH3NH3PbBr3 as the switching matrix, resulting in modulatable diffusive and drift memristors respectively.
•Efficient implementation of computationally expensive Fisher’s Exact Test.•Three new concept drift detection methods based on Fisher’s Exact Test.•Tested against DDM, ECDD, SEED, FHDDM, and STEPD ...using two base classifiers.•Proposed methods are significantly superior to most other Detectors in accuracy.•Proposed methods have better Precision, Recall and F-Measure than the other methods.
Concept drift detectors are software that usually attempt to estimate the positions of concept drifts in large data streams in order to replace the base learner after changes in the data distribution and thus improve accuracy. Statistical Test of Equal Proportions (STEPD) is a simple, efficient, and well-known method which detects concept drifts based on a hypothesis test between two proportions. However, statistically, this test is not recommended when sample sizes are small or data are sparse and/or imbalanced. This article proposes an ingeniously efficient implementation of the statistically preferred but computationally expensive Fisher’s Exact test and examines three slightly different applications of this test for concept drift detection, proposing FPDD, FSDD, and FTDD. Experiments run using four artificial dataset generators, with both abrupt and gradual drift versions, as well as three real-world datasets, suggest that the new methods improve the accuracy results and the detections of STEPD and other well-known and/or recent concept drift detectors in many scenarios, with little impact on memory and run-time usage.
Sea ice drift (SID) is crucial for understanding sea ice dynamics and for navigation safety. This study focuses on a comprehensive analysis of SID retrieval in the Arctic based on spaceborne ...synthetic aperture radar (SAR) data. A state-of-the-art method combining feature tracking and pattern matching techniques was applied to sequential Sentinel-1 (S1) SAR data in 2020 to derive SID from the central Arctic to the Fram Strait. The SAR retrievals were validated with drifting buoys. For temporal intervals of S1 data of approximately 24 hours, 15,254 collocations were collected from January to June and from October to December, yielding a 0.00 cm/s bias for the drift velocity magnitude and 0.27 degrees for direction with corresponding root mean square error (RMSE) of 0.47 cm/s and 4.73 degrees. Using temporal intervals of S1 data of less than 24 hours, we retrieved SID from July to September. A total of 644 collocations yields a comparison with a bias of 0.52 cm/s and 4.62 degrees for the drift magnitude and direction, respectively. The corresponding RMSE values are 1.85 cm/s and 20.73 degrees. The comparisons demonstrate better performance than the operational SAR-based SID product using the MCC method and are consistent with seasonal trends in drift velocity with the coarse-resolution product. We also analyzed the variations in SAR retrievals and further estimated appropriate temporal intervals, making it feasible to conduct long-term SID retrievals based on spaceborne SAR data at high spatial resolution in the Arctic.
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