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First Observation of Temporal Variation of STEVE Altitudes Using Triangulation by Two Color Cameras

JGR:Space physics - Thu, 09/05/2024 - 05:10

Abstract

We present a unique triangulation measurement of Strong Thermal Emission Velocity Enhancement (STEVE) observed on Sept 3rd, 2022, at Athabasca, Canada. Using two Digital single-lens reflex (DSLR) color cameras with all-sky fish-eye lenses, we show the profile of STEVE altitude variation over time in 1 min resolution for the first time. We estimate the altitude variation of its visible purplish arc and green picket fence structures. We also compare the DLSR camera images with narrowband all-sky images of an Optical Mesosphere Thermosphere Imager (OMTI) to see the correspondence of color camera images with 630 nm and OH-band auroral/airglow emission images. The height of the purplish STEVE arc was stable at 150–170 km while present (∼0,546–0,633 UT), except for a short excursion to ∼200 km at 0,600 UT. The green picket fence structures appeared at 0,549 UT when the intensity of the STEVE arc started to intensify. They presented only for ∼7 min, and their altitude was steady at ∼110 km. The vertical movement of the STEVE arc to ∼200 km was found to be accompanied by the motion across the local magnetic field lines, suggesting a southward E × B drift underlying the westward ion drift. From the comparison with the OMTI images, we find that the purplish STEVE arc moved closer to the 630 nm arc in the all-sky image when it rose to a higher altitude, indicating the occurrence of electron heating at a same or slightly higher altitude than the STEVE.

Anomalous ambiguity detection between reference stations based on Box-Cox transformation of tropospheric residual estimation

GPS Solutions - Thu, 09/05/2024 - 00:00

Abstract

With the increasing scale and complexity of network RTK, the reliability of ambiguity resolution becomes particularly crucial. Undetected incorrect fixings may trigger a chain reaction in subsequent atmospheric delay extraction and fitting stages, thereby affecting the reliability of user positioning services. Current methods for checking abnormal ambiguities suffer from issues such as inflexible threshold selection, excessive exclusion, and overlooking observational anomalies. Addressing these concerns, we propose a new method for ambiguity detection of reference stations, referred to as the “Box-Cox transformation & Secondary screening combining Chi-square Test” (BS-CT). Firstly, the tropospheric residuals after ambiguities fixing are extracted and they are unitized through their corresponding co-variance matrix. Secondly, the Box-Cox method is employed to transform the distribution of the unitized residuals, making them conform to a standard normal distribution. This enables the use of a chi-square test to eliminate satellites with observation anomalies. Finally, a secondary-screening method is applied to ensure the reliability of the fixed ambiguity quantity. In the experimental section, the BS-CT method was contrasted with the ordinary chi-square test, Partial Ambiguity Resolution method (PAR), and a method utilizing a decision function g for enhanced fixed fraction and variance strategy. The results indicate that, compared to the other three methods, lower fall-out ratio in anomaly ambiguity testing is observed with the BS-CT method. It is comparable to PAR in terms of omission ratio and performs lower than the other two methods.

Chondrule Properties and Formation Conditions

Space Science Reviews - Thu, 09/05/2024 - 00:00

Abstract

Chondrules are iconic sub-millimeter spheroids representing the most abundant high-temperature dust formed during the evolution of the circumsolar disk. Chondrules have been the subject of a great deal of research, but no consensus has yet emerged as to their formation conditions. In particular, the question of whether chondrules are of nebular or planetary origin remains largely debated. Building upon decades of chondrule investigation and recent headways in combining petrographic observations and O−Ti−Cr isotopic compositions, we here propose a comprehensive vision of chondrule formation. This holistic approach points toward a nebular origin of both NC and CC chondrules, with repetitive high-temperature recycling processes controlling the petrographic and isotopic diversities shown by chondrules. Chondrule precursors correspond to mixing between (i) early-formed refractory inclusions ± NC-like dust and (ii) previous generation of chondrules ± CI-like material. Chondrule formation took place under open conditions with gas-melt interactions with multi-species gas (H2O, Mg, SiO) playing a key role for establishing their characteristics. Petrographic and isotopic systematics do not support disk-wide transport of chondrules but point toward local formation of chondrules within their respective accretion reservoirs. Altogether, this shows that several generations of genetically-related chondrules (i.e., deriving from each other) co-exist in chondrites. In addition to supporting the nebular brand of chondrule-forming scenarios, this argues for repetitive and extremely localized heating events for producing chondrules.

The Sphericity Paradox and the Role of Hoop Stresses in Free Subduction on a Sphere

JGR–Solid Earth - Wed, 09/04/2024 - 10:34

Abstract

Oceanic plates are doubly curved spherical shells, which influences how they respond to loading during subduction. Here we study a viscous fluid model for gravity-driven subduction of a shell comprising a spherical plate and an attached slab. The shell is 100–1,000 times more viscous than the upper mantle. We use the boundary-element method to solve for the flow. Solutions of an axisymmetric model show that the effect of sphericity on the flexure of shells is greater for smaller shells that are more nearly flat (the “sphericity paradox”). Both axisymmetric and three-dimensional models predict that the deviatoric membrane stress in the slab should be dominated by the longitudinal normal stress (hoop stress), which is typically about twice as large as the downdip stress and of opposite sign. Our models also predict that concave-landward slabs can exhibit both compressive and tensile hoop stress depending on the depth, whereas the hoop stress in convex slabs is always compressive. We test these two predictions against slab shape and earthquake focal mechanism data from the Mariana subduction zone, assuming that the deviatoric stress in our flow models corresponds to that implied by centroid moment tensors. The magnitude of the hoop stress exceeds that of the downdip stress for about half the earthquakes surveyed, partially verifying our first prediction. Our second prediction is supported by the near-absence of earthquakes under tensile hoop stress in the portion of the slab having convex geometry.

Strong Lg‐Wave Attenuation Reveals Quarter‐Toroidal Crustal Melting Around the Yakutat Terrane in South‐Central Alaska

JGR–Solid Earth - Wed, 09/04/2024 - 09:54

Abstract

South-central Alaska features a history of massive volcanic activity. How the Denali volcanic gap (DVG) formed and why the Wrangell volcanoes are clustered remain vigorously debated. Investigating the crustal thermal structure can be crucial for understanding subsurface magmatic activity. We present a high-resolution broadband Lg-wave attenuation model to constrain crustal thermal anomalies beneath Alaska. Strong Lg attenuation is observed beneath the volcanoes in south-central Alaska, indicating thermal anomalies and possible melting in the crust. In contrast, the central Yakutat terrane (YT) and DVG are characterized by weak Lg attenuation, suggesting the existence of a cool crust that prevents hot mantle materials from invading the crust. This cool crust is likely the reason for the DVG. Quarter-toroidal crustal melting with strong attenuation is revealed around the YT. This curved zone of crustal melting, possibly driven by toroidal mantle flow, weakly connects the Wrangell and Buzzard Creek-Jumbo Dome magmatic chambers.

Challenging Ring‐Current Models of the Carrington Storm

JGR:Space physics - Wed, 09/04/2024 - 05:28

Abstract

A detailed analysis is made of horizontal-component geomagnetic-disturbance data acquired at the Colaba observatory in India recording the Carrington magnetic storm of September 1859. Prior to attaining its maximum absolute value, disturbance at Colaba increased with an e-folding timescale of 0.46 hr (28 min). Following its maximum, absolute disturbance at Colaba decreased as a trend having an e-folding timescale of 0.31 hr (19 min). Both of these timescales are much shorter than those characterizing the drift period of ring-current ions. Furthermore, over one 28-min interval when absolute disturbance was increasing, the data indicate an absolute rate of change of ≥2,436 nT/hr. If this is representative of disturbance generated by a symmetric magnetospheric ring current, then, assuming a standard and widely used parameterization, an interplanetary electric field of ≥451 mV/m is indicated. An idealized and extreme solar-wind dynamic pressure could, conceivably, reduce this bound on the interplanetary electric field to ≥202 mV/m. If the parameterization for electric-field extrapolation is accurate, but the field strengths obtained are deemed implausible, then it can be concluded that the Colaba disturbance data were significantly affected by partial-ring, field-aligned, or ionospheric currents. The same conclusion is supported by the shortness of the e-folding timescales characterizing the Colaba data. Several prominent studies of the Carrington event need to be reconsidered.

The Dynamic Venusian Bow Shock Model With the Nonlinear Effect of Magnetosonic Mach Number Based on Venus Express Observations

JGR:Space physics - Wed, 09/04/2024 - 05:11

Abstract

Utilizing the 8.5-year Venus Express observations, we investigate the effects of solar wind magnetosonic Mach number MMS $\left({M}_{MS}\right)$, solar extreme ultraviolet (EUV) radiation, solar wind dynamic pressure Pd $\left({P}_{d}\right)$ and interplanetary magnetic field (IMF) on the shape of the Venusian bow shock. Our statistical analysis yields several findings: (a) The spatial scale of the Venusian bow shock varies in a nonlinear manner with MMS ${M}_{MS}$ and shows a linear correlation with the EUV flux. (b) After the variance of the bow shock size caused by different MMS ${M}_{MS}$ and EUV are considered, the bow shock size shows no apparent correlation with the IMF intensity, IMF cone angle and solar wind dynamic pressure. (c) The angle between the IMF and the shock normal θBn $\left({\theta }_{Bn}\right)$ emerges as a significant factor shaping the bow shock's local distance. A two-parameter (MMS ${M}_{MS}$ and EUV) dynamic bow shock model is consequently constructed. This dynamic model not only elucidates the typical behavior of the bow shock under normal solar wind conditions but also unveils the anomalously distant bow shock location characterized by extremely low MMS ${M}_{MS}$.

Solar Flares and the Intricate Response of Earth's Outer Geomagnetic Field Variation

JGR:Space physics - Wed, 09/04/2024 - 04:58

Abstract

In this study, we investigate the intricate electrodynamics of the Earth's horizontal component of the geomagnetic field (ΔH) in response to two significant solar flares (SF) occurring on 03 July and 28 October 2021. These flares are classified as X1.59 and X1.0, respectively. It is noted that the ΔH follows the X-ray variation during the SF, but there is a time lag of a few minutes between the X-ray and ΔH. A possible explanation for the time lag is the neutral atmosphere and ionosphere coupling, via ion drag.

Dynamic Evolution of Dayside Magnetopause Reconnection Locations and Their Dependence on IMF Cone Angle: 3‐D Global Hybrid Simulation

JGR:Space physics - Wed, 09/04/2024 - 04:39

Abstract

We study the dynamic evolution of dayside magnetopause reconnection locations and their dependence on the interplanetary magnetic field (IMF) cone angle via 3-D global-scale hybrid simulations. Cases with finite IMF Bx and Bz but IMF By = 0 are investigated. It is shown that the dayside magnetopause reconnection is unsteady under quasi-steady solar wind conditions. The reconnection lines during the dynamic evolution are not always parallel to the equatorial plane even under purely southward IMF conditions. Magnetopause reconnection locations can be affected by the generation, coalescence, and transport of flux ropes (FRs), reconnection inside the FRs, and the magnetosheath flow. In the presence of an IMF component Bx, the magnetopause reconnection initially occurs in high-latitude regions downstream of the quasi-perpendicular bow shock, followed by the generation of multiple reconnection regions. In the later stages of the simulation, a dominant reconnection region is present in low-latitude regions, which can also affect reconnection in other regions. The global distribution of reconnection lines under a finite IMF Bx is found to not be limited to the region with maximum magnetic shear angle.

A main direction-based noise removal algorithm for ICESat-2 photon-counting LiDAR data

Journal of Geodesy - Wed, 09/04/2024 - 00:00

Abstract

A new generation of space-borne LiDAR (Light Detection And Ranging) satellite ICESat-2 (Ice, Cloud, and land Elevation Satellite-2) equipped with ATLAS (Advanced Topographic Laser Altimeter System) can perform earth observation. The main problem is to remove the noise photons from the data. The study proposes a main direction-based noise removal algorithm based on three sets of photon-counting LiDAR data. In order to extract the main direction, features in the spatial neighborhood (k) of photons are calculated, most of the initial noise is removed according to the angle between the main direction of photons and the along-track distance direction. Qualitative and quantitative evaluations are employed to validate the proposed algorithm. The obtained results and the performed analysis reveal that the proposed algorithm can process day and night data with different signal-to-noise ratios, while the accuracy of various surface types exceeds 96%. More specifically, the accuracy of the proposed algorithm for night data can reach 97.43%. Based on quantitative evaluations using SPL (Single photon LiDAR), MATLAS, and airborne LiDAR data, the average R, P, and F values are 0.951, 0.959, and 0.954, respectively. Meanwhile, the result of the proposed algorithm is compatible with the ATL03 photons with low, medium, and high confidence, and its accuracy is superior to ATL08 products. The proposed algorithm had fewer parameters and significantly outperformed the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and the improved local statistical distance algorithm. This algorithm is expected to provide a reference for subsequent photon-counting LiDAR data processing.

Improving GNSS-RTK multipath error extraction with an integrated CEEMDAN and STD-based PCA algorithm

GPS Solutions - Wed, 09/04/2024 - 00:00

Abstract

To address the background noise interference in GNSS-RTK during prolonged structural monitoring, the integration of the complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and the standard deviation (STD)-based principal component analysis (PCA) method (CEEMDAN-PCA-S) is proposed for de-noising. The CEEMDAN-PCA-S aims to de-noise the internal random noise by leveraging its white noise characteristics and subsequently extract the multipath error by leveraging its periodic repetition characteristics. The efficiency of CEEMDAN-PCA-S is verified with a simulation and a field experiment. The simulation results demonstrate that the STD-based PCA (PCA-S) could achieve superior amplitude consistency with the original signal compared to traditional PCA. Additionally, the correlation coefficients of the multipath error obtained with different algorithms are PCA-S (0.9243) < CEEMDAN (0.9582) < CEEMDAN-PCA-S (0.9945). Moreover, the residual error of CEEMDAN-PCA-S is minimal in terms of amplitude and root mean square error (RMSE), confirming its superior de-noising performance compared to CEEMDAN and PCA-S. The outcomes of a field experiment utilizing the GNSS-RTK indicate that the correlation coefficients between the multipath error extracted with CEEMDAN-PCA-S and the CEEMDAN residual errors are all above 0.94. The CEEMDAN-PCA-S decreases the RMSE of residual error to 0.1599 cm, marking a 79% reduction from the original signal. Moreover, both the amplitude and mean value are reduced by 83% and 16%. In conclusion, the proposed CEEMDAN-PCA-S could effectively remove white noise and subsequently extract the multipath error, enhancing the accuracy of GNSS-RTK for long-term structural monitoring and safety warnings.

Local earthquake monitoring with a low-cost seismic network: a case study in Nepal

Earth,Planets and Space - Wed, 09/04/2024 - 00:00

Seismic monitoring matters both for research and for populations living in areas of seismic hazard; however, it comes with a cost that is not fully affordable for developing countries. Compared to classical ap...

Coherence of Compressional Pc3‐4 Pulsation Driven by Upstream Waves in Topside Ionosphere Observed by the Swarm Constellation

JGR:Space physics - Tue, 09/03/2024 - 20:10

Abstract

In this study, we presented a detailed analysis of ultralow frequency compressional waves with frequencies ranging from 16 to 100 mHz by using magnetic measurements of Swarm A and B, when the two spacecraft were flying in a counter-rotating configuration. These waves are assumed to be driven by processes in the fore-shock region and subsequently termed as upstream waves (UWs). An automatic detection algorithm for identifying UW events has been developed and applied to the Swarm magnetic measurements. Different to previous studies we take advantage of the counter-rotating Swarm constellation to investigate the large-scale homogeneous wavefield. Only B-field oscillations from both Swarm A and B satellites satisfy the following criteria are accepted for UWs analysis: (a) highly correlated with normalized correlation coefficient (Cc) larger than 0.9; (b) shifted by less than 3 s between observations; (c) separated up to 90° in latitude and/or longitude. By this procedure we have identified from the years 2018–2023 in total 577 orbits containing UWs in the magnetic recordings of both spacecraft. In the first step, we checked phase shifts between UW detections at large latitudinal separation. The two counter-rotating spacecraft allowed to make use of the Doppler effect to check the possible propagation of UWs at ionospheric altitude. Although individual events show signs of north-south wave propagation, on average no systematic motion could be found. Similarly, possible wave motions toward or away from noon hours have been checked. By analyzing the simultaneous observations at larger longitudinal separation, also hardly any phase differences are identified in the east-west direction. Further by evaluating the statistical results, a mean tiny local time effect seems to emerge, indicating on average an earlier arrival of the waves in the morning and later in the evening hours.