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Abstract

Local empirical models of the F2 layer peak electron density (NmF2) are developed for 43 low- middle latitude ionosonde stations using auto-scaled data from Lowell GIRO data center and manually scaled data from World Data Center for Ionosphere and Space Weather. Data coverage at these stations ranges from a few years to up to 6 decades. Flare Irradiance Spectral Model index version 2 (FISM2) and ap3 index are used to parametrize the solar extreme ultraviolet (EUV) flux and geomagnetic activity dependence of NmF2. Learning curves suggest that approximately 8 years of data coverage is required to constrain the solar activity dependence of NmF2. Output of local models altogether captures well known anomalies of the F2 ionospheric layer. Performance metrics demonstrate that the model parametrized using FISM2 has better accuracy than a similarly parametrized model with F10.7, as well as than the IRI-2020 model. Skill score metrics indicate that the FISM2 based model outperforms F10.7 model at all solar activity levels. The improved accuracy of model with FISM2 over F10.7 is due to better representation of solar rotation by FISM2, and due to its performance at solar extremum. Application of singular spectrum analysis to model output reveals that solar rotation contributes to about 2%–3% of the variance in NmF2 data and FISM2 based model, while F10.7 based models overestimate the strength of solar rotation to be at 4%–7%. At solar extremum, both F10.7-based model and IRI-2020 tend to overestimate the NmF2 while FISM2 provides the most accurate prediction out of three.

Abstract

This work presents an algorithm for automatic detection of anomalous electron heating (AEH) events in the auroral E-region ionosphere using data from the Poker Flat Incoherent Scatter Radar (PFISR). The algorithm considers both E-region electron temperature and magnetically conjugate electric field measurements. Application of this algorithm to 14 years of PFISR data spanning 2010 through 2023 detected 505 AEH events. Measured electron temperatures increase linearly with plasma drift speeds. Statistical trends of AEH occurrence as a function of space weather indices (AE and F10.7) demonstrate correlations with the solar cycle and geomagnetic activity levels. The magnetic local time occurrence rates show preferences for dusk and dawn with most events in the dusk sector. Observed AEH events tend to appear in regions of relatively low electron density and do not appear inside intense auroral arcs with high electron density. Furthermore, AEH detection requires a higher electric field than predicted by the threshold for a positive growth rate of the Farley-Buneman instability (FBI), according to linear fluid theory. The implications of these findings for kinetic theories of FBI and AEH are discussed.

Abstract

Kelvin Helmholtz Instabilities (KHI) result from interactions between the shocked solar wind and the Earth's magnetosphere. These are formed due to the velocity shear between the plasma in the magnetosphere and magnetosheath. The role of KHI in bringing in the shocked solar wind into the terrestrial magnetosphere has been studied extensively using MHD, Hall-MHD, hybrid and PIC simulations. Such simulations oftentimes make simplifying assumptions of the boundary layer in the magnetopause. To experimentally study the effects of KHI on the boundary layer and its effectiveness in bringing in solar wind, we analyze 43 KHI events. All these events have quasi-constant IMF orientation during its interval, thereby mitigating the effects of variation of IMF in the ongoing transient magnetopause process. In this statistical study of KHIs, we demonstrate that there is a preexisting boundary layer before KHIs begin to develop. As KHI develops to its non-linear state, the ions in the magnetosphere, magnetopause, and magnetosheath are mixed, which is demonstrated using the alpha-to-proton density ratio. As a result of this mixing, the well-defined preexisting boundary layer is replaced by a much more uniformly mixed boundary layer.

Abstract

At ultra-slow spreading ridges, with full spreading rates less than ∼20 mm/yr, spreading is accommodated both by highly spatially and temporally segmented magmatism, and tectonic extension along large-scale detachment faults that exhume ultramafic material to the seafloor. In the most magma-poor regions, detachment faulting alternates in polarity over time, producing a “flip-flopping” effect of subsequent detachment dips. The resulting seafloor in these regions displays a morphology termed “smooth seafloor” comprising elongate, broad ridges with peridotite/serpentinite lithologies. We conducted tomographic travel-time inversion of a 3-D wide-angle seismic data set acquired over a region of smooth seafloor around 64°30′E along the Southwest Indian Ridge (SISMOSMOOTH; Cruise MD199), to produce a seismic velocity volume through the crustal section and into the uppermost mantle. We observe patterns of velocity anomalies that correspond with variations in the bathymetry arising from the mode of spreading and are interpreted as changes in the degree of alteration with depth resulting from spatial and temporal variations in fluid-rock interaction, controlled by faulting and tectonic damage processes. The detachment faults do not show simple planar structures at depth but instead mirror the shapes of the bathymetric ridges that they exhume. Magmatic input is overall highly limited, but there is one region on the lower part of an exhumed detachment footwall where a thickness of volcanic material is observed that suggests a component of syn-tectonic volcanism, which could contribute to detachment abandonment.

Abstract

Body waves traversing the Earth's interior from a seismic source to receivers on the surface carry rich information about its internal structures. Their travel time measurements have been widely used in seismology to constrain Earth's interior at the global scale by mapping the time anomaly along their ray paths. However, picking the travel time of global seismic waves, suitable for studying Earth's fine-scale structures, requires highly skilled personnel and is often fairly subjective. Here, we report the development of an automatic picker for PKIKP waves traveling through the inner core (IC), especially nearly along Earth's diameters, based on the latest advances in supervised deep learning. A convolutional neural network (CNN) we develop automatically determines the PKIKP onset on vertical seismograms near its theoretical prediction of cataloged earthquakes. As high-quality manual onset picks of global seismic phases are limited, we employ a scheme to generate a synthetic supervised training data set containing 300,000 waveforms. The PKIKP onsets picked by our trained CNN automatic picker exhibit a mean absolute error of ∼0.5 s compared to 1,503 manual picks, comparable to the estimated human-picking error. In an integration test, the automatic picks obtained from an extended waveform data set yield a cylindrically anisotropic IC model that agrees well with the models inferred from manual picks, which illustrates the success of this pilot model. This is a significant step closer to harvesting an unprecedented volume of travel time measurements for studying the IC or other regions of the Earth's deep interior.

Abstract

Models of active deformation of the Earth's crust are predominantly represented with dislocations having a downdip continuation into the lower crust, where the fault slips continuously. This model predicts surface strain accumulation concentrated near the fault during the interseismic period. In an alternative model, faults do not extend beneath the elastic portion of the crust and are accompanied by a wide zone of distributed shear underneath, predicting a more constant strain rate lacking concentrations at the faults. We use high-precision GPS data collected across the northern and central Walker Lane, USA— a region of complex faulting near the western edge of the Basin and Range Province to evaluate which model is appropriate. Despite the existence of dense continuous and semi-continuous geodetic networks that have been surveyed for ∼20 years, the horizontal velocities reveal no evidence of localized strain accumulation across the fault surface expressions. Instead, deformation within the Walker Lane is uniformly linear, suggesting that the surface deformation reflects distributed shear within the ductile crust rather than focused deformation at faults. This suggests no downdip extension of the faults below the seismogenic layer. The shear zone is 172 ± 6 km wide in the northernmost Walker Lane narrowing to 116 ± 4 km in the central Walker Lane. The total velocity budget across the shear zone is 7.2 ± 0.1 mm/yr in the north, increasing to 10.1 ± 0.1 mm/yr in the central Walker Lane. We conclude that assuming the presence of lower crustal dislocations when estimating geodetic faults slip rates may be inappropriate.

Abstract

The eastward extrusion of the Tibetan Plateau materials has caused intricate tectonic deformations and frequent seismic activities in the Sanjiang lateral collision zone (SLCZ). To reveal crust structures and deformation mechanisms, we investigate high-resolution structural features of crustal depth (≤40 km). A 3-D S-wave velocity and azimuthal anisotropy model is constructed by the direct tomography method with Rayleigh phase velocity at periods of 2–40 s from multiple temporary seismic arrays and regional permanent network. In the middle-to-lower crust, an obvious low-velocity zone is confined by the large-scale fault systems of Jinhe-Qinghe fault and Chenhai fault (CHF) to the northeast and east, Lancangjiang fault (LCJF) and Red River fault (RRF) to the west, with strong N-S-oriented anisotropy, which evident differs from the ENE-WSW-oriented weak anisotropy in the high-velocity zone on the northeastern side. We consider that the weak material may be obstructed by large faults and the high-velocity zone, resulting in complex crustal deformation and tectonic boundary. The crustal low-velocity materials beneath the Tengchong volcano (TCV) are probably separated with those from the Tibetan Plateau. The low-velocity beneath the Chuxiong basin (CXB) may be combinations of partial melts and fluid derived from shear deformation and deep material upwelling. The segmented anisotropy at the NW end of the RRF suggests complex deformation by crustal flow, emphasizing the important influence of faults on anisotropic pattern. The complex anisotropy in the fault intersection of the Lijiang-Xiaojinhe fault and RRF also highlights the important role of these faults in shaping crustal deformation.

Abstract

In the present work we have modeled diffuse auroral emissions in Jupiter using the recent observations received by JUNO orbiter. Resonant wave-particle interaction by electron-cyclotron harmonic (ECH) waves has been invoked as the mechanism for production of diffuse aurora. Energetic electrons trapped on closed field lines are diffused into the loss-cone via pitch-angle diffusion. Electron precipitation fluxes have been calculated. Electrons entering into the atmosphere undergo collisions with atmospheric constituents atomic H and molecular H2 producing electromagnetic emissions. Four excitations have been considered. These excitations are: HLy-α from excitation of atomic H, HLy-α from dissociative excitation of molecular H2, Lyman and Werner bands of H2. Volume excitation rates have been calculated for these excitations. Height integrated volume excitation rates have been obtained to give auroral intensities. Numerical calculations have been performed at five L-shells; L = 10, 12, 15, 18 and 20. Maximum auroral intensities is obtained at shell L = 10. At higher shell L = 20 the intensity value reduces to a minimum. The intensities in Rayleigh (R) for HLy-α from H, HLy-α from H2, Lyman and Werner bands of H2 are calculated. Comparing these intensities with the diffuse auroral intensities observed at Saturn, it is found that the intensities at Jupiter are higher than the values predicted for Saturn. We have also calculated volume ionization rates for atomic H producing H+, dissociative ionization of H2 producing H+, and ionization of H2 producing H2 +. The continuity equation is solved to obtain the electron density Outcomes are discussed.

Abstract

The interplanetary magnetic field (IMF) north-south component, B z , plays a crucial role in the interaction between the solar wind and the Earth's magnetosphere. We analyze 98 intervals in which B z changed from >3 nT to <−3 nT in 5 min and for which these rapid southward turnings (STs) were surrounded by consistently northward or southward IMF. We separate out events in proximity of interplanetary coronal mass ejections and corotating interaction regions. We find that IMF magnitude, solar wind dynamic pressure and proton density (but also flow speed in ICME-related events) near the turnings are enhanced above their medians. We analyze the maximum responses of the SML, SMU, SYM-H, and PCN magnetospheric indices and their timescales, along with the occurrence of geomagnetic phenomena. We find that most STs were followed by either substorms (60.20%) or enhanced convection (37.76%). While SML has similar median minima (∼−460 nT) and timescales (∼56 min) for substorm and convection events, SMU has noticeable differences. STs were followed by geomagnetic storms (SYM-H ≤ −50 nT) in 46.94% of events within 12 hr, with more storms following ICME-related turnings. PCN has peaks (median 3.8 mV/m) around 30 min after the turning, and larger ones (median 4.9 mV/m) later. Stronger solar wind driving and magnetospheric responses are observed for ICME-related events. The correlation between the geomagnetic and solar wind parameters around STs reveals a more direct link between solar wind driving and geomagnetic response for STs than at other times.

Abstract

We study the geomagnetic storm of 9 October 2012, where it had been generally accepted that the resulting prominent outer radiation belt electron acceleration throughout the storm is due to whistler-mode chorus waves. This storm has been studied previously by two-dimensional Fokker–Planck numerical simulations with data-driven quasi-linear (QL) diffusion rates. However, possible nonlinear (NL) resonant interaction effects on electron flux dynamics haven't been looked at yet. This study aims to fill this gap by demonstrating that theory-informed rescaling of QL diffusion rates accounting for contributions of NL resonant interactions helps to reproduce better observed increase of electron fluxes by diffusion simulations. We use machine learning, uncertainty quantification (UQ), physics-perturbed ensemble of VERB simulations and Van Allen Probes observations to identify optimal rescaling of quasi-linear diffusion rates.

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.

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.

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.

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.

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 ${M}_{MS}$.

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.

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.

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.

Evaluation of on-site calibration procedures for SKYNET Prede POM sun–sky photometers
Monica Campanelli, Victor Estellés, Gaurav Kumar, Teruyuki Nakajima, Masahiro Momoi, Julian Gröbner, Stelios Kazadzis, Natalia Kouremeti, Angelos Karanikolas, Africa Barreto, Saulius Nevas, Kerstin Schwind, Philipp Schneider, Iiro Harju, Petri Kärhä, Henri Diémoz, Rei Kudo, Akihiro Uchiyama, Akihiro Yamazaki, Anna Maria Iannarelli, Gabriele Mevi, Annalisa Di Bernardino, and Stefano Casadio
Atmos. Meas. Tech., 17, 5029–5050, https://doi.org/10.5194/amt-17-5029-2024, 2024
To retrieve columnar aerosol properties from sun photometers, some calibration factors are needed. The on-site calibrations, performed as frequently as possible to monitor changes in the machine conditions, allow operators to track and evaluate the calibration status on a continuous basis, reducing the data gaps incurred by the periodic shipments for performing centralized calibrations. The performance of the on-site calibration procedures was evaluated, providing very good results.

In situ observations of supercooled liquid water clouds over Dome C, Antarctica, by balloon-borne sondes
Philippe Ricaud, Pierre Durand, Paolo Grigioni, Massimo Del Guasta, Giuseppe Camporeale, Axel Roy, Jean-Luc Attié, and John Bognar
Atmos. Meas. Tech., 17, 5071–5089, https://doi.org/10.5194/amt-17-5071-2024, 2024
Clouds in Antarctica are key elements affecting climate evolution. Some clouds are composed of supercooled liquid water (SLW; water held in liquid form below 0 °C) and are difficult to forecast by models. We performed in situ observations of SLW clouds at Concordia Station using SLW sondes attached to meteorological balloons in summer 2021–2022. The SLW clouds were observed in a saturated layer at the top of the planetary boundary layer in agreement with ground-based lidar observations.