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David Sibeck

Publications and source records attributed to David Sibeck.

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

A Feasibility Study of 4-D Tomography of Soft X-ray Magnetosheath Emissivities Using Multi-Spacecraft Measurements

Upcoming heliophysics missions utilize state-of-the-art wide field-of-view (FOV) imaging technology to measure and investigate the space plasma environment on a global scale. At Earth, remote sensing of soft X-ray emissions, which are generated via the charge exchange interaction between heavy solar wind ions and exospheric neutral atoms, is a promising means to investigate the global magnetosheath structure, its response to varying solar wind conditions, and the spatiotemporal properties of the dayside magnetic reconnection. Data analysis techniques such as optical tomography can provide additional structural and time-varying information from the observed target and thus enhance the mission’s scientific return. In this work, we simulate multiple and simultaneous observations of the dayside magnetosphere using soft X-ray imagers located at long-distance vantage points to reconstruct the time-dependent, three-dimensional (3-D) structure of the magnetosheath using a dynamic tomographic approach. The OpenGCCM MHD model is used to simulate the time-varying response of the magnetosheath to solar wind conditions and, subsequently, generate synthetic soft X-ray images from multiple spacecraft vantage points separated along a common orbit. A detailed analysis is then performed to identify the nominal set of spacecraft that produces the highest fidelity tomographic reconstruction of the magnetopause. This work aims to (i) demonstrate, for the first time, the use of dynamic tomography to retrieve the time-varying magnetosheath structure and (ii) identify a nominal mission design for multi-spacecraft configurations aiming for optical tomography.

3-D/4_d tomography↗
NASA NTRS2023

Estimating the Subsolar Magnetopause Position from Soft X-Ray Images Using a Low-Pass Image Filter

The Lunar Environment heliospheric X-ray Imager (LEXI) and Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) missions will image the Earth’s dayside magnetopause and cusps in soft X-rays after their respective launches in the near future, to specify global magnetic reconnection modes for varying solar wind conditions. To support the success of these scientific missions, it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images. In this research, we introduce a new geometric equation that calculates the subsolar magnetopause position ( R s ) from a satellite position, the look direction of the instrument, and the angle at which the X-ray emission is maximized. Two assumptions are used in this method: (1) The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause, and (2) the magnetopause surface near the subsolar point is almost spherical and thus R s is nearly equal to the radius of the magnetopause curvature. We create synthetic soft X-ray images by using the Open Geospace General Circulation Model (OpenGGCM) global magnetohydrodynamic model, the galactic background, the instrument point spread function, and Poisson noise. We then apply the fast Fourier transform and Gaussian low-pass filters to the synthetic images to remove noise and obtain accurate look angles for the soft X-ray peaks. From the filtered images, we calculate R 2 and its accuracy for different LEXI locations, look directions, and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth. Our method estimates R s with an accuracy of <0.3 R E when the solar wind density exceeds >10 cm -3 . The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields. The method captures the magnetopause motion during southward interplanetary magnetic field turnings. Consequently, the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind conditions. This technique will support the LEXI and SMILE missions in achieving their scientific objectives.

Hyangpyo Kim↗
NASA NTRS2022

Regression Bias in using Solar Wind Measurements

Simultaneous solar wind measurements from the solar wind monitors, WIND and ACE, differ due to the spatial and temporal structure of the solar wind. Correlation studies that use these measurements as input may infer an incorrect correlation due to uncertainties arising from this spatial and temporal structure, especially at extreme and rare solar wind values. In particular, regression analysis will lead to a regression function whose slope is biased towards the mean value of the measurement parameter. This article demonstrates this regression bias by comparing simultaneous ACE and WIND solar wind measurements. A non-linear regression analysis between them leads to a perception of underestimation of extreme values of one measurement on average over the other. Using numerical experiments, we show that popular regression analysis techniques such as linear least-squares, orthogonal least-squares, and non-linear regression are not immune to this bias. Hence while using solar wind parameters as an independent variable in a correlation or regression analysis, random uncertainty in the independent variable can create unintended biases in the response of the dependent variable. More generally, the regression to the mean effect can impact both event-based, statistical studies of magnetospheric response to solar wind forcing.

magnetosphere↗
NASA NTRS2022

Dayside Transient Phenomena and Their Impact on the Magnetosphere and Ionosphere

Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth’s radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.

Bow shock↗
NASA NTRS2022

The Cusp Plasma Imaging Detector (Cupid) Cubesat Observatory: Instrumentation

The Cusp Plasma Imaging Detector (CuPID) CubeSat observatory is a 6U CubeSat designed to observe solar wind charge exchange in magnetospheric cusps to test competing theories of magnetic reconnection at the Earth’s magnetopause. The CuPID is equipped with three instruments, namely, a wide field-of-view (4.6° × 4.6°) soft x-ray telescope, a micro-dosimeter suite, and an engineering magnetometer optimized for the science operation. The instrument suite has been tested and calibrated in relevant environments, demonstrating successful design. The testing and calibration of these instruments produced metrics and coefficients that will be used to create the CuPID mission’s data product.

Magnetospheric dynamics↗
NASA NTRS2020

Foreshock Cavities at Venus and Mars

“Foreshock cavities” are regions of turbulent and heated solar wind plasma that form upstream of Earth's bow shock. Despite being common at Earth, none have yet been reported at other planets. Here we present a survey of events encountered by the ESA Venus Express spacecraft consistent with foreshock cavities at Venus and a case study of a foreshock cavity encountered at Mars by NASA's MAVEN orbiter. Cavities appear to be common at Venus, and their properties appear to be very similar to those at Earth. Foreshock cavities appear to be observed preferentially in fast solar wind and when the interplanetary magnetic field is “radial” (parallel to the Sun‐planet line). Our collected observations are consistent with the hypothesis that “foreshock cavities” are simply the result of a transient encounter with a planetary foreshock. We posit foreshock cavities represent one of the following two possibilities: (1) a spacecraft encountering a traveling foreshock formed by a finite bundle of interplanetary magnetic field lines connecting to a shock or (2) the transient temporary motion of the foreshock over the spacecraft.

Foreschock↗
NASA NTRSDate not supplied

Tracking the Subsolar Bow Shock and Magnetopause

Global magnetohydrodynamic models predict that plasma velocities vary almost linearly from 0 km s-1 along the stagnation streamline leading from the nose of the stationary magnetopause to 0.25 Vsw at the nose of the bow shock, where Vsw is the solar wind velocity. This paper presents a proof-of-concept study showing how two-point measurements of the plasma velocity in the subsolar magnetosheath can be used to determine gradients in the plasma velocity and consequently the steady-state or slowly-moving locations of both the nose of the magnetopause and the nose of the bow shock. The results may be of use to those binning magnetosheath observations to develop empirical models, those testing models for magnetopause erosion or deposition in response to magnetic reconnection, and those determining the stand-off distance of the bow shock as a function of solar wind conditions.

David Sibeck↗
NASA NTRSDate not supplied

Reversion to the mean of the Solar Wind Input to the Magnetosphere

Earth’s magnetosphere responds to solar wind input over time scales ranging from minutes to days. On minute times scales, researchers seek to identify discontinuities in the solar wind that may trigger transient magnetospheric phenomena such as flux transfer events or substorm onsets. On hour time scales, researchers seek to determine the solar wind phenomena that drive the growth phase of geomagnetic substorms and the storage of magnetic flux within the magnetotail. On longer time scales, researchers seek to determine the solar wind features than propel geomagnetic storms through their initial, main, and recovery phases. Researchers must, perforce, rely upon spacecraft located near the L1 libration point for observations of the solar wind input into the magnetosphere over periods ranging from hours to days. Some of the hazards of doing this are well known. Features seen far upstream at locations away from the Sun-Earth line may never arrive at Earth due to structure in the solar wind transverse to the Sun-Earth line. Alternatively, they may arrive at unexpected times due to errors in calculating their orientation and velocity. Other hazards when predicting the magnetospheric response to varying solar wind conditions are less well understood. When observations of large solar wind drivers at spacecraft far upstream and off the Sun-Earth line are used to select events for study, the ‘reversion to the mean’ effect associated with spatial structure and errors in arrival timing for solar wind features at Earth demands that the magnetosphere will actually be subjected to and respond to solar wind drivers with much lower strengths. Consequently, the magnetospheric response must saturate for the highest solar wind drivers.

David Sibeck↗