Magnetohydrodynamic Simulation of the Interaction between Interplanetary Strong Shock and Magnetic Cloud and its Consequent Geoeffectiveness 2: Oblique Collision

Numerical studies of the interplanetary "shock overtaking magnetic cloud (MC)" event are continued by a 2.5 dimensional magnetohydrodynamic (MHD) model in heliospheric meridional plane. Interplanetary direct collision (DC)/oblique collision (OC) between an MC and a shock results from their same/different initial propagation orientations. For radially erupted MC and shock in solar corona, the orientations are only determined respectively by their heliographic locations. OC is investigated in contrast with the results in DC \citep{Xiong2006}. The shock front behaves as a smooth arc. The cannibalized part of MC is highly compressed by the shock front along its normal. As the shock propagates gradually into the preceding MC body, the most violent interaction is transferred sideways with an accompanying significant narrowing of the MC's angular width. The opposite deflections of MC body and shock aphelion in OC occur simultaneously through the process of the shock penetrating the MC. After the shock's passage, the MC is restored to its oblate morphology. With the decrease of MC-shock commencement interval, the shock front at 1 AU traverses MC body and is responsible for the same change trend of the latitude of the greatest geoeffectiveness of MC-shock compound. Regardless of shock orientation, shock penetration location regarding the maximum geoeffectiveness is right at MC core on the condition of very strong shock intensity. An appropriate angular difference between the initial eruption of an MC and an overtaking shock leads to the maximum deflection of the MC body. The larger the shock intensity is, the greater is the deflection angle. The interaction of MCs with other disturbances could be a cause of deflected propagation of interplanetary coronal mass ejection (ICME).Comment: 38 pages, 8 figure

The shock-acoustic waves generated by earthquakes

We investigate the form and dynamics of shock-acoustic waves generated by earthquakes. We use the method for detecting and locating the sources of ionospheric impulsive disturbances, based on using data from a global network of receivers of the GPS navigation system and requiring no a priori information about the place and time of associated effects. The practical implementation of the method is illustrated by a case study of earthquake effects in Turkey (August 17, and November 12, 1999), in Southern Sumatera (June 4, 2000), and off the coast of Central America (January 13, 2001). It was found that in all instances the time period of the ionospheric response is 180-390 s, and the amplitude exceeds by a factor of two as a minimum the standard deviation of background fluctuations in total electron content in this range of periods under quiet and moderate geomagnetic conditions. The elevation of the wave vector varies through a range of 20-44 degree, and the phase velocity (1100-1300 m/s) approaches the sound velocity at the heights of the ionospheric F-region maximum. The calculated (by neglecting refraction corrections) location of the source roughly corresponds to the earthquake epicenter. Our data are consistent with the present views that shock-acoustic waves are caused by a piston-like movement of the Earth surface in the zone of an earthquake epicenter.Comment: EmTeX-386, 30 pages, 4 figures, 3 tabl

Compressional perturbations of the dayside magnetosphere during high‐speed‐stream‐driven geomagnetic storms

The quasi‐DC compressions of the Earth’s dayside magnetic field by ram‐pressure fluctuations in the solar wind are characterized by using multiple GOES spacecraft in geosynchronous orbit, multiple Los Alamos spacecraft in geosynchronous orbit, global MHD simulations, and ACE and Wind solar wind measurements. Owing to the inward‐outward advection of plasma as the dayside magnetic field is compressed, magnetic field compressions experienced by the plasma in the dayside magnetosphere are greater than the magnetic field compressions measured by a spacecraft. Theoretical calculations indicate that the plasma compression can be a factor of 2 higher than the observed magnetic field compression. The solar wind ram‐pressure changes causing the quasi‐DC magnetospheric compressions are mostly owed to rapid changes in the solar wind number density associated with the crossing of plasma boundaries; an Earth crossing of a plasma boundary produces a sudden change in the dayside magnetic field strength accompanied by a sudden inward or outward motion of the plasma in the dayside magnetosphere. Superposed epoch analysis of high‐speed‐stream‐driven storms was used to explore solar wind compressions and storm time geosynchronous magnetic field compressions, which are of particular interest for the possible contribution to the energization of the outer electron radiation belt. The occurrence distributions of dayside magnetic field compressions, solar wind ram‐pressure changes, and dayside radial plasma flow velocities were investigated: all three quantities approximately obey power law statistics for large values. The approximate power law indices for the distributions of magnetic compressions and ram‐pressure changes were both −3.Key PointsQuasi‐DC compressions of the dayside magnetosphere are responses to solar wind ram‐pressure changesThe plasma compression in the dayside is greater than the field compression measured by a satelliteField compressions, ram‐pressure changes, and flow velocities obey large‐value power law statisticsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146460/1/jgra52633.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146460/2/jgra52633_am.pd

Mesoscale observations of Joule heating near an auroral arc and ion-neutral collision frequency in the polar cap E region

We report on the first mesoscale combined ionospheric and thermospheric observations, partly in the vicinity of an auroral arc, from Svalbard in the polar cap on 2 February 2010. The EISCAT Svalbard radar employed a novel scanning mode in order to obtain F and E region ion flows over an annular region centered on the radar. Simultaneously, a colocated Scanning Doppler Imager observed the E region neutral winds and temperatures around 110 km altitude using the 557.7 nm auroral optical emission. Combining the ion and neutral data permits the E region Joule heating to be estimated with an azimuthal spatial resolution of ∼64 km at a radius of ∼163 km from the radar. The spatial distribution of Joule heating shows significant mesoscale variation. The ion-neutral collision frequency is measured in the E region by combining all the data over the entire field of view with only weak aurora present. The estimated ion-neutral collision frequency at ∼113 km altitude is in good agreement with the MSIS atmospheric model

Modeling ring current ion and electron dynamics and plasma instabilities during a high‐speed stream driven storm

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94593/1/jgra21840.pd

Effects of the Solar Cycles and Longer-Term Solar Variations: Modulation of Galactic Cosmic Radiation and Filtration of Neutral Atoms from the Local Interstellar Medium

Recent solar conditions include a prolonged solar minimum (2005-2009) and a weak solar maximum. The Heliospheric Magnetic Field (HMF) strength was consistently weaker in solar cycle 24 compared to the previous maxima during the space age. These anomalies may indicate that we are entering an era of persistent decline in solar activity. In my first study, I investigated past solar secular (grand) minima, especially the Maunder period (1645-1715) to gain further insight into grand minima. I found the timescale parameters associated with the magnetic flux balance in the heliosphere. I also investigated the existence of a floor in the heliospheric magnetic flux, in the absence of coronal mass ejections (CMEs), and showed that a floor $\leq 1.49$ nT is sufficient to successfully describe the HMF evolution. As a result of the unprecedentedly low solar activity, the fluxes of galactic cosmic rays (GCRs) have increased to levels never reported previously in the space age, which might limit safe human space exploration over long-term missions (e.g., to Mars). In my second study, I used data from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) to examine the correlation between the heliospheric magnetic field, solar wind speed, and the modulation potential of the GCRs through cycle 24. I applied this correlation to past secular minima conditions, including the Dalton minimum (1790-1830) and the Gleissberg minimum (1890-1920) as extreme scenarios, to estimate the deep space radiation environment throughout cycle 25. I showed that these scenarios could lead to significant increases in dose rates (up to $\sim 60\%$). I used these results to predict the most conservative permissible mission durations (PMD) based on 3$\%$ risk of exposure-induced death (REID) in interplanetary space. Variations in the level of solar activity affect our heliosphere\u27s interaction with the Very Local Interstellar Medium (VLISM), as well. As the sun moves through the LISM, neutral atoms travel through the heliosphere and can be detected by IBEX. We consider Interstellar neutral (ISN) hydrogen atoms with a drifting Maxwellian distribution function in the LISM that travel on almost hyperbolic trajectories to the inner heliosphere. They are subject to solar gravity and radiation pressure as well as ionization processes. For ISN H, the radiation pressure, which exerts an effective force comparable to gravitation, decelerates individual atoms and shifts the longitude of their observed peak relative to that of ISN He. I used the peak longitude of the observed flux in the lowest energy channel of IBEX-Lo to investigate how radiation pressure shifts the ISN H signal over almost an entire solar cycle (2009 to 2018). Thus, I have created a new methodology to determine the Ly$\alpha$ effective radiation pressure over gravity ($\mu_{eff}$) from IBEX ISN H data. My analysis indicates an increase of $\mu_{eff}$ with solar activity albeit with substantial uncertainties. My study of IBEX H response functions prepares for future IMAP data, which will enable a significant reduction of the uncertainties and improvements in our understanding of the effects of radiation pressure on interstellar neutral atoms

Satellite Positioning

Satellite positioning techniques, particularly global navigation satellite systems (GNSS), are capable of measuring small changes of the Earths shape and atmosphere, as well as surface characteristics with an unprecedented accuracy. This book is devoted to presenting recent results and development in satellite positioning technique and applications, including GNSS positioning methods, models, atmospheric sounding, and reflectometry as well their applications in the atmosphere, land, oceans and cryosphere. This book provides a good reference for satellite positioning techniques, engineers, scientists as well as user community

What can the annual 10Be solar activity reconstructions tell us about historic space weather?

Context: Cosmogenic isotopes provide useful estimates of past solar magnetic activity, constraining past space climate with reasonable uncertainty. Much less is known about past space weather conditions. Recent advances in the analysis of 10Be by McCracken & Beer (2015, Sol Phys 290: 305–3069) (MB15) suggest that annually resolved 10Be can be significantly affected by solar energetic particle (SEP) fluxes. This poses a problem, and presents an opportunity, as the accurate quantification of past solar magnetic activity requires the SEP effects to be determined and isolated, whilst doing so might provide a valuable record of past SEP fluxes. Aims: We compare the MB15 reconstruction of the heliospheric magnetic field (HMF), with two independent estimates of the HMF derived from sunspot records and geomagnetic variability. We aim to quantify the differences between the HMF reconstructions, and speculate on the origin of these differences. We test whether the differences between the reconstructions appear to depend on known significant space weather events. Methods: We analyse the distributions of the differences between the HMF reconstructions. We consider how the differences vary as a function of solar cycle phase, and, using a Kolmogorov-Smirnov test, we compare the distributions under the two conditions of whether or not large space weather events were known to have occurred. Results: We find that the MB15 reconstructions are generally marginally smaller in magnitude than the sunspot and geomagnetic HMF reconstructions. This bias varies as a function of solar cycle phase, and is largest in the declining phase of the solar cycle. We find that MB15's excision of the years with very large ground level enhancement (GLE) improves the agreement of the 10Be HMF estimate with the sunspot and geomagnetic reconstructions. We find no statistical evidence that GLEs, in general, affect the MB15 reconstruction, but this analysis is limited by having too few samples. We do find evidence that the MB15 reconstructions appear statistically different in years with great geomagnetic storms

Precise thermospheric mass density modelling for orbit prediction of low earth orbiters

The steady increase in the number of space objects near the Earth has raised critical security concerns for the low Earth orbit (LEO) space environment where most of the near-Earth satellites missions operate. Orbit prediction (OP) is the foundation of many space missions and applications in LEO, e.g., space situational awareness, re-entry prediction and debris removal. However, the precision of OP is limited due to the accuracy of thermospheric mass density (TMD) prediction. In the past few decades, more atmospheric data sets have been inferred from different techniques such as the Global Navigation Satellite System, satellite laser ranging and two-line-element catalogue. However, accurately predicting TMD is still a challenging task due to the limited knowledge of thermospheric dynamics and the lack of measurements with sufficient temporal and spatial resolution. In this research, a precise OP platform for the analysis and prediction of the orbital motion of satellite and and space debris is developed. It consists of various precise perturbation models of gravitational and non-gravitational forces. This includes the high-order Earth gravitational acceleration with the effect of solid and ocean tides, third-body perturbations from other celestial bodies in the solar system, the general relativity effects, aerodynamic acceleration, direct solar radiation pressure, and Earth's albedo and infrared radiation pressure. Coordinate transformation is established on the precise time systems and the measured Earth orientation parameters. The developed OP platform is validated against the historical precise orbits of LEO satellites. In order to evaluate the most representative classes of empirical TMD models, a comprehensive comparison of 12 models is performed. The vertical variability, horizontal scale and the capability to capture the physics-based features of the selected models are investigated. Various validations against the TMD estimated from on-board accelerometer measurements of the GRACE satellites have been conducted. The performance of these models in the OP of the GRACE-A satellite is assessed under different solar and geomagnetic conditions. Also discussed is the coupling effect between the TMD and ballistic coefficient that measures the impact of atmospheric friction on the space object. The impact of TMD variations on orbit dynamics of LEO objects is an important focus in this thesis, which has not been well-quantified in previous studies. Intra-annual, intra-diurnal and horizontal TMD variations are reproduced using the empirical model DTM-2013. Also evaluated are physics-based variations including the equatorial mass density anomaly (EMA) and midnight mass density maximum (MDM), which exhibit both temporal and spatial variations and are simulated by the Thermosphere Ionosphere Electrodynamics General Circulation Model. The analysis is based on the one-day OP simulation at 400 km. The result show that TMD variations have a dominant impact on the predicted orbits in the along-track direction. Semiannual and semidiurnal TMD variations exert the most significant impact on OP among the intra-annual and intra-diurnal variations, respectively. In addition, both EMA and MDM create weaker but still discernible impacts than other TMD variations. Some recommendations for TMD modelling are also presented. Moreover, precise modelling of TMD during geomagnetic quiet time is performed. This is undertaken using the TMD data inferred from GRACE (500 km), CHAMP (400 km) and GOCE (250 km) satellites during the year of 2002-2013. Three different methods including the Fourier analysis, spherical harmonic (SH) analysis and the artificial neural network (ANN) technique are adopted and compared in order to determine the most suitable methodology for the TMD modelling. Additionally, different combinations of time and coordinate representations are also examined in the TMD modelling. The results reveal that the precision of the low-order Fourier-based model can be improved by up to 10% using the geocentric solar magnetic coordinate. Both the Fourier- and SH-based models have drawbacks in approximating the vertical gradient of TMD. The ANN-based model, however, has the capability in capturing the vertical TMD variability and is not sensitive to the input of time and coordinate