Textbooks and popular science books that describe the broad field of space plasma physics are increasingly important as the space physics community seeks to broaden its base of support among both scientists and the public. Introduction to Space Physics is such a text; it provides a survey of space physics observation and theory meant for the upper division or graduate level student who is well-versed in standard classical mechanics and electromagnetism but has not been exposed to the variety of phenomena that occur in space. The text is based on a series of lectures given at UCLA in 1990 by experts in areas ranging from the magnetohydrodynamic (MHD) processes on the Sun and in the solar wind to the solar wind interactions with both magnetized and unmagnetized planets, ULF and plasma waves, and the collisional and chemical processes in planetary ionospheres.

Introduction to Space Physics

The EISCAT (European Incoherent SCATer) Scientific Association has provided versatile incoherent scatter (IS) radar facilities on the mainland of northern Scandinavia (the EISCAT UHF and VHF radar systems) and on Svalbard (the electronically scanning radar ESR (EISCAT Svalbard Radar) for studies of the high-latitude ionised upper atmosphere (the ionosphere). The mainland radars were constructed about 30 years ago, based on technological solutions of that time. The science drivers of today, however, require a more flexible instrument, which allows measurements to be made from the troposphere to the topside ionosphere and gives the measured parameters in three dimensions, not just along a single radar beam. The possibility for continuous operation is also an essential feature. To facilitatefuture science work with a world-leading IS radar facility, planning of a new radar system started first with an EU-funded Design Study (2005–2009) and has continued with a follow-up EU FP7 EISCAT_3D Preparatory Phase project (2010–2014). The radar facility will be realised by using phased arrays, and a key aspect is the use of advanced software and data processing techniques. This type of software radar will act as a pathfinder for other facilities worldwide. The new radar facility will enable the EISCAT_3D science community to address new, significant science questions as well as to serve society, which is increasingly dependent on space-based technology and issues related to space weather. The location of the radar within the auroral oval and at the edge of the stratospheric polar vortex is also ideal for studies of the long-term variability in the atmosphere and global change. This paper is a summary of the EISCAT_3D science case, which was prepared as part of the EU-funded Preparatory Phase project for the new facility. Three science working groups, drawn from the EISCAT user community, participated in preparing this document. In addition to these working group members, who are listed as authors, thanks are due to many others in the EISCAT scientific community for useful contributions, discussions, and support.

/pdf/the-science-case-for-the-eiscat-3d-radar-1sz1v3xun9.pdf

The science case for the EISCAT_3D radar

The polar ionosphere is often characterized by irregularities and fluctuations in the plasma density. We present a statistical study of ionospheric plasma irregularities based on the observations from the European Space Agency's Swarmmission. The in situ electron density obtained with the Langmuir probe and the total electron content from the onboard global positioning system receiver are used to detect ionospheric plasma irregularities.We derive the irregularity parameters from the electron density in terms of the rate of change of density index and electron density gradients. We also use the rate of change of total electron content index as the irregularity parameter based on the global positioning system data. The background electron density and plasma irregularities are closely controlled by the Earth's magnetic field, with averaged enhancements close to the magnetic poles. The climatological maps in magnetic latitude/magnetic local time coordinates show predominant plasma irregularities near the dayside cusp, polar cap, and nightside auroral oval. These irregularities may be associated with large‐scale plasma structures such as polar cap patches, auroral blobs, auroral particle precipitation, and the equatorward wall of the ionospheric trough. The spatial distributions of irregularities depend on the interplanetary magnetic field (IMF). By filtering the irregularity parameters according to IMF By, we find a clear asymmetry of the spatial distribution in the cusp and polar cap between the Northern (NH) and Southern Hemispheres (SH). For negative IMF By, irregularities are stronger in the dusk (dawn) sector in the NH (SH) and vice versa. This feature is in agreement with the high‐latitude ionospheric convection pattern that is regulated by the IMF By component. The plasma irregularities are also controlled by the solar activity within the current declining solar cycle. The irregularities in the SH polar cap show a seasonal variation with higher values from September to April, while the seasonal variation in the NH is only obvious around solar maximum during 2014–2015.

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Ionospheric Plasma Irregularities Characterized by the Swarm Satellites: Statistics at High Latitudes

We discuss, in a limited way, some of the challenges to advancing our understanding and description of the coupled plasma and neutral gas that make up the ionosphere and thermosphere (I‐T). The I‐T is strongly influenced by wave motions of the neutral atmosphere from the lower atmosphere and is coupled to the magnetosphere, which supplies energetic particle precipitation and field‐aligned currents at high latitudes. The resulting plasma dynamics are associated with currents generated by solar heating and upward propagating waves, by heating from energetic particles and electromagnetic energy from the magnetosphere and by the closure of the field‐aligned currents applied at high latitudes. These three contributors to the current are functions of position, magnetic activity, and other variables that must be unraveled to understand how the I‐T responds to coupling from the surrounding regions of geospace. We have captured the challenges to this understanding in four major themes associated with coupling to the lower atmosphere, the generation and flow of currents within the I‐T region, the coupling to the magnetosphere, and the response of the I‐T region reflected in the neutral and plasma density changes. Addressing these challenges requires advances in observing the neutral density, composition, and velocity and simultaneous observations of the plasma density and motions as well as the particles and field‐aligned current describing the magnetospheric energy inputs. Additionally, our modeling capability must advance to include better descriptions of the processes affecting the I‐T region and incorporate coupling to below and above at smaller spatial and temporal scales. Plain Language Summary The ionosphere is the region of Earth's upper atmosphere made up of a mixture of charged and neutral gases between approximately 50 and 1,000 miles (80–1,600 km) above the Earth's surface. Sandwiched between the lower atmosphere and the magnetosphere, the ionosphere reacts to weather and climate near the Earth's surface and to eruptions and sunspot activity on the Sun. The ionosphere absorbs the harmful radiation from the Sun and determines the fidelity of all radio communication, navigation, and surveillance transmissions through it. It is part of a complex, coupled system that changes on scales from meters to the planetary radius, and from seconds to decades. Understanding how the behavior of this region is controlled, by internal interactions and by the external regions to which it is coupled, is the preeminent challenge for the next generation of scientists. These challenges in understanding Earth's ionosphere are associated with deciphering the many changes in neutral and plasma density and their relationships to the coupling with the Earth's lower atmosphere, the generation and flow of currents within the region, and the coupling to the magnetosphere. Addressing these challenges requires advances in observing the composition and dynamics of the neutral particles and simultaneous observations of the charged particles, as well as the particles and field‐aligned current describing the coupling of the ionosphere to the magnetosphere. Additionally, our modeling capability must advance to include better descriptions of the processes affecting the ionosphere and thermosphere region and to incorporate coupling with the regions below and above at smaller spatial and temporal scales.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019JA027497

Challenges to Understanding the Earth's Ionosphere and Thermosphere

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017SW001785

A New Method of Physics‐Based Data Assimilation for the Quiet and Disturbed Thermosphere

Ionospheric storms can have important effects on radio communications and navigation systems. Storm time ionospheric predictions have the potential to form part of effective mitigation strategies to these problems. Ionospheric storms are caused by strong forcing from the solar wind. Electron density enhancements are driven by penetration electric fields, as well as by thermosphere-ionosphere behavior including Traveling Atmospheric Disturbances and Traveling Ionospheric Disturbances and changes to the neutral composition. This study assesses the effect on 1 h predictions of specifying initial ionospheric and thermospheric conditions using total electron content (TEC) observations under a fixed set of solar and high-latitude drivers. Prediction performance is assessed against TEC observations, incoherent scatter radar, and in situ electron density observations. Corotated TEC data provide a benchmark of forecast accuracy. The primary case study is the storm of 10 September 2005, while the anomalous storm of 21 January 2005 provides a secondary comparison. The study uses an ensemble Kalman filter constructed with the Data Assimilation Research Testbed and the Thermosphere Ionosphere Electrodynamics General Circulation Model. Maps of preprocessed, verticalized GPS TEC are assimilated, while high-latitude specifications from the Assimilative Mapping of Ionospheric Electrodynamics and solar flux observations from the Solar Extreme Ultraviolet Experiment are used to drive the model. The filter adjusts ionospheric and thermospheric parameters, making use of time-evolving covariance estimates. The approach is effective in correcting model biases but does not capture all the behavior of the storms. In particular, a ridge-like enhancement over the continental USA is not predicted, indicating the importance of predicting storm time electric field behavior to the problem of ionospheric forecasting.

/pdf/ionospheric-data-assimilation-and-forecasting-during-storms-1ilbihm91p.pdf

Ionospheric data assimilation and forecasting during storms

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017JA024811

Annual Occurrence Rates of Ionospheric Polar Cap Patches Observed Using Swarm

https://purehost.bath.ac.uk/ws/files/202572/Chartier_Adv-Space-Res_2012_49_9_1348.pdf

A 12 year comparison of MIDAS and IRI 2007 ionospheric Total Electron Content

[1] Data assimilation has been used successfully for real-time ionospheric specification, but it has not yet proved advantageous for forecasting. The most challenging and important ionospheric events to forecast are storms. The work presented here examines the effectiveness of data assimilation in a storm situation, where the initial conditions are known and the model is considered to be correct but the external solar and geomagnetic drivers are poorly specified. The aim is to determine whether data assimilation could be used to improve storm time forecast accuracy. The results show that, in the case of the storm of Halloween 2003, changes made to the model's initial thermospheric conditions improve electron density forecasts by at least 10% for 18 h, while changes to ionospheric fields alone result in >10% forecast accuracy improvement for less than 4 h. Further examination shows that the neutral composition is especially important to the accuracy of ionospheric electron density forecasts. Updating the neutral composition gives almost all the benefits of updating the complete thermospheric state. A comparison with real, globally distributed observations of vertical total electron content confirms that updating the thermospheric composition can improve forecast accuracy.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013JA019034

A comparison of the effects of initializing different thermosphere‐ionosphere model fields on storm time plasma density forecasts

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JA021561

Alex T. Chartier

Papers

Ionospheric data assimilation and forecasting during storms

Annual Occurrence Rates of Ionospheric Polar Cap Patches Observed Using Swarm

A 12 year comparison of MIDAS and IRI 2007 ionospheric Total Electron Content

A comparison of the effects of initializing different thermosphere‐ionosphere model fields on storm time plasma density forecasts

Imaging the topside ionosphere and plasmasphere with ionospheric tomography using COSMIC GPS TEC