SCOSTEP/PRESTOオンラインセミナーシリーズ

国際学術会議(ISC)傘下の太陽地球系物理学科学委員会(SCOSTEP)と連携して、 ISEE国際連携研究センターではSCOSTEP/PRESTOオンラインセミナーシリーズを下記の通り実施しています。セミナーの録音はこちらから聞くことができます。

9th SCOSTEP/PRESTO Online Seminar

Author: Richard Eastes, University of Colorado Boulder, USA
Date and Time: Sep 23 (Thu), 2021, 14:00-15:00 UT
Title: "Space Weather in the Thermosphere-Ionosphere System - observations and Insights from the GOLD* Mission (*Global-scale Observations of the Limb and Disk)"

Abstract: The GOLD mission’s spatial-temporal observations of thermospheric composition, density, and temperature, as well as of ionospheric structure and peak density at low-latitudes, provide an unprecedented window into space weather in the Thermosphere-Ionosphere (T-I) system. Imaging the Earth from geostationary orbit at 47.5°W longitude, the GOLD imager provides simultaneous images of thermospheric composition (O/N_2 ) and temperature near 160?km on the dayside every 30 minutes from 06:10 to 23:10 UT (03:00-20:00 local time at the satellite). In addition GOLD images the nighttime equatorial ionization anomaly (EIA) over the Atlantic and South America every evening. Observations of geomagnetic storms, solar eclipses, the nighttime EIA and O_2 density profiles have all provided unanticipated results. Examples include observations of “gravity” waves and global-scale responses to weak geomagnetic activity in the sunlit thermosphere; and in the nighttime EIA, correlations between peak densities and waves in the mesosphere. These observations provide tests of our current understanding of both the T-I system and how it interacts with other regions of the geospace system. The GOLD mission observations and some of the implications for space-weather will be discussed.

8th SCOSTEP/PRESTO Online Seminar

Author: Kristof Petrovay, ELTE Eotvos Lorand University, Hungary
Date and Time: Jun 8 (Tue), 2021, 13:00-14:00 UT
Title: "The Sun making history. The mechanism behind the varying amplitude of the solar cycle"
Link to the video

Abstract: The amplitudes of 11-year solar cycles vary in a wide range, sometimes displaying sudden marked changes from one cycle to the next. The decadal time scales involved are comparable to the life cycle of space missions -and of human beings. The impact of solar activity on space climate and terrestrial climate calls for a prediciton capability, a precondition for which is a good understanding of the mechanism driving intercycle variations in the solar dynamo. The past decade has seen significant advance in this direction. A promising scenario has emerged in which intercycle variations are driven by the vagaries of magnetic flux emergence from the solar interior into the atmosphere in the form of active regions (ARs). A variety of nonaxisymmetric dynamo models incorporating individual Ars have been developed, along with surface flux transport models used for prediction relying on the polar magnetic field as a proxy for the next cycle amplitude. The results indicate that a combination of nonlinear feedback effects and stochastic noise may govern the run-of-the-mill intercycle variations, while a low number of large "rogue" ARs with unusual properties bear the brunt of the responsibility for large, unexpected intercycle changes. The talk will review these developments, focusing on the issue of how the properties of individual ARs determine their "dynamo effectivity", i.e. how they will impact on the polar magnetic field built up during a cycle that will serve as the seed for the next solar cycle. The importance of maintaining and, where possible, reconstructing long term data sets on solar activity will be stressed and some aspects of the Sun's unexpected historical changes will be discussed.

7th SCOSTEP/PRESTO Online Seminar

Author: Franz-Josef Lübken (SCOSTEP 2021 Distinguished Service Award Winner), Leibniz-Institute of Atmospheric Physics, Germany
Date and Time: May 21 (Fri), 2021, 12:00-13:00 UT
Title: "Physics at the edge between Earth's atmosphere and space"
Link to the video

Abstract: The importance of basic physical processes in the atmosphere changes fundamentally in the upper mesosphere/lower thermosphere (UMLT, appr. 80 to 130 km) primarily due to the reduction of gas density being orders of magnitude smaller compared to the troposphere. For example, molecules are no longer in thermodynamic equilibrium with radiation, and mixing ratios of inert species change with height. Furthermore, gravity waves being generated in the troposphere achieve large amplitudes in the UMLT, get instable and produce turbulence. This in turn causes a modification of the general circulation which leads to a substantial cooling (heating) in the summer (winter) mesosphere. The summer mesopause (appr. 90 km) at polar latitudes is special in many ways. It is the coldest place in the Earth's atmosphere (appr. 130 K), nearly 100 K colder compared to the radiatively controlled state (despite permanent sunshine) which is a consequence of the `residual circulation' introduced above. This region is very sensitive to dynamical forcing, in particular due to gravity waves and tides, and can therefore be used to test physical descriptions. The extremely low temperatures at the summer mesopause lead to ice particles known as noctilucent clouds (NLC) or polar mesosphere clouds (PMC). The same ice particles produce very strong radar echoes (PMSE, polar mesosphere summer echoes). NLC, PMSE, and PMC are studied in detail by lidars, radars, and satellites, respectively, which has clarified some important physical processes involved. Since ice particles are very sensitive to atmospheric temperatures and water vapor, they are proposed to be sensitive indicators for climate change effects in the middle atmosphere (MA). Indeed, large temperature trends (cooling) are observed in the middle atmosphere at mid latitudes, much larger (in sign) compared to the warming in the troposphere. However, models suggest that the summer mesopause is the only region in the entire Earth's MA where warming (instead of cooling) should prevail. In the presentation, some basic physical processes leading to the thermal structure of the upper atmosphere and to ice particles are explained including the role of dynamical forcing, solar cycle effects, and trends due to climate change.

6th SCOSTEP/PRESTO Online Seminar

Author: Mateja Dumbović (SCOSTEP 2020 Distinguished Young Scientist Award Winner), University of Zagreb, Croatia
Date and Time: Jan 19 (Tue), 2021, 12:00-13:00 UT
Title: "Utilizing galactic cosmic rays as signatures of interplanetary transients"
Link to the video

Abstract: Coronal mass ejections (CMEs), interplanetary shocks and corotating interaction regions are drivers of heliospheric variability and cause various interplanetary as well as planetary disturbances. One of their very common in-situ signatures are short-term reductions in the galactic cosmic ray (GCR) flux (i.e. Forbush decreases). These phenomena are caused by the interaction of GCRs with a magnetic structure, therefore it is expected that different types of interplanetary substructures cause different types of GCR depressions, allowing us to distinguish between shock/sheath, flux rope and SIR-type of FDs. Moreover, since the interaction of GCRs and CME magnetic structure (presumably flux rope) occurs all the way from Sun to Earth, FDs should also reflect the evolutionary properties of CMEs, which is supported by the results from our recent modeling efforts. In the light of these recent studies, we will discuss if and how GCR depressions can be used more efficiently as signatures of interplanetary transients.

5th SCOSTEP/PRESTO Online Seminar

Author: Q.-G. Zong (SCOSTEP 2020 Distinguished Scientist Award Winner), Peking University, China
Date and Time: Jan 14 (Thu), 2021, 00:00-01:00 UT
Title: "Magnetospheric Response to Interplanetary Shocks: ULF Wave-Particle Interaction Perspective"
Link to the video

Abstract: Impact of interplanetary shocks on the Earth’s magnetosphere manifests many fundamental processes in space physics including generation of electromagnetic waves, plasma heating, and energetic particle acceleration. This lecture summarizes our present understanding of the magnetospheric response to interplanetary shocks in the aspects of interaction of shock generated ULF waves with radiation belt electrons, ring current ions, and plasmaspheric plasma based on in-situ spacecraft measurements, ground-based magnetometer data, MHD and kinetic simulations. Magnetospheric response to interplanetary shocks is not a “one-kick” scenario. Interplanetary shocks compress the magnetosphere and generate different types of waves including poloidal mode ultra-low frequency (ULF) waves in the magnetosphere. Plasma heating and energetic particle acceleration start nearly immediately after the impact of interplanetary shocks and can last several hours. The fast acceleration of radiation belt electrons and ring current ions usually contain two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression; (2) followed by resonant acceleration by global or localized poloidal ULF waves. A general theory of drift and drift-bounce resonance between charged particles and growing or decaying localized ULF waves has been developed to interpret in-situ spacecraft observations. The observed features associated with waves, such as the energy dispersion as well as boomerang and fishbone pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma, can be explained in the framework of this general theory. It is worth noting that poloidal ULF waves are much more efficient than toroidal ULF waves in accelerating and modulating radiation belt electrons (fundamental mode) and ring current ions (second harmonic). The results presented in this lecture can be applied to the solar wind interaction with other planets such as Mercury, Jupiter, Saturn, Uranus, and Neptune, as well as other magnetized astrophysical objects.

4th SCOSTEP/PRESTO Online Seminar

Author: Thomas Immel, University of California, Berkeley, USA
Date and Time: Nov 17 (Tue), 2020, 23:00-24:00 UT
Title: "The Ionospheric Connection Explorer - Results from the first year on orbit"
Link to the video

Abstract: The NASA Ionospheric Connection Explorer has provided a full year of coordinated measurements of the ionosphere and thermosphere, with excellent performance of its instruments and the observing platform. Its measurements support ICON’s specific mission objectives to 1) determine the source of strong day-to-day variability in ionospheric densities, 2) determine how large-scale atmospheric waves propagate upward and interact with the ionosphere, and 3) understand how these effects interact with and modify geomagnetic storm phenomena. We will discuss some of the more remarkable effects observed by ICON, and how the analysis of these data is leading to new understanding of the behavior of the ITM system. This will include a brief review of comparisons to other measurements and a summary of validation efforts for improved data products.

3rd SCOSTEP/PRESTO Online Seminar

Author: Joe Borovsky, Space Science Institute, USA
Date and Time: Sep 10 (Thu), 2020, 22:00-23:00 UT
Title: "Developing a Highliy Predictable Geomagnetic Index to Gauge Magnetospheric Activity and Space Weather"
Link to the video

Abstract: A composite geomagnetic index that is highly predictable from a knowledge of the upstream solar wind is being developed using the mathematical technique “canonical correlation analysis”. This “canonical” geomagnetic index will be constructed from multiple existing geomagnetic indices measuring different current systems and activity types in the magnetosphere-ionosphere system. The canonical index will describe global activity in the magnetosphere-ionosphere system. Of the many possibilities, the one “canonical” index will be selected based on high predictability and on availability of the geomagnetic indices used. This canonical index will be robust, in that it is as well predicted for high activity levels as it is for low activity, and is expected to be well predicted for as-yet-unseen extreme solar-wind conditions. Once the canonical index is derived, along with its canonical solar-wind driver function), superposed-epoch analysis and other statistical techniques will be used to familiarize the index by gauging CME-driven storms, high-speed-stream-driven storms, substorms, steady magnetospheric convection intervals, etc.

2nd SCOSTEP/PRESTO Online Seminar

Author: Ilya Usoskin, University of Oulu, Finland
Date and Time: Jul 20 (Mon), 2020, 12:00-13:00 UT
Title: "Extreme solar events: A new paradigm"
Link to the video

Abstract: The Sun provides the energy for life on Earth and always shine in seemingly the same way, as was believed until recently. But we also know that it can produce sporadic eruptive events, such as solar bright flares and huge coronal mass ejections. Such events are often accompanied by the so-called solar particle storms, which are short-term events with very intense fluxes of solar energetic particles (SEPs) observed in space near Earth. These events remained beyond our detection abilities even several decades ago, but now we know that they may pose a serious threat to our modern technological society and even human lives outside the protective Earth's atmosphere and magnetosphere. Our knowledge of such events was limited to nearly 70 years, with the strongest directly observed solar particle storm occurred on 23-Feb-1956 with a ~5000 % enhancement over the galactic cosmic-ray background. The following questions may arise: Can even stronger storms appear? How much stronger and how often? What could be the "worst-case scenario''? What consequences of such events would be for modern society? The era of direct measurements is too short to answer these questions, but nature gives us a unique chance to get answers. Thanks to the recent discoveries, we know that there are extreme events on the Sun on the large-time scale and on distant sun-like stars. Here we present an overview of the current state of the art in the study of extreme SEP events based on different indirect methods, including cosmogenic isotope (14C, 10Be, 36Cl) in terrestrial archives and lunar rocks, as well as an extensive statistic of the superflares on sun-like stars.

1st SCOSTEP/PRESTO Online Seminar

Author: Kanya Kusano, Institute for Space-Earth Environmental Research (ISEE), Nagoya University, Japan
Date and Time: May 26 (Tue), 2020, 12:00-13:00 UT
Title: "A challenge to Physics-based Prediction of Giant Solar Flares"
Link to the video

Abstract: Solar flares are catastrophic explosions in the solar corona and may potentially cause a severe space weather disaster. However, because the onset mechanism of solar flares is not yet well elucidated, most of the flare forecasts in operation rely on empirical methods. We recently developed a new physics-based model, called the κ-scheme, for predicting giant solar flares as one of the major outcomes of the Project for Solar-Terrestrial Environment Prediction (PSTEP), which is the Japanese nation-wide project for space weather and space climate study. Theκ-scheme is able to predict imminent giant solar flares through the critical condition of magnetohydrodynamic (MHD) instability triggered by magnetic reconnection. An analysis of the largest solar flares in solar cycle 24 indicates that the κ-scheme can provide precise information, including location and size, of possible giant solar flares with a small exception. Through this study, we also discovered that the magnetic twist flux density in the vicinity of the magnetic polarity inversion line (PIL) on the solar surface plays a crucial role in determining when, where, and how large solar flares may occur. Finally, we will discuss how important is the development of physics-based prediction to improve our predictive capability and the scientific understanding of solar-terrestrial system dynamics.