Solar Terrestrial Physics

Plasma Physics of the Terrestrial Magnetosphere

The Solar Terrestrial Physics (STP) Program in Kiruna has long been working on satellite-measured ion data (from Prognoz-7, Viking, Freja, Atrid-1 and -2, Munin, and Cluster) related to auroral acceleration, plasma entry across the magnetopause and cusp, magnetosphere-ionosphere coupling, ion escape from the ionosphere, fate of ionospheric ions in the magnetosphere, inner-magnetospheric dynamics, and relevant substorm activity. Our current main involvement is in the ESA Cluster project and Future mission planning, in both we study dynamics of heavy (O+-N+ group) ions in comparison to H+ and He+ and resultant circulation. We mainly analyse Cluster Ion Spectrometer (CIS) and the Research with Adaptive Particle Imaging Detectors (RAPID) as co-investigators.
   In addition to research related to the satellite ion data, we also study long-term trend of the magnetospheric and ionospheric activity using our observatory data and similar ground-based data.
   During the past 5 years we have studied:
   * Ion escape and relevant energization process
   * Dynamics of inner magnetosphere at L<6
   * H+-He+-O+ difference in the magnetospheric dynamics
   * Preparing mission proposal to study Nitrogen and N/O budget of the Earth
   * Collaborative projects involving Cluster ion data
   * Long-term (>50 years) variation of Sun-Earth coupling

Ion escape and relevant energization process

   We take advantage of ion data and its analyses on Mars and Venus, and tune our Cluster study in a planetary perspective, i.e., to compare the terrestrial ion dynamics (escape, acceleration, and circulation) on the viewpoint of comparative planetary study at both magnetized and unmagnetized planets. The questions are we have been and are questing are, for examples, "Does a planetary magnetic field protect an atmosphere from solar wind scavenging?" "Within what bounds must stellar winds stay in order to allow planets to retain their atmospheres?". The actual studies are:
   1. Identification and quantification the acceleration mechanisms operating on the cusp related heavy ion outflow at Earth
   2. Dependence of escaping ions (energy, direction, amount) on the external parameters (solar wind conditions).
   3. Determination of the fate of the cusp related ion outflow, whether these ions can enter the tail plasma sheet.
More recently we have started to study ion behavior in the tail (dynamics, amount, and final destination of the ion return from the tail) because only a part of ion in the tail can return to the inner magnetosphere.

Dynamics of inner magnetosphere at L<6

   We have long been working on the low-energy (< 10 keV) ions in the inner magnetosphere. While energetic ions in the inner magnetosphere are basically adiabatically energized ions from the magnetotail, low energy ions are convolution of tail-origin ions, near-earth plasma sheet origin ions, directly supplied from the ionosphere, and locally energized ions of plasmaspheric origin or plasma sheet origin. We have recently classified all proton patterns and its temporal variation and spatial distribution.
* Yamauchi, M., Dandouras, I., Reme, H., Lundin, R., and Kistler, L. M. (2013): Cluster observation of few-hour-scale evolution of structured plasma in the inner magnetosphere, Ann. Geophys., 31, 1569-1578, doi:10.5194/angeo-31-1569-2013.
* Yamauchi, M., Ebihara, Y., Nilsson, H., and Dandouras, I. (2014): Ion drift simulation of sudden appearance of sub-keV structured ions in the inner magnetosphere, Ann. Geophys., 32, 83-90, doi:10.5194/angeo-32-83-2014.


H+-He+-O+ difference in the magnetospheric dynamics

   In both inner magnetosphere and magnetotail, we found unexpected difference among H+, He+, and O+ in distributions, energizations, and flow direction. This indicates that one many not assume same source cold ions in both inner magnetosphere and plasma sheet. Furthermore, very localized electric field (at places where magnetic field is nominal) must play important roles in the magnetospheric dynamic. This study requires good instrumental knowledge to fight against contaminations (both cross talks and radiation belt noises), and we are one of very few groups who is capable of such work in the world.
* Yamauchi, M., Dandouras, I., Reme, H., and El-Lemdani Mazouz, F. (2012): Equatorially confined warm trapped ions at around 100 eV near the plasmapause, Geophys. Res. Lett., 39, L15101, doi:10.1029/2012GL052366.
* Yamauchi, M., Dandouras, I., Reme, H., and Nilsson, H. (2014): Cluster observations of hot He+ events in the inner magnetosphere, J. Geophys. Res., 119(4), 2706-2716, doi:10.1002/2013JA019724 (accepted manuscript).


Preparing mission proposal to study Nitrogen and N/O budget of the Earth

   Limitation of Cluster ion data is that the instrument cannot distinguish nitrogen from oxygen. This is not only Cluster problem but also all past magnetospheric missions at energy range 0.05-30 keV. However, nitrogen and oxygen are expected to show completely different dependency on the solar and solar wind condition, and nitrogen can escape more than oxygen for extremely large events. Furthermore, nitrogen is as important as oxygen for life because as the basic element to form amino acid. Therefore, both nitrogen behavior an oxygen behaviors against the solar and solar wind activity is the fundamental information in understanding the evolution of the Earth in terms of habitability.
   To study this, we need dedicated mission to study, and this is why we have proposed NITRO to ESA's call for medium-class mission (M4). The detail is found at NITRO site.

Collaborative projects involving Cluster ion data

   Since we are local (Swedish) co-investigators on the Cluster ion instrument, it is our responsibility to assist other (primarily Swedish) groups in the use of ion data and to keep the general knowledge of the ion instruments up to date. For example, we participate studies of energy budget in the magnetotail (collaboration with Umeå University), auroral-related ion phenomena (collaboration with Royal Institute of Technology, Stockholm), and wave-related ion phenomena (collaboration with Uppsala group). In addition, we participate ISSI working group of both magnetotail dynamics and auroral studies, part of which are related to our study of "Ion escape and relevant energization process".

Long-term (>50 years) variation of Sun-Earth coupling

   The current solar cycle #24 is known to be very low activity compared to previous several cycles, i.e., at the same level as cycle #15. Accordingly, the geomagnetic and auroral activities until 2013 was very low. Further examination revealed that the geomagnetic/auroral activity for the same level of solar wind input is low, and therefore the caused of low geomagnetic/auroral activity is not only the solar wind problem, namely the Sun-Earth coupling efficiency also decreased. We examine this relation systematically. One of the most warning result is that low Sun-Earth coupling is valid only for low to moderate solar wind conditions, and the coupling efficiency could be higher for extreme solar wind event such as related to large CME. This means that we might have extreme event (that can cause power outage and satellite damage) during coming declining phase of solar cycle #24.
* Yamauchi, M. (2015): Decreased Sun-Earth energy coupling efficiency starting from 2006, Earth Planets Space., 67, in press.
Created: 2011 HN; Last change: MY, 2015-03-19.