Research topics in TERRESTRIAL MAGNETOSPHERIC PHYSICS

Topology of the Earths magnetosphere, plasma populations and currents
(picture by J. Burch, Southwest Research Institute, San Antonio, USA)
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The largest scientific efforts will be devoted to plasma entry through the magnetopause and processes in the cusp, cleft and flanks. Questions to be answered include for example: What is the relative importance of different types of reconnection and direct entry mechanisms? How do direct entry mechanisms work? What is the relative importance of different entry sites? How do they depend on solar wind conditions? What is the low-altitude signature of various entry mechanisms? What is the morphology of the outer cusp and how does it relate to the low-altitude cusp? We are using Freja and Astrid-2 data for the low-altitude studies, Viking and Interball-2 at a few RE, Interball-1, PROGNOZ 7 and 8, and Polar for the altitude range out into the solar wind. This work will also be preparation for the scientific analysis of Cluster, which will begin during the later part of 2000.

Ion outflow has been studied with Viking, Freja and also recently with Interball-2. Interball-2 has found examples of outflow of molecular ions within an higher energy range than detected before. The mechanism for this outflow and energization is one topic of study. Ion outflow processes give important information on the development of planetary atmospheres on long time scales. Information on plasma density, waves, currents as well as structure and extension of the acceleration region are used to classify different heating events and to show their relative importance. Broadband low-frequency waves, electromagnetic ion cyclotron waves, lower hybrid waves and spatial structures or transient fields are some of the possible ways to accelerate ions. It is also necessary to find the source of the waves and to take into account effects on electrons to get a self-consistent picture of these processes. The outflowing ions are originally heated at low-altitude (as is observed in Freja and Astrid-2) and accelerated in the acceleration region at Viking altitude. Such heating and acceptation mechanisms, which have been intensively studied by different groups in Sweden, is a natural topic in the analysis of the new data from Astrid 2. [Full size picture]

Auroral particle acceleration has been one of the main scientific topics at IRF for over 30 years using in situ as well as ground-based instrumentation. The Viking data are still very useful and not fully explored. The more recent spacecraft such as Freja, FAST and Polar cover different altitude ranges. The auroral acceleration dependence on the phase of the solar cycle and season has also shown the importance of not only relying on measurements during events studies with specific solar wind, magnetosphere and ionosphere conditions but to acquire data during all seasons and during several solar cycles. Recent results from Freja and FAST demonstrate that to be able to solve several problems related to auroral particle acceleration multipoint measurements on a temporal and spatial scale not acheived hitherto are required. Therefore the Swedish space science groups have agreed to give highest priority to the project Auroral Quartet which is a natural follower of Viking and Freja. The Cluster mission will give information on solar wind - magnetosphere interaction, cusp dynamics, acceleration processes, source regions and hopefully also data that can help increase the knowledge about the generation of field aligned currents in the magnetosphere. [Full size picture]

Our study on the ring current includes ENA modelling/measurement, composition measurements for different phases of the substorms, and its extraordinary precipitation. We believe that our finding of DPS region (structured sub-keV ions equatorward of CPS) is related to this, and we will continue this pioneer work. Viking, Freja and Astrid-2 will contribute for the direct ion measurement whereas Astrid-1 will contribute to the ENA measurements. In our studies of the ring current development we will concentrate on the global structure. The main method of research will be ENA imaging. We plan to use the ENA data from the Astrid-1 spacecraft and different models to answer the question whether or not the ring current global dynamics and composition can be detected in ENA images. One of the questions directly related to this is how the global ENA production rate, which can be measured by a remotely located spacecraft, is connected to the Dst index. If our previous findings about the relation of the Dst index and the global ENA production rate are indeed correct, we can propose a novel way to monitor the energetic content of the ring current with very high time resolution, of the order of minutes, something which is very important for magnetospheric models used in space weather predictions, for example, Magnetic Specification Model. [ More details]

Lower hybrid cavities, which is a low-altitude plasma-physics phenomenon, have been investigated by the Freja satellite. A surprising result is that they are generated by some sort of random process. Since we now have the Astrid-2 spacecraft, which is well fitted for such research, we continue the investigation on the cavities. [More details]

We will also contribute to studies led by scientists from other groups. In order to make this work easier we are now improving our satellite data analysis software and are making data more readily available via Internet. Our long-term plan is to eventually give access to data from all satellites, but this will involve a very big effort, in particular since software to take care of a number of instrument effects must also be developed. During 2000 we plan to complete this work with Viking, Interball and Astrid-2.