The goals of SOHO require comparison and analysis of data-sets from very different experiments. Such interdisciplinary studies require careful planning, prior to the observations, and involve complex analysis procedures. In recognition of this, the SOHO Coronal and Particle Working Group (SCPWG, now merged to the Science Planning Working Group, SPWG) initiated a study to provide an overview of the nature of such activities.
The underlying goal of the ESA Solar Terrestrial Science Programme (STSP) is to develop an understanding of the activity of the Sun and its influence on the Earth. SOHO and the Cluster spacecraft fleet were designed to provide the backbone of such a study. Even with such a co-ordinated effort, it is difficult to correlate solar and space plasma events and structures. Complexites arise because of time delays and the uncertainty of propagation paths, as well as the linking of observations made with fundamentally different instruments, such as spectrometers and particle detectors.
At the SCPWG meeting in the Spring of 1991, attempts were made to bring the scientific discussion to focus on operations. As part of this an overall picture of interdisciplinary operations was developed by constructing a matrix which describes each experiment's activities during certain campaigns. .5cm Studies .25cm
Several scientific studies or campaigns which involve inter-experiment operations on SOHO are presented in matrix form. The entries are limited to those schemes suggested by people who responded to the call for input. Most are derived from detailed schemes, with specific operations for each instrument.
Included here are only studies which involve many instruments, and especially those involving instruments belonging to more than one of the experiment groups (see Table 1.1 in Chapter 1). For the present, we are concentrating on the interdisciplinary aspects of the solar atmospheric and space plasma observations and will not consider the operations of the GOLF, VIRGO and MDI experiments.
The studies fall into three categories: E = Event driven study. For this, a specific feature may be tracked through different regimes by the experiments, e.g. tracking a mass ejection from the Sun to 1AU. C = Campaign. R = Regular or periodic observation.
The participation of an instrument in each study is noted by the letters x, w or d. Non-participation is denoted by a `-'. An x entry simply denotes that the experiment is participating. A w entry means that the instrument is waiting for an event, probably operating in a ``sit and stare'' mode until a flag is triggered. A d denotes some time delay during an event driven study (E) from the onset of the event observation in the first instruments. For example, a flare seen in CDS, which was operating in a w mode, might generate a stream of particles seen in ERNE some 10 min later.
Each study is denoted by a three letter identifier: FIL = Filament eruption study.
CME = Coronal mass ejection study.
HOL = Coronal hole study.
ION = Ion abundance study.
ELE = Element abundance study.
FIN = Fine scale structure study.
STR = Streamer study.
FLA = Flare study.
COR = Coronal evolution study.
SCT = Sector boundary study.
SHK = Development and propagation of shocks.
BRT = Bright point study.
Most of the studies are of a campaign nature. This will probably be the most productive interdisciplinary approach. These will be relatively easy to operate since they do not attempt to make direct links between observed features, the observations can be easily defined and plans may be made well ahead of the campaign. The event driven studies involve some of the coronal instruments ``waiting'' in a pre-event ``sit and stare mode''. This may be wasteful. Once an event has occurred, we are very dependent on it's path of propagation to receive signals in the high coronal or in situ devices. Most of the studies require specific ground-based input, and will, most likely require supporting satellite data. Good information exchange and communication between SOHO and ground based and other satellite instrument groups is essential. .25cm One way ahead is for the SPWG to extend the Matrix by filling in the detailed operation for each instrument for each entry in the Matrix. From that point one may input a schematic event, such as a simple mass ejection, to produce dummy data. Methods for comparing the different signatures may be discussed, then, for a known input. The Flare Study SOHO is not a flare mission, but discussion of how we would hunt a flare provides one extreme in potential operations. The sequence of events could be as follows: (i) Some weeks prior to the observation, at the EOF planning meetings, the details of a FLA campaign is discussed. The plan is to observe a flare within a region 30-60 degrees from the western limb, so we may observe low coronal structure with CDS and SUMER, and the high coronal response with LASCO and UVCS. EIT and MDI would be involved. The particle instruments are informed, in case flare generated particles arrive at the spacecraft. (ii) Having identified a candidate active region crossing the eastern hemisphere, in the preceding week, contacts are made to ground based observatories to ensure good H monitoring, vector magnetogram data on the relevant region, and to the receipt of coronameter data. Similarly, approaches are made to relevant spacecraft teams. (iii) CDS is chosen to be the inter-instrument flag Master. An intensity threshold in a particular hot line is chosen as the flag generation mechanism. Flags will be used by SUMER, to home in on the flare region, and by UVCS and LASCO to change mode to scan the overlying corona. The other instruments will not change mode during the operation. (iv) At the specified time CDS points to the identified active region. The other instruments may continue other observations or also view the active region or overlying corona. (v) A flare occurs and a flag is sent. Automatic repointing and mode changing is immediately performed by the other instruments, as specified during the planning, to enhance the observation. There is no time for control by ground contact; this is flag driven. The operation continues for a specified time. (vi) A team has been appointed to co-ordinate the analysis of the data-set. In practice, this should be individuals from the involved experiment groups and would include someone from each of the other non-SOHO instruments. The SOHO data-sets should be processed and forwarded to the team, as should other space-based and ground-based data. An initial report on the success of the campaign (i.e. the operational aspects such as the performance of the flag, the delay in getting data, the loss of any data due to weather, drop outs etc.) should be reported to the SPWG within a month of the campaign. This provides the experience for improving future campaigns. The analysis of the data-set and the publications should be co-ordinated by the team over the following months. The Matrix The columns 2-10 represent the SOHO instruments and column denoted G-B includes comments on ground-based support.
The suggested ground-based support is taken from the following list:
1 - Magnetograph (e.g. Marshall Space Flight Cente)
2 - Mauna Loa Solar Observatory (coronagraph and H limb monitor)
3 - H (e.g. Big Bear Solar Observatory)
4 - He I 10830Å (e.g. Kitt Peak).
5 - Metric radio observations (Type II)