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Issues related to designing a VO for Heliophysics
Bob Bentley (UCL-MSSL)
13 June 2007VOiG Conference, Denver CO, USA
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Outline
Examine some of the items needed to facilitate a virtual observatory for heliophysicsIdentify deficiencies and suggest solutions
Talk evolved as I was preparing it…Started looking at proton events and GLEs because of space weather effects related to aviation
Found problems with the metadata
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Heliophysics
Heliophysics explores the Sun-Solar System Connection
An extension of the study of space weather (SWx++)
Heliophysics sits in the boundary between two communities
Astrophysicso An understanding of solar phenomena helps in the
understanding of stellar observations
Planetary sciences (including Geosciences)o Solar activity can influence the environment on/around the
planets
The discipline must be aware of the need to support the interests of both communities
A virtual observatory that supports Heliophysics must facilitate access to data from a number of communities
Solar, heliospheric, magnetospheric and ionospheric physics
As such, it is in essence a next generation VxO
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Heliophysics
The communities that constitute heliophysics have evolved independently over decades and even centuries
Little or no coordination of how each has evolved Each has very different ways of describing, storing and exploiting the data from their observations
The desire to solve science problems that span disciplinary boundaries is driving the need to provide combined access to these data To do this, we need to find ways to:
Tie the data together through searches across all the datasetsPresent any results in a form that does not require a detailed understanding of each discipline
This requires the re-evaluation of the capabilities provided within each community and some correctative action
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Types of metadata
To facilitate a VxO for heliophysics we need to examine the metadata that is required.
There are many ways these can be described, one is:Search metadata
o Metadata used to identify time intervals and sets of data of interest
Observational metadatao Metadata used to describes the observations, e.g. FITS
headers
Storage metadatao Metadata that describes how the data are stored and
accessed
Administrative metadatao Metadata that allows the system to exploit the available
resources
The rest of the talk will concentrate on issues related to the first two sets
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Searches
In heliophysics, we are interested in how an event on or near the solar surface can propagate through the heliosphere and affect a planetary environment
Searches should identify interesting time intervals based on a combination of event, features, etc. metadata
Each community of some from of these data
There are concerns about the quality and integrity of the metadata and whether it is adequate to support the searches we would like to undertake
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Solar search metadata
Phenomena occur on or near the solar surfaceEvent data gives time and location of phenomenaFeature data provides details of location and size of structures that may be relevant
Time information can be expressed in many waysEssentially these are the same, with simple transformations
Spatial information can be expressed in terms of:Coordinates in the observing frame – e.g. arcsecs from disc centreCoordinates on the rotating body of the Sun – Carrington coords.
The position of the observer was ignored for the most part
Helio-seismology is an exception
In the bigger picture of heliophysics, also need to include the viewing perspective
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Other search data
Observation of phenomena in the heliosphere and near/on planets are more complex
For in-situ observations in the heliosphereTime is when a phenomena affected (passed) the observer
Position of the observer relative to the Sun is key to understanding
When the in-situ observations are made on/near a planet
Position of the observer relative to the planet is also important
Relating events that are defined from in-situ data to those on/near the Sun requires an understanding of how events propagate
Details of the velocity structure of CMEs and the solar wind are not easy to determine…
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Simple, but not so simple
In principle this all seems fairly obvious, but lets look in detail at some common solar event data
On 20 January 2005 there was an X7.1 flare that was intensely geo-effective.
The flare was associated with particle event and a CME; it was also observed by ground-level neutron monitors – a GLE.Many superlatives were used to describe the event
o "The solar energetic particle event of January 20 2005 has been called, by some measures, the most intense in 15 years..." (Mewaldt et al., 2005)
o ”The fastest rising SEP event of current cycle [cycle 23]" (Rawat et al., 2006)
o ”The most spectacular [solar event] of the Space Age" (Tylka et al., 2006)o ”The largest GLE [GLE 69] in half a century" (Bartol Research Institute)
But event is absent from the NOAA SEC list of "Solar Proton Events Affecting the Earth Environment"
When you look at the data and how lists are created, you realize that the lists are deficient in several ways
o Humans and SmFCACs can understand what happened, but o it is harder for machines...
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X7.1 of 20 Jan 2005
The event was one of several from AR 10720Two other X class flares and several M class flares occurred in previous 3 days; others before this
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X7.1 of 20 Jan 2005
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X7.1 of 20 Jan 2005
At the time of the event, the proton levels had not returned to normal after previous events
The criteria fails to recognize a new event
o NOAA lists event on 16 Jan
The X-ray data also suffers from problems
The end of an event is defined by when the counts drop to 50%
o New events can “interrupt” existing events
The shape and true duration of the decay phase are lost
o NOAA gives start 0636; end 0726
Not all locations are tagged!!Significant brightenings seen on images not declared as flares
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Some of the problems
That major events can be “missed” is worrying and makes automated searches difficultA search for long duration events would yield spurious resultsSince the locations of all flares are not known, it is impossible to know if they will be geo-effectiveInstrument flare lists have gaps – nights, off times, etc. – but the reason for a null result is not included
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Improving event data
Existing flare lists can give a distorted picture what has occurred
Such deficiencies make it difficult for non-experts to use themThe community “knowledge” is not written down
Need to re-evaluate and regenerate the event data in all domains with the idea that the data will be used in a joint search across the domains
Ensure events more accurately describedInclude information that might explain null results
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Observation metadata
Metadata related to observations gives information about how the observation was made, etc.
There are often quality issues related to the metadata that is provided – parameters sometimes missing, or wrong
In solar data, space-based observations much better described than their ground-based counterparts
Researchers often used to deficiencies in the data in their own domain
Difficult for machines to handle if it is not quantified properly
VxOs can sometimes develop ways of patching the gaps
What do we do with this information? How is it shared?
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Observation metadata
In solar physics we have tried to introduce standardsSOHO made good start with their keyword documentEGSO enhanced concepts with its data model
Situation better than it was but adoption still not universal
Even some problems within SOHO…
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Standards
Need to extend the use of standards to all domains so that all future data are more compatible with the VxOs
The situation has changed with enhancements in technology; providers need to ensure they are more compliantVxO will need to handle problems with the older data; providers cannot be expected to do it
Standards need to be developed in collaboration with the community and funding agencies
Core part that is requiredAdditional information that may be specific to a domainOther information that the instrument team wants to add
In developing standards need to draw on the experience gained within the general VO community and adopt the best ideas available
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Conclusions
Developing a virtual observatory to support heliophysics will not be simpleSome of the possible problems have been highlightedTo address them, we need to engage the communities in all the domains that constitute heliophysics and develop standards that will facilitate the process
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