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Issue 9: 12 May 2003
Latest News

Welcome to the CDS Newsletter. The goal of this Newsletter is to inform the CDS user community of
  • current CDS science topics
  • developments in CDS data analysis
  • instrumental matters
  • operational issues
We invite your contributions on CDS-related matters: data analysis, science results, instrument calibration, software and questions on these topics. Your responses will influence the content of future issues. Please send newsletter inputs and correspondence to the editor,

This Month's Topics:

A. Fludra

CDS featured prominently at the NAM/UK Solar Physics meeting in Dublin, 7-11 April 2003. On 10 April we held a special session on "Results from CDS", and several talks using CDS data were given in other solar sessions as well. The CDS User Group Meeting was held on 11 April, 2003.

Main objectives of the CDS Users' meeting were:
  • Present updates on selected data analysis topics
  • Identify and solve remaining problems with data analysis
  • Share useful analysis techniques and tricks
  • Find new, better ways of exploiting the CDS data
  • Begin the process of evaluating the observing programmes and results (e.g., large data sets): main achievements, lessons learned
  • Discuss future observations, analysis, and planning
With this meeting, we have accelerated the process of taking stock of the CDS achievements, reviewing the status of the data analysis, and seeking inspiration for future observations with CDS. All presentations are listed below. Where available, a link to the MS Power Point file or a web page is included. I wish to express thanks to all contributors and participants.

1. CDS Status - A. Fludra / J. Payne

CDS in numbers:
  • created 157,350 fits files until the end of March 2003
  • 233 Gigabytes of data
  • Over 500 publications
  • set of web sites has now had over 10.6 million hits, averaging 6,500 requests a day from 137 countries
Status of the instrument:
  • GIS: nominal. No recalibration or changes to High Voltages have been necessary in the past 18 months.
  • NIS: nominal. No adjustments have been necessary in the past two years.
  • The OPS mechanism and mirror behave nominally, showing no signs of wear.
  • The doors open/close satisfactorily.
  • The slit mechanism has shown a problem when used in a rastering mode, where movement appears to become 'sticky' when entering a certain but short range. It does free itself and catch up as movement exits this area.
  • A restriction on the range of movements when rastering the slit has been imposed. This applies to all slit numbers. The current allowed range of movement is 15'' in the N-S direction. Analysis will be made to assess if the range can be extended to include the entire bottom half of the raster.
  • The change of slit numbers is not affected by this problem. The restriction applies only to using GIS rasters.
  • We continue to see a slow steady increase in the temperatures of the Front Bulkhead and the Side Frame +Y (Top), which in turn leads to seasonally raised temperatures at the telescope mount and within parts of the Optical Bench.
  • However, the NIS wavelength calibration remains within tolerances.
  • We also see abrupt changes during major SOHO & CDS activities, which remain unexplained, but are still within wavelength calibration tolerances (see the previous newsletter report): ../newsletter/issue8/latest.shtml#niswavelength Another known thermal effect is the wavelength change after off-limb observations. Therefore, caution is needed when measuring velocities less than 30 km/s from NIS.
2. Grazing Incidence Spectrometer: a mini-tutorial on GIS data analysis - Carl Foley
Carl is preparing an easy guide to analysing GIS data, including ways to identify ghost-free regions. The first, still evolving version is available at:
Note that for a particular line of interest, it is possible to design the GIS look-up table to make that wavelength range ghost-free (this applies only to new studies).
A draft of a somewhat specialized paper about the GIS gain depression is available at:

3. Sensitivity Differences in Pre-Loss and Post-Recovery NIS/CDS Spectrum - Steven Chapman

4. Cross-Calibration of CDS USUN and TIMED Spectra - Bill Thompson

The conclusion from Steven's and Bill's results is that the NIS-1 sensitivity decreased after the SOHO recovery by about a factor of two. The comparison of USUN and TIMED spectra provides a direct measure of this decrease, while Steven's approach gives some insight into the variation of the Mg IX intensity with the solar cycle.

5. Introduction to Active Region Results - Peter Young
Peter's intention was to stimulate a discussion on what are the most important results from active region observations. Some answers are in the presentations that follow:

6. Oslo Sunspot Studies - Olav Kjeldseth-Moe
This is one of the Large Data Sets (see below for more explanations of this term). It has resulted in many papers by Brynildsen et al.

7. A Destructive Effect of Solar Rotation on Analysis of Oscillations - Olav Kjeldseth-Moe

8. Results from Active Region Campaigns - Giulio Del Zanna
A vast amount of results which will some day become available online.

9. Oslo Active Region Loop Studies - Olav Kjeldseth-Moe
Another large data set, and more papers from the Oslo group. Movies are included separately:

10. UCLAN Polarity Reversal Studies - Barbara Bromage
According to Barbara, a full polarity reversal has not taken place yet. This large volume of data will be a part of Steven Chapman's thesis.

11. NIS Spectral Diagnostics - Giulio Del Zanna
This is a practical advice on useful density diagnostics line ratios and CDS calibration.

12. European Grid of Solar Observations (EGSO) and CDS - Simon Martin

13. Large Data Sets - Andrzej Fludra

A number of studies has been run regularly for an extended period of time and accumulated a large volume of data. Some of them have been run since the beginning of the mission (e.g. SYNOP, or the NIS quiet sun spectral atlas), others started in 1997 or later. This group of studies is called here 'large data sets'. Any observation that is a consistent set of data obtained regularly over a period of several months or more, falls into this category. There is a natural curiosity about the progress in their analysis. Perhaps those programmes and all of us could benefit from pondering the following questions:
  • Have these observations achieved their purpose?
  • Is there a need to continue the same studies?
  • What other projects could this data be applied to?
  • What experience has been gained: handling large quantities of data, processing the data automatically; CDS-specific recommendations (line lists, exposure times, raster sizes, study durations, targets & pointing, etc.)
This is a vast topic - there is at least a dozen of such studies and it would take a dedicated workshop to review all data. At this meeting, we have taken first steps in this direction and selected four data sets: Oslo Sunspot studies, Oslo Active Region Loops study, UCLAN Polarity Reversal Study, and Cambridge Active Region studies as examples from this category of data. Therefore, while perusing those presentations and their results, let's keep in mind that there is a lot of data behind them, possibly with plenty of still untapped potential.

MERCURY TRANSIT - Andrzej Fludra

On May 7, 07:50 - 13:17 UT, Mercury transited the solar disk. SOHO instruments carried out special observations of this transit. CDS made wide slit movies and sit & stare observations with the 2x240 and 4x240 slit. CDS movies are shown at
(see at the middle of that page).

An example of the sit & stare study in the He I 584 A line is shown below (the right-hand panel is contrast enhanced). That Mercury is not seen as a perfect black circle qualitatively agrees with our present knowledge of the CDS spatial point spread function - this data set should help us quantify the PSF better.

Dynamics of Blinkers

D. Bewsher, C.E. Parnell, C.D. Pike and R.A. Harrison (Solar Phys., in press)

The relative Doppler and non-thermal velocities of quiet-Sun and active-region blinkers identified in O V with CDS are calculated. Relative velocities for the corresponding chromospheric plasma below are also determined using the He I line. O V blinkers and the chromosphere directly below, have a preference to be more redshifted than the normal transition region and chromospheric plasma. The ranges of these enhanced velocities, however, are no larger than the typical spread of Doppler velocities in these regions. The anticipated range of Doppler velocities of blinkers are 10 - 15 km/s in the quiet-Sun (10 - 20 km/s in active-regions) for He I and 25 - 30 km/s in the quiet-Sun (20 - 40 km/s in active-regions) for O V. Blinkers and the chromosphere below also have preferentially larger non-thermal velocities than the typical background chromosphere and transition region. Again the increase in magnitude of these non-thermal velocities is no greater than the typical ranges of non-thermal velocities. The range of non-thermal velocities of blinkers in both the quiet-Sun and active-regions are estimated to be 15 - 25 km/s in He I and 30 - 45 km/s in O V. There are more blinkers with larger Doppler and non-thermal velocities than would be expected in the whole of the chromosphere and transition region. The recently suggested mechanisms for blinkers are revisited and discussed further in light of the new results.

A self-consistent treatment of radiation in coronal loop modelling

S.J. Bradshaw and H.E. Mason (A&A, in press)

We perform a hydrodynamic simulation of a cooling coronal loop and calculate the time-dependent ion populations of the most abundant elements of the solar atmosphere at each time-step. We couple the time-dependent ion balance equations to the hydrodynamic equations in order to treat the energy loss through radiation in a self-consistent way by allowing for the emission from a potentially nonequilibrium ion population.
We present results for the response to the changing conditions in the loop of the population of C VII ions and find significant deviations from equilibrium in the coronal and footpoint regions of the loop. The former is due to the tenuous nature of the coronal plasma causing recombinations to be rare and the latter is due to the strong downflows that develop as the loop cools, which carry persistent C VII ions into the lower regions of the loop. We also present a comparison between total plasma emissivity curves calculated during this simulation and an almost identical simulation that assumed an equilibrium ion population for the calculation of the radiation term. As a result of the nonequilibrium ion populations we find significant differences between the emissivity curves of each simulation and the loop cooling times.
We suggest that a consideration of nonequilibrium ionisation and radiation might help to (a) explain the thermal broadening observed in some emission lines during explosive events, and (b) reconcile differences between theory and observations relating to the longevity of some loops observed in the TRACE filters.

Evidence for a Flux Rope driven EUV wave and CME: Comparison with the Piston Shock Model

C.R. Foley, L.K. Harra, S.A. Matthews, J.L. Culhane, R. Kitai, 2003, A&A, 399, 749

This paper examines the relationship between a coronal wave, filament eruption, flare and Coronal Mass Ejection (CME) which occurred on 2001, April 10th. We study the pre-flare activity which includes the eruption of a filament and a coronal wave. A large X-ray flare and a CME follow. We discuss how these phenomena are related and compare our results to recent models. These are found to be largely consistent with the numerical simulations of a flux rope driven CME as presented recently in Chen et al. (2002).
A summary image is on the following page:
and the paper can be retrieved from

From the CDS Operations Management Team in the Space Science & Technology Department at CCLRC Rutherford Appleton Laboratory
Site maintained by John Rainnie.
Last revised on Tuesday (22/Jan/2019) at 15:07.