• current CDS science topics
• developments in CDS data analysis
• instrumental matters
• operational issues

• Report on the CDS User Group Meeting at NAM/UKSP 2003
• Mercury Transit
• Paper Abstract - D. Bewsher et al.
• Paper Abstract - S. Bradshaw and H.E. Mason
• Paper Abstract - C. Foley et al.

• 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

• created 157,350 fits files until the end of March 2003
• 233 Gigabytes of data
• Over 500 publications
• solg2.bnsc.rl.ac.uk set of web sites has now had over 10.6 million hits, averaging 6,500 requests a day from 137 countries

• 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.

• 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.)

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