A1D5.5

Name: D5.5 Intercalibration of TSI/VUV measurements

Lead Beneficiary: CNRS

Beneficiaries involved: CNRS, ROB, PMOD-WRC

Due Date: Month 30 (May 2010)

Contents 1 Goal 2 Progress so far 3 Problem areas 4 Participants

Goal

This part of WP5 consists of three tasks :

1. systematic statistical comparison of the solar UV spectral irradiance with the Total Solar Irradiance (TSI) and various proxies, on medium and long time scales (days and beyond).
2. idem, but for short time scales (minutes and below) once the data from PROBA2/LYRA become available
3. study of the impact of solar flares on the TSI

Progress so far

1. we have started comparing solar UV and TSI measurement with a lower (one-day cadence), coming from other instruments. In particular, we have used a multiscale approach to show that depending on the time-scale of interest, the TSI does not correlate always with the same proxies for solar activity. This result sheds new light on the origin of the variability of the TSI. A publication on this result is under way.
2. the comparison of the spectral variability using high cadence data will be start once the data from PROBA2/LYRA (launch Nov 2009) and PICARD/PREMOS (launch March 2010) are available. This is a totally new field as there have been no high cadence measurements so far in that spectral range.
3. we have found by statistical analysis that solar flares (and even the small ones) do impact the varibility of the TSI. Actually the energy emitted by a flare in the visible part of the spectrum exceeds by two orders of magnitude the energy observed in the X-ray range. This is a surprising and very exciting finding that may have deep consequences on the origin of the long term varibility of the TSI. A publication on this topic has been submitted (M. Kretzschmar et al.)

Of particular interest is the unusually long decline of the present solar cycle, during which various solar activity indices including the TSI have evolved differently from what they used to for past solar cycles. This unusual behaviour offers us a unique opportunity to put new constraints on the models. In partcular, we have found that the long-term evolution of the open solar magnetic flux (which is strongly correlated with the TSI) does not evolve in the same way as the closed magnetic flux (which is strongly correlated with the sunspot number). This analysis, which is based on 150 years of geomagnetic data is very intriguing. A spin-off of this is a new collaboration between LPC2E and UOulu.

Problem areas

None. The first results about the high cadence measurement will be 2-3 late because of the delayed launch of Proba 2.

Participants

List the name of the people working on this deliverable by each beneficiary involved.

• CNRS: T. Dudok de Wit, M. Kretzschmar, G. Cessateur
• PMOD-WRC : W. Schmutz
• ROB : S. DeWitte
• UOulu : K. Mursula