A1S3WP5
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A brief summary of the status
Work-package 5 concentrates on the measurement and the modelling of the solar spectral variability in spectral bands that are of particular importance for solar-terrestrial studies and for space weather applications: total solar irradiance, and irradiance in the UV. The focus is on the variability rather than on the analysis of spatial structures. There are 4 main tasks in this work-package.
Task 1 : Variability in the TSI and in the UV spectrum
main partners: PMOD, CNRS, ROB
The overall objective is to better understand the spectral variability of the solar UV irradiance and that of the Total Solar Irradiance (TSI). Of major importance is a proper understanding of the interplay between the various physical mechanisms that causes the variability. These results feed into deliverable A1D5.5.
A major fraction of the work is based on detailed statistical analyses of existing measurements of the solar UV flux (from TIMED/SEE and SORCE/SIM) and TSI (from SOHO/VIRGO and SORCE/TIM), and various proxies for solar activity, such as the sunspot number. A remarkable result that was obtained within the frame of SOTERIA is the discovery of a significant impact of solar flares on the TSI. This work, which is based on the statistical analysis of 10 years of TSI measurements by SOHO, suggests that solar flares radiate at least 100 times more in the visible part of the spectrum than in the X-ray part. This result questions the role of thermalisation processes of flares but also impacts the origin of the long-term variability of the TSI and hence the Sun-climate connection. An article has been submitted (Kretzschmar et al., 2009) and results were presented during the Space Climate Symposium (Finland, March 2009).
Also of major interest is the long term evolution of the TSI and the UV irradiance, on time scales of years and beyond. The present declining solar cycle is unusual in the sense that the empirical correlation between the TSI and other measures of solar activity has broken down. This puts new constraints on the mechanisms that govern the long-term evolution of the TSI. Luis Vieira, the post-doc that has been hired at CNRS (Orléans) for developing the UV spectral reconstruction model (see next task) is an expert in the modelling of solar magnetic field for TSI reconstructions. His contribution will be most valuable for expanding this topic.
The unusually long solar cycle provides an excellent opportunity for addressing the large public demand on the Sun-climate connection. Several of us have delivered public lectures on this topic in 2009.
Task 2: Impact of the VUV on the thermosphere/ionosphere system
main partners: CNRS, ROB
The objective is to improve the VUV (Visible Ultraviolet, 10-200 nm) spectral reconstruction for specifying the conditions of the thermosphere/ionosphere system and for input to operational models.
There is a remarkable similarity between the time evolution of the UV irradiance in different wavelengths, which suggests that the full spectrum can be reconstructed from the measurement of a few lines or spectral bands only. This powerful result will soon be implemented in the online nowcast of the UV spectrum (deliverable A1D5.3) using data delivered by the LYRA radiometer onboard PROBA2. Although part of model can be developed independently of the PROBA2 mission, it requires data to be properly tuned. This is why the delivery of the model (milestone A1M5.3) is constrained by the launch of PROBA2, which took place on November 2, 2009. A post-doc (Luis Vieira) has been hired on this project at the CNRS (Orléans) starting Sept. 2009. The delivery is expected for March 2010, once the satellite commissioning phase is over. The data will be used as input for the upper atmosphere chemical composition model developed at PMOD-WRC (deliverable A1D5.4), which is now almost ready.
A key finding is a graphical representation for determining how strongly different solar proxies and UV bands are related to each other. This result (T. Dudok de Wit et al., Geoph. Res. Lett. 36, 2009) is an important step towards the identification of proper proxies for the solar UV flux. In contrast to previous studies, the correlation between various quantities is established on different time scales, so that the contribution from individual physical processes can be better separated. From this, we are now considering the online delivery of an improved reconstruction of the irradiance of the Hydrogen Lyman-alpha line.
Another important aspect is the modelling of the solar forcing on the ionosphere; this task is mostly carried out in collaboration with CNRS (Grenoble). We are working on the making of a code that computes the effect of the EUV (Extreme UltraViolet) solar flux on the ionosphere, based on the existing TRANSSOLO code. The model takes into account new parameters such as the energy left to the ion during an ionisation and the energy left to the electrons in a multiple ionisation. For that purpose, Gael Cessateur, a PhD student from CNRS (Orléans) will spend several months at CNRS (Grenoble) with the support of SOTERIA.
Task 3: Impact of the UV spectrum on the middle atmosphere
main partners: PMOD, CNRS, ROB
This task is strongly connected to the previous one, except that the focus is on the modelling of the middle atmosphere and longer wavelengths (121-300 nm) are considered in the UV spectrum. Most of the activities are carried out by PMOD-WRC where a scientist (Eugene Rozanov) has been hired for working for this. The modelling of the middle atmosphere is entirely carried out at PMOD-WRC (deliverable A1D5.4), whereas the solar forcing will be provided by CNRS (deliverable A1D5.3), based on data from PROBA2 (milestone A1M5.1).
The global chemistry-climate-ionosphere model SOCOL-i was developed in a precursor project and has been expanded to the lower ionosphere with the support of SOTERIA. We are ready to take up the operational service and provide nowcasts at 6 hr intervals of the state of neutral and charged species in the middle atmosphere. Present activities deal with the validation of the model results against different measurements and the development of a web site for public use by the space-weather community (in collaboration with Institut für 4D-Technologien und Data Spaces (Windisch, Switzerland). Two papers have been submitted on this (Egorova et al., 2009, and Shapiro et al., 2009).
Task 4: Flare prediction
main partners: ROB, OBSPARIS
The objective is to provide at ROB an online flare prediction model based on the automated analysis of solar EUV and soft X-ray images and time series. This model builds upon the experience of the operational B2X flare detection model that had previously been developed at ROB.
The basic version of the model is ready but we are now awaiting data from SDO and PROBA2 to incorporate spatial information, which is crucial for developing robust flare predictors. For that reason, we decided to put this activity in standby and wait for the delivery of EUV solar images from PROBA2/SWAP (launched on 2 November 2009) and SDO/AIA (launch March 2010) to develop a new strategy and incorporate spatial information as well.
The associated deliverable A1D5.1, which was scheduled for November 2010 (Month 24) will therefore be delayed by 6 months. Present activities deal with the preparation of the flare prediction model using SOHO data, and the preparation of the data streams.
Major inter-beneficiary collaborations
- An unforeseen spin-off of the comparison of solar UV proxies is the possibility to identify the proper solar proxies for describing the solar forcing on atmospheric drag. The latter is important for space weather applications. A working team has started on this, in collaboration with engineers from the French space agency (Sean Bruinsma, CNES), a French SME working on orbitography (Jean-Jacques Valette, CLS) and scientists from the University College London (Alan Aylward).
- The long-term evolution of the TSI is strongly connected to that of the solar magnetic flux. Recently, the open magnetic flux has been found to strongly increase during the 20th century (Lockwood et al., Nature, 1999), a result that has stirred a fierce debate. By reanalysing 150 years of geomagnetic data, the CNRS team managed for the first time to separate the contributions from open and closed solar magnetic fields, showing that they actually evolve differently. A new collaboration has started between UOulu and CNRS in order to check this result with other geomagnetic indices.
- Participants from ROB, CNRS and OBSPARIS are investigating the possibility for developing a new radiometer for the robust monitoring of the VUV spectrum. CNRS (Grenoble) is conceiving a new airglow measurement telescope that will observe the airglow intensity variations of the the atmospheric lines and their polarisation variations versus the solar activity.
Progress toward completion
| Code | Name | Lead | Due date | Progress | Status | Comment |
|---|---|---|---|---|---|---|
| A1D5.1 | Online flare prediction model | ROB | Nov 2010 | 40% | in standby | ready in basic version but awaiting data from SDO and PROBA2 for full operational model |
| A1D5.2 | 4-peer reviewed scientific publications | all | Oct 2010 | 90% | in progress | 1 published, 3 being reviewed with minor comments |
| A1D5.3 | Online nowcast of the VUV spectrum | CNRS | Mar 2010 | 20% | in progress | model development in progress but awaiting calibrated data from PROBA2 for transitioning to operational model |
| A1D5.4 | Nowcast of the middle atmosphere | PMOD-WRC | Mar 2010 | 80% | in progress | model is ready. Now waiting for A1D5.3 for completion. |
| A1D5.5 | Intercalibration of the TSI/VUV measurements | CNRS | May 2010 | 40% | in progress | several key results already obtained, but now awaiting data from SDO, PROBA2 and PICARD for more detailed analysis |
See also WP5 milestones:
- A1M5.1 Start of exploitation of data from PROBA2, CORONAS & SDO
- A1M5.2 Delivery of middle atmosphere nowcast mode
- A1M5.3 Delivery of VUV spectral reconstruction mode
- A1M5.4 Delivery of flare prediction model
Major problems
- Two spacecraft whose data are important for the deliverables are suffering a launch delay. PROBA2 was successfully launched on November 2, 2009 and SDO is scheduled for March 2010. This will the delay the development of the VUV nowcast model by 3 months, and the that of the flare prediction model by 6 months.
Minor problems
- Following the start of the SOTERIA project (Nov 2008), CNRS had a few months delay in hiring a post-doc with the adequate profile to work on the VUV spectral nowcast model.
Suggestions for new directions and improvements
- The application of the VUV spectral reconstruction for atmospheric density nowcast is a promising spin-off. This has enabled several members from CNRS to answer the recent FP7 call on space.
- The organisation of a workshop on future instruments and strategies for VUV spectral irradiance is planned.
