I9: SolarGeoMag

Improving Solar and Geo-dynamo predictability: towards advanced integrated data assimilation techniques

 

  • The main goal of the project is to improve our physical understanding, and our capability to predict, the long-term magnetic activity of the Sun and the Earth. This understanding will be based on the analysis of 3D simulations that will be parameterized and implemented in low dimensional models amenable to data assimilation experiments.

     Three-dimensional, self-consistent numerical simulations of solar and Earth interior magnetic field generation have made tremendous progress over the past 15 years, due to the dramatic increase in computational power.

    full 3D simulation of the Sun

    Full 3-D simulation of the Sun. Shown is the radial normalized velocity from the Sun’s core r=0 up to its surface at 99% Rsol (Alvan et al. 2015, Brun et al. 2016 in prep). Note the busy surface convective patterns and the excitation of internal gravito-inertial waves by the turbulent convective flows.

     

    Solar rotation profile in the meridional plane as computed with ASH code in Alvan et al. 2015.

    Solar rotation profile in the meridional plane as computed with ASH code in Alvan et al. 2015. Note the strong outer differential rotation and the fast transition (so-called tachocline) to inner core solid-body rotation (Alvan et al. 2015).

    Magnetic field lines within a three-dimensional simulation of the solar dynamo computed with ASH code

    Magnetic field lines within a three-dimensional simulation of the solar dynamo computed with ASH code (after Augustson et al., ApJ, 2015)

    butterfly diagram

    Butterfly diagram from a cyclic numerical simulation of the solar dynamo (Augustson et al., 2015). Note the equatorward propagation of the dynamo wave at mid/low latitude and the period of minima between cycle 11 and 16.

    Solar Wind computed from a Wilcox Observatory magnetogram during cycle 22 using PLUTO code (Reville, Brun et al. 2015). Field lines are coded with Br amplitude and the grey shade corresponds to the Alfven surface, beyond which the wind speed is super-Alfvenic.

    Solar Wind computed from a Wilcox Observatory magnetogram during cycle 22 using PLUTO code (Reville, Brun et al. 2015). Field lines are coded with Br amplitude and the grey shade corresponds to the Alfven surface, beyond which the wind speed is super-Alfvenic.

    In parallel advanced data assimilation pipelines have been implemented in geo and solar magnetohydrodynamics (MHD) to better constrain the short-term evolution of the magnetic field B. However, predictions of the long-term magnetic variations on the Earth and the Sun are intractable with 3-D simulations. This imposes to develop more conceptual, lower dimensional models in order to support (by objective comparison with data) our 3-D studies of the origin of the long-terms variations of B, such as rare and irregular polarity reversals, or solar grand minima. Our group has developed such models (of the mean-field flux transport type) together with a variational assimilation scheme to predict solar activity over one solar cycle (11 yr). We propose here to improve these models, and to propose new models, to be able to characterize the long term behavior of the Earth and the Sun.

    The questions that we wish to address are :

    • What are the physical mechanisms responsible for the long-term magnetic variability of the Sun and the Earth?
    • What is the predictability of the low-frequency/rare events such as solar minima and geomagnetic reversals?
    • Can we make robust forecasts of these events using, eg., partly simplified (parameterized) models?

    These questions, whose answers must rely on the available observational evidence, can be cast in the general framework of data assimilation. Utilizing data assimilation techniques to study the long-term behaviour of the magnetism of the Sun and the Earth is currently out of reach if one wishes to resort to high-resolution 3-D models based on first-principles (the cost of assimilation is 10 to 100 times that of a single model integration). Our goal is to analyze complex, 3-D simulations of the solar- and geo-dynamo in order to extract the fundamental mechanisms which control the long-term magnetic variability of these objects, and to test these mechanisms against observations by placing them at the core of conceptual models of moderate size well-suited for data assimilation. These observations will include systematic sunspot count since the early 1600s for the Sun (encompassing the Maunder minimum) and geomagnetic intensity for the past 2 Myr (covering 5 reversals of polarity).

    • Alexandre Fournier (IPGP)
    • Sacha Brun (AIM/CEA-Université Paris-Diderot),
    • Ching-Pui Hung (IPGP/AIM/CEA-Université Paris-Diderot
    • Gauthier Hulot (IPGP)
    • Laurène Jouve (IRAP/AIM)
    • Antoine Strugarek (AIM/CEA-Université Paris-Diderot & Groupe Solaire/Université Montréal)

  • Coming soon

  • Hung, C.P., Jouve, L., Brun, A.S., Fournier, A., and Talagrand O., Estimating the deep solar meridional circulation using magnetic observations and a dynamo model: a variational approach,The Astrophysical Journal, 814, 151 (21 pp), 2015. doi:10.1088/0004-637X/814/2/151

     

    Svanda, M., Brun, A.S., Roudier, T., Jouve, L., Polar cap magnetic field reversals during solar grand minima: could pores play a role?, Astronomy and Astrophysics, 586, A123 (11 pp), 2016.
    10.1051/0004-6361/201527314

     

    Brun, A.S., Browning, M.K., Dikpati, M., Hotta, H., Strugarek, A., Recent Advances on Solar Global Magnetism and Variability, Space Science Reviews, 196, 101 (35 pp), 2015

     

    Réville, V., Brun, A.S., Strugarek, A., et al., From Solar to Stellar Corona: The Role of Wind, Rotation, and Magnetism, The Astrophysical Journal, 814, 99 (9 pp), 2015
    10.1088/0004-637X/814/2/99

     

    Alvan, L., Strugarek, A., Brun, A.S., Mathis, S., Garcia, R.A., Characterizing the propagation of gravity waves in 3D nonlinear simulations of solar-like stars, Astronomy and Astrophysics, 581, A112 (13 pp), 2015.

    10.1051/0004-6361/201526250

     

    Augustson, K., Brun, A.S., Miesch, M., Toomre, J., Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo, The Astrophysical Journal, 809, 149 (25 pp), 2015

    10.1088/0004-637X/809/2/149