Variational estimation of the large scale time dependent meridional circulation in the Sun: proofs of concept with a solar mean field dynamo model

Abstract

We present in this work the development of a solar data assimilation method based on an axisymmetric mean field dynamo model and magnetic surface data, our mid-term goal is to predict the solar quasi cyclic activity. Here we focus on the ability of our algorithm to constrain the deep meridional circulation of the Sun based on solar magnetic observations. To that end, we develop a variational data assimilation technique. Within a given assimilation window, the assimilation procedure minimizes the differences between data and the forecast from the model, by finding an optimal meridional circulation in the convection zone, and an optimal initial magnetic field, via a quasi-Newton algorithm. We demonstrate the capability of the technique to estimate the meridional flow by a closed-loop experiment involving 40 years of synthetic, solar-like data. By assimilating the synthetic magnetic proxies annually, we are able to reconstruct a (stochastic) time-varying meridional circulation which is also slightly equatorially asymmetric. We show that the method is robust in estimating a flow whose level of fluctuation can reach 30% about the average, and that the horizon of predictive capability of the method is of the order of 1 cycle length.

arXiv commentAccepted for publication in ApJ. 23 figures, 20 pages. 1 Institut de Physique du Globe de Paris, 75005 Paris, France, 2 AIM/SAp CEA-Saclay, 91191 Gif-Sur-Yvette, France, 3 Institut de Recherche en Astrophysique et Planétologie, 31028 Toulouse, France, 4 Laboratoire de météorologie dynamique, Ecole Normale Supérieure, Paris, France

References in corpus (25)

• Revisiting the Sunspot Number
• Detection of Equatorward Meridional Flow and Evidence of Double-Cell Meridional Circulation inside the Sun
• Reconstruction of the Sunspot Group Number: the Backbone Method
• Exploring the Physical Basis of Solar Cycle Predictions: Flux Transport Dynamics and Persistence of Memory in Advection versus Diffusion Dominated Solar Convection Zones
• Predicting the Sun's Polar Magnetic Fields with a Surface Flux Transport Model
• A Revised Collection of Sunspot Group Numbers
• Solar Meridional Circulation from Doppler Shifts of the Fe I line at lambda 5250 Angstroms as Measured by the 150-foot Solar Tower Telescope at the Mt. Wilson Observatory
• Solar Magnetic Field Reversals and the Role of Dynamo Families
• Solar Cycle Prediction
• On the role of meridional flows in flux transport dynamo models
• Global helioseismic evidence for a deeply penetrating Solar meridional flow consisting of multiple flow cells
• Systematic Center-to-Limb Variation in Measured Helioseismic Travel Times and Its Effect on Inferences of Solar Interior Meridional Flows
• Is a deep one-cell meridional circulation essential for the flux transport Solar Dynamo?
• Magnetoconvection and dynamo coefficients: II. Field-direction dependent pumping of magnetic field
• On Predicting the Solar Cycle using Mean-Field Models
• Characteristics of solar meridional flows during solar cycle 23
• Polar Field Reversal Observations with Hinode
• Prediction of Sunspot Cycles by Data Assimilation Method
• Meridional Flow in the Solar Convection Zone I: Measurements from GONG Data
• Speed of Meridional Flows and Magnetic Flux Transport on the Sun
• Modeling a Maunder Minimum
• Effects of Solar Active Regions on Meridional Flows
• Assimilating data into an αω dynamo model of the sun: A variational approach
• Ensemble Kalman filter data assimilation in a Babcock-Leighton solar dynamo model: an observation system simulation experiment for reconstructing meridional flow-speed
• Estimating the deep solar meridional circulation using magnetic observations and a dynamo model: a variational approach

Cited by in corpus (10)

• Solar cycle prediction
• Surface Flux Transport on the Sun
• Models for the long-term variations of solar activity
• Simulations of solar wind variations during an 11-year cycle and the influence of north-south asymmetry
• Connecting the large- and the small-scale magnetic fields of solar-like stars
• Torsional Oscillations in Dynamo Models with Fluctuations and Potential for Helioseismic Predictions of the Solar Cycles
• Does the mean-field alpha effect have any impact on the memory of the solar cycle?
• Forecasting the solar cycle using variational data assimilation: validation on cycles 22 to 25
• Forecasting Solar Flares by Data Assimilation in Sandpile Models
• Can meridional flow variations explain the observed rising/declining phase asymmetry in the solar cycle?