EVALUATING POTENTIAL FOR DATA ASSIMILATION IN A FLUX-TRANSPORT DYNAMO MODEL BY ASSESSING SENSITIVITY AND RESPONSE TO MERIDIONAL FLOW VARIATION

摘要

We estimate here a flux-transport dynamo model's response time to changes in meridional flow speed. Time variation in meridional flow primarily determines the shape of a cycle in this class of dynamo models. In order to simultaneously predict the shape, amplitude, and timing of a solar cycle by implementing an ensemble Kalman filter in the framework of Data Assimilation Research Testbed, it is important to know the model's sensitivity to flow variation. Guided by observations, we consider a smooth increase or decrease in meridional flow speed for a specified time (a few months to a few years), after which the flow speed comes back to the steady speed, and implement that time-varying meridional flow at different phases of solar cycle. We find that the model's response time to change in flow speed peaks at four to six?months if the flow change lasts for one?year. The longer the changed flow lasts, the longer the model takes to respond. Magnetic diffusivity has no influence in the model's response to flow variation as long as the dynamo operates in the advection-dominated regime. Experiments with more complex flow variations indicate that the shape and amplitude of flow perturbation have no influence in the estimate of the model's response time.