HAO 2012 Profiles In Science: Dr. Mausumi Dikpati
Contact:
303-494-1512
dikpati@ucar.edu
Dr. Mausumi Dikpati is a Scientist III in the High Altitude Observatory of the National Center for Atmospheric Research. She received her PhD in 1996 from the Indian Institute of Science, Bangalore. She has been at NCAR since the fall of 1996 when she assumed a postdoctoral fellowship in the Advanced Study Program. Her main research interest is in modeling dynamics and MHD of the solar interior and the solar dynamo. Read More »
Professional Web Site(s):
http://www.hao.ucar.edu/Public/about/Staff/dikpati/index.html
Summary of Achievements
Over the past year, Mausumi Dikpati's research has focussed on modeling evolution of large-scale, cyclic solar magnetic fields. Simulating polar magnetic field patterns of cycles 22 and 23 using a flux-transport dynamo, she has demonstrated that, flux-transport dynamo models and surface transport models, despite some differences in their ingredients, produce remarkably similar responses in the polar fields' patterns to the changes in the meridional flow speed when the same latitudinal profile for the poleward surface flow is used.
As a collaborative effort, Dikpati has also continued investigations of the physics behind the differences in the speed and latitudinal profile of meridional circulation derived from Doppler measurements and Magnetic Feature Tracking (MFT) technique. Gustavo Guerrero, Matthias Rheinhardt and Axel Brandenburg at NORDITA, and Dikpati, have performed simulations of magnetic feature tracking speed in both 1D and 2D flux-transport models, using Alternating-Direction-Implicit 2D transport code and the PENCIL code, and have found that the simulated MFT speed is always the same as the plasma meridional flow speed in a 1D transport model, but is different in a 2D model.
Publications
(1) Dikpati, M. and J. L. Anderson, 2012: Evaluating Potential for Data Assimilation in a Flux-transport Dynamo Model by Assessing Sensitivity and Response to Meridional Flow Variation, ApJ, 756, 20.
Abstract: 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 (DART), 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 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 model's response time.
Figure caption: Green-dashed, blue dash-dotted, and black long-dashed lines in panel (a) present three different amplitudes of flow perturbations, 25%, 50%, and 100% with respect to steady flow (14 m/s). In panel (b), the corresponding curves present toroidal flux integrals and in panel (c) small-sized green, medium-sized blue, and large black diamonds present lag-correlation plots for the above three flow perturbations, respectively. Flow perturbation lasts for one year and occurs during the rising phase of the cycle.