[Astronomy seminar] Astronomy seminar on Friday 20th of October

[Astronomy seminar announcements]

Title: What causes the solar seasons?
Speaker: Mausumi Dikpati (HAO/NCAR)

Friday 20th of October from 10:30 to 11:30 at FC61.

Abstract:
Recent observations indicate that solar cycle variability consists of 
short-term quasi-periodic bursts of magnetic activity, or the ``solar 
seasons''. Burst periods are 6-18 months. Using a nonlinear MHD shallow 
water tachocline model we show that a back-and-forth exchange of energy 
between tachocline latitudinal differential rotation and Rossby waves 
occurs with a periodicity of 2-19 months, for a wide range of effective 
gravities, differential rotation amplitude, latitude location of 
toroidal magnetic bands and their peak field strength. These Tachocline 
Nonlinear Oscillations (TNO) can cause enhanced activity bursts when the 
Rossby wave energy grows to its maximum, because the tachocline top 
surface is maximally deformed then. Hence, nearly 'frozen-in' toroidal 
fields can enter the convection zone from the tachocline, starting their 
buoyant rise to the surface to erupt as active regions. The bursty phase 
is followed by a relatively quiet phase, during which the differential 
rotation gets restored by extracting energy from Rossby waves and top 
surface deformations subside. Our results indicate that the solar 
seasons can be caused by TNO's. I will close by discussing how we can 
forecast these seasons by coupling with data assimilation.