Sunspots

Introduction: Sunspots are some of the most notable features of the Sun. Use a telescope to track the changes in position and shape of sunspots over time. This activity requires adult supervision.McDonald Observator

Incomplete information and self-fulfilling prophecies

This paper shows that incomplete information can be a rich source of sunspots equilibria. This is demonstrated in a standard dynamic general equilibrium model of monopolistic competition … la Dixit-Stiglitz. In the absence of fundamental shocks, the model has a unique certainty (fundamental) equilibrium, but there are also multiple stochastic (sunspots) equilibria that are not mere randomizations over fundamental equilibria. In other words, sunspots can exist in infinite-horizon dynamic models with a unique saddle path steady state. In contrast to the recent sunspots literature (e.g., Benhabib and Farmer 1994), sunspots arising under incomplete information can be serially correlated and are robust to parameters associated with production technologies and preferences. Markup is always countercyclical in sunspots equilibria (which is consistent with empirical evidence) and fluctuations driven by sunspots look very similar to fluctuations driven by technology shocks.Business cycles ; Prices

Effect of suppressed excitation on the amplitude distribution of 5-min oscillations in sunspots

Five-minute oscillations on the Sun (acoustic and surface gravity waves) are excited by subsurface turbulent convection. However, in sunspots the excitation is suppressed because strong magnetic field inhibits convection. We use 3D simulations to investigate how the suppression of excitation sources affects the distribution of the oscillation power in sunspot regions. The amplitude of random acoustic sources was reduced in circular-shaped regions to simulate the suppression in sunspots. The simulation results show that the amplitude of the oscillations can be approximately 2-4 times lower in the sunspot regions in comparison to the quiet Sun, just because of the suppressed sources. Using SOHO/MDI data we measured the amplitude ratio for the same frequency bands outside and inside sunspots, and found that this ratio is approximately 3-4. Hence, the absence of excitation sources inside sunspots makes a significant contribution (about 50% or higher) to the observed amplitude ratio and must be taken into account in sunspot seismology.Comment: 12 pages, 5 figures, accepted to ApJ