Space Physics Seminar spring-2015

A possible mechanism for heating the solar corona is via impulsive bursts or “nanoflares” The bursts might be the result of reconnection events among braided magnetic fields or possibly due to the dissipation of magnetohydrodynamic turbulence inside the loop structures. We will present evidence of nanoflare type processes using EUV coronal observations with Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We investigate intensity variations and energy deposition in five coronal loops in non-flaring active region (AR) cores. These were selected for their strong variability in the AIA/SDO 94 Å intensity channel. Isolating the hot Fe XVIII and Fe XXI components of the 94 Å and 131 Å signals, we find that the loop apex intensity, the temperature, and electron density indicate an impulsive heating process compatible with high intensity nanoflare storms characterized by a progressive cooling pattern with the hot channels leading the emission. To account for possible non-stationary properties of intensity fluctuations we apply the method of Detrended Fluctuation Analysis (DFA). This technique allows the calculation of a scaling exponent that characterizes the correlation properties of the signal and which can be related both to the spectral and the Hurst exponents. A cross over time appears with scaling properties differing for short and long time scales. In the AR core exponents indicate a process with positive correlation which can correspond to fractional Brownian motion at long time scales. Qualitative differences exist between the exponents of the hotter and the cooler channels. In areas of diffuse emission and for all the spectral channels the time series of intensity fluctuations tend to 1/f scaling for long time scales. We show that the properties of the data can be reproduced with a physically motivated model for impulsive heating with added Gaussian noise.