Diffusivity of Isolated Internetwork Ca II H Bright Points Observed by SuFI/SUNRISE
Abstract
We analyze trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to obtain their diffusivity behaviors. We use high spatial and temporal resolution image sequences of quietSun, disccentre observations obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager (SuFI) on board the SUNRISE balloonborne solar observatory. In order to avoid misidentification, the BPs are semimanually selected and then automatically tracked. The trajectory of each BP is then calculated and its diffusion index is described by a power law exponent, using which we classify the BPs' trajectories into sub, normal and super diffusive. In addition, the corresponding diffusion coefficients (D) based on the observed displacements are consequently computed. We find a strong superdiffusivity at a height sampled by the SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to the temperature minimum). We find that 74% of the identified tiny BPs are superdiffusive, 18% move randomly (i.e. their motion corresponds to normal diffusion) and only 8% belong to the subdiffusion regime. In addition, we find that 53% of the superdiffusion regime (i.e. 39% of all BPs) have the diffusivity index of 2 which are termed as "Ballistic BPs". Finally, we explore the distribution of diffusion index with the help of a simple simulation. The results suggest that the BPs are random walkers superposed by a systematic (background) velocity in which the magnitude of each component (and hence their ratio) depends on the time and spatial scales. We further discuss a simple sketch to explain the diffusivity of observed BPs while they migrate within a supergranule (i.e. internetwork areas) or close to the network regions.
 Publication:

SDO4: Dynamics and Energetics of the Coupled Solar Atmosphere. The Synergy Between StateoftheArt Observations and Numerical Simulations
 Pub Date:
 March 2012
 Bibcode:
 2012decs.confE..99J
 Keywords:

 SDO;
 SDO4;
 SDO 4;
 SDO Workshop;
 SDO4/IRIS/Hinode Workshop;
 Solar Dynamic Observatory