Mapping the magnetic field in the solar corona through magnetoseismology

Magnetoseismology,a technique of magnetic field diagnostics based on observations of magnetohydrodynamic(MHD)waves,has been widely used to estimate the field strengths of oscillating structures in the solar corona.However,previously magnetoseismology was mostly applied to occasionally occurring oscillation events,providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure.This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter(CoMP).Using several CoMP observations of the Fe xiii 1074.7 nm and 1079.8 nm spectral lines,we obtained maps of the plasma density and wave phase speed in the corona,which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky.We also examined distributions of the electron density and magnetic field strength,and compared their variations with height in the quiet Sun and active regions.Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

Solar ultraviolet bursts in a coordinated observation of IRIS,Hinode and SDO

Solar ultraviolet(UV) bursts are small-scale compact brightenings in transition region images. The spectral profiles of transition region lines in these bursts are significantly enhanced and broadened, often with chromospheric absorption lines such as Ni ii 1335.203 and 1393.330 A superimposed. We investigate the properties of several UV bursts using a coordinated observation of the Interface Region Imaging Spectrograph(IRIS), Solar Dynamics Observatory(SDO), and Hinode on February 7, 2015. We have identified 12 UV bursts, and 11 of them reveal small blueshifts of the Ni ii absorption lines. However, the Ni ii lines in one UV burst exhibit obvious redshifts of ~20 km s^-1, which appear to be related to the cold plasma downflows observed in the IRIS slit-jaw images. We also examine the three-dimensional magnetic field topology using a magnetohydrostatic model, and find that some UV bursts are associated with magnetic null points or bald patches. In addition, we find that these UV bursts reveal no obvious coronal signatures from the observations of the Atmospheric Imaging Assembly(AIA) on board SDO and the EUV Imaging Spectrometer(EIS) on board Hinode.

Generation of solar spicules and subsequent atmospheric heating

The temperature drops from^16 million Kelvin at the core of the Sun to 5700 K at the solar surface(photosphere).However,the temperature increases with height above the photosphere,reaching one million degrees or more in the solar corona.Due to this high temperature,the corona naturally expands to the interplanetary space,forming the solar wind.What causes the temperature increase in the corona is one of the biggest mysteries in astronomy.