Figure 1. Clockwise from top left: the intensity, velocity, degree of linear polarization, line-of-sight magnetic field, field azimuth and line-width as observed by the CoMP instrument on 4/21/05.
Figure 2. This figure shows the sensitivity of the Stokes parameters in the Fe XIII line at 1074.7 nm to the presence and strength of an axisymmetric equatorial current sheet in the Sun's corona. These synthetic images have 4x4 arcsecond resolution. Panel (a): Magnitude (image density from 0 to 5 erg cm-2 s-1 sr-1) and magnitude and direction of linear polarization P (short lines) computed for a relatively strong current sheet with sufficient magnetic free energy to launch a CME [33]. The solid lines are magnetic field lines. Panel (b) Stokes V/I (relative circular polarization between ±10-3) for the same case as seen from the Earth with the Sun's S. pole inclined towards us by 7 degrees. Dashed lines show a global dipolar magnetic field which has the same radial magnetic field at the surface as the current carrying case. Panels (c) and (d) show the same calculations for a weaker current sheet with insufficient energy for CME launch. Note the very different polarization signatures of the two cases.
Priority 1: Exploring Atmospheric, Earth System, and Solar Processees, Variability and Change
Coronal Magnetometry (CoMP and COSMO)
Background
Space weather can cause significant disruptions to power grids, high frequency communications, and GPS systems on Earth and pose significant hazards to airplanes and to astronauts traveling in space. Driven by society's need to understand the origins of space weather and minimize potential disruptions, NCAR scientists, along with colleagues at the University of Hawaii and the University of Michigan, plan to build the Coronal Solar Magnetism Observatory (COSMO) to anticipate these disruptions.
The term space weather is a collective reference to phenomena that originate in our Sun and are responsible for driving the space environment and its evolution at Earth. NCAR scientists study the role of Sun's coronal magnetic field in causing explosive events that eject plasma and fields into space and produce large perturbations in solar radiation, most obvious in bursts of radio, EUV, X-ray, and gamma-ray emissions. These particulate, magnetic, and radiative emissions can lead to the disruptive events on Earth.
The significance of the coronal magnetic field has been known for decades, yet until recently, magnetic fields in the corona have been extremely difficult to measure under typical conditions. The COSMO facility will remedy this situation by obtaining routine synoptic observations of coronal magnetic fields with a 1-meter class coronagraph and associated instrumentation.
Progress
The concepts underlying COSMO have been developed over the past four years through the support of NCAR's Strategic Initiative on Coronal Magnetism. This has allowed the parallel development of theoretical and instrumental tools with which to advance the state of observation and interpretation of coronal magnetism.
Instrument development efforts have concentrated on the design and construction of a prototype instrument capable of inferring the properties of coronal magnetic fields through the observation of the polarization of infrared forbidden coronal emission lines. This instrument is called the Coronal Multi-channel Polarimeter (CoMP). This instrument has started taking exciting observations at the 20-cm aperture coronagraph operated by the National Solar Observatory at Sacramento Peak, New Mexico; an example of the observations is shown in Figure 1.
To prepare for the exploitation of these new observations, NCAR has started developing tools and techniques for comparing forward models of coronal magnetic fields with anticipated observations. Figure 2 shows a simulation of an axisymmetric equatorial current sheet embedded in the Sun's corona as it would be observed by the Fe XIII emission line at 1074.7 nm.
The COSMO team held a workshop on August 22-23, 2006 to define the scientific requirements of the COSMO facility.
Plans
The major activity for COSMO in FY07 will be the submission of a proposal to the NSF/ATM Mid-range Infrastructure account. Engineering studies are currently underway to develop designs for the COSMO coronagraph and associated instrumentation which will form the basis for estimates of cost and schedule. The team will also evaluate the sky conditions at two candidate sites in Hawaii. The CoMP instrument will continue to take observations.
For further detail, please read the full project report linked below.