Archive for category MDI
The most recent LASCO, EIT, COR1/2 and EUVI images are currently unavailable to Helioviewer Project browse clients. This is because the computer that converts the science data to JPEG 2000 images experienced a mechanical failure on Friday January 13th. We will replace the failed machine, and make an announcement via the blog concerning the resumption of the availability of images from LASCO, EIT, COR1/2 and EUVI. We are apologize for any inconvenience this may cause. Finally, images from AIA and HMI should be unaffected.
Today we are making available images from the Helioseismic Magnetic Imager (HMI), an instrument on board the Solar Dynamics Observatory. HMI is designed to study oscillations and the magnetic field at the solar surface, or photosphere. We are providing line-of-sight magnetograms and continuum images* based on HMI science data. A line-of-sight magnetogram measures the flux of magnetic field as seen along the line of sight from HMI to the Sun. A continuum image is formed by filtering portions of the visible light part of the spectrum.
The line-of-sight magnetograms shows blobs of dark emission, and blobs of brighter emission. These correspond to opposite polarity magnetic fields breaking through the Sun’s photosphere. The magnetic field is important as it is related to the activity seen in layers of the Sun’s atmosphere such as the corona (which is observed by AIA). The continuum images allow us to track the evolution of sunspots. These images are important as they allow us to better understand the dynamic nature of the solar atmosphere.
The primary goal of the Helioseismic and Magnetic Imager (HMI) investigation is to study the origin of solar variability and to characterize and understand the Sun’s interior and the various components of magnetic activity. HMI makes measurements of the motion of the solar photosphere to study solar oscillations and measurements of the polarization in a specific spectral line to study all three spatial components of the photospheric magnetic field. HMI produces data to determine the interior sources and mechanisms of solar variability and how the physical processes inside the Sun are related to surface magnetic field and activity. It also produces data to enable estimates of the coronal magnetic field for studies of variability in the extended solar atmosphere, which is where the Earth is. Solar variability that affects the Earth is called “space weather”. HMI observations will help establish the relationships between internal dynamics and magnetic activity. In turn this will lead to better understanding of solar variability and its effects.
For much more information on HMI, please visit http://hmi.stanford.edu/. For more information on SDO, please visit http://sdo.gsfc.nasa.gov.
* HMI is a successor to the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). The Helioviewer Project has MDI line-of-sight magnetogram and continuum images going back to early 1996.
Around 2010/10/29-30 the SOHO spacecraft changed flight operations so it is no longer constantly aligned with the rotation axis of the Sun. SOHO now points to ecliptic north, which makes an approximate seven degree angle with the equator of the Sun. SOHO will still flip 180 degrees in order to maintain optimal communication with the Earth, but the rotation will now flip the spacecraft relative to ecliptic north. The raw image data that SOHO takes therefore shows the new orientation. At the Helioviewer Project, we rotate the data so that solar north is towards the top of your screen and the rotation axis of the Sun is vertical (i.e., parallel to the left and right hand side of a rectangular screen). Our science data processing software – JP2Gen – now takes account of the new rotation of SOHO and rotates SOHO science data appropriately. This is done to maintain homogeneity with the existing images we already provide, and makes it easy to compare images from multiple telescopes.