Solar Chromosphere

The chromosphere is a thin layer (approximately 2,000 km) above the photosphere. The plasma density decreases to about 10,000 times lower than the photosphere. Historically, chromospheric observations were often made in the Calcium II H & K and H-alpha spectral lines. The Calcium K index can be used as an indicator of solar activity.

NOAA NCEI has acquired these legacy data sets from multiple sources over many decades. The data presented here are provided, ‘as is,’ and in most cases the linked documentation is the entirety of available information. In some cases, older data may also be found in the Space Weather Legacy Print Publications.

Questions and comments may be directed to ncei.info@noaa.gov

H-alpha image of the sun (2014-09-10) from the Big Bear Solar Observatory

H-alpha image of the sun (2014-09-10) from the Big Bear Solar Observatory

Daily full disk calcium images are reduced to provide calcium plage positions and areas or summed to produce a daily Ca K index. Ca K active regions can be seen moving across the solar disk, above the white light sunspot regions, and higher in the solar atmosphere (chromosphere).

Calcium K Index

Index of the excess intensity in the Calcium K line observations.

Calcium Plage Areas

Digitizations of the Plage data published in the monthly Solar-Geophysical Data (SGD) bulletin.

Facular data

The K-line data presented here were obtained from photometric images taken at the San Fernando Observatory (SFO) with a 2.5 cm telescope and photometer known as the Cartesian Full Disk Telescope no. 1 (CFDT1). The system and the method of acquiring these data are described more fully in Chapman et al. (1992, 1996). The filter used in these observations has a FWHM of 1 nm centered on the Ca II K-line (393.4 nm).

San Fernando Observatory, 30 May 1988 - 31 Dec 1998

Calcium II K

The calcium datasets consist of full-disk images of the sun in Calcium (Ca) II K wavelength (393.4 nm). Ca II K imagery reveals magnetic structures of the sun from about 500 to 2000 km above the photosphere that are not evident in white light images. The Ca II K absorption lines are extremely sensitive to local magnetic fields wherein the presence of stronger magnetic fields results in less absorption (brighter features) than weaker fields (more absorption = darker features). Unique features of the chromosphere evident in Ca II K are plage, pores, supergranulation cells and the chromospheric network. Also observed in Ca II K are solar features typically discussed in the context of the photosphere, including sunspots and faculae.

H-alpha

These datasets consist of full-disk, daily photographs of the sun taken at the H-alpha wavelength. The collection includes a variety of H-alpha photographic datasets contributed by a number of national and private worldwide solar observatories. Solar observations in hydrogen-alpha (656.3 nm) reveal the structure and dynamics of chromospheric features including prominences, filaments, plage, filaments, and the chromospheric network.

Magnetograms

Ground-based observations of magnetically sensitive emission lines. The magnetograms indicate the strength of the magnetic field along the line of sight.

Prominences and Filaments

Prominences and filaments are two manifestations of the same phenomenon. Both prominences and filaments are features formed above the chromosphere by cool, dense gasses held in place by solar magnetic fields. Filaments are observed on the solar disk as dark structures as seen against the hotter chromosphere whereas prominences on the limb appear bright against the perspective of outer space. The scale sizes for prominences and filaments are typically many thousands kilometers. Solar observers typically view prominences and filaments in Hydrogen alpha (656.3 nm). Filaments are sometimes referred to as floccule (plural of flocculus).

Prominences and filaments can rapidly form over a period of a day, but then typically persist for several weeks and, in some cases, several months. At breakup, the plasma within these previously stable structures may be explosively released into space in the form of a coronal mass ejection (CME). Space weather operators have and continue to monitor the location and character of prominences and filaments as potential precursors to near-earth geomagnetic activity.

Prominences

This dataset consists of a limited number of drawings of solar prominences provided from the solar observatories located at Lomnicky and Wendelstein. The Lomnicky Stit Observatory (49o 11’ 45” N; 20o 12’ 46” E; 2,632 m) is located atop the Lomnicky stit mountain in the High Tatras mountains of Slovakia near the border of Poland. The Lomnicky Stit Observatory is maintained by the Astronomical Institute of the Slovak Academy of Science. The Wendelstein Observatory (47o 42’ N, 12o 00’ E; 1,838 m) is situated on the summit of Mount Wendelstein, a prominent mountain located in the bavarian Alpes. It is operated by the University Observatory of the University of Munich. The Kanzelhohe Observatory (46o 40’ 40” E; 13o 54’ 09” E; 1526 m) is located in Austria and is affiliated with the Institute of Geophysics, Astrophysics and Meteorology at the University of Graz.

Filaments

This dataset consists of listings from observations of solar features. The Carte Synoptiques is a compendium of reduced solar observations on the behavior of filaments which were first provided by Lucien d’Azambuja in 1920 as the “Carte Synoptique de la Chromosphere Solaire et Catalogue des Filaments de la Couche Superieure” covering the time period March 1919 to January 1920. The listings included here for the Carte Synoptiques have been extended through 1989. Other tables and listings included here include Limb-disk features (1957-2011), listings of solar filament disappearances (1964-1980), and the SGD tables. Also included are the Solar Disk and Limb Activity Summaries (DALAS) files (2010-2012) from the USAF Solar Observing Optical Network (SOON).

About

The McIntosh Archive (McA) consists of a set of hand-drawn solar Carrington maps created by Patrick McIntosh from 1964 to 2009. McIntosh used mainly H-alpha (Hα), He-I 10830Å and photospheric magnetic measurements from both ground-based and NASA satellite observations.

He traced polarity inversion lines (PILs), filaments, sunspots and plage, and later, coronal holes over a period of about 45 years. This has yielded a unique record of synoptic maps of features associated with the large scale solar magnetic field over four complete solar cycles. The NCAR High Altitude Observatory (HAO) undertook a project to digitize and update this important dataset.

The McA now consists of the preserved original data and electronic products produced by scanning and digitally processing the maps into a consistent, machine-readable format. The maps are preserved in three formats: (1) Level0 GIF images which are direct scans of the original hand-drawn McIntosh maps; (2) Level1 GIF images which have been cropped, reoriented and scaled for consistency; (3) Level3 FITS format files and associated GIF images characterize the fully processed maps. More background on this dataset is available in this document and at the HAO page.

Data and Documentation

Example of an original, hand-drawn McIntosh Archive (McA) synoptic solar map -- vertical axis is solar latitude (from South to North pole) and horizontal axis is solar longitude (representing one solar Carrington rotation of approximately 27 days)