Metadata Catalogue

Hourly Geomagnetic Variations Database
The National Geophysical Data Center maintains an active database of 1 min geomagnetic variations to further the understanding of Earth magnetism and the Sun-Earth environment. To measure the Earth's magnetism in any place, we must measure the direction and intensity of the field. The parameters describing the direction of the magnetic field are declination (D), inclination (I). D and I are measured in units of degrees. The intensity of the total field (F) is described by the horizontal component (H), vertical component (Z), and the north (X) and east (Y) components of the horizontal intensity. These components may be measured in units of Oersted (1 oersted=1gauss) but are generally reported in nanoTesla (1nT * 100,000 = 1 0ersted). The Earth's magnetic field intensity is roughly between 25,000 - 65,000 nT (.25 - .65 oersted). Magnetic declination is the angle between magnetic north and true north. D is considered positive when the angle measured is east of true north and negative when west. Magnetic inclination is the angle between the horizontal plane and the total field vector. The geomagnetic field measured at any point on the Earth's surface is a combination of several magnetic fields generated by various sources. These fields are superimposed on and interact with each other. More than 90% of the field measured is generated INTERNAL to the planet in the Earth's outer core. This portion of the geomagnetic field is often refered to as the Main Field. The Main Field varies slowly in time and can be described by Mathematical Models such as the International Geomagnetic Reference Field (IGRF) and World Magnetic Model (WMM). The Main Field creates a cavity in interplanetary space called the magnetosphere, where the Earth's magnetic field dominates in the magnetic field of the solar wind. The magnetosphere is shaped somewhat like a comet in response to the dynamic pressure of the solar wind. It is compressed on the side toward the sun to about 10 Earth radii and is extended tail-like on the side away from the sun to more than 100 Earth radii. The magnetosphere deflects the flow of most solar wind particles around the Earth, while the geomagnetic field lines guide charged particle motion within the magnetosphere. The differential flow of ions and electrons inside the magnetosphere and in the ionosphere form current systems, which cause variations in the intensity of the Earth's magnetic field. These EXTERNAL currents in the ionized upper atmosphere and magnetosphere vary on a much shorter time scale than the INTERNAL Main Field and may create magnetic fields as large as 10% of the Main Field. Other important sources are the fields arising from electrical currents flowing in the ionized upper atmosphere, and the fields induced by currents flowing within the Earth's crust. The Main field component varies slowly in time and can be grossly described as that of a bar magnet with north and south poles deep inside the Earth and magnetic field lines that extend well out into space. The Earth's magnetic field varies both in space and time. Historically, magnetic observatories were established to monitor the secular change of the Earth's magnetic field, and this remains one of their most important functions. This generally involves absolute measurements sufficient in number to monitor instrumental drift and to produce annual means. Over 70 countries operate more than 200 observatories worldwide. The magnetic observatory mean data are crucial to the studies of secular change, investigations into the Earth's interior, and to global modeling efforts. One minute geomagnetic field variations are archived in the database since March 1901.

Monthly Geomagnetic Variations Database
The National Geophysical Data Center maintains an active database of 1 min geomagnetic variations to further the understanding of Earth magnetism and the Sun-Earth environment. To measure the Earth's magnetism in any place, we must measure the direction and intensity of the field. The parameters describing the direction of the magnetic field are declination (D), inclination (I). D and I are measured in units of degrees. The intensity of the total field (F) is described by the horizontal component (H), vertical component (Z), and the north (X) and east (Y) components of the horizontal intensity. These components may be measured in units of Oersted (1 oersted=1gauss) but are generally reported in nanoTesla (1nT * 100,000 = 1 0ersted). The Earth's magnetic field intensity is roughly between 25,000 - 65,000 nT (.25 - .65 oersted). Magnetic declination is the angle between magnetic north and true north. D is considered positive when the angle measured is east of true north and negative when west. Magnetic inclination is the angle between the horizontal plane and the total field vector. The geomagnetic field measured at any point on the Earth's surface is a combination of several magnetic fields generated by various sources. These fields are superimposed on and interact with each other. More than 90% of the field measured is generated INTERNAL to the planet in the Earth's outer core. This portion of the geomagnetic field is often refered to as the Main Field. The Main Field varies slowly in time and can be described by Mathematical Models such as the International Geomagnetic Reference Field (IGRF) and World Magnetic Model (WMM). The Main Field creates a cavity in interplanetary space called the magnetosphere, where the Earth's magnetic field dominates in the magnetic field of the solar wind. The magnetosphere is shaped somewhat like a comet in response to the dynamic pressure of the solar wind. It is compressed on the side toward the sun to about 10 Earth radii and is extended tail-like on the side away from the sun to more than 100 Earth radii. The magnetosphere deflects the flow of most solar wind particles around the Earth, while the geomagnetic field lines guide charged particle motion within the magnetosphere. The differential flow of ions and electrons inside the magnetosphere and in the ionosphere form current systems, which cause variations in the intensity of the Earth's magnetic field. These EXTERNAL currents in the ionized upper atmosphere and magnetosphere vary on a much shorter time scale than the INTERNAL Main Field and may create magnetic fields as large as 10% of the Main Field. Other important sources are the fields arising from electrical currents flowing in the ionized upper atmosphere, and the fields induced by currents flowing within the Earth's crust. The Main field component varies slowly in time and can be grossly described as that of a bar magnet with north and south poles deep inside the Earth and magnetic field lines that extend well out into space. The Earth's magnetic field varies both in space and time. Historically, magnetic observatories were established to monitor the secular change of the Earth's magnetic field, and this remains one of their most important functions. This generally involves absolute measurements sufficient in number to monitor instrumental drift and to produce annual means. Over 70 countries operate more than 200 observatories worldwide. The magnetic observatory mean data are crucial to the studies of secular change, investigations into the Earth's interior, and to global modeling efforts. One minute geomagnetic field variations are archived in the database since January 1813.

Ionospheric Database
The ionosphere is that part of the upper atmosphere where free electrons occur in sufficient density to have an appreciable influence on the propagation of radio frequency electromagnetic waves. This ionization depends primarily on the Sun and its activity. Ionospheric structures and peak densities in the ionosphere vary greatly with time (sunspot cycle, seasonally, and diurnally), with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions), and with certain solar-related ionospheric disturbances. The major part of the ionization is produced by solar X-ray andultraviolet radiation and by corpuscular radiation from the Sun. The most noticeable effect is seen as the Earth rotates with respect to the Sun; ionization increases in the sunlit atmosphere and decreases on the shadowed side. Although the Sun is the largest contributor toward the ionization, cosmic rays make a small contribution. Any atmospheric disturbance effects the distribution of the ionization. The ionosphere is a dynamic system controlled by many parameters including acoustic motions of the atmosphere, electromagnetic emissions, and variations in the geomagnetic field. Because of its extreme sensitivity to atmospheric changes, the ionosphere is a very sensitive monitor of atmospheric events. In some circles it is thought that there is persuasive evidence of an ionospheric precursor to large earthquakes that can be used a predictor. Besides the obvious acoustic waves generated before and during an earthquake, a part of the preparation process of large earthquakes is the generation of electromagnetic emissions (EMEs). These EMEs have been detected in the ionosphere up to six days prior to a large earthquake, such as with the May 1960, Chilean 8.3 earthquake. The most accurate way of measuring the ionosphere is with a ground-based ionosonde, which records data as ionograms. Usually Ionograms are recorded with 15 min or 1 hr time step. The first ionograms in our database are dated by Jan, 1942.

Solar Cosmic Rays Database (4096 format)
Cosmic rays are energetic particles that are found in space and filter through our atmosphere. Cosmic rays have interested scientists for many different reasons. They come from all directions in space, and the origination of many of these cosmic rays is unknown. Cosmic rays were originally discovered because of the ionozation they produce in our atmosphere. Cosmic rays also have an extreme energy range of incident particles, which have allowed physicists to study aspects of their field that can not be studied in any other way. In the past, we have often referred to cosmic rays as "galactic cosmic rays", because we did not know where they originated. Now scientists have determined that the sun discharges a significant amount of these high-energy particles. "Solar cosmic rays" (cosmic rays from the sun) originate in the sun's chromosphere. Most solar cosmic ray events correlate relatively well with solar flares. Scientists have postulated that cosmic rays can affect the earth by causing changes in weather. Cosmic rays can cause clouds to form in the upper atmosphere, after the particles collide with other atmospheric particles in our troposphere. The process of a cosmic ray particle colliding with particles in our atmosphere and disintegrating into smaller pions, muons, and the like, is called a cosmic ray shower. These particles can be measured on the Earth's surface by neutron monitors. The cosmic ray data from neutron monitors, ionization chambers and muon telescopes are primarily hourly-value data held as tabulations on paper, or in digital format (currently 130 stations and over 100 Mbytes). Some of these data are regularly published in both tabular and graphical forms in Solar-Geophysical Data (http://www.ngdc.noaa.gov/stp/SOLAR/sgdintro.html)

Solar Cosmic Rays Database (general format)
Cosmic rays are energetic particles that are found in space and filter through our atmosphere. Cosmic rays have interested scientists for many different reasons. They come from all directions in space, and the origination of many of these cosmic rays is unknown. Cosmic rays were originally discovered because of the ionozation they produce in our atmosphere. Cosmic rays also have an extreme energy range of incident particles, which have allowed physicists to study aspects of their field that can not be studied in any other way. In the past, we have often referred to cosmic rays as "galactic cosmic rays", because we did not know where they originated. Now scientists have determined that the sun discharges a significant amount of these high-energy particles. "Solar cosmic rays" (cosmic rays from the sun) originate in the sun's chromosphere. Most solar cosmic ray events correlate relatively well with solar flares. Scientists have postulated that cosmic rays can affect the earth by causing changes in weather. Cosmic rays can cause clouds to form in the upper atmosphere, after the particles collide with other atmospheric particles in our troposphere. The process of a cosmic ray particle colliding with particles in our atmosphere and disintegrating into smaller pions, muons, and the like, is called a cosmic ray shower. These particles can be measured on the Earth's surface by neutron monitors. The cosmic ray data from neutron monitors, ionization chambers and muon telescopes are primarily hourly-value data held as tabulations on paper, or in digital format (currently 130 stations and over 100 Mbytes). Some of these data are regularly published in both tabular and graphical forms in Solar-Geophysical Data (http://www.ngdc.noaa.gov/stp/SOLAR/sgdintro.html)

Solar Cosmic Rays Database (preliminary)
Cosmic rays are energetic particles that are found in space and filter through our atmosphere. Cosmic rays have interested scientists for many different reasons. They come from all directions in space, and the origination of many of these cosmic rays is unknown. Cosmic rays were originally discovered because of the ionozation they produce in our atmosphere. Cosmic rays also have an extreme energy range of incident particles, which have allowed physicists to study aspects of their field that can not be studied in any other way. In the past, we have often referred to cosmic rays as "galactic cosmic rays", because we did not know where they originated. Now scientists have determined that the sun discharges a significant amount of these high-energy particles. "Solar cosmic rays" (cosmic rays from the sun) originate in the sun's chromosphere. Most solar cosmic ray events correlate relatively well with solar flares. Scientists have postulated that cosmic rays can affect the earth by causing changes in weather. Cosmic rays can cause clouds to form in the upper atmosphere, after the particles collide with other atmospheric particles in our troposphere. The process of a cosmic ray particle colliding with particles in our atmosphere and disintegrating into smaller pions, muons, and the like, is called a cosmic ray shower. These particles can be measured on the Earth's surface by neutron monitors. The cosmic ray data from neutron monitors, ionization chambers and muon telescopes are primarily hourly-value data held as tabulations on paper, or in digital format (currently 130 stations and over 100 Mbytes). Some of these data are regularly published in both tabular and graphical forms in Solar-Geophysical Data (http://www.ngdc.noaa.gov/stp/SOLAR/sgdintro.html)