Summary: Thermal ion density and composition measurements made at 840 km altitude by the SSIES instruments on DMSP spacecraft which are in polar orbit.
The ion composition at the 848 km altitude has been measured by the SSIES instruments on spacecraft of the Defense Meteorological Satellite Program (DMSP) from July to Nov 1987 and from Dec 1990 to present. The ion density has been measured from July 1987 to present. At and near the maximum of the solar cycle, as measured by the 10.7 cm solar flux, the ionosphere at 848 km altitude is composed of > 50% O+ (singly charged oxygen) ions at all local times and latitudes and > 95% O+ ions at almost all local times and latitudes. This indicates that the transition altitude from an ionosphere dominated by O+ to one dominated by light ions is >> 840 km. In the transition from sunspot maximum to sunspot minimum, the flux of 10.7 cm solar flux (which is a proxy for the EUV flux) decreases. The ratio of H+ and/or He+ to O+ increases in the mid-latitude, winter, night time ionosphere. This indicates that the O+ to light ion transition altitude is only slightly higher than 840 km in these locations. When sunspot minimum conditions are present, the O+ abundance is equal to or less than the H+ and/or He+ abundance for the mid-latitude ionosphere from fall to winter to spring. This effect is much more prominent in the Southern Hemisphere where the O+ abundance is often less than 0.1% of the light ion abundance. This indicates that the O+ transition altitude is less than 848 km altitude and probably less than 600 km altitude for these conditions.
Point of Contact: Kevin Martin, Boston College Kevin.Martin@bc.edu) - Summaries of the data or data for a specific period of time are available upon request. Please include an explanation of what the data will be used for in your request.
FORMAT OF GRAPHICAL DATA PRESENTATION
The data are presented in a series of color contour plots. The x-axis is the year and fraction of a year. The y-axis is the Corrected Geomagnetic Latitude (CGM) for the sub-satellite point from 60° S to 60° N. The color is used to represent the third axis. Some of the plots represent Log10(Total Ion Density in units of ions/cm^3) and other plots represent the difference between Log10(Total Ion Density in units of ions/cm^3) and Log10(Density of the O+ ions).
The following images show 27 day running averages of the data. (Click on the thumbnail images to see the actual images of the data.)
| Total Ion Density Observed in dawn/morning sector by: | Ion Composition Observed in dawn/morning sector by: |
| F8 from Jul 1987 to Jul 1994 near 6a.m. L. T. | |
| F11, F13 & F17 from Jan 1992 to Dec 2009 near 5:30 a.m. L. T. | F11, 13 & F17 from Jan 1992 to Dec 2009 near 5:30 a.m. L. T. |
| F9 from 1987 to 1992 near 10:30 a.m. L. T | |
| F10, F12, F14 & F15 from Jan 1991 to Dec 2009 near 9 a.m. L. T. | F10, F12, F14 & F15 from Jan 1991 to Dec 2009 near 9 a.m. local time |
| Total Ion Density Observed in dusk/evening sector by: | Ion Composition Observed in dusk/evening sector by: |
| F8 from Jul 1987 to Jul 1994 near 6 p.m. L. T. | |
| F11, F17 & F17 from Jan 1992 to Dec 2009 near 5:30 p.m. L. T. | F11, F13 & F17 from Jan 1992 to Dec 2009 near 5:30 p.m. L. T. |
| F9 from 1987 to 1992 near 10:30 p.m. L. T | |
| F10, F12, F14 & F15 from Jan 1991 to Dec 2009 near 9 p.m. L. T. | F10, F12, F14 & F15 from Jan 1991 to Dec 2009 near 9 p.m. local time |
The following images represent one day averages of the data for the period 1 July 2009 to 31 December 2010. (Click on the thumbnail images to see the actual images of the data.)
| F15 | F16 | F17 | F18 | |
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| Ion Composition (a.m.) | |
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| Ion Composition (p.m.) | |
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| Electron Temperature (am) | |
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| Electron Temperature (pm) | |
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The data recording system on F13 died 18 November 2009.
Current Posting: 06 January 2011
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