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Sondre Stromfjord Fabry-Perot


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The Sondre Stromfjord Fabry-Perot is operated by the University of Michigan with support from the National Science Foundation.

Data Description

The Sondre Stromfjord Fabry Perot interferometer, operated by the Space Physics Research Laboratory, Department of Atmospheric, Oceanic and Space Sciences of the University of Michigan is located at latitude 66.99N and longitude 50.95W. The invariant latitude is 74 degrees, the inclination of the magnetic field is 80 degrees and the declination of the field is -39 degrees (39 degrees to the west). Midnight local solar time at the site occurs at 03:24 UT, while midnight magnetic local time is 01:57 UT at the equinoxes. Magnetic midnight varies with season, being 15 minutes earlier at the winter solstice and 15 minutes later at the summer solstice compared to the equinox value.

Currently, the interferometer observes the line profiles of the forbidden emissions OI (557.7nm) and OI (630.0nm). Most of the data in the CEDAR Database are 630.0nm (code 7001), with additional 557.7nm (code 7002) data starting in 2002. The filter wheel was changed in 2002, resulting in brighter relative emissions.

The geophysical parameters obtained from the data reduction are the gas kinetic temperature of the emitting region from the natural width of the sky profile, the line of sight wind from the Doppler shift of the sky profile, and the surface brightness of the emission line. OI (630.0nm) nightglow emission is generally believed to issue from the altitude range 175 to 500 km, with the major contribution originating from a narrow height interval (a few scale heights thick) centered roughly one neutral scale height below the altitude of maximum electron density. Thus, the peak altitude of emission and the parameters of the F region are interdependent and it is difficult to assign a unique altitude to each ground based OI (630.0nm) interferometer measurement. If no other information is available, we generally ascribe 250 km as the altitude of emission.

Line of sight winds derived from the observed shift of the emission line from a zero reference position requires the determination of a zero wind. The reference zero wind is taken to be the average of an entire nights vertical wind data. Generally, the four cardinal directions are also sampled as well as the vertical. There is no exclusion of any data in the CEDAR Data Base, so cloudy night fits are also included. The cloud cover (code 440) measured by the Sondre Stromfjord meteorological station is given in octas of the sky covered. Values range from 0 (clear) to 9 (overcast). In general, temperatures and relative emissions are good for cloud cover values between 0 and 6, while winds are good for for cloud cover values between 0 and 3. When there is a lot of cloud cover, the horizontal winds become small, near zero.

Between roughly Aug-Dec, the cloud cover is 0-3 about 36% of the time, and between 0-6 about 57% of the time, where these estimates can vary by about +/-15%. The cloud cover is about 17% less between about Jan-May, where values of 0-3 occur about 52% of the time while values of 0-6 occur about 75% of the time between 1984 and 2004. When the cloud cover is 7-9 (about 43% of the time in Aug-Dec and about 25% of the time in Jan-May), then the horizontal winds appear to be close to zero and the temperatures may not be very good. Do not use the data without considering the effects of cloud cover!

Summary plots of the cloud cover, relative emission, neutral temperature and vertical wind are plotted with error bars for the vertical look direction. For look directions in opposite cardinal directions, horizontal winds are plotted without error bars. For periods where there are plots of the vertical wind, but not of the horizontal wind, then the look directions are not cardinal. This is the case for all of 1983, almost all of 1984, and part of 1987. The summary plots were redone to plot all observations including cloud cover in September 2004 for data before mid-1994.

References for the instrument and data processing procedures

Killeen et al., Appl. Opt. 23, 612 (1984)
McCormac et al., Planet. Space Sci. 35, 1255 (1987)
Meriwether et al., Opt. Eng. 22, 128 (1983)
Niciejewski et al., SPIE Proceedings, 1745, 165 (1992)

Summary Plots for Sondre Stromfjord Fabry-Perot

at 630.nm (red line ~250 km) and at 557.7nm (green line ~97 km) starting in 2002 ==

The cloud cover is in octas (eigths of the sky), and values from 0-3 have good winds, and 0-6 have good temperatures and emissions, while larger cloud cover values (overcast=9) tend to show small horizontal winds since the Doppler shift cannot be found. Do not use the data and ignore the cloud cover values!

1980's Summary Plots

1990's Summary Plots

2000's Summary Plots

-Revised 07 Sep 2004 by Barbara Emery