Five years of 160-to 400-nm solar flux measurements by the Solar Backscattered Ultraviolet experiment on Nimbus 7 have been analyzed. The flux in the center of strong lines and at shorter wavelengths varies with periods that correspond to modulation by the rotation of active regions. The modulation is greater at the centers of strong lines and at shorter wavelengths, corresponding to radiation that originates at higher levels in the solar atmosphere. The ratio of the irradiance in the core of the Mg 280-nm line to the irradiance at neighboring wavelengths is used as an index of solar variation. A scaling factor is derived by comparing rotational modulation at other wavelengths with the rotational modulation of the index. The scaled Mg II 280-nm strength successfully represents both rotational and long-term variations across the AI absorption edge near 210 nm. This ratio can therefore provide an empirical representation of long-term ultraviolet solar variability. Scaling factors are derived and changes estimated at several ultraviolet wavelengths. At 204 nm, in the wavelength region that drives atmospheric photochemistry, the solar irradiance drops about 4% from its average level for 1979-1980 to late 1983. The total estimated range of variation of the 27-day averaged (one rotation) 204-nm irradiance is 6%, over the 5 years of measurements. A least squares fit shows that over the 5 years, 27-day averages of 10.7-cm radio flux and of the Mg II index follow a linear relation. The radio flux can therefore be used to estimate changes in the solar ultraviolet for times before the launch of Nimbus 7. 1. INTRODUCTION Solar ultraviolet radiation at wavelengths from 170 to 300 nm is a driver of the photochemistry of the middle atmosphere. In recent years, evidence has been accumulating that variations in solar radiation at these wavelengths could lead to changes in the physical processes and chemical balance of the middle atmosphere [-Brasseur and Solomon, 1984] and in the overall global climate [National Academy of Sciences, 1982]. In general, two techniques have been used to measure changes in the ultraviolet solar flux: continuous monitoring by a single space-borne instrument and comparison of measurements at different times from balloon and rocket platforms. However, instrument calibration problems complicate both techniques. For continuous monitoring by a single instrument the instrument characteristics may change with time [e.g., Heath, 1980]. Changes in the signal resulting from changes in the instrument must then be separated from those arising from actual variations in the sun. For repeated measurements on separate flights the instruments must be intercalibrated. Mount and Rottman [1983a, b] have measured the solar spectrum from 180 to 310 nm with instruments aboard several rocket flights, but their quoted errors are on the order of 10%, larger than the anticipated changes in solar irradiance, especially at the longer wavelengths. While changes in instrument sensitivity complicate determination of long-term solar ...
Abstract. The Flexible Image Transport System -FITS -has been in use in the astronomical community for over two decades. A newly updated version of the standard has recently been approved by the International Astronomical Union FITS Working Group. This new version of the standard appears here in its entirety. As a preface we briefly describe the process by which the standard evolves and revisions are approved, and note two minor changes to NOST 100-2.0 which were adopted by the IAU FWG.
The Mg II core to wing index was first developed for the Nimbus 7 solar backscatter ultraviolet (SBUV) instrument as an indicator of solar variability on both solar 27-day rotational and solar cycle time scales. This work extends the Mg II index to the NOAA 9 SBUV 2 instrument and shows that the variations in absolute value between Mg II index data sets caused by interinstrument differences do not affect the ability to track temporal variations. The NOAA 9 Mg II index accurately represents solar rotational modulation but contains more day to day noise than the Nimbus 7 Mg II index. Solar variability at other UV wavelengths is estimated by deriving scale factors between the Mg II index rotational variations and at those selected wavelengths. Because radiation near the Mg II line core originates at levels in the solar atmosphere comparable to those giving rise to the continuum near 200 nm, the Mg II index accurately tracks the flux in this photochemically important region. Based on the 27-day average of the NOAA 9 Mg II index and the NOAA 9 scale factors, the solar irradiance change from solar minimum in September 1986 to the beginning of the maximum of solar cycle 22 in 1989 is estimated to be 8.6% at 205 nm, 3.5% at 250 nm, and less than 1% beyond 300 nm. 11,613
Backscattered ultraviolet (BUV) data from the Nimbus‐4 spacecraft for the period 1970–1977 have been recently processed to final form. This paper is based upon an analysis of all the total ozone data available in the 7‐year data set. The seasonal and interannual variations of total ozone over the globe are examined, using daily zonal means of 10° latitude bands and a time latitude cross section. A harmonic analysis was performed on the daily zonal means, and the amplitude, phase, and percentage of variance were computed for the annual, semiannual, and higher harmonics for several years and for individual years. Many of the features observed earlier for the period 1970–1972, such as the asymmetry of the annual wave in the two hemispheres, persist over the longer data period. Variations with regular periods shorter than a few months were sought, but none were evident systematically throughout the latitude zones. Examination of the zonal mean data with the mean annual wave removed revealed a clear quasibiennial oscillation (QBO) strongest in the tropics, where it is comparable to the annual wave, persisting to mid‐latitudes in both hemispheres with some evidence of its existence at high latitudes. An estimation of the QBO period, using a superposition analysis (for no more than three cycles) for each latitude zone, revealed a decreasing period with latitude in both hemispheres. The maximum period of 27 months occurs in the tropics while the minimum in the northern hemisphere is about 20 months. This result suggests that the observed QBO in total ozone at high and low latitudes may not be directly related. This is of particular significance to studies of ozone trends since the result indicates interannual variations are latitude dependent.
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