Estimates of solar variability using the solar backscatter ultraviolet (SBUV) 2 Mg II index from the NOAA 9 satellite

Abstract

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

A composite Mg II index spanning from 1978 to 2003

“…The Mg II coreto-wing ratio has been found to be a better driver than F10.7 for thermospheric models that calculate satellite drag [Thuillier and Bruinsma, 2001;Rhoden et al, 2000] and has been incorporated into empirical spectral models of the solar EUV [Tobiska et al, 2000]. The Mg II index has also been shown to be a good proxy for solar UV irradiances [Heath and Schlesinger, 1986;Donnelly, 1988] especially near 205 nm [Cebula et al, 1992]. The Mg II index has been used as a proxy for the solar driver in studies of stratospheric ozone and temperatures [e.g., Hood and Zhou, 1998] and the Mg II core-to-wing ratio has been used in models of solar UV irradiance as well [Pap et al, 1996;Lean et al, 1997Lean et al, , 2001.…”

“…The NOAA 11 data were available from 1989 to 1992. As mentioned above, alternate methods of calculating the Mg II ratio using different grating steps and different electronic ranges is discussed by Cebula et al [1992] and these time series will also be considered here. They are referred to as the NOAA 9DC (for DeLand and Cebula) mode and NOAA 11DC data sets.…”

Comparison of Magnesium II core-to-wing ratio observations during solar minimum 23/24

“…A fourth instrument on the NOAA 19 satellite went into operation part way through solar minimum, but data from this instrument have not yet been made available to the public, so we do not include it in our analysis. MgII measurements from the SBUV/2 series began with NOAA 9, and were first described in Cebula et al (1992). The SBUV/2 instrument can measure the solar spectrum in either a ''sweep'' mode where the detector is read while the grating scans in a continuous fashion, or with a ''discrete'' mode where the grating pauses at pre-defined angles and the detector is only sampled during these pauses.…”

“…The GOME-2 aboard Metop A (Callies et al 2000) was launched by EUMETSAT in late 2006. Near 280 nm, the spectral resolution is about 0.3 nm which means that the emission cores are barely visible.…”

Solar Influences on Global Change

“…Various instruments have been launched on rockets, satellites, and the Space Shuttle during the past 20 years (about two solar activity cycles) with the goal of acquiring knowledge of the Sun's ultraviolet spectral (Heath and Schlesinger, 1986) and subsequently on a series of National Oceanic and Atmospheric Administration (NOAA) satellites (Donnelly, 1988;Cebula et al, 1992). Coincident with these observations from 1982 to 1989 are measurements by the solar spectrometer on board the Solar Mesosphere Explorer (SME) (Rottman, 1988;London and Rottman, 1990).…”