mi008.lean02 Posted: 17-Jul-95 Updated: 08-Apr-96 Events specified: N/A
Judith Lean (NRL), David Siskind (NRL), John Mariska (NRL), Harry Warren (NRL) and Loren Acton (MSU)
Motivation: The Yohkoh SXT has recorded the soft x-ray flux from the solar disk during the descending phase of solar cycle 22. Concurrent with these measurements, the Upper Atmosphere Research Satellite (UARS) has monitored the concentrations of NO in the Earth's upper atmosphere. Previous studies by Siskind et al. in solar cycle 21 identified a correlation between the variable solar Lyman alpha flux and the NO densities measured by the Solar Mesosphere Explorer, but noted that the geophysically-relevant solar fluxes were not Lyman alpha, but rather the soft X-rays and Lyman beta, neither of which were available during solar cycle 21.
Approach: The goal is to determine the response of terrestrial NO to variable solar flux inputs during solar cycle 22, focusing on the three years (1992, 1993 and 1994) of the descending phase of the cycle. This period is sufficiently long to cover both rotational and solar cycle modulations. Initially, correlation analyses will be used to identify common variance in both the solar and terrestrial time series. Additional solar times series will be generated by using parts of the SXT image histograms to simulate solar flux variations at other wavelengths. The solar forcing will be input to NRL's middle-atmosphere coupled photochemical-dynamical models. Comparison of modelled and measured NO variability at different altitudes and latitudes should help to clarify the extent of solar forcing of NO, and of the resultant impact on atmospheric ozone.
Data: Simultaneous solar soft X-ray images from the Yohkoh SXT, Lyman alpha data from the UARS (as a proxy for Lyman beta emission) and NO concentrations measured by the HALOE on UARS.
Related topics: mi005: Application of SXT fluxes to photochemical model of Earth's atmosphere
Update 08-Apr-96
Comparisons of the UARS HALOE NO densitites with UARS solar H Lyman alpha and Yohkoh SXT fluxes are being used to investigate the physical origins of the observed solar cycle variation apparent in the NO densities, with the goal of distinguishing between the soft X-ray and longer wavelength H Lyman beta contributions. Preferable to the broad band soft X-ray flux for modelling the forcing of NO by solar variability is the proper specification of the solar soft X-ray spectral irradiance (see Siskind et al., JGR, 100, 19687, 1995). Work to develop this spectrum is in progress jointly with TBB topic qs066, guided by the needs for modelling atmospheric NO.
Preliminary results presented at the Fall AGU meeting:
D. Siskind et al., Long term variation of nitric oxide in the middle and upper atmosphere, Abstract SA42B-2, Eos Fall 1995 AGU Meeting, page F445.