Reconstruction of the solar spectral UV irradiance for nowcasting of the middle atmosphere state on the basis of LYRA measurements

T Egorova,E Rozanov,W Schmutz,J.-F Hochedez

doi:10.5194/acp-8-2965-2008

Abstract

Abstract. The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lyman-alpha (121.6 nm) and the Herzberg continuum (~200–220 nm wavelength range). Because the nowcasting of the neutral and ionic state of the middle atmosphere requires the solar irradiance for the wide spectral range (120–680 nm) we have developed the statistical tool for the reconstruction of the full spectrum from the LYRA measurements. The accuracy of the reconstructed irradiance has been evaluated with 1-D transient radiative-convective model with neutral and ion chemistry using the daily solar spectral irradiance measured with SUSIM and SOLSTICE instruments onboard UARS satellite. We compared the results of transient 1-year long model simulations for 2000 driven by the observed and reconstructed solar irradiance and showed that the reconstruction of the full spectrum using linear regression equation based on the solar irradiance in two LYRA channels can be successfully used for nowcasting of the middle atmosphere. We have also identified conditions when the proposed approach does not yield spectral reconstruction with sufficient accuracy.

Highlights

The nowcasting and short-term forecasting of the space weather driven by the different observational data gained recently a lot of attention, because the Solar activity variations are able to induce substantial changes in the Earth environment, which turn out to be important for the space operations (Wilkinson, 1994), radio-wave propagation, GPS functioning and many other aspects of the mankind activity (Jansen et al, 2000)
The LYRA instrument onboard ESA PROBA2 satellite will provide 6-hourly solar irradiance at the Lymanalpha (121.6 nm) and the Herzberg continuum (∼200– 220 nm wavelength range)
We compared the results of transient 1-year long model simulations for 2000 driven by the observed and reconstructed solar irradiance and showed that the reconstruction of the full spectrum using linear regression equation based on the solar irradiance in two LYRA channels can be successfully used for nowcasting of the middle atmosphere

Summary

Introduction

The nowcasting and short-term forecasting of the space weather driven by the different observational data gained recently a lot of attention, because the Solar activity variations are able to induce substantial changes in the Earth environment, which turn out to be important for the space operations (Wilkinson, 1994), radio-wave propagation, GPS functioning and many other aspects of the mankind activity LYRA will monitor the solar irradiation in four wavelength bands that are essential for the Sun-Earth connection: Lyman-alpha (115–125 nm), Herzberg (200– 220 nm), Zirconium (1–20 nm) and Aluminium (17–70 nm) including He II at 30.4 nm It will be the first space assessment of the pioneering UV detectors from the BOLD program (http://bold.oma.be), which make use of wideband-gap materials instead of silicon. The LYRA and PREMOS observations can be used as input data for global climate-chemistry-ionosphere models in order to evaluate the response of the terrestrial atmosphere to the solar UV irradiance variability These results are indispensable for space whether and global climate applications. Because we are interested mostly in the accuracy of the final product (i.e., state of the middle atmosphere) it is worthwhile to apply a goal-oriented approach and compare the temperature and species distributions simulated with a model driven by the reference and reconstructed solar UV irradiance.

Model description

Regression analysis

Accuracy evaluation

Findings

Conclusions