Solar irradiances and radiances of UV and EUV lines during the minimum of sunspot activity in 1996

Abstract

Full Sun observations in UV and EUV emission lines were performed by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (Solar and Heliospheric Observatory) in 1996. The radiometric pre-flight calibration of SUMER is traceable to a primary radiometric source standard - the electron storage ring BESSY. Based on this calibration, the irradiance values at SOHO and at 1 AU have been obtained for the lines He i (lambda 584.33 { Angstroms}), O v (lambda 629.74 { Angstroms}), Ne viii (lambda 770.41 { Angstroms}), S v (lambda 786.47 { Angstroms}), O iv (lambda 787.72 { Angstroms}), S vi (lambda lambda 933.39, 944.52 { Angstroms}), H i Ly epsilon (lambda 937.80 { Angstroms}), C iii (lambda 977.04 { Angstroms}), N v (lambda 1238.81 { Angstroms}), Si i (lambda 1256.52 { Angstroms}), and C iv (lambda 1548.20 { Angstroms}). The spatially resolved measurements allowed good estimates to be made of the active region contributions to the irradiance of the quiet Sun. The centre-to-limb radiance variations of these lines have also been obtained from these measurements. For quiet solar conditions, a radiance spectrum was determined for wavelengths from 800 { Angstroms} to 1500 { Angstroms} near the centre of the solar disk.