太阳辐照的观测研究进展

太阳总辐照是指在地球大气层顶接收到的太阳总辐射照度,也叫"太阳常数",但它实际上并非常数。太阳总辐照随波长的分布即为太阳分光辐照。太阳辐照变化的研究,对理解太阳表面及内部活动的物理过程、机制,研究地球大气、日地关系,解决人类面临的全球气候变暖的挑战等,都具有重要意义。首先简单介绍了太阳辐照,回顾了太阳辐照的空间观测;接着介绍了观测数据的并合,以及对合成数据的一些研究;然后讨论了太阳辐照变化的原因,简述了太阳总辐照的重构及其在气候研究上的一些应用,并进行必要的评论;最后对未来的研究方向提出了一些看法。

Progress in the Measurement and Study of Solar Irradiance

Total solar irradiance（TSI） is the total amount of solar electromagnetic energy irradiated from the Sun over the entire spectrum at the top of the Earth’s atmosphere per unit area and per unit time.The spectrally distributed total solar irradiance is the Spectral Solar Irradiance（SSI）.Solar irradiance input is the driving term in the Earth’s energy budget,and its variations are reckoned to be the prime solar factors exerting influence on the Earth’s climate.The absorbtion,scattering,reflection of the solar energy by the Earth’s atmosphere,clouds,or surface depend greatly on wavelength,and light of different wavelength comes from different regions of the sun’s atmosphere.There are two main variability components which affect the energy received by the Earth related to the Sun.The first is due to changes in the orbital parameters of the Earth’s position relative to the Sun induced by the other planets,and the second component is due to variability within the Sun itself.Since the first can be predicted precisely and it varies rather slow,we only discuss the second component here,i.e.,solar irradiance.Due to the low precision of the ground-based instruments,total solar irradiance was believed to be constant before it was measured with space radiometers started in 1978,and it was consequently know as the "solar constant".But now we know that besides modulated by the 11-year solar cycle,it varies at all time scales at which it has been measured,i.e.,minutes to decades,and most probably,on longer time scales as well. The variability of solar irradiance has important implication for our understanding of solar internal structure,solar activities,global changes in the Earth’s climate system,and the solarterrestrial relationship.Thus,accompanied with more and more data from space-borne satellites during the recent three decades,lots of work has been done.It is believed that Irradiance variability on timescales from minutes to hours is mainly caused by convection.Short-term changes of total solar irradiance on timescales of few days to weeks are dominated by magnetic structures. Over the solar cycle,variations of 0.1%is believed to come mainly from the combination of the sunspots blocking and the intensification due to bright faculae,plages,and network elements. Some indexes seems to have certain relationship with the variations of solar irradiance,for example sunspot number,Mg II index,faculae area,F10.7 flux index,solar modulation of cosmogenic isotopes such as ¹⁴C and ¹⁰B and other solar related records.Based on this knowledge as well as the measurements of solar surface magnetic field,some models have been developed to reconstruct both total and spectral solar irradiance.Some of them are very successful and can account for most of the variance in the observed irradiance time series.There are still some problems with the three commonly used composite data,because significant uncertainties remain related to the calibration of the instruments and their degradation over time,and this uncertainty is a serious problem underlying current solar-climate research. In Sect.2 the total and spectral solar irradiance measurements are reviewed.Sect.3 describes a statistical analysis of one of the TSI composite,and discuss the trend of TSI during the recent two solar minimum.Sect.4 summaries explanations why solar irradiance varies.Sect.5 describes reconstructions of solar irradiance and the implication to climate change.Finally,Sect.6 points out some directions of future development.