Solar Radiation

The Sun’s illumination is the ultimate energy source for the Earth's biosphere, and the ultimate driving force for atmospheric, and oceanic circulations. The Sun is a variable star as one can see from sunspots recorded back to Galileo’s time in the early 1600s. Satellite observations over the past three decades show that the sunspot activity is associated with changes in solar output energy. The total solar irradiance (TSI), improperly called “solar constant” until a few years ago, has been found to change about 0.1% in an 11-year solar sunspot activity. The current most accurate TSI values from the Total Irradiance Monitor (TIM) on NASA’s Solar Radiation and Climate Experiment ( SORCE ) is 1360.8 ± 0.5 W/m2 during the 2008 solar minimum as compared to previous estimates of 1365.4 ± 1.3 W/m2 established in the 1990s.

Sun-climate research is an interdisciplinary field focusing on understanding solar variability and climate response on different time scales, and is critical for understanding and isolating human-induced climate change. Accurate and continuous observation of the TSI is required to monitor and understand the causes of the Earth’s radiation (im)balance, over time. Still, knowledge of TSI alone is not sufficient for understanding the physical processes in the Earth’s ocean and atmosphere system. Recent studies have shown that even for identical TSI variations, atmospheric and ocean temperatures responsd differently depending on the details of Spectral Solar Irradiance (SSI) variations. SSI observations from the Spectral Irradiance Monitor (SIM) instrument on SORCE revealed variations of SSI in the descending phase of solar cycle 23 that were not anticipated by some semi-empirical models. These groundbreaking continuous SIM observations of near full solar spectrum SSI are unprecedented in the history of Sun observations and have helped scientists to understand the important role on climate of SSI variations. Improved TIM and SIM instruments on an upcoming Total Solar and Spectral Irradiance Sensor (TSIS) mission, expected to launch in 2016, will provide even more accurate Sun observations for detecting yet unresolved solar variations, and for further strengthening our understanding the role solar variations have in a changing planet.

Sun-climate research activities in Climate and Radiation Laboratory focus on analyzing observed solar irradiance for understanding solar variability, and investigating observed and simulated climate responses to solar variations recorded in satellite observations in order to pin down the physical mechanisms in the Sun-climate connection. Recently a joint Sun-Climate Research Center (SCRC) between NASA’s Goddard Space Flight Center and the University of Colorado’s Laboratory for Atmosphere and Space Physics (LASP) has been formed to foster collaborative studies of Sun effects on Earth’s climate. The center provides opportunities for scientist collaboration, and is a means for post-doctoral scientists and graduate students in science, engineering, and mission operations to move between LASP and Goddard.

Contact:  Guoyong Wen