High-Resolution Image

Spectral solar irradiance (SSI) is the energy emitted by the Sun at various wavelengths ranging from ultraviolet (UV) (< ~400 nm) to visible (between ~400 nm to 700 nm) and near-infrared (IR) (> ~700 nm). This image shows how changes in solar emission at different wavelengths are correlated in time, represented as the correlation matrix of SSI from the Spectral Irradiance Monitor (SIM) instrument on-board the Solar Radiation and Climate Experiment (SORCE) satellite. The changes in radiance at nearby wavelengths tend to be strongly correlated, which shows up in the figure as the strong red diagonal line. The blue colors far from the diagonals indicate that the SSI in well-separated spectral regions are not very correlated.

High correlation of SSI at two wavelengths suggests that light at these wavelengths is from the same layer of the solar atmosphere. Low correlation suggests that light at these wavelengths is being emitted from different regions or depths of the sun. The solar UV spectrum is primarily from the Sun's chromosphere, while the visible and near-IR is from the photosphere. The SSI in visible and near-IR is weakly correlated with near-UV from ~300 nm to ~400 nm. Even within visible and near-IR the spectral irradiances are not perfectly correlated. This indicates that the SSI does not simply move up and down together at all wavelengths as total solar output varies. Since the Earth's atmosphere, surface, and ocean respond differently to different wavelengths of solar irradiance, long term monitoring of these spectral details is important for understanding climate variations.

(Submitted by Guoyong Wen)