Solar Irradiance Variations During Solar Cycle 24
Tom Woods [Tom.Woods@lasp.colorado.edu], Laboratory for Atmospheric and Space
Physics (LASP), University of Colorado, Boulder
The solar cycle 23/24 minimum in 2008-2009 is deeper and broader than recent cycle
minima and appears to be similar to the low minima in the early 1900s. This minimum offers
a unique opportunity to advance our understanding of secular (long-term) changes in the
solar irradiance and its influence on Earth’s climate and atmosphere. The Total Solar
Irradiance (TSI) appears to have lower irradiance in 2008 than in 1996 by about 200 ppm
according to some of the TSI observations and also for some of the TSI models. The solar
extreme ultraviolet irradiance appears to be even lower at about 10% less in 2008 than in
1996. The rise of solar activity during the current cycle 24 has been slow, more than a factor
of two slower than recent solar cycles but slightly faster than the low Dalton Minimum
cycles in the early 1800s. This slow rise, as well as many other predictions for this cycle,
suggests that a low solar cycle maximum is expected for solar cycle 24.