Drop in Total Solar Irradiance

by wanliss on December 19, 2017

in Science and Technology

Over 400 years of sunspot numbers show how sunspots usually oscillate over a period of about eleven years. There are other times when sunspot numbers stay relatively low, or high, for decades. For five decades through the twentieth century solar activity rose steadily to rare heights.

Now, in a new millennium, we encounter a weaker sun than ever in living history. If the current pitiful solar activity continues, it may signal a future low period for the sun like that associated with the “Little Ice Age,” with its coldest periods characterized by the Maunder (about 1645–1715) and Dalton (about 1790–1830) minima. The figure below shows the sunspot cycle  indicating the decline of highs at solar maximum and lows at solar minimum over the past several decades.


To add to the low sunspot number, consider the latest solar irradiance data measured from NASA’s SDO satellite. In the figure below red data in plus signs show the daily average total solar irradiance (TSI). TSI is a measure of the total power from solar electromagnetic radiation incident on the Earth’s atmosphere. The red vertical bar shows a 0.3% change in TSI. The black curve shows the annual average TSI. The yellow dashed horizontal line shows the minimum value of year-averaged TSI data. The vertical black bar shows the 0.09% variation we see in that average. The bottom plot in blue shows the annual sunspot number from the SIDC in Belgium in blue.

These data demonstrate a few things. First, brightness does follow the sunspot cycle. Second, the Sun is not getting brighter with time, but rather the level of solar activity has been decreasing for over three decades.


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