The Sun

Variations in Solar Radiation

Variations in solar radiation

Variations in solar radiation (solar variations) is a term that characterizes the changes in the time of the current radiation of the Sun, its spectral distribution and the phenomena that accompany these changes. A distinction is made between the periodic components of these changes, the main one of which is the eleven-year solar cycle, and aperiodic changes. In other words, the solar energy that leaves the Sun and reaches the Earth's surface varies periodically.

There are periodic components such as the eleven-year sunspot and aperiodic cycle. In the last years of the twentieth century, solar activity was monitored thanks to artificial satellites in orbit. Thanks to other natural indicators, history has been deduced in previous centuries. Climatologists are interested in understanding how much, if any, solar variations affect the climate on earth.

Causes of Solar Radiation Variations

These changes in solar radiation are due to the amount of energy emitted by the Sun and are detectable thanks to changes in brightness, variations in the solar wind and the magnetic field. Among the causes that produce this phenomenon, the most likely has been formulated by Horace Welcome Babcock, who says that there is a link between the electrodynamic phenomena of the Sun and electromagnetic phenomena.

This could be explained by the different rotation of our star in several latitudes: for example, the equatorial zone rotates every three years more than the area at 50 ° latitude; This could produce a distortion of the magnetic field lines that leave the surface and then re-enter forming a kind of loop.

Observations of the First Cyclic Variations of Solar Radiation

Heinrich Schwabe was a German pharmacist who had astronomy as a hobby. For 17 years, Schwabe periodically observed the solar disk every day and discovered that there was a slight increase in its number over a period of 4.6 years due to a minimal presence of spots. During this time, solar radiation reached a maximum value and, subsequently, continued with a decrease for 6.4 years until reaching a new minimum. In total between the two minimums 11 years elapsed.

Since the observations began in 1755, it was common to progressively number the cycles from this date. We are now in cycle 24 that began in June 2009 and will end in 2020. There is a close relationship between the magnetic field and the activity cycle.

Polarity of Solar Cycles

George Ellery Hale and Seth Barnes Nicholson were two prominent American astronomers. Both astronomers indicated that most of the sunspot cycle in the same asset in the northern hemisphere of the Sun has the same polarity reversed if we consider the southern hemisphere.

This provision will remain compatible for the duration of the cycle, but the polarities will be reversed when the next cycle takes over; therefore, it would be more correct to talk about cycles of 22 years so that similar conditions are repeated.

Discovery of the Long Solar Cycles

Gustav Sporer and, presumably Father Scheiner, noted that the spots formed within 10 ° and 35 ° latitude; they began to form around 35 ° and then, as the cycle progressed, they migrated to lower latitudes until at the end of the same cycle they appeared at the height of the equator. These 11-year cycles in turn vary over a period of 80 years forming a kind of Supercycle. Other longer periods have also been found: 200-400-600 years.

The journals "Geophisical Research Letters" and "Science" published a report in which they said that the tropospheric layers of the Earth's atmosphere vary due to a sudden decrease in ultraviolet solar radiation and that the eleven-year solar cycle varies much more. than I did before.

Differences Between Solar Radiation Cycles

Stanley Solomon, a member of the National Atmospheric Research Center (NCAR) team in Boulder, Colorado, states that the minimums of solar cycles are not all the same, modifying the orbits of artificial satellites that revolve around the Earth from the part layer upper atmosphere, the thermosphere, its density decreases.

In periods of low intensity of the solar flow (SF, that is, "solar flow"), the thermosphere cools and its density variation seems to be even 30% higher than the expected average value. From 1996 to 2008 there was a decrease in the density of the thermosphere equal to 31%, where only 3% seems to be caused by carbon dioxide (a potent greenhouse gas). From this it would arise that both the low temperatures and the densities of the thermosphere are caused by low levels of ultraviolet radiation.

Global Warming

Until about 2009, the most influential group of experts believed that variations in solar radiation did not play a decisive role in modern climate change. In this sense, it is believed that the measured value of current solar activity is much less significant compared to the effect on the climate of greenhouse gases in the atmosphere.

In general, theories that describe modern climate change due to variations in solar radiation can be attributed to one of the following three groups:

  • The first group starts from the assumption that changes in visible luminosity directly affect the weather. In general, this statement is considered unlikely due to the small extent of the change in brightness;
  • The following group suggests that the most significant effect on climate is exerted by changes in the UV part of the spectrum. Since the amplitude of the variations in this part of the spectrum is much greater than the average general spectral changes, these changes can cause a greater impact on the climate;
  • The third group refers to the study of side effects associated with a decrease in solar activity, in which there is an increase in galactic cosmic radiation, which improves cloud formation and affects the climate.

In 1991, a correlation was found between the number of points and the temperature change in the northern hemisphere based on a comparison of astronomical and meteorological data during the time interval from 1861 to 1989, then these studies were confirmed and extended during several centuries

However, after eliminating errors in these data, the sensational confirmation of the connection between solar activity and modern global warming was refuted. Despite this, this graph is often represented as a relationship between the level of solar activity and the weather, which is incorrect.

In 2000, an article was published indicating that an increase in solar activity is responsible for half of the temperature increase since 1900, but cannot explain the increase in 0.4 ° C since 1980. The additional increase is explained by an increase in the concentration of greenhouse gases in the atmosphere. In the same year, a work was published in which the most modern climatic model of the 20th century was used, taking into account changes in solar activity, the influence of volcanic eruptions and anthropogenic factors, that is, taking into account the increase in the concentration of greenhouse gases and sulfate aerosols.

We also take into account the unequal change in the luminosity of the Sun in different parts of the spectrum and do not consider the amplification of the influence of cosmic radiation with weak solar activity. The result of this work was the conclusion that a change in solar activity played a dominant role in the early twentieth century. The work determined that the greenhouse effect is responsible for warming at the end of the century and will play a growing role in the planet's climate. In addition, the uncertainty in the "historically determined impact on the climate" or the incomplete image of the influence of the high heat capacity of the oceans on the current state of the climate is highlighted.


Published: October 25, 2019
Last review: October 25, 2019