12 April 1999

Solar Cycle, Wind and Climate

Researchers have found that the variations in the energy given off from the sun effect the Earth's wind patterns and consequently the climate of the planet.

For decades, scientists have tried to understand the link between winds and temperature and the sun and its cycles. There were tell-tale signs of a connection. For instance, the Little Ice Age recorded in Europe between 1550 and 1700 happened during a time of very low solar activity. But how the sun and climate were linked continued to elude researchers.

According to Drew Shindell, a climate researcher from NASA's Goddard Institute for Space Studies, a key piece of the puzzle was missing. Previous studies neglected to take into account the effects of increased solar activity on the ozone layer or the complex chemistry of the upper atmosphere where most of the high-energy radiation, including ultra-violet radiation (the kind responsible for creating the ozone layer) gets absorbed.

"When we added the upper atmosphere's chemistry into our climate model, we found that during a solar maximum major climate changes occur in North America." The changes, according to Shindell, are caused by stronger westerly winds. Changes also occur in wind speeds and directions all over the Earth's surface.

"Solar variability changes the distribution of energy," said Shindell. "Over an 11-year solar cycle, the total amount of energy has not changed very much. But where the energy goes changes as wind speeds and directions change." During the sun's 11-year cycle, from a solar maximum to a solar minimum, the energy released by the sun changes by only about a tenth of a percent.

When the solar cycle is at a maximum, it puts out a larger percentage of high-energy radiation, which increases the amount of ozone in the upper atmosphere. The increased ozone warms the upper atmosphere and the warm air affects winds all the way from the stratosphere to the Earth's surface. "The change in wind strength and direction creates different climate patterns around the globe," said Shindell.

According to Shindell, the new study also confirms that changing levels of energy from the sun are not a major cause of global warming.

Many scientists have argued that the radiation change in a solar cycle - an increase of two to three tenths of a percent over the 20th century - are not strong enough to account for the observed surface temperature increases. The GISS model agrees that the solar increases do not have the ability to cause large global temperature increases, leading Shindell to conclude that greenhouse gasses are indeed playing the dominant role.

The general circulation model used in the study included solar radiation data from NASA's Upper Atmospheric Research Satellite, launched in 1991. With data from UARS, which was used to calculate ozone changes, scientists have good measurements of how much radiation the sun puts out, increasing the accuracy of the new model.