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Study could improve the predictability of the largest El Nino and La Nina events

The Sun emits the energy required to sustain life on Earth and drive our planet’s atmospheric circulation. However, establishing a solid physical connection between solar and tropospheric variability has posed a considerable challenge.

North Atlantic Oscillation (NAO) or the El Nino Southern Oscillation events are little more than anecdotal. These events have several seasonal climate effects on land.

During La Nina, the southern U.S. tends to be warmer, whereas the northern U.S. tends to be colder and wetter.

A new study by the National Center for Atmospheric Research sheds light on the association between the end of solar cycles and a switch from El Nino to La Nina conditions in the Pacific Ocean. It suggests that solar variability can drive seasonal weather variability on Earth.

Scott McIntosh, a scientist at the National Center for Atmospheric Research (NCAR) and co-author of the paper, said, “Energy from the Sun is the major driver of our entire Earth system and makes life on Earth possible. The scientific community has been unclear on the role that solar variability plays in influencing weather and climate events here on Earth. This study shows there’s reason to believe it does and why the connection may have been missed in the past.”

Scientists are observing sunspots for centuries. The waxing and waning of sunspots occur every 11-years, but these 11-year cycles do not have distinct beginnings and endings.

This fuzziness in the length of any particular cycle has made it challenging for scientists to match up the 11-year cycle with Earth changes.

In this new study, scientists depend on a more precise 22-year “clock” for solar activity derived from the Sun’s magnetic polarity cycle. This 22-year cycle occurs when charged magnetic bands appear near the star’s polar latitudes.

Over the cycle, these bands relocate toward the equator—causing sunspots to show up as they traverse the middle. The process closes when the groups compromise, commonly destroying each other in what the examination group calls a terminator event. These terminators give exact guideposts to the furthest limit of one cycle and the start of the following.

Scientists imposed these terminator events over sea surface temperatures in the tropical Pacific stretching back to 1960. They found that the five terminator events between that time and 2010-11 all coincided with a flip from an El Nino (when sea surface temperatures are warmer than average) to a La Nina (when the sea surface temperatures are cooler than average). The end of the most recent solar cycle—which is unfolding now—is also coinciding with the beginning of a La Nina event.

Leamon said, “We are not the first scientists to study how solar variability may drive changes to the Earth system. But we are the first to apply the 22-year solar clock. The result—five consecutive terminators, lining up with a switch in the El Nino oscillation—is not likely to be a coincidence.”

Scientists performed several statistical analyses to determine the possibility that the correlation was just a fluke. They found there was only a 1 in 5,000 chance or less that all five terminator events included in the study would randomly coincide with the flip in ocean temperatures.

Scientists noted, “Now that a sixth terminator event—and the corresponding start of a new solar cycle in 2020—has also coincided with an La Nina event, the chance of a random occurrence is even more remote.”

The paper doesn’t dive into what actual association between the Sun and Earth could be liable for the relationship. Yet, the scientists note a few prospects that warrant further investigation, remembering the Sun’s magnetic field’s impact on the number of cosmic rays that escape into the solar system and eventually bombard Earth. In any case, a strong actual connection between cosmic rays variations and climate has yet to be determined.

McIntosh said, “If further research can establish that there is a physical connection and that changes on the Sun are truly causing variability in the oceans, then we may be able to improve our ability to predict El Nino and La Nina events.”

Journal Reference:
  1. Robert J. Leamon et al., Termination of Solar Cycles and Correlated Tropospheric Variability, Earth and Space Science (2021). DOI: 10.1029/2020EA001223

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