Electrical currents in the atmosphere flowing out of lightning storms from almost a century ago were influenced by changes in distant ocean currents, new research has shown.
The discovery by weather and climate scientists, using pre-Second World War data records from Australia and Scotland, opens the door to a new source of data that could help calibrate the accuracy of future global and regional climate predictions.
The El Niño/La Niña cycle of ocean currents around the equator in the Pacific Ocean is well known for its influence on global patterns of rainfall and temperature. Now scientists from the Universities of Reading and East Anglia have discovered a new way in which it affects the atmosphere.
The study, published today in Environmental Research Letters, has found that the warming and cooling of sea-surface temperatures in the Pacific Ocean also affects the natural global network of electric currents flowing in the atmosphere. This means that temperatures changes in the Pacific are coupled through atmospheric electricity changes across the globe.
The research team made this discovery by analysing historical electric field observations recovered from Watheroo, Western Australia, and from Lerwick, Shetland. Atmospheric electricity measurements in these two locations were shown to be correlated with temperature changes in the Pacific.
Giles Harrison, Professor of Atmospheric Physics at the University of Reading, who led the study, said: “With this finding, we have uncovered a new piece of the jigsaw of connections across and within the atmosphere.
“The warm and cool fluctuations of El Niño and La Niña strongly influence weather patterns across the globe. We have demonstrated that El Niño also changes the global system of electric current flow in the atmosphere, and quite possibly always has.
“It confirms that the global circuit is embedded in the climate system, so as the climate system changes, the global circuit responds.”
This discovery is useful because atmospheric electricity data is complementary to climate data, so it provides additional information for testing climate modelling. The work will also help researchers to understand effects of atmospheric electricity on clouds and, potentially, climate.
Co-author Manoj Joshi, Professor of Climate Dynamics at UEA, said: “Climatologists usually think of El Niño and La Niña as influencing global climate by altering weather patterns such as the jet stream. This is an example of El Niño and La Niña affecting the physics of our atmosphere in a very different way.
“It’s amazing to think that every thunderstorm and any rain shower anywhere in the world affects atmospheric current flow in a tiny way everywhere in the world. The El Niño and La Niña phenomena are such an important part of the climate system though that the changes in rainfall that they cause are not only large enough to be measured, but large enough to give us a clear signature of their presence.”
In a paper in 2011, Prof Harrison and colleagues uncovered the effect of El Niño- La Niña in a short period of data from Lerwick Observatory during the 1970s. This finding has since been confirmed and explained, through modelling by independent scientists. This latest work extends the original discovery using newly recovered data from both hemispheres, during the first half of the twentieth century.
The researchers examined archived atmospheric electricity data from Observatory sites in Watheroo, operated by the Carnegie Institution for Science in Washington D.C., and from Lerwick, operated by the UK Met Office.
Historically, atmospheric electricity measurements tend to come from observatories primarily established for Earth magnetism monitoring, so their archives are unexpected sources for climate-related work.
Prof Ed Hawkins, a climate scientist at the University of Reading, co-authored the new study. His Weather Rescue project has recovered and digitised more than three million past weather records with the help of thousands of volunteers.
“Exploring what El Niño and La Niña was doing in the past helps us to more accurately predict climate patterns in the future,” said Prof Hawkins.
“We need as much data as possible for this, going back a long time. Our discovery that records of the global atmospheric electrical system also carry the imprint of El Niño, helps verify the El Niño reconstructions. It's revealed a new and untapped source of climate data.”
‘Empirical evidence for multidecadal scale global atmospheric electric circuit modulation by the El Niño-southern oscillation’ is published in Environmental Research Letter on December 28.