"Ions formed in the atmosphere by high-energy particles may play a role in the initiation of lightning, and they may influence the transfer of long wave radiation," says Giles Harrison of the University of Reading, UK, an atmospheric electricity specialist and a guest editor of the focus issue. "This high-energy topic involves cosmic rays, lightning, the upper and lower atmosphere, clouds, aerosols, chemistry… all substantial subjects in and around atmospheric science."

High-energy particles have lots of subtle effects in the atmosphere, according to Harrison. "They release charge, they influence the chemistry and they may even trigger lightning," he says. "So it’s about small-scale things affecting larger scales. To say it’s just about cosmic rays and clouds is somewhat throwing out the baby with the bathwater." It was obvious there was a need for somewhere for this broad range of topics to be explored. "ERL seemed like a good choice because in many ways physics forms its core home territory, but it’s an environmental journal," Harrison explains.

The articles that came through have borne out that thinking. "There was a great range of papers," Harrison says. Researchers submitted letters not only on cosmic rays and clouds but also on high-energy particles and the stratosphere, high-energy particles and lightning, the effects of the state of the Sun on lightning, stratospheric perspectives on particle production, and on links between the interplanetary magnetic field and atmospheric pressure. "The generation of lightning streamers and electrons above thunderclouds also represented something I wasn’t expecting was going to come out – new detection techniques."

Lightning up

Whilst the idea that thunderstorms are sufficiently electrified to accelerate electrons goes back to British physicist CTR Wilson in the first half of the 20th century, Harrison says that "the evidence for this is looking stronger". Wilson was the father of many of these subjects before detailed observations were possible; he predicted that thunderstorms could accelerate electrons and also proposed the global atmospheric electrical circuit, as well as winning a Nobel Prize for developing the cloud chamber, which reveals the presence of high-energy particles when the ions they form in air create condensation nuclei for water droplets, leaving a trail of mist in their wake.

"There have been few opportunities to develop this further," says Harrison, of progress on high-energy particles and atmospheric processes since CTR Wilson’s day. "And I think this [ERL focus issue] has moved it on a bit. We had a nice variety of different topics. We put them all in one place and I think that helps the subject identify as a new area that can then develop."

The interdisciplinary nature of the field has held it back from "progressing in the way more clearly defined topics have done", Harrison believes. "Everyone wants to do interdisciplinary science but how do you actually make that happen? You need a journal that is able to find reviewers across those boundaries, for the different language of the different subjects not to be an obstacle, and you also need to make sure that people working in one area can express things in a way that the people working in another area can understand and that they recognize and have some respect for the other subject’s development." To Harrison, ERL looked like a journal that "ought to be able to straddle those boundaries".

Some mysteries remain. Papers in the focus issue examined how electrical effects influence the formation of water droplets or rain in thunderstorm clouds, and how ions in the atmosphere alter the long-wave radiation balance. "These are small subtle effects we now need to put some numbers on," Harrison says. "We identified several through this focus issue, but we need to know how big or small they are. That’s where we need more work."

Harrison himself would like to know "what’s going on with lightning – what explains the Sun’s effects on lightning, and what’s the mechanism behind it". Measurements in the atmosphere could help.

"There are lightning-mapping arrays now that tell us how lightning moves through clouds and we can plot its 3-D paths," he says. "They need to be combined with knowledge of the incoming particles and their energies, which might need balloon or aircraft platforms to measure them in clouds. And we could also know the electric fields in the clouds beforehand. In other words a rather complicated array of measurements at a place where there’s lightning." In Reading, Harrison’s base, there are only a few thunderstorms a year so this is statistically and logistically difficult. The challenge is finding a location where lightning is frequent but not so often that it masks the smaller effects. "It will be difficult to work out where to do those experiments and I expect they will be tough to do anyway," Harrison says. "We also plan to do some measurements in electrified clouds using balloons when there are particles coming in. To get good stats is going to be tricky." The future might look difficult but the ERL Focus stimulated interactions and collaborations, Harrison believes. "We have learnt that one of the tools to encourage interdisciplinary work is to have an ERL focus issue!" he says. "It’s very useful to have a defining group of papers at one point in time." Now the plan is to organize a one-day meeting to follow up with the Royal Meteorological Society. Watch this (atmospheric) space.

• Giles Harrison is also a board member of ERL. Find out about paper submission or access all content for free, including the Focus issue.

Related links

Related stories