How thunderstorms are generated in clouds is still not fully understood. But John Latham, who has died aged 83, did much to explain the physical processes of cloud electrification, cloud lightning and precipitation – how water falls from clouds in various forms. Later he proposed a way in which clouds could provide a crucial if temporary role in reducing the impact of global warming.

The research he began under John (BJ) Mason in 1958 at what is now Imperial College London focused on the role of ice crystals in cloud electrification. His laboratory studies of thunderstorms involved the concept of a temperature difference between graupel – soft hail – and ice crystal surfaces. He and Mason developed the Temperature Gradient Theory and provided numerical predictions of the mechanism. Like all theories of thunderstorm electrification, it proved controversial.

After obtaining a lectureship in 1961 at Umist, now part of Manchester University, John constructed a succession of cold rooms in order to study thunderstorm electrification.

He and colleagues devised the “who grows faster” hypothesis, exploring whether under certain circumstances during ice-particle collisions the particle growing faster from the vapour becomes positively charged and the other negatively charged, leading to the development of electric fields that can result in lightning discharges. This conclusion, subsequently supported by further data, remains the basis for models of electrification to this day.

Lightning strikes over Kolkata. Though concerned with analysing natural phenomena down to a molecular level, John Latham never lost a sense of wonder at the imaginative effect they have on us.
Lightning strikes over Kolkata. Though concerned with analysing natural phenomena down to a molecular level, John Latham never lost a sense of wonder at the imaginative effect they have on us. Photograph: Piyal Adhikary/EPA

Perhaps his greatest contribution came in 1979, in relation to droplet growth and microphysics in warm clouds – those containing water vapour and the droplets condensed from it, rather than ice. A major problem in cloud physics was to explain how rain in warm clouds formed in an observed time of about 20 minutes. None of the models at the time were able to explain this.

John suggested a novel hypothesis for the process, which he termed “inhomogeneous mixing”. On this account, discrete blobs of dry air are carried along into the clouds, completely evaporating nearby droplets, while others further away are unaffected. Reducing the overall concentration of drops decreases the competition for the available water vapour and allows the largest drops to grow faster and rain to develop within the observed time.

In 1988, John left Umist for the National Center for Atmospheric Research in Boulder, Colorado.

Two years after arriving there, he addressed the problem of global warming by proposing that marine cloud brightening (MCB) could be temporarily used to reflect incoming solar radiation back. It would achieve this through exploiting what is known as the Twomey effect: for the same amount of liquid water, a large number of small droplets reflect more incoming solar radiation than a smaller number of larger ones. He proposed to bring about this radiative cooling by using a sea-salt spray of specified size, generated from wind-driven ships, and from 2008 onwards published the supporting science.

Researchers at the Centre for Climate Repair, Cambridge, and elsewhere are currently working on prototypes to test the idea. US businesses have helped sponsor the work, and parallel studies are being conducted at the University of Washington, Seattle.

As a writer, John published six collections of poetry, including All-Clear (1990), Sailor Boy (2006) and From Professor Murasaki’s Notebooks on the Effects of Lightning on the Human Body (2017). The title poem of the last had won second prize in 2006 in the National Poetry Competition in Britain. He also produced short fiction, plays for BBC Radio 4 and a surrealistic novel, Ditch-Crawl (2006).

Though concerned with analysing natural phenomena down to a molecular level, John never lost a sense of wonder at the imaginative effect they have on us, as in the poem Double-jointed (from the Murasaki collection):

I’m back now in the Rockies,

a spurting, crackling fire

sends flame-shadows scudding

round stripped-log cabin walls,

and a light up high, outside, shows

us snowflakes crazy-dancing into oblivion.

In his later years, while living in that cabin in Gold Hill, near Boulder, he wrote the poem Dusk Words (from Crossing Over, 2017), as he became aware of the onset of dementia: “I’m not afraid of it, not much, not yet, / but I can feel it coming, the dawning dark, / wisps of altostratus that subdue the sun”. In 2018 he returned to his birthplace, Frodsham, in Cheshire.

His father, Jack (William John), was an electrician and ran a shop in the village with his mother, Ruth (nee Barrow). From Helsby high school John went to Imperial, where he completed his PhD.

At Umist he was awarded a DSc (1968) before being appointed professor, and I knew him as a colleague there from 1985. He gave workshops on the physics of lightning at universities around the world, his work was recognised by the Royal Meteorological Society, and he served as president of the International Commission on Atmospheric Electricity (1975-83). The thought that his work might help combat global warming kept him working at NCAR as long as he could, and we continued to collaborate on research projects.

In 1961 John married Ann Bromley, also from Frodsham, and they had four children; they divorced amicably in 1992. He was predeceased by two sons, Rob and Mike, and is survived by his children David and Rebecca, seven grandchildren, Samuel, Shane, Jessica, Natasha, Molly, James and Evie, and a great-grandchild, Tamara.

John Latham, climate physicist, born 21 July 1937; died 27 April 2021



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