Expert in turbulence and dispersion and key instigator of the HARMO initiative died on 20 April 2026.

Julian’s interest in atmospheric dispersion was tweaked at a young age when he was fascinated by kite flying in India where he was born, and on school holidays spent with his great uncle LF Richardson, who ran the UK Met Office’s Eskdalemuir Observatory and liked to conduct atmospheric experiments! After graduating at Cambridge University in mechanical sciences and conducting a PhD in magnetohydrodynamics, Julian spent time at the research laboratories of the Central Electricity Research Board where he studied the collapse of the Ferrybridge power station cooling towers.

In 1970 he returned to Cambridge as a lecturer and subsequently professor. It was here that he applied his brilliant mind and inexhaustible energy to a wide range of fluid mechanical problems. These ranged from fundamental studies of turbulence near surfaces and around obstacles, including his seminal papers on the rapid distortion theory of turbulence, to many ground-breaking studies with more immediate applications, including: turbulent airflow over hills; structure of the atmospheric boundary layer; atmospheric dispersion of pollutants over complex terrain; and airflow in urban and coastal environments.

Julian was always keen on communicating his research and applying it to practical applications. Amongst many initiatives this led to him being a key driving force behind the instigation of the HARMO series of workshops and conferences. He was also a founding director of Cambridge Environmental Research Consultants. At CERC, he was the leading force in the development of a range of fast environmental models incorporating state-of-the-art science. The most well-known of these is the Atmospheric Dispersion Modelling System, ADMS. ADMS was first released in 1991 and is now widely used across the world. Making extensive use of his theoretical advances, Julian constructed a model that was pioneering in its treatment of the atmospheric boundary structure and in extending treatment of Gaussian plume dispersion modelling to complex flows.

Subsequent to Cambridge, Julian became Director-General of the UK Met Office in 1992 and then Professor of climate modelling at University College London in 1997.

Julian was Chairman of CERC until as recently as 2022, when he was still full of new ideas.