I am a Royal Society University Research Fellow at Imperial College London in the Space and Atmospheric Physics Group, where I investigate the controlling factors of clouds, particularly the impact of ships and aircraft.
Clouds are a central component of the Earth's energy budget, both reflecting incoming sunlight (a cooling effect) and trapping outgoing infra-red (a warming), as well as being an important component of the water cycle. Cloud processes span a range of scales, from the formation of cloud droplets at the micron scale to the dynamics of supercell storms and extra-tropical cyclones that are hundreds of km across. This complexity also leads to uncertainty, clouds are responsible for some of the largest uncertainties in the human forcing of the climate system and the feedbacks that determine the temperature change in response to that forcing.
My research focussing on understanding the processes controlling clouds - what sets these properties at a global scale, how can we best observe and simulate them and how do they respond to human activity? This work falls into three main areas:
Developing observational insights into cloud processes
A key pillar of my work is developing novel methods of using Earth observation data to understand how clouds work. Some questions that my work has previously addressed include:
Does pollution increase cloud lifetime? (Gryspeerdt et al., 2014)
This paper introduces techniques to isolate the impact of atmospheric aerosol on cloud by observing cloud development in a selection of objective cloud regimes.
How can you isolate the causal impact of aerosol on cloud? (Gryspeerdt et al., 2016)
Many of the factors that affect cloud properties are also correlated to atmospheric aerosol. This can generate artificial relationships between aerosol and cloud. This paper applies a collection of techniques, more common in economics and public health, to isolate a causal relationship in a complex system.
How does aerosol affect ice cloud processes? (Gryspeerdt et al., 2018)
Ice cloud processes are comparatively poorly understood when compared to liquid clouds. This paper is one of the first satellite studies showing behaviour consistent with both homogeneous and heterogeneous nucleation. More details on the DARDAR product here: DARDAR-Nice
Understanding and improving climate models
Clouds are responsible for significant uncertainties in our understanding of the current and future climate. My work in this area has focussed on improving the comparison between models and satellite observations, ensuring the best and most appropriate comparisons are made
What is the best measure of aerosol to understand its impact on cloud? (Gryspeerdt et al., 2017)
Satellites retrieve multiple different potential aerosol parameters, the aerosol optical depth (AOD) is most commonly used for aerosol-cloud interactions. This paper shows that using the AOD will underestimate the aerosol impact on clouds, while the aerosol index (AI) is capable of producing estimates to within 20% (assuming it can be accurately measured).
Where are the largest uncertainties in simulated aerosol-cloud interactions? (Gryspeerdt et al., 2020)
Models simulate processes, but satellites observe bulk cloud properties. This paper demonstrates how to reconcile this difference, showing surprising similarities between model and observation-based estimates of aerosol-cloud interactions.
Earth observation techniques for climate and pollution monitoring
Satellite data has a wide variety of applications outside of climate science. My more recent work has been focussed on developing methods to use it for tracking pollution from ships and aircraft.
Are controls on ship fuel effective in the open ocean? (Gryspeerdt et al., 2019)
Ship fuel often contains large amounts of sulphur, which creates large amounts of particulates that are bad for human health when the fuel is burned. In this work, we show that by identifying the cloud perturbations caused by individual ships, we can determine the SOx emissions of the ship and hence the fuel the ship was burning. This showed that at least in 2015, ships were largely complying with the new fuel regulations in the Californian emission control region.
I am also interested in the history of meteorology, writing a chapter for a book on John Ruskin (Ruskin and meteorology) and giving a talk on the history of cloud physics at Imperial College.