Resolving climate sensitivity associated with shallow mixed phase cloud in the oceanic mid- to high latitudes
M-Phase will run from 1/2/2020 – 31/1/2024.
The overarching objective of M-Phase is to reduce the uncertainty in how mixed-phase clouds will respond to changes in climate, and thereby reduce uncertainty in climate sensitivity. We will do this by improving our understanding of the physical processes that determine the properties of mixed-phase clouds and their response to climate drivers (sea-surface temperatures and aerosols). This will be achieved by addressing the following specific objectives:
- Experimentally define the relationship between aerosol, dynamics, and mixed-phase cloud radiative properties in the climatically critical mid-to high-latitudes (WP 1).
We will make in-situ measurements of cloud properties, meteorology and aerosols needed to build models of this important class of mixed-phase clouds with the objective of understanding how changes in sea surface temperature (SST), thermodynamic profiles and aerosols will affect cloud microphysical processes and radiative properties. To do this we will use the FAAM aircraft to study cold-air outbreaks (CAOs), a frequent source of mixed-phase clouds, which offer the opportunity to study the physical processes that control the formation and evolution of cloud systems in a relatively well-defined flow. We will target conditions of most relevance to the cloud feedback problem: moderately cold clouds that will be most sensitive to changes in temperature, and where high INP concentrations are likely to influence large regions of the N Atlantic. This will complement our Partner’s low INP cold-air outbreak cases or much colder conditions in other regions of the world.
- Define high-latitude ice-nucleating particle (INP)concentrations and sources across the northern hemisphere (WP 2).
(INP concentrations are vital input to cloud models to understand present-day ice formation as well as future changes, which determine the magnitude of cloud feedback [Tan et al., 2016; Vergara-Temprado et al., 2018b]. To do this we will measure INP at a location strategically chosen to identify sources of INP relevant for the North Atlantic’s climatically critical 45-70olatitude band, quantify INP on a cruise through the Labrador Sea and Baffin Bay, study source material in the laboratory and collate relevant INP data from around the globe from the literature and Partners. This will allow us to build a global model of INP and use it to define cloud glaciation in the cloud modelling work package (WP 3).
- Determine the response of mixed-phase cloud systems to SST and INP in order to estimate cloud responses to changing environmental conditions on a regional basis (WP 3).
A physically realistic model of mixed-phase clouds that links observed and modelled INP through to cloud radiative properties and variability is essential for quantifying cloud feedbacks. We will use the field data and INP modelling to build a regional high-resolution model constrained by observations from our focused FAAM flights. The detailed data on cloud microphysics, aerosol and boundary layer structure will allow us to build an accurate physical understanding of the processes leading to the persistence (or not) of supercooled water and the radiative properties of dynamic cloud systems.
- Use the improved models of cloud microphysics as well as INP to extend the analysis of mixed-phase cloud properties to other regions of the world (WP 3).
We will do this in collaboration with our Partners by modelling cases in contrasting environments (e.g., the Southern Ocean and Norwegian Sea) in different seasons and with different aerosol inputs. We will quantify, for the first time, cloud responses to changes in SST and aerosol on a regional basis.5. In follow-on funding, extend the results to the global model to quantify cloud-phase feedbacks and reduce the uncertainty in climate sensitivity. This will be done in the second closed round of proposals to NERC’s ‘Uncertainty in Climate Sensitivity Due to Clouds.’