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ERC Start up grant 'Mixed-phase clouds and climate (MC2)'

The project aims to better understand the role that clouds play in global climate change, with a particular focus on cold clouds that can consist of both ice and liquid water. Such clouds are common at high latitudes and can be affected by both pollution and rising temperatures in the atmosphere.

European Research Council

About the project

The importance of mixed-phase clouds (i.e. clouds in which liquid and ice may co-exist) for weather and climate has become increasingly evident in recent years. We now know that a majority of the precipitation that reaches Earth’s surface originates from mixed-phase clouds, and the way cloud phase changes under global warming has emerged as a critically important climate feedback. Atmospheric aerosols may also have affected climate via mixed-phase clouds, but the magnitude and even sign of this effect is currently unknown.

Mixed-phase clouds and climate (MC2) — Mixed-phase clouds contains water in both liquid and ice form. Such skies play an important role for distribution of precipitation to Earth’s surface. Illustration: Projects own (MC2)

Satellite observations have recently revealed that cloud phase is misrepresented in global climate models (GCMs), suggesting systematic GCM biases in both precipitation formation and cloud-climate feedbacks. Such biases give us reason to question GCM projections of the climate response to increasing CO₂ concentrations or changing atmospheric aerosol loadings.

In the MC2 project we seek to address the above issues, through a multi-angle and multi-tool approach:

(i) By conducting extensive field measurements of cloud phase at mid- and high latitudes, we seek to identify the small-scale structure of mixed-phase clouds.

(ii) Large Eddy Simulations will thereafter be employed to identify the underlying physics responsible for the observed structures, and the field measurements will provide case studies for regional cloud-resolving modelling in order to test and revise state-of-the-art cloud microphysics parameterizations.

(iv) GCMs, with revised microphysics parameterizations, will be confronted with cloud phase constraints available from space.

(v) Finally, the same GCMs will be used to re-evaluate the climate impact of mixed-phase clouds in terms of their contribution to climate forcings and feedbacks.

Objectives

Overall objective: Through a synergistic combination of tools for the study of mixed-phase clouds at a range of scales, the proposed research has the potential to bring the field of climate science forward, from improved process-level understanding at small scales, to better climate change predictions on the global scale.

MC2 sub-objectives:

To determine the small-scale structure of mixed-phase clouds, and the extent to which it matters. Specifically, determine to what extent cloud phase is spatially homogeneous, as opposed to non-uniform and ‘patchy’, and whether environmental factors like turbulent mixing play a role in cloud homogeneity.
To re-evaluate the aerosol effect on mixed-phase clouds. By first assessing the ability of GCMs with the most sophisticated cloud microphysics representations available to reproduce observed mixed-phase clouds, we will re-evaluate the aerosol effect on mixed-phase clouds.
To determine the large-scale variability of mixed-phase clouds, and specifically whether spatial and temporal variations in cloud phase for a given isotherm can be explained predominantly by variations in INP.
To provide new and improved estimates of the strength of the cloud-phase feedback and a re-evaluation of its importance for mid- and high-latitude climate change.

Background

MC2 is motivated by and centered around the following research questions:

What processes are misrepresented in climate models in order to cause the severe underestimation of the amount of liquid in mixed-phase clouds relative to observations? Is liquid-to-ice conversion “hyperactive” in GCMs because of erroneous assumptions of horizontally uniform cloud phase?
Are models more or less sensitive to INP perturbations, for example caused by anthropogenic emissions, because of their cloud phase bias?
How does cloud phase differ with latitude and season, and what proportion of cloud phase variability can be explained by the presence of INP and the efficiency of the WBF process?
What are the broader implications of such a bias? Will all models reveal an equally strong relationship between cloud phase and climate sensitivity as the one found in the CESM model, or does that model stand out in this respect?

We wil address this research questions using the following research tools:

In situ observations of arctic, sub-arctic and mid-latitude mixed-phase clouds with research aircraft, in collaboration with Andøya Space Center.
Large-eddy simulations and cloud-resolving modelling with WRF/WRF-CHEM model: www.mmm.ucar.edu/weather-research-and-forecasting-model.
Satellite observations from CALIPSO and EarthCARE: www-calipso.larc.nasa.gov.
Global climate modelling with the NorESM Earth System Model: wiki.met.no/noresm/start,

Financing

Starting Grants (StG). The full name of this project is 'Mixed-phase clouds and climate (MC2) – from process-level understanding to large-scale impacts'.

The project period: Date for start: 2018-01-31. Deadline: 2023-02-28.