Jessica Vial ~ Climate scientist and researcher in atmospheric physics
Laboratoire de Météorologie dynamique (LMD
Institut Pierre Simon Laplace (IPSL
Étude et Modélisation du Climat et du Changement Climatique (EMC3
Room no: 309
Campus Pierre et Marie Curie (Paris 5e)
4 place Jussieu, T 45-55, 3rd floor
from the Climatic Reasearch Unit
), University of East Anglia (Norwich, UK). "Climate model simulations of winter northern hemisphere atmospheric blocking: statistical assessment, dynamical perspective, regional impacts and future change."
How do clouds influence climate and climate change?
Clouds are ubiquitous on Earth. By interacting with solar and terrestrial radiation, they exert a radiative heating/cooling - at the top of the atmosphere, within the atmosphere and at the surface - and as such play a fundamental role in atmospheric circulation and energetics of the climate system.
My interest is on the role of shallow convective clouds and the various factors that control their spatio-temporal variability. This includes:
- The diurnal cycle of oceanic tradewind cumuli. Early field campaigns in the Tropical North Atlantic ocean, more than 40 years ago, have made important contributions to its discovery. But since then this topic has received very little attention, so that our knowledge of the diurnal processes in this oceanic shallow cumulus regime and their influence on climate at broader scales remains extremely limited. I recently relaunched the exploration of this topic, which today is subject to a growing interest in the community.
The diurnal cycle reflects the evolution of two cloud populations:
- a population of non-precipitating small cumuli with weak vertical extent (orange curve in panel b), which grows during the day and maximizes around sunset
- a population of deeper precipitating clouds with a stratiform cloud layer below the trade inversion (blue curve in panel b), which grows during the night and maximizes just before sunrise
- Climate projections of global warming.
By revisiting the concepts of radiative forcing and climate feedbacks, we have developed a methodology to separate the relative contribution of the direct response to CO2 increase and the response to surface warming in climate projections of global warming. This has never been done before. This work has thus allowed to interpret the real contribution of climate feedbacks to the inter-model dispersion of climate sensitivities estimated by climate models. Among all climate feedbacks, that of low-level clouds over tropical oceans is the most uncertain.
➥ Vial J., Dufresne J.-L. and Bony S. On the interpretation of inter-model spread in CMIP5 climate sensitivity estimates. Climate Dynamics, 41 (11-12), 3339-3362
. ✴ Highly Cited Paper ✴
- The role of shallow convective mixing in the tropical low-level cloud feedback.
How marine clouds in the tropical planetary boundary layer will change in a future climate, is known to be critical in the estimation of the magnitude and pace of global warming.
In recent years, significant progress has been made in identifying the physical processes that govern the response of these clouds to warming. The analysis of these processes through a hierarchy of models and numerical experiments has shown that the representation of the vertical mixing of the lower troposphere by shallow convection in models constitutes a key uncertainty for the change in low-level clouds with warming, especially in regimes with tradewind cumuli (see Figure below).
➥ Vial J., Bony S., Dufresne J.-L., Roherig R. Coupling between lower-tropospheric convective mixing and low-level clouds : physical mechanisms and dependence on convection scheme. JAMES, 8 (4), 1892-1911
➥ Vial J., Bony S., Stevens B., Vogel R. Mechanisms and model diversity of trade-wind shallow cumulus cloud feedbacks: a review. Surveys in Geophysics, 38 (6), 1331-1353
My research has contributed to this effort, by developing an analysis framework, which allowed us to better articulate the local interplay between cumulus convection, turbulence and cloud radiative effects - and by this the physical mechanisms through which tropical boundary layer clouds depend on the shallow convective mixing.
Based on our understanding of the physical processes involved in the tropical low-level feedbacks, we hope to assess soon, using observations from the upcoming field campaign EUREC⁴A (Elucidating the Role of clouds-circulation coupling in climate), the credibility of the different feedbacks predicted by the climate models.
- Clouds and circulation coupling at meso-scale and synotpic scale.
How water in the atmosphere interacts with atmospheric dynamics is a topic of long standing interest that is still recognized as key to solve major weather and climate issues in the context of climate change. It is of the upmost importance in reducing uncertainties in climate change prediction both at global and regional scales. For instance, these interactions largely influence low-level cloud feedbacks in the tropics and mid-latitudes (and thus climate sensitivity) and the changes in the regional distribution of rainfall and extreme weather events with global warming.