Tropical Convection and Climate

Tropical clouds and thunderstorms, known as tropical convection, are often organized into clusters maintaining many individual cells. This organized convection spans a range of scales, from squall lines, to mesoscale convective complexes, to tropical cyclones, to the Madden-Julian Oscillation. Organized convection contributes significantly to tropical rainfall and cloudiness, and, when clouds cluster together more, they change the amount of cloudiness and humidity in the surrounding large-scale environment. Therefore, the behavior of tropical convection and its coupling with circulation is essential to understanding tropical and global climate and climate sensitivity. However, this is a difficult problem, due to the scale separation between large-scale tropical dynamics and convection, models generally must parameterize convection or parameterize or omit large-scale dynamics.

We study several aspects of this problem. Much of our work has focused on better understanding the mechanisms by which tropical convection organizes, by using idealized cloud resolving model simulations as a tool. In particular, we study the physical mechanisms controlling the self-aggregation of convection, in which interactions between the environment and the convection allow the convection to spontaneously organize into one or several clusters. We also investigate the response of clouds, circluation, and climate sensitivity to warming in a model configuration that has both explicit convection and, through the existence of self-aggregation of convection, large-scale circulations. Prof. Wing is leading RCEMIP, an international, coordinated, intercomparison of models configured in radiative-convective equilibrium (RCE), which is a popular idealization of the tropical atmosphere that has long been used to study basic questions in climate science and for understanding the behavior of tropical clouds and convection. Through RCEMIP, we will advance our understanding of the response of clouds to warming, the robustness of self-aggregation of convection across the spectrum of models and the extent to which the degree of aggregation depends on temperature, and the climate sensitivity of the RCE state and the impact of self-aggregation on the climate sensitivity. The first results of RCEMIP are summarized in a recorded presentation from the AGU Fall Meeting in December 2020.

What does self-aggregation look like?

Self-Aggregation of Tropical Convection from Ryan Abernathey on Vimeo

The movie to the left shows the evolution of clouds and humidity during a cloud resolving model simulation of spontaneous organization of tropical convection, known as “self-aggregation". The simulation uses a framework of non-rotating radiative-convective equilibrium. The white shading is the mixing ratio of total cloud condensate, indicating the presence and amount of clouds, and the colors indicate the water vapor mixing ratio near the surface. Each frame is a 6-hourly snapshot and the simulation runs for 100 days. Thanks to Ryan Abernathey for helping to create this visualization!

Link --> Self-aggregation in a long channel: This movie shows the evolution of aggregation for a long channel simulation; the channel is ~12,000 km long and ~200 km wide. The top subplot shows the cloud-top temperature and the precipitation rate, and the bottom subplot shows the precipitable water. In order to zoom in on the elongated channel, it is divided into quarters and each segment is wrapped left-to-right, as if it were lines of text. Movie from Wing and Cronin (2016).

Link --> Self-aggregation in varied domain geometry: This movie shows a five day period from simulations at four different aspect ratios, to scale (64:1, 16:1, 4:1, and 1:1). The variables plotted are the same as in the previous movie. Movie from Wing and Cronin (2016).

Papers on this topic
Carstens, J. and A.A. Wing, (2020): Tropical cyclogenesis from self-aggregated convection in numerical simulations of rotating radiative-convective equilibrium, J. Adv. Model. Earth Syst., 12, e2019MS002020, doi:10.1029/2019MS002020.
Wing, A. A. (2019): Self-aggregation of deep convection and its implications for climate, Curr. Clim. Change Rep., doi:10.1007/s40641-019-00120-3.
Wing, A.A., K. Emanuel, C.E. Holloway, and C. Muller (2017), Convective self-aggregation in numerical simulations: A review, Surveys in Geophysics, 38, 1173-1197, doi:10.1007/s10712-017-9408-4.
Wing, A.A. and T.W. Cronin (2016), Self-aggregation of convection in long channel geometry, Q.J.R. Meteorol. Soc., 142, 1-15, doi:10.1002/qj.2628.
Emanuel, K., A.A. Wing, and E. Vincent (2014), Radiative-Convective Instability, J. Adv. Model. Earth Sys., 6, 75-90, doi:10.1002/2013MS000270.
Wing, A.A. and K.A. Emanuel (2014), Physical mechanisms controlling self-aggregation of convection in idealized numerical modeling simulations, J. Adv. Model. Earth Sys., 6, 59-74, doi:10.1002/2013MS000269.
Clouds & Climate
Cronin, T.W. and A.A. Wing (2017), Clouds, circulation, and climate sensitivity in a radiative-convective equilibrium channel model, J. Adv. Model. Earth Sys., 9, 2833-2905, doi:10.1002/2017MS001111.
Holloway, C.E., A.A. Wing, S. Bony, C. Muller, H. Masunaga, T.S. L'Ecuyer, D.D. Turner, P. Zuidema (2017), Observing convective aggregation, Surveys in Geophysics, 38, 1199-1236, doi:10.1007/s10712-017-9419-1.
Wing, A. A., Reed, K. A., Satoh, M., Stevens, B., Bony, S., and Ohno, T. (2018): Radiative-Convective Equilibrium Model Intercomparison Project, Geosci. Model Dev., 11, 793-813, doi:10.5194/gmd-11-793-2018.
Wing, A.A., C.L. Stauffer, T. Becker, K.A. Reed, M.-S. Ahn, N.P. Arnold, S. Bony, M. Branson, G.H. Bryan, J.-P. Chaboureau, S.R. de Roode, K. Gayatri, C. Hohenegger, I.-K. Hu, F. Jansson, T.R. Jones, M. Khairoutdinov, D. Kim, Z.K. Martin, S. Matsugishi, B. Medeiros, H. Miura, Y. Moon, S.K. Müller, T. Ohno, M. Popp, T. Prabhakaran, D. Randall, R. Rios-Berrios, N. Rochetin, R. Roehrig, D.M. Romps, J.H. Ruppert, Jr., M. Satoh, L.G. Silvers, M.S. Singh, B. Stevens, L. Tomassini, C.C. van Heerwaarden, S. Wang, and M. Zhao (2020): Clouds and convective self-aggregation in a multi-model ensemble of radiative-convective equilibrium simulations, J. Adv. Model. Earth Syst., 12, e2020MS002138, doi:10.1029/2020MS002138.
Becker, T. and A.A. Wing (2020): Understanding the extreme spread in climate sensitivity within the Radiative-Convective Equilibrium Model Intercomparison Project, J. Adv. Model. Earth Syst., 12, e2020MS002165, doi:10.1029/2020MS002165.
Reed, K.A., L.G. Silvers, A.A. Wing, I.-K. Hu, and B. Medeiros (2020): Reference radiative convective equilibrium climate in the Community Atmosphere Model, J. Adv. Model. Earth Syst., in review.