The Interaction between Moist Convection and the Atmospheric Circulation in the Tropics

Abstract

Theories of the interaction between moist convection and the atmospheric circulation in the tropics are reviewed. Two main schools of thought are highlighted: (i) one which emphasizes the lower-level control of convection through moisture convergence and variations in convective inhibition, and (ii) one which sees convection as an adjustment process in reaction to larger-scale instabilities, referred to as convective quasi-equilibrium theory. Conceptually the two views consider moist convection to have fundamentally different roles in the tropical circulation. In one case the presence of low-level inhibition and the conditional nature of the atmospheric instability allows for convective vertical motion and latent heating to drive and reinforce synoptic-scale disturbances and overturning circulations; in the other case, because low-level inhibition is not acknowledged to be a widespread controlling barrier, convection is believed to balance and dampen vertical instabilities at the rate they are created by larger-scale processes over the vertical extent of the atmosphere. More recently, investigations of the moisture dynamics surrounding organized convective structures have led to an emerging consensus on the theory of convection-circulation coupling in the tropics which acknowledges the important role of lower- to mid-tropospheric moisture variations, and the significance of moist convection and convective clouds for initiating and establishing circulations. However, the implementation of these new insights in numerical models lags behind. This is exemplified by the apparent inadequacy of climate models to correctly represent decadal variability in the tropical Pacific, a fact that potentially has implications for the confidence in climate change projections based on such models.

Precipitation Extremes and Water Vapor

“…Examination of climate change impacts on the probability of strong precipitation events has been an ongoing effort since the late 1980s (Noda and Tokioka 1989) and much work since then (e.g., Meehl et al 2000;Allen and Royal Netherlands Meteorological Institute, De Bilt, Netherlands Ingram 2002;Trenberth et al 2003;Tebaldi et al 2006;Min et al 2011;Chou et al 2012; O'Gorman 2012; Wuebbles et al 2014;Sillmann et al 2013;Pendergrass and Hartmann 2014;Myhre et al 2019;Papalexiou and Montanari 2019;Tabari 2020) including reviews by Schneider et al (2010), Trenberth (2011), O'Gorman (2015) and Donat et al (2020). However, confidence in projections of precipitation change is affected by limitations in simulations of various aspects of precipitation in current climate (e.g., Biasutti et al 2006;Qian et al 2015;Lintner et al 2017;Hagos et al 2021;Biasutti et al 2018), by differences in the projection of changes in extreme precipitation among models, especially in the tropics (Pendergrass et al 2019), by sensitivity to model parameters (e.g., Knight et al 2007;Sanderson 2011;Covey et al 2013;Bernstein and Neelin 2016;Qian et al 2018), and by limited understanding of the interaction between the large-scale flow and small-scale convective precipitation (Tomassini 2020). Narrowing uncertainties in simulated precipitation probability distribution changes becomes all the more important as procedures for event attribution (Haustein et al 2016;Eden et al 2016;van der Wiel et al 2017;…”

Prediction Challenges From Errors in Tropical Pacific Sea Surface Temperature Trends

“…As Sohn et al (2016) point out, too much upper-level warming would act to weaken the overturning Walker circulation (also weakening the SST gradient). They demonstrate that models with a weaker Walker circulation are also models with static stability that is too strong and speculate that issues with convective parameterizations may be the root of this disparity (e.g., Tomassini, 2020). Others have discussed potential errors in ocean physics as well, contributing to an amplified surface heat flux feedback that may result in too much warming in the cold tongue region of the eastern Pacific (e.g., Seager et al, 2019).…”

Unprecedented Climate Change in India and a Three-Pronged Method for Reliable Weather and Climate Prediction

“…In the process of CISK, the buoyant convection can occur only when low-level stability is weakened (see Figure 2; Ooyama, 1969), and in the other, moist convection is governed by the vertically integrated measure of instability. As noted by Tomassini (2020), meteorological conditions vary greatly from one region to the other in the tropics and also in the same region from one season to another (see Ashok et al, 2000;Rao et al, 2000;Raymond et al, 2015). Raymond mentions two tropical places, Sahel and the Western Pacific, where conditions are very different.…”