Understanding Convective Organization and Seeking it Through Observations

This study pursues two main objectives: firstly, to unravel the sensitivity of convective self-aggregation (SA) to diverse physical parameterizations, and secondly, to comprehend the characteristics of convective organization in observations, shedding light on associated physical mechanisms. Studying organization is of profound significance due to its impact on the radiation budget, climate feedbacks, hydrological cycle, and extreme precipitation patterns, impacting society and climate. Addressing the first objective, radiative-convective equilibrium simulations explore the effects of 24 parameterization combinations on aggregated and random convective patterns. Key to our analysis is understanding the role of maximum free convection distance dclr, found crucial for SA, and its modulation by parameterizations. SA predominantly emerges in scenarios with limited convective cores and extensive dclr values (since they are anticorrelated), influenced by sub-grid scale mixing, planetary boundary layer (PBL), and microphysics. Horizontal mixing primarily influences SA by determining the size of convective cores, which is tight to their number and spacing. On the other hand, the influence of microphysics primarily stems from rain evaporation and its subsequent effects on CPs. Surprisingly, perturbations to ice cloud microphysics had a notably limited effect. Non-local PBL mixing schemes enhance SA by reducing PBL heights and increasing entrainment at the PBL top, facilitated by stronger vertical moisture gradients. This heightened entrainment to the CPs gust fronts, diminishing CPs sizes and intensities. This reduction hampers efficient moisture redistribution and convective triggering, as strong entrainment limits gust front convergence, constraining convective initiation, increasing dclr and fostering the formation of dry patches that drive SA. For our second objective, we move beyond idealized models, utilizing state-of-the-art observations, reanalysis data, advanced numerical models, and machine learning techniques. Applying multivariate analysis typically used for SA, we examine convective organization and its impact on total column water vapor variability in three mesoscale sized domains within the tropical western Pacific warm pool region, lying either north of the equator (2-9N or 3-10N), or directly straddling the equator 3S-4N). During periods with limited SST gradients (boreal summer/autumn), convection tends to be random, with small horizontal humidity gradients. In periods with a weak zonal SST gradient (> 10^-3 K/km, boreal winter/spring), aggregated convection prevails, exhibiting larger humidity gradients, stronger outgoing longwave radiation, and a drier atmosphere. Intermittent episodes of random convection and smaller humidity gradients disrupt this pattern. A composite analysis of such events associates them with westward propagating convectively coupled wave-like modes in the three regions, suggesting these modes play a key role in mesoscale water vapor variability during boreal winter and spring, potentially influencing long-term variations in convective organization. To further understand the mechanisms that lead and prevent the development of convection organization. Our study leverages on realistic simulations, underscoring the important role of humidity advection in orchestrating the organization and disorganization of convection, with wind shear playing a dual role in either organizing or disorganizing convection, contingent on its strength and direction. In terms of its characteristics, when convection is organized, the atmosphere is significantly drier compared to the random state. Diabatic feedbacks consistently works to cluster convection, but large-scale dynamics play a more important role in instigating and disrupting organization over the warm pool region, since the large-scale dynamics can export moist gross static energy from moist to dry regions, disallowing organization.

This study pursues two main objectives: firstly, to unravel the sensitivity of convective self-aggregation (SA) to diverse physical parameterizations, and secondly, to comprehend the characteristics of convective organization in observations, shedding light on associated physical mechanisms. Studying organization is of profound significance due to its impact on the radiation budget, climate feedbacks, hydrological cycle, and extreme precipitation patterns, impacting society and climate. Addressing the first objective, radiative-convective equilibrium simulations explore the effects of 24 parameterization combinations on aggregated and random convective patterns. Key to our analysis is understanding the role of maximum free convection distance dclr, found crucial for SA, and its modulation by parameterizations. SA predominantly emerges in scenarios with limited convective cores and extensive dclr values (since they are anticorrelated), influenced by sub-grid scale mixing, planetary boundary layer (PBL), and microphysics. Horizontal mixing primarily influences SA by determining the size of convective cores, which is tight to their number and spacing. On the other hand, the influence of microphysics primarily stems from rain evaporation and its subsequent effects on CPs. Surprisingly, perturbations to ice cloud microphysics had a notably limited effect. Non-local PBL mixing schemes enhance SA by reducing PBL heights and increasing entrainment at the PBL top, facilitated by stronger vertical moisture gradients. This heightened entrainment to the CPs gust fronts, diminishing CPs sizes and intensities. This reduction hampers efficient moisture redistribution and convective triggering, as strong entrainment limits gust front convergence, constraining convective initiation, increasing dclr and fostering the formation of dry patches that drive SA. For our second objective, we move beyond idealized models, utilizing state-of-the-art observations, reanalysis data, advanced numerical models, and machine learning techniques. Applying multivariate analysis typically used for SA, we examine convective organization and its impact on total column water vapor variability in three mesoscale sized domains within the tropical western Pacific warm pool region, lying either north of the equator (2-9N or 3-10N), or directly straddling the equator 3S-4N). During periods with limited SST gradients (boreal summer/autumn), convection tends to be random, with small horizontal humidity gradients. In periods with a weak zonal SST gradient (> 10^-3 K/km, boreal winter/spring), aggregated convection prevails, exhibiting larger humidity gradients, stronger outgoing longwave radiation, and a drier atmosphere. Intermittent episodes of random convection and smaller humidity gradients disrupt this pattern. A composite analysis of such events associates them with westward propagating convectively coupled wave-like modes in the three regions, suggesting these modes play a key role in mesoscale water vapor variability during boreal winter and spring, potentially influencing long-term variations in convective organization. To further understand the mechanisms that lead and prevent the development of convection organization. Our study leverages on realistic simulations, underscoring the important role of humidity advection in orchestrating the organization and disorganization of convection, with wind shear playing a dual role in either organizing or disorganizing convection, contingent on its strength and direction. In terms of its characteristics, when convection is organized, the atmosphere is significantly drier compared to the random state. Diabatic feedbacks consistently works to cluster convection, but large-scale dynamics play a more important role in instigating and disrupting organization over the warm pool region, since the large-scale dynamics can export moist gross static energy from moist to dry regions, disallowing organization.