Observing Convective Aggregation

Abstract

Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of 123Surv Geophys (2017) 38:1199-1236 https://doi.org/10.1007/s10712-017-9419-1 model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a groundbased observational network.

An Observational View of Relationships Between Moisture Aggregation, Cloud, and Radiative Heating Profiles

“…As reviewed carefully by Holloway et al (2017;this issue), the organization of convection has been thought of for many years as being intimately linked to mesoscale systems organized by gravity and other convectively coupled waves (e.g., Mapes 1993) or large-scale circulations. The Earth's atmosphere does exhibit some characteristics of convective self-aggregation, including the tendency of more organized atmospheres to have lower humidity in clear areas, reduced domain-mean high cloudiness, and increased low cloudiness in non-convective areas, with corresponding impacts on surface and radiative fluxes (Tobin et al 2012;Stein et al 2017;Tobin et al 2013).…”

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

“…The convective organization established by surface-based precipitation-induced cold pools differs fundamentally from the larger-scale convective self-aggregation discussed elsewhere in this volume (e.g., Holloway et al 2017;Wing et al 2017). In convective selfaggregation, radiative subsidence produces an expansive ([ 1000 km), convectively suppressed, dry region (a ''dry pool'') that is growing in time, neighboring a moist, deep convective region.…”

Circling in on Convective Organization

“…Observed maximal radii in fact vary by an order of magnitude, between 10 and 100 km (Black, 1978;Feng et al, 2015;Zuidema et al, 2012). This may also help to better assess models of self-organization, such as those employed in the idealized self-aggregation case (Holloway, 2017;Holloway et al, 2017;Wing & Cronin, 2016;Wing et al, 2017;Yang, 2018). This may also help to better assess models of self-organization, such as those employed in the idealized self-aggregation case (Holloway, 2017;Holloway et al, 2017;Wing & Cronin, 2016;Wing et al, 2017;Yang, 2018).…”