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Article Dans Une Revue Journal of Climate Année : 2021

Transient Aggregation of Convection: Observed Behavior and Underlying Processes

Hirohiko Masunaga
  • Fonction : Auteur
Christopher E Holloway
  • Fonction : Auteur
Hironari Kanamori
  • Fonction : Auteur
Thorwald H M Stein
  • Fonction : Auteur

Résumé

Convective self-aggregation is among the most striking features emerging from radiative-convective equilibrium simulations, but its relevance to convective disturbances observed in the real atmosphere remains under debate. This work seeks the observational signals of convective aggregation intrinsic to the life cycle of cloud clusters. To this end, composite time series of the Simple Convective Aggregation Index (SCAI), a metric of aggregation, and other variables from satellite measurements are constructed around the temporal maxima of precipitation. All the parameters analyzed are large-scale means over 108 3 108 domains. The composite evolution for heavy precipitation regimes shows that cloud clusters are gathered into fewer members during a period of 612 h as precipitation picks up. The high-cloud cover per cluster expands as the number of clusters drops, suggesting a transient occurrence of convective aggregation. The sign of the transient aggregation is less evident or entirely absent in light precipitation regimes. An energy budget analysis is performed in search of the physical processes underlying the transient aggregation. The column moist static energy (MSE) accumulates before the precipitation peak and dissipates after, accounted for primarily by the horizontal MSE advection. The domainaveraged column radiative cooling is greater in a more aggregated composite than in a less aggregated one, although the role of radiative-convective feedback behind this remains unclear.
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Dates et versions

hal-03448556 , version 1 (25-11-2021)

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Hirohiko Masunaga, Christopher E Holloway, Hironari Kanamori, Sandrine Bony, Thorwald H M Stein. Transient Aggregation of Convection: Observed Behavior and Underlying Processes. Journal of Climate, 2021, 34 (5), pp.1685 - 1700. ⟨10.1175/jcli-d-19-0933.1⟩. ⟨hal-03448556⟩
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