Intraseasonal Vertical Cloud Regimes Based on CloudSat Observations over the Tropics

Meng-Pai Hung,Peng-Jen Chen,Wei-Ting Chen,Chien-Ming Wu,Pei-Ning Feng

doi:10.3390/rs12142273

Meng-Pai Hung, Peng-Jen Chen + Show 3 more

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https://doi.org/10.3390/rs12142273

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Abstract

This study identifies the evolution of tropical vertical cloud regimes (CRs) and their associated heating structures on the intraseasonal time scales. Using the cloud classification retrievals of CloudSat during boreal winter between 2006 and 2017, the CR index is defined as the leading pair of the combined multivariate empirical orthogonal functions of the daily mean frequency of deep, high, and low clouds over the tropical Indian Ocean, Maritime Continents, and the Western Pacific. The principal components of the CR index exhibit robust temporal variance in the 30 to 80 day intraseasonal band. Based on the propagation stages of the CRs, the coherent vertical structures of cloud composition and large-scale moisture and vertical motion exhibit a westward-tilted structure. The associated Q1-QR diabatic heating and cloud radiative forcing are consistent with the key characteristics of the Madden Julian Oscillation (MJO) documented in the previous studies. Lastly, an MJO case study showcases that the presented approach characteristically captures the propagation of moisture, cloud vertical structure, and precipitation activity across spatial and temporal scales. The current results suggest that the CR index can potentially serve as an evaluation metric to cloud-associated processes in the simulated tropical intraseasonal variability in global climate models.

Highlights

Tropical convective clouds and the associated precipitation are essential modulators of the climate system
As previous studies have shown that satellite-derived cloud regimes (CRs) correspond well to the large-scale states of the Tropics [15,16,29] and the CloudSat observations composited for various phases of the intraseasonal variability revealed distinct patterns of vertically-resolved cloud structure [24,25,26,27,28], the goal of the present study is to identify the major tropical vertical CRs at intraseasonal time scales as a description index from the CloudSat regarding the relative abundance of multiple cloud types
CR-EOF1 and CR-EOF2 explained around 24% and 20% of the variance of the original cloud frequency data, which was significantly higher than the remaining empirical orthogonal functions (EOFs)

Summary

Introduction

Tropical convective clouds and the associated precipitation are essential modulators of the climate system. Tropical convection systems exhibit multiple scales; the cumulus can upscale to mesoscale systems and further to planetary-scale such as the Madden Julian Oscillation (MJO), the dominant intraseasonal (30–90 days) variability during the boreal winter. Mapes [13] noted the progression from shallow to deep convection to stratiform anvils is self-similar in the tropical variabilities of various time scales. They argued that the multiscale structure, which is modulated by larger scale waves, consists of mesoscale convection systems (MCSs) with varying durations of shallow, deep, and stratiform anvil clouds, instead of simple superpositions of fixed cloud structures. Multiple cloud species usually coexist in the Tropics, and their relative composition reflects the changes in the large-scale states

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