A Relationship Between ITCZ Organization and Subtropical Humidity

Cathy Hohenegger,Christian Jakob

doi:10.1029/2020gl088515

Abstract

AbstractMotivated by the results of idealized studies on the self‐aggregation of convection, we investigate a potential relationship between the degree of organization of the Intertropical Convergence Zone (ITCZ) and humidity based on reanalysis data. We focus on the Atlantic ITCZ and use the number of long convergence lines occurring per month to define the degree of organization. The latter shows a weak enhancement during June to August (JJA) and a large interannual variability. On an interannual time scale and particularly during JJA, a relationship exists between organization and humidity: Years with more organized ITCZs are associated with a moister ITCZ region and drier subtropics. Even though we cannot demonstrate any causality and cannot rule out the presence of another agent, we show that these moisture anomalies are not incompatible with an effect of organization. We also note that the annual cycle in sea surface temperature (SST) gradient may contribute to the intra‐annual variability in organization.

Highlights

The propensity of convection to organize is undisputable
Motivated by the results of idealized studies on the self-aggregation of convection, we investigate a potential relationship between the degree of organization of the Intertropical Convergence Zone (ITCZ) and humidity based on reanalysis data
The goal of this study was to test the applicability of relationships derived from idealized studies on the self-aggregation of convection to the tropical Atlantic

Summary

Introduction

The propensity of convection to organize is undisputable. A prominent example is the large-scale organization of convection in the tropics in the form of the Intertropical Convergence Zone (ITCZ). Such studies have shown that the transition from a state with randomly distributed convection to a state made of one convective cluster is accompanied by a strong drying of the subsidence region (e.g., Bretherton et al, 2005). The enhanced drying has not been formally explained, it is generally assumed that one convective cluster, which tends to remain stationary, is less efficient at moistening the subsidence region given the longer distances that moisture has to travel, as noted in Tompkins and Semie (2017). With organized convection being associated with a higher precipitation

Objectives

Methods

Results

Conclusion