Attribution of the seasonality of atmospheric heating changes over the western tropical Pacific with a focus on the spring season

Shuheng Lin,Song Yang,Shan He,Jiaxin Chen,Zhenning Li,Wenjie Dong,Jiaxue Wu

doi:10.1007/s00382-021-06020-3

Abstract

Atmospheric diabatic heating, a major driving force of atmospheric circulation over the tropics, is strongly confined to the tropical western North Pacific (TWNP) region, with the global warmest sea surface temperature (SST). The changes in diabatic heating over the TWNP, which exert great impacts on the global climate system, have recently exhibited a noticeable seasonal dependence with a remarkable increase in boreal spring. In this study, we applied observations, reanalysis data, and numerical experiments to investigate the causes of the seasonality in heating changes. Results show that in boreal spring convection is more sensitive to the TWNP SST, leading to a more significant enhancement of deep convection, although the increase in the SST is nearly the same as that in the other seasons. In the non-spring seasons, the enhanced convection due to increased local SST is suppressed by the anomalous anticyclonic wind shear over the TWNP, generated by the easterly wind anomalies induced by the tropical Indian Ocean (TIO) warming via the Kevin waves. However, the TIO warming does not show any suppressing effect in spring because it is much weaker than that in the other seasons and thus the warming itself cannot induce sufficient convective heating anomalies to excite the Kelvin waves.

Highlights

In the tropics, atmospheric diabatic heating, especially the latent heating from cumulus convective condensation, is the major driving force of large-scale atmospheric circulation (Webster 1972)
We have examined the long-term changes in diabatic heating over the tropical western North Pacific (TWNP) during 1979–2015 and found that diabatic heating has increased significantly in the boreal spring, caused by enhanced deep convection
We explore the cause for this seasonality of the changes in diabatic heating by analyzing multiple observational and reanalysis datasets, and by performing several numerical experiments

Summary

Introduction

Atmospheric diabatic heating, especially the latent heating from cumulus convective condensation, is the major driving force of large-scale atmospheric circulation (Webster 1972). The long-term changes in TWNP diabatic heating and the resultant impacts on regional climate have received considerable attentions in recent studies. The changing observing system may have induced some spurious signals of the tropical climate changes derived from the atmospheric reanalysis products (Basist and Chelliah 1997; Bengtsson et al 2004; Kinter et al 2004), and affected the assessment of long-term trend of diabatic heating using such reanalysis data before 1979. We first examined the characteristics of changes in TWNP heating of all seasons during the recent decades (1979–2015) using multiple reanalysis and observations datasets. Given the close relationship between SST and convection, we examine the impacts of TWNP and TIO SST warming on the TWNP convection in all seasons to interpret the seasonality of changes in diabatic heating. The NOAA Extended Reconstructed SST V4 (ERSST4; Huang et al 2015) and Centennial in situ Observation-Based Estimates (COBE) SST data (Folland and Parker 1995) are used for validations

Data and numerical experiments

Significant increase in springtime atmospheric heating

Influence of local SST warming on deep convection changes

Impact of recent TIO warming on TWNP convection

Findings

Summary and discussion