Impact of the Spring North Atlantic Oscillation on the Northern Hemisphere Tropical Cyclone Genesis Frequency

Leying Zhang,Jiuwei Zhao,Xiting Yang

doi:10.3389/feart.2022.829791

Abstract

A majority of studies have documented basin-dependent factors for predicting interannual variability of tropical cyclone genesis frequency (TCGF) over basins. In this study, we find that the spring North Atlantic Oscillation (NAO) has cross-basin impacts on summer and autumn TCGF over the whole North Hemisphere. The positive NAO suppresses the TCGF in the North Atlantic (NA) but promotes the TCGF in the North Pacific (NP) via modulating the large-scale environment parameters and vice versa. The positive NAO in spring can induce negative sea surface temperature (SST) anomalies in the NA, which persists into summer via the ocean memory. The negative SST anomalies cool the overlying atmosphere and damp the precipitation, leading to a low-level anti-cyclonic circulation and thereby counteracting the TCGF over the NA in summer and autumn. The southerly anomaly west of the anti-cyclonic circulation increases the SST and precipitation over the northeast Pacific in summer. Accordingly, a cyclonic circulation appears western NP via Gill response and sustains by the warm advection via the air–ocean positive feedback, which devotes the NP TCGF in summer and autumn. The composite results in high-resolutions numerical model from Coupled Model Intercomparison Project Phase 6 further verify the relationship between the spring NAO and TCGF.

Highlights

Tropical cyclone (TC) often associates with destructive weather, resulting in enormous death and property damage (Kossin et al, 2016; Peduzzi et al, 2012; Schultz and Cecil, 2009)
This study investigates the influence of spring NAO on the NH TC genesis frequency (TCGF) in summer and autumn and finds that positive NAO suppresses the TCGF over the North Atlantic (NA) (NP) through modulating the vorticity, relative humidity, and vertical wind shear
The positive NAO in spring can induce negative SST anomalies over the NA, which persist into summer via ocean memory

Summary

INTRODUCTION

Tropical cyclone (TC) often associates with destructive weather, resulting in enormous death and property damage (Kossin et al, 2016; Peduzzi et al, 2012; Schultz and Cecil, 2009). Humidity with positive wind shear over the NA suppress the TCGF, while the anomalous circulations promote TCGF over the NP, forming a see-saw variability of circulations and TCGF across two basins These confirm the bridge role of the NA SST between the spring NAO and TCGF in summer and autumn. The negative air temperature over the tropical NA corresponds to the anomalous descent, which benefits the anti-cyclonic circulation at lower troposphere and cyclonic circulation at upper troposphere in summer (Yu et al, 2016) These devote to the negative vorticity and relative humidity anomaly and positive vertical wind shear (Figures 5A,C), which counteract the TCGF over the NA. To verify the relationship between the spring NAO and TCs in summer and autumn, 35 (40) positive (negative) NAO years in five ECWMF members are selected according to the ±0.7 normalized NAO index to composite the TCGF and the associated large-scale environment parameters (Figure 7). The westerly wind south of the anomalous cyclone warms the tropical SST in the NP and enhances the cyclone via the air–ocean positive feedback, which benefits the TCGF over the NP in autumn

SUMMARY AND DISCUSSION

DATA AVAILABILITY STATEMENT