# Changes of upper ocean disturbance caused by tropical cyclones in the Western North Pacific main development region (1993–2021)

## TL;DR

This study examines how tropical cyclones have affected the upper ocean in the Western North Pacific from 1993 to 2021, linking these changes to climate patterns like ENSO.

## Contribution

A novel UOD index was developed to quantify upper ocean disturbances caused by tropical cyclones, incorporating multiple environmental factors.

## Key findings

- The UOD index is strongly correlated with ENSO, showing higher values during El Niño and lower during La Niña years.
- Ocean thermal factors in the UOD index have increased in recent years, especially during La Niña events.
- Changes in SST, MLD, and salinity have altered upper ocean stratification over the study period.

## Abstract

During the passage of tropical cyclones (TCs) cause severe disturbances in the upper ocean, especially the TC main development region (MDR) (5°-23°N, 127°-160°E) in the Western North Pacific. The main attributes affecting the upper ocean disturbance were selected and weighted by the CRITIC weight method. An upper ocean disturbance (UOD) index with TCs intensity factors (MSW, Vh), ocean dynamic factors (SSC, RV, EPV) and ocean thermal factors (ΔSST, ΔMLD) was established. The change of UOD index in different time scales was analyzed by calculating each TC accumulation, monthly accumulation, and Interannual accumulation. The UOD index was closely related to the ENSO (El Niño–Southern Oscillation) climate anomaly, and their interannual correlation was as high as 0.83. Generally, the UOD index was higher in El Niño years and lower in La Niña years. In the past 10 years, the ocean thermal factors of UOD index have been increasing, especially in La Niña years. This is mainly due to the increasing SST, decreasing MLD and seawater salinity in recent years, which have changed upper ocean stratification. These results offer insights for the comprehensive analysis of the response and variation trend of the upper ocean to TC in the MDR of the Western North Pacific in recent years.