太平洋經向模態對臺灣夏季溫度和熱浪的影響

Abstract

在過去的一個世紀中，臺灣夏季溫度的上升和熱浪事件的加劇，可能對人們的日常生活造成相當大的災害，因此我們迫切的需要進一步研究它們的特徵以及對人類生活的影響。太平洋經向模態是一個發生在東太平洋南北向海平面溫度異常增溫的氣候變異，根據前人的研究，太平洋經向模態是西太平洋以及亞洲部分國家的極端高溫的主因，包括中國、印度等等，然而，太平洋經向模態和臺灣夏季溫度變化之間的關係卻仍需要更近一步的討論與研究。本研究旨在釐清太平洋經向模態與臺灣夏季溫度之間的關係與其中的物理機制，並進一步的分析太平洋經向模態增強時對臺灣的極端高溫與熱浪事件造成的影響，以及評估暴露在極端高溫之下的人口數量。我們發現太平洋經向模態是在十年的時間尺度上造成臺灣夏季溫度變化的主要因素之一，在太平洋經向模態正相位期間異常的溫暖海表面溫度將會激發向東移動的波列，延伸到北太平洋，進入東亞，引起中國東南方和臺灣附近的反氣旋環流的發展，這些環流伴隨下沉，導致更穩定的大氣，減少夏季西南季風的影響，並增強地表的短波輻射，最終導致夏季溫度的升高。這種機制可以通過使用Taiwan Earth System Model version 1進行實驗來驗證。在太平洋經向模態正相位期間，極端高溫和熱浪事件的規模變得更大、頻率增加，且持續時間延長，在對熱浪的人口暴露度部分，臺中市、彰化縣和苗栗縣等西部縣市的對熱浪的人口暴露量增加最多。本研究希望能夠增加我們對臺灣夏季溫度在年代際尺度變化的瞭解，並提供更多的資訊給各領域的專家制定中長期氣候調適計畫。

Over the past century, Taiwan have experienced intensifying temperatures and heatwaves in prolonged summer duration. These climatic shifts can pose considerable disasters, raising the urgency for further examination of their characteristics and impacts on human daily life. Pacific Meridional Mode (PMM), an anomalous north-south sea surface temperature gradient over the east subtropical Pacific, has been recognized influencing extreme temperatures in countries including China and India. However, the specific association between the variation of temperatures in Taiwan and the PMM remains under investigation. This study found that PMM is one of main drivers modulating summer temperatures in Taiwan on a decadal scale. The warm SST anomaly during the PMM positive phase can excite a wave train moving eastward over the Northern Pacific extends into East Asia, causing the development of anticyclonic circulations in the vicinity of southeastern China and Taiwan. These circulations are accompanied by subsidence, leading to atmospheric stabilization, diminishing the impact of southwesterly monsoon and enhances shortwave radiation at the surface. This mechanism can be reproduced by experiments using the Taiwan Earth System Model version 1 with PMM-like SST forcing. Our analysis also revealed that extremely high temperatures and heatwave events are more intensified, along with heightened frequency and prolonged duration of heatwaves, during the positive phase of PMM. A heightened exposure to heatwaves is evident in the northern, northwestern, and eastern regions of Taiwan. This impact extends to over 800,000 people in a single county, marking a tenfold increase compared to the effects observed in the global warming trend over one year. These findings of the relationship between summer temperatures in Taiwan and PMM on decadal scale could offer valuable insights into heatwave impact, facilitating future strategies to adapt the disaster of heatwave.