The record-breaking 2022 long-lasting marine heatwaves in the East China Sea

Abstract

In 2022, record-breaking long-lasting marine heatwaves (MHWs) occurred in the East China Sea (ECS), which persisted for 62 days during boreal summer. This exceeded the average MHWs duration of 10 days by a factor of 6. In addition, 2022 was also recorded as a year of many extreme events throughout Asia, such as summer floods in China and Pakistan, droughts and extreme heat in Europe, raising the question of whether they were caused by a “triple-dip” La Niña, which has persisted since September 2020. Here we examine the key local and remote processes that led to the 2022 MHWs in the ECS using mixed-layer heat budget analysis. During the onset of the MHWs, a salinity-stratified shallow mixed-layer due to the large river discharge from the Yangtze-Huaihe River floods in June enhanced warm ocean temperature in the ECS. Simultaneously, an anomalous anticyclone maintained by the stationary Rossby wave, which is generated by vorticity forcings in mid-latitudes and thermal forcing in Pakistan, settled in the corresponding region and led to the long-lasting MHWs until Typhoon Hinnamnor began to dissipate the wave in early September. This study improves our understanding of the physical mechanism of flood-related MHWs that have increased with recent climate change.

Marine Heatwaves in the East Asian Marginal Seas Facilitated by Boreal Summer Intraseasonal Oscillations

“…Some investigations have explicitly identified the crucial role of land heatwave factors, such as increased shortwave radiation and reduced wind speed resulting from changes in the local ocean-atmospheric interactions (Cai et al, 2017;Gao et al, 2020). Other studies have emphasized the importance of warm water advection, local stratification and the shoaling of oceanic surface mixed layers as critical factors driving the genesis of MHWs in this region (Gao et al, 2020;Lee et al, 2023;Oh et al, 2023;Yan et al, 2020). Gao et al (2020) suggested that the consecutive occurrences of MHWs in the summers of 2016-2018 were primarily governed by the excess shortwave, reduced wind speed and advection of warm water over the NECS-SYS region.…”

“…However, they found a minor contribution of freshwater stratification to the mixedlayer shoaling during these major MHW events. Oh et al (2023) pointed out that the recent long-lasting MHW during the summer of 2022 was initiated by the shallow mixed layer resulting from the large river discharge from the Yangtze-Huaihe River floods. While it is well-known that the factors responsible for land heatwaves often trigger marine heatwaves, the significance of oceanic factors, including reduced mixed layer depth (MLD), has only recently gained attention (Amaya et al, 2021;Capotondi et al, 2022;Elzahaby et al, 2022;Jacox et al, 2022;Oh et al, 2023;Sallée et al, 2021;Yan et al, 2020).…”

Seasonal variation of Marine Heat Wave in the East China Sea

“…Notably, several MHW hotspots have been identified, encompassing regions such as the western area adjacent to the Changjiang River, the near-coast of Zhejiang Province, and the near-coast of Jiangsu Province [14]. Additionally, research efforts have investigated the phenomena and underlying mechanisms of an unprecedented MHW event in the ECS [15,16]. One potential trigger of MHW in the ECS is the influence of relatively fresh water [17].…”

The dominant role of upper tropospheric-lower stratospheric process in increasing summer heatwave intensity over East Asia and Northwestern Pacific

“…In the summers of 2013, 2016, and 2017, strong heat wave events attacked these areas [14][15][16] . Especially in July-August of 2022, an unprecedented strong heatwave event swept across East Asia [17][18][19] and the Northwestern Pacific 4,5,20 . The extremeness of this event is the largest in both magnitude and duration, causing substantial loss of economy, human community as well as the marine organisms and ecosystem 5,17,21 .…”

“…Previous studies documented that the extreme heatwave event in 2022 is attributed to the widespread easterly wind anomalies at the south flank of the South Asian high (SAH). The easterly wind anomalies enhance subsidence, suppress the development of cloud cover, and increase insolation at the ground surface and surface air temperature (SAT) in East Asia and the adjacent oceans 3,4,23 . It has been accepted that the atmospheric circulations associated with this heatwave event are closely related to the La Niña-like SST pattern, a west-east difference in the tropical Pacific SST, the tropical Indian Ocean basin-wide cooling, the Indian Ocean Dipole, the tropical North Atlantic Ocean warming, and the North Atlantic tripole SST pattern under global warming [1][2][3][4][5][6]24 .…”