Search for: All records

Abstract This study examines the climate response to a sea surface temperature (SST) warming imposed over the southwest Tropical Indian Ocean (TIO) in a coupled ocean-atmosphere model. The results indicate that the southwest TIO SST warming can remotely modulate the atmospheric circulation over the western North Pacific (WNP) via inter-basin air-sea interaction during early boreal summer. The southwest TIO SST warming induces a “C-shaped” wind response with northeasterly and northwesterly anomalies over the north and south TIO, respectively. The northeasterly wind anomalies contribute to the north TIO SST warming via a positive Wind-Evaporation-SST(WES) feedback after the Asian summer monsoon onset. In June, the easterly wind response extends into the WNP, inducing an SST cooling by WES feedback on the background trade winds. Both the north TIO SST warming and the WNP SST cooling contribute to an anomalous anticyclonic circulation (AAC) over the WNP. The north TIO SST warming, WNP SST cooling, and AAC constitute an inter-basin coupled mode called the Indo-western Pacific ocean capacitor (IPOC), and the southwest TIO SST warming could be a trigger for IPOC. While the summertime southwest TIO SST warming is often associated with antecedent El Niño, the warming in 2020 seems to be related to extreme Indian Ocean Dipole in 2019 fall. The strong southwest TIO SST warming seems to partly explain the strong summer AAC of 2020 over the WNP even without a strong antecedent El Niño. 

Heavy Meiyu‐Baiu rainfall occurred over central‐east China and Japan in June–July 2020. This study analyzes observational and reanalysis data and performs atmospheric model simulations to investigate its causes. It is found that low Arctic sea ice cover (SIC) in late spring‐early summer of 2020 along the Siberian coast was an important factor. The low SIC caused local warming and high pressure, resulted in excessive atmospheric blockings over East Siberia, which caused cold air outbreaks into the Meiyu‐Baiu region, stopped the seasonal northward march of the Meiyu‐Baiu front, and increased the thermal contrast across the front, leading to record‐breaking rainfall in June–July 2020. Our results suggest that the 2020 extreme Meiyu‐Baiu was partly caused by the low SIC around the Siberian coast through its impact on East Siberian blockings. As sea ice along the Siberian coast decreases under global warming, its variations and thus influence on Meiyu‐Baiu rainfall may weaken.