Professor Zhemin Tan’s group, from the MOE Key Laboratory of Mesoscale Severe Weather (LMSWE), NJU has achieved major breakthroughs in northwestern Pacific typhoon study. The related paper, titled "Westward migration of tropical cyclone rapid-intensification over the Northwestern Pacific during short duration El Niño", was published in the April 17 issue of Nature Communications.
Typhoons, or tropical cyclones (TCs) are one of the severest sudden onset natural disasters in the world and exhibit the highest frequency over the North Paciﬁc (WNP) basin. As WNP TCs inflict significant damage and loss of life to the coastline of China each year, it is important to understand their variability and underlying mechanisms for the benefit of national economy and people’s livelihood. WNP TCs classified as severe and super typhoons mostly undergo a rapid-intensification (RI) before making landfall. Yet the roles of relative contributors in this intensity change remain unclear, bringing much challenge to RI forecasting. The unavoidable delay in disaster prevention and mitigation has caused heavy losses in affected areas. El Niño events are known to be important contributors to the WNP TC RI, and can be categorized into two subtypes based on their durations. In the new study, researchers investigated the respective impacts of the two subtypes and found that during short duration (SD) El Niño events, the WNP tropical cyclone rapid-intensification mean occurrence position migrates westward by ~8.0° longitude (Fig. 1). In other words, the WNP TC RI occurs much closer to the East Asian mainland during SD El Niño events, which increases the chances for severe typhoon genesis in China’s coastal waters. The westward migration of RI occurrence also brings great challenge to forecasts and narrows the time window for disaster prevention and mitigation, leaving China’s coastal areas more vulnerable in typhoon hazards. The authors further point that, during the summer of SD El Niño events, the upper Ocean Heat Content (OHC) increase over the South China Sea and the Western Philippine Sea are large enough to provide persistent energy fueling for the TC intensification, while during the summer of LD El Niño events the OHC increase is lacking. In addition, as the frequency of SD El Niño is projected to increase under global warming, more near-land TC RI would occur in China’s coastal areas because of high-emission scenarios, potentially aggravating the TC destructiveness in the future.
This work was jointly supported by the National Key Research and Development Program of China under grant 2017YFC1501601, the National Natural Science Foundation of China (41461164008 and 41705057), the National Key Project for Basic Research (973 Project) under grant 2015CB425803, and the Natural Science Foundation of Jiangsu Province (BK20170637). Professor Zhemin Tan’s group, from the School of Atmospheric Sciences at Nanjing University has been dedicated to the study of typhoon dynamics, mutual impacts between TC’s inner core and ambient environment and typhoon simulation and prediction for many years and has achieved important results in these areas. Doctor Yipeng Guo is the first author of this paper, and Professor Zhemin Tan is the corresponding author.
Fig.1 (a) The time series of monthly mean Niño-3.4 indices based on ERSST reanalysis dataset from January of the El Niño developing year to December of the decaying year for a short duration (SD) El Niño events. (b) The composite tropical cyclone (TC) rapid intensification (RI) occurrence positions from JTWC best-track dataset for SD El Niño events.
Link to the paper:
Guo Y.-P., and Tan Z.-M., 2018: Westward migration of tropicalcyclone rapid-intensification over the northwestern Pacific during shortduration El Niño. Nature Communications, 9, 1570. doi: 10.1038/s41467-018-03945-y.