Prediction of summer extreme hot days in China using the SINTEX‐F2

• Published in: International journal of climatology 2021-08, Vol.41 (10), p.4966-4976
• Main Authors: Lu, Xinyu, Yuan, Chaoxia, Yang, Mengzhou, Doi, Takeshi, Wahiduzzaman, Md, Luo, Jing‐Jia
• Format: Article
• Language: English
• Subjects: Anomalies; Anticyclonic circulation; Circulation anomalies; Climatic extremes; Coefficients; Correlation coefficient; Correlation coefficients; Cyclonic circulation; Divergence; Extreme weather; Lead time; Meandering; Ocean basins; Oceans; Planetary waves; Plateaus; Predictions; Rossby waves; Seasonal forecasting; Skills; Summer; Trends; Tropical climate; Troposphere; Upper troposphere
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.7110

Accurate prediction of extreme weather and climate is crucial for their devastating impacts on our society and environment. Here, predictability of frequency of summer (June–August) extreme hot days (SEHDs) in China has been assessed in the SINTEX‐F2 seasonal forecast system during the period of 1983–2015. The hindcast had 12 ensemble members and was initialized on the first day of March, April and May, respectively. Results show that overall, the SINTEX‐F2 predicts more regions with good prediction skills at shorter lead time due to its better capture of the linear trends. Whereas, in Southwest China and eastern Tibetan Plateau, the prediction skills are consistently increased at shorter lead time even without the impacts of linear trends; the correlation coefficients between the region‐mean anomalies in the observed and predicted SEHD frequencies are 0.74, 0.68 and 0.61 at 1–3 month lead, respectively, and they remain as high as 0.56, 0.49 and 0.40 when the linear trends are removed. This is because the SINTEX‐F2 can reproduce the observed influences of Indian Ocean Basin Mode (IOBM) on the SEHD frequency. The warm IOBM can cause anomalous ascending and strong divergence in the upper troposphere over the tropical Indian Ocean and Indian subcontinent. The strong divergence causes direct convergence and descending over Southwestern China and eastern Tibetan Plateau. It also causes substantial descending over the western North Pacific that can introduce anomalous cyclonic circulation over northeastern Asia via the Pacific‐Japan or East‐Asia pattern. The latter serves as a source of wave energies, excites the Rossby waves meandering westward in the mid‐latitude, and enhances the anticyclonic circulation anomalies over Southwestern China and eastern Tibetan Plateau. The anomaly correlation coefficients (ACCs) between the observed and predicted SEHD frequencies when the SINTEX‐F2 was initialized on the first day of (a, d) March, (b, e) April and (c, f) May (a–c) without or (d–f) with the linear trends removed. The ACCs significant at the 90% confidence level are stippled. The dark rectangles in (a–f) denote the region of Southwest China and Eastern Tibetan Plateau.