Research Highlights
Lastest Update: 6 May 2024
Dynamic pathway linking Pakistan flooding to East Asian heatwaves
In July–August 2022, Pakistan suffered historic flooding while record-breaking heatwaves swept southern China, causing severe socio-economic impacts. Similar extreme events have frequently coincided between two regions during the past 44 years, but the underlying mechanisms remain unclear. Using observations and a suite of model experiments, here we show that the upper-tropospheric divergent wind induced by convective heating over Pakistan excites a barotropic anomalous anti-cyclone over eastern China, which further leads to persistent heatwaves. Atmospheric model ensemble simulation indicates that this dynamic pathway linking Pakistan flooding and East Asian heatwaves is intrinsic to the climate system, largely independent of global sea surface temperature forcing. This dynamic connection is most active during July–August when convective variability is large over Pakistan and the associated divergent flow excites barotropic Rossby waves that propagate eastward along the upper troposphere westerly waveguide. This robust waveguide and the time delay offer hopes for improved sub-seasonal prediction of extreme events in East Asia.

A dry, cracked riverbed near Poyang Lake, China, October 2022. Credit: Dike Su/ZQA Weather Hub of China
Reference:
- Fu, Z.-H., W. Zhou*, S.-P. Xie*, R. Zhang, and X. Wang, 2024: Dynamic Pathway Linking Pakistan Flooding to East Asian Heatwaves. Science Advances, 10, eadk9250. https://doi.org/10.1126/sciadv.adk9250, [Magazine cover], [News in ScienceAAAS], [News in Fudan]
Multiple Tropical Cyclone Events under Climate Change: Mechanisms, Projections, and the Deterministic-Probabilistic Model
Multiple tropical cyclone events (MTCEs) can cause extreme precipitation, winds, and surge storms due to their persistent and accumulated effects beyond the impacts of a single TC, which are important for socioeconomic management but difficult for operational forecast. Understanding the mechanism and potential changes in MTCE under a warmer climate are crucial for effective risk management and ensuring human safety, however, it remains tricky.
Based on an objective method called K-means, our study first explores the corresponding large-scale dynamic conditions of three clustered types of MTCEs over the western North Pacific (WNP). After that, we propose a multiple linear regression model to predict the interannual variability of WNP-MTCEs.
Furthermore, we project changes in MTCEs by 2050 in the major basins of the Northern Hemisphere (NH) using high-resolution climate models. Results show that a significant increase in the frequency and duration of MTCEs over the North Atlantic is tied to vertical wind shear, and a notable decrease over the WNP is attributed to mid-level vertical motion. These findings give a first understanding of future changes in MTCEs and give implications for disaster mitigation and prevention among countries in the NH. (Fu et al. 2023, GRL)
To further facilitate the understanding between the change of MTCE and TC genesis frequency, TC lifespan, as well as TC seasonality, we propose a Deterministic-Probabilistic MTCE model. This part of research is ongoing…

A satellite image of MTCE, taken on September 14, 2022, from digital-typhoon
References:
Fu, Z.-H., R. Zhan*, J. Zhao, Y. Yamada, and K. Song, 2023: Future Projections of Multiple Tropical Cyclone Events in the Northern Hemisphere in the CMIP6-HighResMIP Models. Geophysical Research Letters. 50, e2023GL103064. https://doi.org/10.1029/2023GL103064, [Outreach Video], [News in ZQA], [News in 科普中国]
Fu, Z.-H., and R. Zhan*, 2024: Objective clusters of multiple tropical cyclone events over the western North Pacific: physical process and seasonal prediction. In preparation.
Fu, Z.-H. et al., 2024: Disentangling changes of global multiple tropical cyclone events in a warming climate. In preparation.
Characteristics of Aerosol Chemistry and Acidity in Shanghai after PM2.5 Satisfied National Guideline: Insight into Future Emission Control
With continuous endeavors to control air pollutant emissions, the average concentration of PM2.5 in Shanghai in 2019-2020 satisfied the national secondary standard (35 μg m-3) for the first time. In this study, the two-year dataset of hourly resolution PM2.5 compositions observed in downtown Shanghai was used to investigate the relative contribution of sulfate and nitrate as well as particulate acidity. The average concentration of SO2 was reduced to 7.7 μg m-3, while the concentration of NOx remained above 40 μg m-3, indicating that the control of SO2 was more effective than that of NOx during the 13th Five-Year Plan period. Thus, the sulfate pollution was significantly reduced whereas the nitrate loading remained almost constant. The monthly N/S ratio varied from below 0.6 to above 2.0, indicating that the contribution of automobile exhaust to PM2.5 is seasonally dependent. Contrary to sulfate, the nitrate fraction increased rapidly with the increase of PM2.5 mass, suggesting that the explosive growth of nitrate has become a major driver of haze formation. ISORROPIA simulations show that PM2.5 was moderately acidic with pH values following the trend of winter > spring > autumn > summer. The diurnal variation of nitrate was related to the changes in aerosol water content, indicating the effect of heterogeneous aqueous reactions on secondary aerosol formation. The effectiveness of emission control for reducing inorganic PM2.5 varied with different gas precursors and seasons. The abatement of NH3 emissions will increase particle acidity and acid rain pollution, although it is more effective than that of NOx when the emission reduction is larger than 60%. This study suggests that the control of vehicle exhaust should be given priority in the Yangtze River Delta for coordinately mitigating PM2.5 and acid rain pollution.

Graphical Abstract of Fu et al. 2022 STOTEN
Reference:
- Fu, Z.-H., L. Cheng, X. Ye*, Z. Ma, R. Wang, Y. Duan*, J. Huo, and J. Chen, 2022: Characteristics of aerosol chemistry and acidity in Shanghai after PM2.5 satisfied national guideline: Insight into future emission control, Science of The Total Environment, 154319. https://doi.org/10.1016/j.scitotenv.2022.154319, [News in ZQA]