Zheng-Hang Fu

Zheng-Hang Fu

fuzh23@m.fudan.edu.cn

Research Highlights

Lastest Update: 20 May 2025

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.


Graphical Abstract
A dry, cracked riverbed near Poyang Lake, China, October 2022. Credit: Dike Su/ZQA Weather Hub of China

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Multiple Tropical Cyclone Events under Climate Change: Mechanisms, Projections, and the Probabilistic Modeling

Multiple tropical cyclones (TC) could be present concurrently within one basin. Such multiple TC events (MTCEs) can induce compound hazards within a short time window, causing disproportionate damages.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.

Firstly, We focus on spatial diversity in MTCE occurrence over the western North Pacific (WNP), revealing their underlying mechanisms. Based on spatial features, MTCEs are classified into three clusters: Eastern Induced (EI) cluster, Western Induced in the Nearshore (WI-N) cluster, and Western Induced in the Open Sea (WI-O) cluster. The EI cluster is driven by the strengthened South China Sea summer monsoon, with TCs forming within the monsoon trough and confluence regions. The WI-N cluster primarily arises from the interaction between the monsoon westerlies and easterlies associated with an anomalous anticyclone. The WI-N cluster is characterized by tropical wave trains, potentially linked to TC-induced Rossby wave dispersion and easterly waves. Dynamic genesis potential analysis reveals that enhanced mid-level vertical motion dominates the dynamic factors controlling the MTCE formation across the WNP. Meanwhile, barotropic energy conversions, arising from the convergence and meridional shear of large-scale zonal winds, serve as the primary sources of eddy kinetic energy for MTCE formation. Upper-level baroclinic energy conversions also play a significant role, especially for the WI-N and WI-O clusters. Our findings offer a comprehensive view to better understand the spatial diversity of MTCE over the WNP. (Fu et al. 2025, submitted)

Furthermore, we project changes in MTCEs by 2050 in the major basins of the Northern Hemisphere using high-resolution climate models. Results show a significant increase in the frequency and duration of MTCEs over the North Atlantic (NA), a notable decrease over the WNP, and little change over the eastern North Pacific (ENP). The increase in MTCEs over the NA is concentrated in August–September, while the decrease over the WNP occurs in most months. In contrast, the ENP exhibits large yet insignificant seasonal variation, suggesting considerable uncertainty in this basin. Further analysis shows that mid-level vertical motion dominates the MTCE changes over the WNP, while vertical wind shear contributes the most to the NA, which may be linked to future changes in tropical convection. (Fu et al. 2023, GRL)

While the WNP has historically been home to the most MTCEs, we further find that the NA has emerged as a MTCE hotspot during recent decades. Using observations and high-resolution climate model simulations, we develop a probabilistic model assuming that TCs are mutually independent and occur randomly. Against this baseline, we identify outliers as MTCEs with dynamic interactions between TCs. We find that recent global warming pattern induces a hotspot shift in MTCE occurrence from the WNP to the NA by modulating TC frequency and synoptic-scale wave activity. Our probabilistic modeling indicates a tenfold increase in the likelihood of MTCE frequency in the NA surpassing that in the WNP, from 1.4 ± 0.4% to 14.3 ± 1.2% over the past 46 years. (Fu et al. 2025, NCC)


Graphical Abstract
A satellite image of MTCE, taken on September 14, 2022, from digital-typhoon

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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
Graphical Abstract of Fu et al. 2022 STOTEN

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