Hans W. Chen

Chalmers University of Technology

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Deliang Chen

University of Gothenburg

Lanlan Guo

Beijing Normal University

Bin He

Guangdong Academy of Sciences

Wenping Yuan

Sun Yat-sen University

Judah Cohen

Atmospheric and Environmental Research

Xingming Hao

Xinjiang Institute of Ecology and Geography

Fuqing Zhang

East China University of Technology

Ziqian Zhong

Beijing Normal University

Richard B. Alley

Pennsylvania State University

Rui Tang

Shihezi University

Cooperative Institutions

Chinese Academy of Sciences

Beijing Normal University

University of Chinese Academy of Sciences

Peking University

Northwest Institute of Eco-Environment and Resources

Nanjing University of Information Science and Technology

Sun Yat-sen University

Pennsylvania State University

Lanzhou University

State Key Laboratory of Remote Sensing Science

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Interdecadal variability of the warm Arctic-cold Eurasia pattern linked to the Barents oscillation

Atmospheric Research (2023)

Ziyi Cai Qinglong You Hans W. Chen Ruonan Zhang Zhiyan Zuo

Atmospheric Circulation

Arctic oscillation

Anticyclone

Anomaly (physics)

Siberian High

Jet stream

Middle latitudes

10.1016/j.atmosres.2023.106712

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Citations (14)

Arctic amplification modulated by Atlantic Multidecadal Oscillation and greenhouse forcing on multidecadal to century scales

Nature Communications (2022)

Miao Fang Xin Li Hans W. Chen Deliang Chen

Abstract Enhanced warming in the Arctic (Arctic amplification, AA) in the last decades has been linked to several factors including sea ice and the Atlantic Multidecadal Oscillation (AMO). However, how these factors contributed to AA variations in a long-term perspective remains unclear. By reconstructing a millennial AA index combining climate model simulations with recently available proxy data, this work determines the important influences of the AMO and anthropogenic greenhouse gas forcing on AA variations in the last millennium, leading to identification of a significant downward trend of AA on top of a sustained strong AMO modulation at the multidecadal scales. The decreased AA during the industrial era was strongly associated with the anthropogenic forcing, proving the emerging role of the forcing in reducing the AA strength.

Forcing (mathematics)

Arctic oscillation

Proxy (statistics)

10.1038/s41467-022-29523-x

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Citations (36)

Cooperative simultaneous inversion of satellite-based real-time PM2.5 and ozone levels using an improved deep learning model with attention mechanism

Environmental Pollution (2023)

Xing Yan Chen Zuo Zhanqing Li Hans W. Chen Yize Jiang

Ground-level fine particulate matter (PM2.5) and ozone (O3) are air pollutants that can pose severe health risks. Surface PM2.5 and O3 concentrations can be monitored from satellites, but most retrieval methods retrieve PM2.5 or O3 separately and disregard the shared information between the two air pollutants, for example due to common emission sources. Using surface observations across China spanning 2014-2021, we found a strong relationship between PM2.5 and O3 with distinct spatiotemporal characteristics. Thus, in this study, we propose a new deep learning model called the Simultaneous Ozone and PM2.5 inversion deep neural Network (SOPiNet), which allows for daily real-time monitoring and full coverage of PM2.5 and O3 simultaneously at a spatial resolution of 5 km. SOPiNet employs the multi-head attention mechanism to better capture the temporal variations in PM2.5 and O3 based on previous days' conditions. Applying SOPiNet to MODIS data over China in 2022, using 2019-2021 to construct the network, we found that simultaneous retrievals of PM2.5 and O3 improved the performance compared with retrieving them independently: the temporal R2 increased from 0.66 to 0.72 for PM2.5, and from 0.79 to 0.82 for O3. The results suggest that near-real time satellite-based air quality monitoring can be improved by simultaneous retrieval of different but related pollutants. The codes of SOPiNet and its user guide are freely available online at https://github.com/RegiusQuant/ESIDLM.

10.1016/j.envpol.2023.121509

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Citations (22)

Regionalization of Seasonal Precipitation over the Tibetan Plateau and Associated Large-Scale Atmospheric Systems

Journal of Climate (2020)

Hui‐Wen Lai Hans W. Chen Julia Kukulies Tinghai Ou Deliang Chen

Abstract Precipitation over the Tibetan Plateau (TP) has major societal impacts in South and East Asia, but its spatiotemporal variations are not well understood, mainly because of the sparsely distributed in situ observation sites. With the help of the Global Precipitation Measurement satellite product IMERG and the ERA5 dataset, distinct precipitation seasonality features over the TP were objectively classified using a self-organizing map algorithm fed with 10-day averaged precipitation from 2000 to 2019. The classification reveals three main precipitation regimes with distinct seasonality of precipitation: the winter peak, centered at the western plateau; the early summer peak, found on the eastern plateau; and the late summer peak, mainly located on the southwestern plateau. On a year-to-year basis, the winter peak regime is relatively robust, whereas the early summer and late summer peak regimes tend to shift mainly between the central and northern TP but are robust in the eastern and southwestern TP. A composite analysis shows that the winter peak regime experiences larger amounts of precipitation in winter and early spring when the westerly jet is anomalously strong to the north of the TP. Precipitation variations in the late summer peak regime are associated with intensity changes in the South Asian high and Indian summer monsoon. The precipitation in the early summer peak regime is correlated with the Indian summer monsoon together with anticyclonic circulation over the western North Pacific. The results provide a basic understanding of precipitation seasonality variations over the TP and associated large-scale conditions.

Anticyclone

Seasonality

East Asian Monsoon

Atmospheric Circulation

10.1175/jcli-d-20-0521.1

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Citations (37)

The disproportionate impact of enhanced evaporation from melting arctic sea ice on cold-season land precipitation trends

npj Climate and Atmospheric Science (2024)

Yubo Liu Qiuhong Tang Chi Zhang Deliang Chen Jennifer A. Francis

Abstract Diminishing Arctic sea ice has led to enhanced evaporation from the Arctic marginal seas (AMS), which is expected to alter precipitation over land. In this work, AMS evaporation is numerically tracked to quantify its contribution to cold-season (October–March) precipitation over land in the Northern Hemisphere during 1980–2021. Results show a significant 32% increase in AMS moisture contribution to land precipitation, corresponding to a 16% increase per million square km loss of sea ice area. Especially over the high-latitude land, despite the fractional contribution of AMS to precipitation being relatively low (8%), the augmented AMS evaporation contributed disproportionately (42%) to the observed upward trend in precipitation. Notably, northern East Siberia exhibited a substantial rise in both the amount and fraction of extreme snowfall sourced from the AMS. Our findings underscore the importance of the progressively ice-free Arctic as an important contributor to the escalating levels of cold-season precipitation and snowfall over northern high-latitude land.

10.1038/s41612-024-00680-8

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Citations (2)

Interannual Arctic sea ice variability and associated winter weather patterns: A regional perspective for 1979–2014

Journal of Geophysical Research Atmospheres (2016)

Hans W. Chen Richard B. Alley Fuqing Zhang

Abstract Using Arctic sea ice concentration derived from passive microwave satellite observations in autumn and early winter over the 1979–2014 period, the Arctic region was objectively classified into several smaller regions based on the interannual sea ice variability through self‐organizing map analyses. The trend in regional sea ice extent (RSIE) in each region was removed using an adaptive, nonlinear, and nonstationary method called Ensemble Empirical Mode Decomposition, which captures well the accelerating decline of Arctic RSIEs in recent decades. Although the linear trend in RSIE is negative in all regions in both seasons, there are marked differences in RSIE trends and variability between regions, with the largest negative trends found during autumn in the Beaufort Sea, the Barents‐Kara Seas, and the Laptev‐East Siberian Seas. Winter weather patterns associated with the nonlinearly detrended RSIEs show distinct features for different regions and tend to be better correlated with the autumn than early winter RSIE anomalies. Sea ice losses in the Beaufort Sea and the Barents‐Kara Seas are both associated with a cooling of Eurasia, but in the former case the circulation anomaly is reminiscent of a Rossby wave train, whereas in the latter case the pattern projects onto the negative phase of the Arctic Oscillation. These results highlight the nonuniform changes in Arctic sea ice and suggest that regional sea ice variations may play a crucial role for the winter weather patterns.

Arctic oscillation

Sea ice concentration

Anomaly (physics)

Arctic geoengineering

Beaufort scale

Beaufort sea

10.1002/2016jd024769

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Citations (35)

Contrasting characteristics, changes, and linkages of permafrost between the Arctic and the Third Pole

Earth-Science Reviews (2022)

Xuejia Wang Youhua Ran Guojin Pang Deliang Chen Bo Su

Active layer

Arctic geoengineering

10.1016/j.earscirev.2022.104042

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Citations (83)

Worldwide impacts of atmospheric vapor pressure deficit on the interannual variability of terrestrial carbon sinks

National Science Review (2021)

Bin He Chen Chen Shangrong Lin Wenping Yuan Hans W. Chen

Interannual variability of the terrestrial ecosystem carbon sink is substantially regulated by various environmental variables and highly dominates the interannual variation of atmospheric carbon dioxide (CO2) concentrations. Thus, it is necessary to determine dominating factors affecting the interannual variability of the carbon sink to improve our capability of predicting future terrestrial carbon sinks. Using global datasets derived from machine-learning methods and process-based ecosystem models, this study reveals that the interannual variability of the atmospheric vapor pressure deficit (VPD) was significantly negatively correlated with net ecosystem production (NEP) and substantially impacted the interannual variability of the atmospheric CO2 growth rate (CGR). Further analyses found widespread constraints of VPD interannual variability on terrestrial gross primary production (GPP), causing VPD to impact NEP and CGR. Partial correlation analysis confirms the persistent and widespread impacts of VPD on terrestrial carbon sinks compared to other environmental variables. Current Earth system models underestimate the interannual variability in VPD and its impacts on GPP and NEP. Our results highlight the importance of VPD for terrestrial carbon sinks in assessing ecosystems' responses to future climate conditions.

Carbon sink

Terrestrial ecosystem

Sink (geography)

10.1093/nsr/nwab150

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Citations (98)

The Robustness of Midlatitude Weather Pattern Changes due to Arctic Sea Ice Loss

Journal of Climate (2016)

Hans W. Chen Fuqing Zhang Richard B. Alley

Abstract The significance and robustness of the link between Arctic sea ice loss and changes in midlatitude weather patterns is investigated through a series of model simulations from the Community Atmosphere Model, version 5.3, with systematically perturbed sea ice cover in the Arctic. Using a large ensemble of 10 sea ice scenarios and 550 simulations, it is found that prescribed Arctic sea ice anomalies produce statistically significant changes for certain metrics of the midlatitude circulation but not for others. Furthermore, the significant midlatitude circulation changes do not scale linearly with the sea ice anomalies and are not present in all scenarios, indicating that the remote atmospheric response to reduced Arctic sea ice can be statistically significant under certain conditions but is generally nonrobust. Shifts in the Northern Hemisphere polar jet stream and changes in the meridional extent of upper-level large-scale waves due to the sea ice perturbations are generally small and not clearly distinguished from intrinsic variability. Reduced Arctic sea ice may favor a circulation pattern that resembles the negative phase of the Arctic Oscillation and may increase the risk of cold outbreaks in eastern Asia by almost 50%, but this response is found in only half of the scenarios with negative sea ice anomalies. In eastern North America the frequency of extreme cold events decreases almost linearly with decreasing sea ice cover. This study’s finding of frequent significant anomalies without a robust linear response suggests interactions between variability and persistence in the coupled system, which may contribute to the lack of convergence among studies of Arctic influences on midlatitude circulation.

Middle latitudes

Arctic oscillation

Sea ice concentration

Arctic geoengineering

10.1175/jcli-d-16-0167.1

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Citations (79)

Precipitation variability related to atmospheric circulation patterns over the Tibetan Plateau

International Journal of Climatology (2023)

Hui‐Wen Lai Deliang Chen Hans W. Chen

Abstract Precipitation is affected by intricate atmospheric dynamic and thermodynamic processes. Horizontal winds are frequently used to represent the dynamic component as winds play a critical role in transporting moisture. Previous studies on precipitation over the Tibetan Plateau (TP) focused on the influence of summer monsoons and westerlies in isolation. However, the collective seasonal dynamics and their combined effects on the precipitation distribution remain less explored. This study aims to determine the seasonal evolutions of the wind patterns and the associated regional precipitation patterns over the TP using a neural network approach and focuses on their interannual variability and long‐term trends. A self‐organizing map (SOM) was used to classify the wind patterns based on 500 hPa winds and related precipitation from the ERA5 reanalysis. The classified wind patterns show seasonal shifts between the Asian summer monsoon circulations and the westerlies along with the westerly jets migrating between the north and south of the TP from summer to winter. The locations of abundant precipitation during the winter and transition seasons are mainly associated with variations in the intensity and locations of the strong westerlies. There is a significant positive trend in the occurrences of the summer‐type wind pattern, which has likely led to a wetter TP, and an earlier‐ended winter and advanced spring wind patterns. The interannual variability of westerlies is highly related to the variability of precipitation in the western TP during its wet season (January–April). In the eastern TP, the interannual variability of the precipitation is linked to the wind patterns associated with the westerly jets to the south of the TP, while precipitation variability in the central TP is controlled by thermodynamic components. This study reveals the spatial precipitation distributions according to the different wind patterns and identifies the contributions from atmospheric components to the regional precipitation over the TP.

Westerlies

Global wind patterns

Atmospheric Circulation

Prevailing winds

Seasonality

10.1002/joc.8317

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Citations (6)