Prof. Yaocun Zhang's group has made progress in the research of the relations between the local wave activity (LWA) and extreme weather events. The research papers were lately published in AGU's Geophysical Research Letters, and NPJ Climate and Atmospheric Science of the Nature.
Local wave activities have prominent connections with the anomalies of atmospheric circulation and regional climate variations. The zonal circulation patterns caused by LWA manifest the atmospheric circulation anomalies of the mid-latitude, for example, through the longitudinal inversion method, one can define the blocking system by its geopotential height gradient. Meanwhile, the atmospheric circulation anomalies, especially the anomalies of westerly jet, will regulate the intensification and spreading of LWA, thus making the LWA develop sustainably. With the interactions between LWA and atmospheric circulations, the Northern Hemisphere circulation systems, and reginal climate variations will be further affected and the extreme weather events downstream will be event triggered or developed thereof. The mutual feedback mechanism has become one of the frontier research topics.
Finite-amplitude wave activity is developed as an objective measure for the areal displacement of a physical quantity. In this research, finite-amplitude wave activity was applied to 500hPa geopotential height. Evaluating the trends of the both zonal-mean and local wave activities shows that the observed Arctic sea ice loss leads to insignificant hemispherical-wide increase of the total wave activity, while locally, the reduction of the sea ice over Barents-Kara Sea can induce an increase of anticyclonic local wave activity(LAWA) over central northern Eurasia. Due to this change, the anomalies in eddy heat flux transport accompanied with the reginal circulation changes increase the occurrence frequency of cold weather extremes over Eurasia.
Figure 1. Schematic for the concepts of column integrated water vapor (CWV) local wave activity (LWA). The blue area represents the wet moisture wave activity, and the orange one, the dry moisture wave activity.
In addition, after analyzing the eddy activity characteristics of the whole layer moisture, the group has found that when moisture is being transported continuously from the tropical areas to the mid-latitudes, the extreme precipitation led by eddy moisture activities has an important role in the hydrological cycle. In winter, in the range of atmospheric river, large quantities of moisture are transported to the lower reaches, like western states of the America, in which extreme precipitation happen; in summer, however, monsoon areas get rainstorms, for which moisture anomalies should take responsibility. Under climate change scenario RCP8.5, the middle latitude areas will get higher portion of moisture; the stirring length of water vapor wave activities is enhanced with little resident time of hydrological cycle. Thus, there are going to be more extreme precipitation within shorter time, leading to disastrous rainfall thereof.
Fig. 2. Demonstrate the characteristics of moisture wave activity under climate change scenario RCP8.5 in western regions of the America in winter (left) and summer monsoon region (right).
Prof. Yaocun Zhang's research group and Jian Lu, et al. in Paciﬁc Northwest National Laboratory are dedicated to this series of researches. Dr. Daokai Xue is the first author and/or the joint first author of the relevant three papers. The National Key R&D Program of China, National Nature Science Foundation of China, and other program grants jointly supported this series of work.
Xue, D., J. Lu, L. Sun, G. Chen, and Y. Zhang, 2017: Local increase of anticyclonic wave activity over northern Eurasia under amplified Arctic warming, Geophys. Res. Lett., 44, 3299–3308, doi:10.1002/2017GL072649
Lu J.*, D. Xue*, Y. Gao, G. Chen, L. Leung, and P.W. Staten.,2018: Enhanced hydrological extremes in the western United States under global warming through the lens of water vapor wave activity. NPJ?Climate and Atmospheric Science, 1:7;?doi:10.1038/s41612-018-0017-9
Xue, D., Lu, J., Leung, L. R., & Zhang, Y.,2018: Response of the hydrological cycle in Asian monsoon systems to global warming through the lens of water vapor wave activity analysis. Geophysical Research Letters, 45. https://doi.org/10.1029/2018GL078998