The East Asian Subtropical Jet, East Asian Polarfront Jet, and Transient Activities in FGOALS

Abstract A 200-hPa zonal momentum budget is performed to examine the role that western North Pacific tropical cyclones (TCs) play in helping to organize intraseasonal extratropical circulation anomalies that occur with the Madden–Julian oscillation (MJO). Zonal wind is linearly decomposed into components that occur on MJO time scales (i.e., 20–100-day periods), as well as those that occur with lower and higher frequency. Dates during Northern Hemisphere fall that feature nonrecurving TCs within a search radius centered on a South China Sea grid point when the MJO is convectively active over the Maritime Continent and west Pacific warm pool are used to generate composites of relevant budget terms. These composites are then compared to others that are based on the full list of dates that feature a convectively active MJO in the same location during NH fall without regard for TC presence. Composite results highlight the primary momentum sources that guide the evolution of the NH extratropical zonal wind and associated mass field in each event set. TCs help to accelerate the East Asian subtropical jet that evolves with the MJO by modulating the high-frequency subtropical circulation over Southeast Asia. The phasing of this circulation with its underlying MJO time-scale component enables it to transfer momentum to the emerging subtropical jet. This momentum is integrated into the more slowly evolving flow and carried forward by other processes, which leads to the development of a westerly momentum surge along the subtropical jet that spans the length of the North Pacific Ocean.

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The 10–30-day oscillation of winter zonal wind in the entrance region of the East Asian subtropical jet and its relationship with precipitation in southern China

Dynamics of Atmospheres and Oceans ◽

10.1016/j.dynatmoce.2018.05.001 ◽

2018 ◽

Vol 82 ◽

pp. 76-88

Author(s):

Chenyu Yao ◽

Qian Huang ◽

Bin Zhu ◽

Fei Liu

Keyword(s):

Zonal Wind ◽

Southern China ◽

East Asian ◽

Entrance Region ◽

Subtropical Jet

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Jet–Precipitation Relation and Future Change of the Mei-Yu–Baiu Rainband and Subtropical Jet in CMIP5 Coupled GCM Simulations

Journal of Climate ◽

10.1175/jcli-d-18-0426.1 ◽

2019 ◽

Vol 32 (8) ◽

pp. 2247-2259 ◽

Cited By ~ 10

Author(s):

Takeshi Horinouchi ◽

Shinji Matsumura ◽

Tomoaki Ose ◽

Yukari N. Takayabu

Keyword(s):

Climate Models ◽

Asian Summer Monsoon ◽

East Asian ◽

First Century ◽

Future Change ◽

Subtropical Jet ◽

Coupled Climate Models ◽

The Future ◽

Asian Summer

Abstract Through extensive modeling efforts, it has been established that the ongoing global warming will increase the overall precipitation associated with the East Asian summer monsoon, but the future change of its spatial distribution has not reached a consensus. In this study, meridional shifts of the mei-yu–baiu rainband are studied in association with the subtropical jet by using outputs from atmosphere–ocean coupled climate models provided by CMIP5. The models reproduce observed associations between the jet and precipitation over wide time scales from synoptic to interannual. The same relation is found in intermodel differences in simulated climatology, so that the meridional locations of the jet and baiu precipitation are positively correlated. The multimodel-mean projection suggests that the both are shifted southward by the late twenty-first century. This shift is not inconsistent with the projected tropical expansion, not only because the change is local but also because the projected tropical expansion occurs mainly in the Southern Hemisphere. No significant future change in the continental mei-yu precipitation location is identified, which might be because the jet change is weak there. For comparison, the summertime Atlantic jet position, which shifts northward, is investigated briefly. This study suggests that the future change of the subtropical jet is an important aspect to investigate possible future changes of the baiu rainband, and it prompts further studies including the role of the ocean.

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Modified Three-Dimensional Jet Indices and Their Application to East Asia

Atmosphere ◽

10.3390/atmos10120776 ◽

2019 ◽

Vol 10 (12) ◽

pp. 776 ◽

Cited By ~ 1

Author(s):

Haishan Li ◽

Ke Fan ◽

Zhiqing Xu ◽

Hua Li

Keyword(s):

East Asia ◽

East Asian ◽

Three Dimensional ◽

Vertical Direction ◽

Jet Stream ◽

Jet Streams ◽

Zonal Winds ◽

Subtropical Jet Stream ◽

Subtropical Jet ◽

The Relationship

A set of three-dimensional jet indices (jet speed index, jet pressure index, jet latitude index) has been proposed in previous literature to describe the variation of jet streams in both the horizontal and vertical direction. We refer to these indices at the ‘AC’ indices, after the names of the researchers involved. However, the physical meaning of the AC indices and the relationship between AC indices and climate systems are not fully understood. Further study is still needed for applying the indices in East Asia (70°–140° E). In this study, based on the understanding of the physical meaning of the AC indices, latitudinal ranges of East Asian jet streams are determined, and a set of modified AC indices is proposed. Based on the modified AC indices, the linear trends in East Asian jet streams are studied, and the relationship between East Asian jet streams and the climate is researched. The results show that the jet speed index corresponds to the meridional temperature gradient (MTG) of the middle to upper troposphere (500–200 hPa); the jet pressure index corresponds to the pressure level at which the MTG equals zero; and the jet latitude reflects the meridional MTG distribution. The latitudinal ranges of jet streams are determined based on the meridional profiles of climatological zonal-mean zonal winds. Within such a latitudinal range, the climatological zonal-mean zonal winds between 400 and 100 hPa are only westerly, and the maximum wind speed in the vertical direction at every latitude appears between 400 and 100 hPa. The jet streams can be further classified according to the features of the profiles. For East Asia (70°–140° E), jet streams can be classified into winter subtropical jet streams (15°–47.5° N), summer subtropical jet streams (27.5°–60° N), and summer polar front jet streams (60°–87.5° N). The classification of jet streams can be supported by their correspondence to the distribution of tropospheric baroclinicity. A set of modified AC indices can be acquired by using the new ranges of East Asian jet streams in the definition of the original AC indices. Descriptions of jet streams using the modified AC indices are more in accordance with the distributional features of the climatological zonal winds over East Asia, and the physical meanings of the modified AC indices are more definite than the original indices. Using the modified AC indices, we find a significant weakening trend in the strength of the summer subtropical jet stream (−0.13 m/s/10 yr) and a significant northward shift of the winter subtropical jet stream (0.22°/10 yr), and the possible reasons for these trends are studied. Finally, the relationships of East Asian jet streams in winter and summer with atmospheric circulation, temperature, and precipitation are also investigated in this study.

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