Influence of the southwards shift of North American continent on North American monsoon

Mei, Hu; Xu, Haiming; Deng, Jiechun; Ma, Jing; He, Jinhai

doi:10.1002/joc.6572

Cited by 3 publications

(5 citation statements)

References 52 publications

(63 reference statements)

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“…As shown in Figure 10, the diabatic heating rate increases with altitude in the lower troposphere, but decreases with altitude in the mid‐to‐upper troposphere. According to Hu et al (2020), such a vertical heating structure would favour the strengthening and maintaining of the circulation pattern with the southerlies on its east and the northerlies on its west in the lower troposphere and a corresponding out‐of‐phase structure in the upper troposphere (Figure 6).…”

Section: Impact Of Rms' Height On the Monsoon Regionmentioning

confidence: 93%

“…Thus, a higher MPI indicates a greater seasonal transition between wet and dry seasons. Due to the prominent dry‐wet contrast between winter and summer but relatively weak seasonal variation of wind direction in the NAM region, Hu et al (2020) noted that the MPI is much more sensitive to model simulation results than the DNS index when studying impacts of the latitude of the North American continent on associated monsoon area. Therefore, we used the MPI to investigate the change of the monsoon region over North America in our sensitivity experiments, that is, a monsoon domain is defined as the MPI value greater than 0.5 and precipitation difference between dry and wet seasons exceeding 300 mm.…”

Section: Methodsmentioning

confidence: 99%

“…As shown in Figure 10, the diabatic heating rate increases with altitude in the lower troposphere, but decreases with altitude in the mid-to-upper troposphere. According to Hu et al (2020), such a vertical heating structure would favour the strengthening and maintaining of the circulation pattern with the southerlies on its east and the northerlies on its west in the lower F I G U R E 8 Longitude-height cross sections of winter mean zonal circulation (vector; units: mÁs −1 ; the magnitude of vertical velocity is enlarged by 100 times) and vertical velocity (shading; units: 10 −2 mÁs −1 ) averaged over 35 -45 N in (a) CTL, (b) UP3, and (c) UP5.…”

Section: Primary Mechanism In Summermentioning

confidence: 99%

“…The above mechanism can also be easily understood by the eq. ( 4) of Hu et al (2020), and this expression is deduced by the thermal wind argument to interpret the relationship among zonal land-sea thermal contrast, vertical shear of meridional wind, and vertical motion.…”

Section: Primary Mechanism In Summermentioning

confidence: 99%

“…One can see that the land-sea contrast over North America and the Atlantic is similar to that in East Asia with the ocean in the east and the large terrain in the west, but it is still unclear why North America lacks a large-scale monsoon. Hu et al (2020) claimed that the meridional position of the North American continent plays a fundamental role in the existence of the NAM based on a series of sensitivity experiments. They found that when the whole North American continent is shifted to relatively low latitudes, most of the North American non-monsoon region is transformed into monsoon region.…”

Section: Introductionmentioning

confidence: 99%

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Why a large‐scale monsoon does not exist in North America: Orographic effects

Qin

Chen

et al. 2023

Intl Journal of Climatology

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To understand why a large‐scale monsoon does not exist in North America, we performed a series of sensitivity simulations to investigate orographic effects of the Rocky Mountains (RMs) using the Community Atmosphere Model version 5.1. Results show that the height of the RMs plays a fundamental role in shaping the monsoon over North America that is confined to a small area from northwestern Mexico to the southwestern United States. When the RMs' height is increased by five times their actual height, a larger part of the non‐monsoon region over North America becomes a monsoon region. The mechanical effects of the RMs uplift dominate in winter, while thermal effects dominate in summer. During winter the mechanical effects induce an equivalent barotropic atmospheric response in the troposphere. With the uplift of the RMs, the ridge and trough located on the western and eastern sides of Canada are strengthened. Most areas of North America are influenced by the northerlies during winter such that enhanced descending motion over the eastern RMs favours a dry winter climate. However, thermal effects dominate during summer through enhanced baroclinic atmospheric responses. The Mexico high and lower‐level cyclonic circulation are strengthened with the RMs uplift, triggering large‐scale ascending motion. Eastern North America is mainly controlled by the enhanced southerly wind along the western flank of the North Atlantic subtropical high. Thus, the enhanced water‐vapour transport and upward motion on the eastern side of the RMs increase summer precipitation. As a result, an obvious seasonal variation with the feature of ‘dry winter and wet summer’ finally develops, indicating that the height of the RMs plays a crucial role in shaping the monsoon over the central United States. Additional experiments show that the base area of the RMs has little effect on the large‐scale monsoon formation over North America.

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Section: Impact Of Rms' Height On the Monsoon Regionmentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Primary Mechanism In Summermentioning

confidence: 99%

Section: Primary Mechanism In Summermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Why a large‐scale monsoon does not exist in North America: Orographic effects

Qin

Chen

et al. 2023

Intl Journal of Climatology

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Why is the mid-tropospheric North Atlantic subtropical high much stronger than the North Pacific subtropical high in boreal summer?

Chen

et al. 2021

Clim Dyn

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Relative Impacts of the Orography and Land–Sea Contrast over the Indochina Peninsula on the Asian Summer Monsoon between Early and Late Summer

Zhuang

Duan

et al. 2022

Journal of Climate

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The Indochina Peninsula (ICP) has a critical effect in shaping the Asian summer monsoon (ASM). However, the seasonal responses of the ASM to the ICP are not fully understood. This study employs a 1° atmospheric general circulation model to examine the different contributions of the ICP’s orography and land–sea contrast to the ASM during the early and late summer. Results indicate that the orographic effect increases South Asian rainfall and reduces the rainfall over the South China Sea (SCS) and North China in early summer, but its influence on monsoonal circulation and rainfall is limited to East Asia in late summer. The impact of the ICP’s land–sea contrast is basically opposite in the two summer stages. With the presence of the ICP, SCS rainfall is enhanced but South Asian rainfall is weakened in early summer. In late summer, however, rainfall from the ICP to the northwestern Pacific is strikingly reduced, accompanied by intensified rainfall over South Asia. Relatively, the orographic effect seems to be more important in modulating the South Asian monsoon in early summer, while the land–sea contrast is dominant in strengthening the SCS monsoon and suppressing the Northwest Pacific monsoon via the interaction between the induced local circulation and multi-level ASM subsystems. In late summer, the orographic effect on the ASM is much weaker compared to the land–sea contrast, which plays a critical role by shifting the subtropical high southwestwards and through the “thermal adaption” feedback mechanism. Therefore, the orographic impact of the ICP on the ASM differs from that of the land–sea contrast in the two summer stages.

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Influence of the southwards shift of North American continent on North American monsoon

Cited by 3 publications

References 52 publications

Why a large‐scale monsoon does not exist in North America: Orographic effects

Why a large‐scale monsoon does not exist in North America: Orographic effects

Why is the mid-tropospheric North Atlantic subtropical high much stronger than the North Pacific subtropical high in boreal summer?

Relative Impacts of the Orography and Land–Sea Contrast over the Indochina Peninsula on the Asian Summer Monsoon between Early and Late Summer

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