Atmospheric responses to idealized urban land surface forcing in eastern China during the boreal spring

Deng, Jiechun; Xu, Haiming

doi:10.1002/2015jd023748

Cited by 5 publications

(11 citation statements)

References 101 publications

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“…Although the low‐level monsoonal flow is reasonably reproduced, precipitation over the southern TP (eastern China) is still overestimated (underestimated) in the model (Figures d and e). However, these systematic model biases are common in other climate models [ Sperber et al ., ; Su et al ., ] and in the models we used previously [ Deng and Xu , , ]. Overall, the model exhibits a reasonable performance in simulating the Asian summer monsoon and gives us confidence for further sensitivity analysis.…”

Section: Data Model and Methodsmentioning

confidence: 99%

Impacts of northern Tibetan Plateau on East Asian summer rainfall via modulating midlatitude transient eddies

Deng

Shi

et al. 2017

JGR Atmospheres

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Roles of the Tibetan Plateau (TP) in forming and changing the seasonal Asian climate system have been widely explored. However, little is known about modulation effects of the TP on extratropical transient eddies (TEs) and subsequent synoptic responses of the East Asian rainfall. In this study, the Community Atmosphere Model version 5.1 coupled with a slab ocean model is employed to highlight the important role of the TP in regulating the upper‐tropospheric transient wave train. Comparison between sensitivity experiments with and without the TP shows that the northern TP excites a strong anomalous anticyclone, which shifts the upper‐level East Asian westerly jet northward and helps transfer barotropic and baroclinic energy from the mean flow to the synoptic TE flow. The transient wave train is primarily shifted northward by northern TP and is forced to propagate southeastward along the eastern flank of the TP until reaching eastern China. Before the strengthening of monsoonal southerlies, the TP‐modulated transient wave train cools the troposphere, which decreases the static stability over northern China. Meanwhile, the associated anomalous warm advection induces ascending motion, leading to excessive rainfall by releasing unstable energy as the southerly strengthens. Due to the southeastward propagation of the wave train, anomalous heavy rainfall subsequently appears over eastern China from north to south, which increases day‐to‐day rainfall variation in this region. Additionally, occurrence of this upper‐tropospheric transient wave train associated with low‐level southerly peak is substantially increased by northern TP.

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Section: Data Model and Methodsmentioning

confidence: 99%

Impacts of northern Tibetan Plateau on East Asian summer rainfall via modulating midlatitude transient eddies

Deng

Shi

et al. 2017

JGR Atmospheres

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“…The relationship between urban land expansion and exporting efficiency is also impacted by the urbanization‐induced changes in zonal winds, especially during July. As indicated in Deng and Xu [], during boreal springs, the change in zonal winds is closely linked to urbanization‐induced changes in the atmospheric thermal structure, which follows the thermal wind equation

U_{T} = - \frac{R}{f} ln \frac{P_{0}}{P_{1}} {(\frac{\partial \overset{T}{true}}{\partial y})}_{P}

where R is the gas constant for dry air, f is the Coriolis parameter, P 0 and P 1 are two referenced pressure layers, and the zonal thermal wind ( U T ) is negatively correlated with the mean meridional temperature gradient (MTG,

{(∂ \bar{T} / ∂ y)}_{P}

) between these two constant pressure layers. Similar linkage is also found for each month in this work, and there is an opposite perturbation in zonal winds for adjacent latitude ranges (Figure S17 in supporting information).…”

Section: Impacts Of Urban Land Expansion On the Exporting Efficiency mentioning

confidence: 99%

“…We focus on the scenarios of URB5 and URB20 during April and July for the detailed analysis (Figure ). During April, in the URB5 scenario, the air becomes cooler in the middle upper troposphere over middle latitudes after urbanization, alike the findings in Deng and Xu []. The initial surface warming induced by external forcings would trigger rather complicated chains of thermal feedback in the large‐scale atmospheric dynamic system [e.g., Kelly and Mapes , ].…”

Section: Impacts Of Urban Land Expansion On the Exporting Efficiency mentioning

confidence: 99%

“…Zhang et al, 2010]. Urban sprawl could also impact the large-scale circulation [Chen and Frauenfeld, 2016;Deng and Xu, 2015;Ma et al, 2016]. Third, urban land expansion has also been found to impact atmospheric chemistry even with fixed anthropogenic emissions through different mechanisms [Civerolo et al, 2007;Li et al, 2016;Ryu et al, 2013;Tao et al, 2015;Yu et al, 2012].…”

Section: Introductionmentioning

confidence: 99%

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Potential impacts of urban land expansion on Asian airborne pollutant outflows

et al. 2017

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Eastern part of China (EPC) has experienced rapid urbanization during the past few decades. Here we investigate the impacts of urban land expansion over EPC on the export of Asian pollutants to the western Pacific during January, April, July, and October of 2009 using the Weather Research and Forecasting model coupled to Chemistry (WRF/Chem) and a single‐layer urban canopy scheme. Over urbanizing areas, increases in the urban land fraction result in a linearly enhanced uplift of surface primary pollutants to higher altitudes. We further examine how this local effect would change outflows of Asian pollutants to the western Pacific using the tagged black carbon (BC) and carbon monoxide (CO) tracers emitted from EPC (denoted by BCt and COt, respectively). Overall, a 0.1 increase in the fraction of land area that is urban over EPC would linearly (R2 = 0.70–0.96) increase the mean tropospheric eastward export of BCt and COt across meridional planes (i.e., 135°E and 150°E) by 4–40% and 1–6% in different months, respectively. The relative perturbation in exporting efficiency generally maximizes during July while minimizes during April. The urbanization‐export relationship is largely driven by the elevation effect and is also impacted by urbanization‐forced changes in zonal winds. The spatial pattern of the response of BCt over the downwind Pacific differs from that of COt mainly due to aerosol‐cloud interactions. Our findings demonstrate that extensive urban land expansion could substantially impact climate and air quality from a local scale to a regional scale, especially for shorter‐lived air pollutants such as BC and other aerosols.

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“…However, enhanced prevailing southwesterly wind over southern China induced by urban cover forcing alone is no longer present in this case, and only westerly wind anomalies occur in the main urban areas, implying that urban‐forced responses would be overwhelmed by the nonlinear contribution when anthropogenic aerosol forcing is prescribed. Once again, these responses to urban land surface forcing qualitatively resemble the urban‐forced spring climate changes obtained using the same AGCM [ Deng and Xu , ].…”

Section: Individual Forcing Effect With the Presence Of Nonlinear Effectmentioning

confidence: 99%

Nonlinear effects of anthropogenic aerosol and urban land surface forcing on spring climate in eastern China

Deng

Zhang

2016

JGR Atmospheres

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Anthropogenic aerosols and urban land cover change induce opposite thermal effects on the atmosphere near surface as well as in the troposphere. One can think of these anthropogenic effects as composed of two parts: the individual effect due to an individual anthropogenic forcing and the nonlinear effects resulting from the coexistence of two forcing factors. In this study, we explored the role of such nonlinear effects in affecting East Asian climate, as well as individual forcing effects, using the Community Atmosphere Model version 5.1 coupled with the Community Land Model version 4. Atmospheric responses were simulated by including anthropogenic aerosol emission only, urban cover only, or the combination of the two, over eastern China. Results showed that nonlinear responses were different from any effects by an individual forcing or the linear combination of individual responses. The nonlinear interaction could generate cold horizontal temperature advection to cool the troposphere, which induced anomalous subsidence along the Yangtze River Valley (YRV). This anomalous vertical motion, together with a weakened low‐level southwesterly, favored below‐normal (above‐normal) rainfall over the YRV (southern China), shifting the spring rain belt southward. The resultant diabatic cooling, in turn, amplified the anomalous descent and further decreased tropospheric temperature over the YRV, forming a positive feedback loop to maintain the nonlinear effects. Consequently, the nonlinear effects acted to reduce the climate anomalies from a simple linear combination of two individual effects and played an important role in regional responses to one anthropogenic forcing when the other is prescribed.

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Atmospheric responses to idealized urban land surface forcing in eastern China during the boreal spring

Cited by 5 publications

References 101 publications

Impacts of northern Tibetan Plateau on East Asian summer rainfall via modulating midlatitude transient eddies

Impacts of northern Tibetan Plateau on East Asian summer rainfall via modulating midlatitude transient eddies

Potential impacts of urban land expansion on Asian airborne pollutant outflows

Nonlinear effects of anthropogenic aerosol and urban land surface forcing on spring climate in eastern China

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