asian monsoons
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Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 152
Author(s):  
Chia-Ying Ho ◽  
Tien-Hsi Fang ◽  
Cheng-Han Wu ◽  
Hung-Jen Lee

In the coupled estuary–shelf system, plumes originating from the New Hu-Wei and Choshui rivers, consisting of many terrestrial materials, could contaminate the water of the Mailiao industrial harbor. To determine the contribution of the two rivers to pollution, the interaction between river-forced, tide-generating, and monsoon-driven water motions in and around the Mailiao industrial zone harbor was examined by performing a series of numerical model experiments. We used a three-dimensional general circulation model to examine the interplay between Asian monsoon-driven, river-forced, and tide-induced water motions, one of which could primarily affect the plume. The model-derived results for different river discharges revealed that almost all of the ammonium entering the harbor had a slope-positive trend, with oscillations in response to flood–ebb tidal cycles. The ammonium increased with time and flux, except for the 10 m3/s flux. Although the river discharge flux exceeded 200 m3/s, the ammonium entering the harbor was the same as that of the 200 m3/s flux; the ammonium concentration did not increase significantly with time after the flux exceeded 200 m3/s. In addition, irrespective of flood or ebb tidal currents being suppressed by strong Asian monsoons, this mechanism avoided contaminating the water quality of the harbor while northeasterly winds prevailed. By contrast, the southwesterly monsoon drove the geostrophic current northward along the coast; concurrently, the coastal sea level increased to form the surface isobar slope up toward the coast, producing a secondary flow to accelerate geostrophic alongshore currents. The northward geostrophic currents compressed the plumes shoreward, forming a relatively narrow-band plume; the coupling model demonstrated that the southwesterly monsoon-driven current pushed plumes favorably along the west pier into the harbor.


2021 ◽  
Vol 9 ◽  
Author(s):  
Jian Zhang ◽  
Yonggang Liu ◽  
Xiaomin Fang ◽  
Tao Zhang ◽  
Chenguang Zhu ◽  
...  

Uplift of the Gangdese Mountains is important to the evolution of Asian monsoons and the formation of Tibetan Plateau, but its paleoaltitude before the India-Asia collision (Late Cretaceous) is less constrained so far. In this study, we investigate whether the geological records, which are indicators of soil dryness, discovered in East Asia can provide such a constraint. Through climate modeling using the Community Earth System Model version 1.2.2, it is found that the extent of dry land in East Asia is sensitive to the altitude of the Gangdese Mountains. It expands eastwards and southwards with the rise of the mountain range. Comparison of the model results with all the available geological records in this region suggests that the Gangdese Mountains had attained a height of ∼2 km in the Late Cretaceous.


2021 ◽  
Author(s):  
Kwok Pan Chun ◽  
Qing He ◽  
Bastien Dieppois ◽  
Benjamin Pohl ◽  
Ömer Yetemen ◽  
...  

<p>Drought conditions of Southeast China are associated with the sea surface temperature warm pool in the tropical Western Pacific, which is related to low-frequency hydroclimatic patterns and their teleconnections. Empirically, the moisture influx to the region is linked to the interannual and decadal teleconnections, including the Pacific Decadal Oscillation (PDO), the Pacific-Japan Oscillation (PJO) and the Silk Road Pattern (SRP). However, it is still unclear how those teleconnection patterns affect drought conditions in Southeast China via changes in monsoons’ dynamics or wave activities. In this study, we use ERA5 reanalysis over the 1950-2019 period to explore the impacts of the PDO, PJO and SRP on Asian monsoons’ dynamics and regional drought conditions over Southeast China, based on a self-calibrating Palmer Drought Severity Index (scPDSI). We specially use station data from the Greater Bay Area (GBA) which is a national key region for development in Southeast China which is affected by seasonal droughts in winters. Results indicate that drought conditions in Southeast China are significantly related to monsoons: the East Asia Monsoon (EAM), the Western North Pacific Monsoon (WNPM) and the Webster-Yang Monsoon (WYM), between 1950-2019. The strength of monsoons is modulated by PDO, PJO and SRP. A negative phase of SRP corresponds to a southward shift of the Asian westerly jet, strengthening winter Asian monsoons and causing drier conditions in the GBA. Similarly, a cold phase of PDO contributes to drier conditions in the GBA, by weakening Asian monsoons. For the negative phase of PJO, the trade wind of the Walker cell is weakened by the meridional pressure dipole over the West Pacific adjacent to the Southeast China coast. This pressure dipole reduces moisture influx to the continent by the weakened trade wind and leads to less precipitation over East China. Such three climate factors are also interacted through the modulations of monsoons and wave-activities. An extension of the Eliassen-Palm (EP) flux shows that the SRP relates to convective and dynamic wave-activities, which could explain changes in monsoons’ dynamics and drought conditions in Southeast China. To investigate the future drought conditions over Southeast China, bias-corrected historical and RCP8.5 scenarios are used for six of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models (i.e. ACCESS1, BCC, CNRM, IPSL, MPI, and GFDL) between 1861-2100. Among six models, IPSL and GFDL models reproduce the teleconnections well between changes in the monsoons and drought conditions over the GBA, for both historical simulations and future projections. Our results provide insights into the mechanisms of teleconnection patterns affecting drought monitoring and risk management in Southeast China. </p>


2021 ◽  
Author(s):  
Clay Tabor ◽  
Bette Otto-Bliesner ◽  
Zhengyu Liu

<p>Compared to preindustrial, the mid-Holocene (6 ka) had significantly greater Northern Hemisphere summer insolation, slightly warmer global surface temperature, and slightly lower CO<sub>2</sub> concentration. Vegetation was also different during the mid-Holocene. Possibly most prominent was the growth of temperate vegetation in the now barren Sahara. This Saharan vegetation response was related to intensification of the African Monsoon associated with the mid-Holocene orbital configuration. Hydroclimate of the Asian Monsoon and South American Monsoon also responded to mid-Holocene forcings, with general wetting and drying, respectively.</p><p>The mid-Holocene is frequently used for model-proxy comparison studies. However, climate models often struggle to replicate the proxy signals of this period. Here, we attempt to reduce these model-proxy discrepancies by exploring the significance of a vegetated Sahara during the mid-Holocene. Using the water isotopologue tracer enabled version of the Community Earth System Model (iCESM1), we perform mid-Holocene simulations that include and exclude temperate vegetation in the Sahara. We compare our model results with δ<sup>18</sup>O values from mid-Holocene speleothem records in the Asian and South American Monsoon regions.</p><p>We find that inclusion of vegetated Sahara during the mid-Holocene leads to global warming, alters the hemispheric distribution of energy, and generally amplifies the δ<sup>18</sup>O of precipitation responses in the South American and Asian Monsoon regions; these feedbacks improve the δ<sup>18</sup>O agreement between model outputs and speleothem records of the mid-Holocene. Our results highlight the importance of regional vegetation alteration for accurate simulation of past climate, even when the region of study is far from the source of vegetation change.</p>


2021 ◽  
Author(s):  
Benjamin Clouser ◽  
Clare Singer ◽  
Sergey Khaykin ◽  
Martina Krämer ◽  
Alexey Lykov ◽  
...  

<p>In-situ measurements of the HDO/H<sub>2</sub>O isotopic ratio from the Chicago Water Isotope Spectrometer (ChiWIS) during the 2017 StratoClim campaign help diagnose convective processes in the Asian Monsoon. Isotopic measurements show enormous diversity in isotopic composition, likely reflecting degree of recent convective influence. Eight flights in July—August sampled a wide range of convective influence at near-tropopause altitudes, with timescales of minutes to weeks, and mean isotopic compositions from -700 per mil in recent convective outflow to -350 per mil in more aged air that is at least several days from last convective influence. Above the tropopause, we use isotopic composition to understand the fate of convective remnants. Isotopic measurements suggest much in-situ cirrus measured during  StratoClim campaign is actually secondary cirrus which has reformed in an area of prior convective moistening. These flights allow detailed comparison between North American and Asian monsoons, and we compare StratoClim results to both satellite and in-situ measurements in other monsoon and tropical locations. Finally, we discuss prospects for detection and interpretation of convective remnants during the in the 2021/2022 ACCLIP campaign.</p>


2021 ◽  
Author(s):  
Adrienne Foreman ◽  
Gordon Bromley ◽  
Brenda Hall ◽  
Margaret Jackson

<p>Late Pleistocene stadials were global events, associated with weakened Asian monsoons and Atlantic Meridional Overturning Circulation (AMOC), shifts in atmospheric boundaries and precipitation belts, and warming of the Southern Hemisphere and tropics. In the Northern Hemisphere, stadials are traditionally viewed as dramatic cooling events centred on the North Atlantic, with their abrupt onset attributed to meltwater-induced suppression of the AMOC due to melting of large Northern Hemisphere ice sheets. As warmer temperatures are required for sustained meltwater input, however, there is an apparent inconsistency with this model of Northern Hemisphere stadial cooling. To investigate this inconsistency, we reconstructed the timing and nature of glacial fluctuations in Connemara, western Ireland, located within the in the North Atlantic basin, during Heinrich Stadial 1 (HS1). Fifteen internally consistent cosmogenic beryllium-10 ages of erratic boulders indicate rapid and widespread deglaciation of the former Connemara ice centre at ~17.5 ka. The apparent abruptness of ice retreat, coupled with stratigraphic correlation with geomorphic features indicative of meltwater, suggest that HS1 deglaciation was driven by enhanced melting during the summer ablation season. This interpretation supports evidence for enhanced meltwater discharge and summertime warming elsewhere in Europe during HS1 but may conflict with the traditional view of stadials as severe cooling events.</p>


2020 ◽  
Author(s):  
Xiao-Mei Xia ◽  
Miao-Qin Yang ◽  
Cong-Li Li ◽  
Si-Xin Huang ◽  
Fei Wang ◽  
...  

Abstract How large cosmopolitan plant genera survived great environmental changes and rediversified remains largely unknown. Here we investigated mechanisms underlying the rediversification of Rhododendron, the largest genus of woody plants in the Northern Hemisphere. Using 3437 orthologous nuclear genes, we reconstructed the first completely resolved and dated phylogeny of Rhododendron. We found that most extant species of Rhododendron originated by Neogene rediversification from Paleogene relicts during southern migration. The geographically uneven rediversification of Rhododendron led to a much higher diversity in Asia than in other continents, which was driven by two main environmental variables, i.e., habitat heterogeneity represented by elevation range and annual precipitation related to the Asian monsoons, and can be explained by leaf functional traits that show strong phylogenetic signals and correspond well with leaf-forms and geographical regions. Our study highlights the importance of integrating phylogenomic and ecological analyses in revealing the spatiotemporal evolution of species-rich cosmopolitan plant genera.


2020 ◽  
Vol 12 (23) ◽  
pp. 10049
Author(s):  
Teerachai Amnuaylojaroen ◽  
Jirarat Inkom ◽  
Radshadaporn Janta ◽  
Vanisa Surapipith

This paper aims to investigate the potential contribution of biomass burning in PM2.5 pollution in Northern Thailand. We applied the coupled atmospheric and air pollution model which is based on the Weather Research and Forecasting Model (WRF) and a Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT). The model output was compared to the ground-based measurements from the Pollution Control Department (PCD) to examine the model performance. As a result of the model evaluation, the meteorological variables agreed well with observations using the Index of Agreement (IOA) with ranges of 0.57 to 0.79 for temperature and 0.32 to 0.54 for wind speed, while the fractional biases of temperature and wind speed were 1.3 to 2.5 °C and 1.2 to 2.1 m/s. Analysis of the model and hotspots from the Moderate Imaging Spectroradiometer (MODIS) found that biomass burning from neighboring countries has greater potential to contribute to air pollution in northern Thailand than national emissions, which is indicated by the number of hotspot locations in Burma being greater than those in Thailand by two times under the influence of two major channels of Asian Monsoons, including easterly and northwesterly winds that bring pollutants from neighboring counties towards northern Thailand.


2020 ◽  
Author(s):  
Ruth Geen ◽  
Francis Hugo Lambert ◽  
Geoffrey K Vallis
Keyword(s):  

2020 ◽  
Vol 47 (22) ◽  
Author(s):  
Clay Tabor ◽  
Bette Otto‐Bliesner ◽  
Zhengyu Liu

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