14 results
Search Results
2. Effect of the Asian monsoon on the northward migration of the brown planthopper to northern South China.
- Author
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Yang, Shi‐Jun, Bao, Yun‐Xuan, Zheng, Xin‐Fei, and Zeng, Juan
- Subjects
NILAPARVATA lugens ,MONSOONS ,ATMOSPHERIC circulation ,INSECT populations ,PREDICTION models ,REGRESSION analysis - Abstract
As wind‐borne migration of insects is strongly influenced by atmospheric circulation and weather systems, the relationships between insect population abundance and meteorological conditions are substantial. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major wind‐borne insects hampering rice production in Asia, and its migration is significantly influenced by the Asian monsoon, a main component of the Asian climate system. However, the degree and mechanisms of the effects of monsoon on BPH migration have been little studied. In this paper, the effect of the Asian monsoon on the northward migration of BPH from the Indochina Peninsula to northern South China (NSC) was investigated based on the BPH light‐trap data and meteorological data for 39 years. The results show that the level of BPH migration in May could indicate the degree of annual pest outbreaks in NSC and that the southeast monsoon was more critical in this northward migration than the previously recognized southwest monsoon. The significance of the southeast monsoon stemmed from the strong effect of South China Sea subtropical high on BPH migration under a unique weather system distribution, the Polar low–Continental low–West Pacific subtropical high pattern. Furthermore, based on the key areas of migration obtained from the composite analysis, the multivariable linear regression prediction model could effectively predict the occurrence of BPH in NSC. These results indicate the importance of interactions between monsoons during BPH northward migration, which reflects the complex relationship between BPH migration and atmospheric motion. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Attributing the Decline of Evapotranspiration over the Asian Monsoon Region during the Period 1950–2014 in CMIP6 Models.
- Author
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Zhu, Xiaowei, Kong, Zhiyong, Cao, Jian, Gao, Ruina, and Gao, Na
- Subjects
EVAPOTRANSPIRATION ,RAINFALL ,SOLAR radiation ,SURFACE temperature ,SURFACE forces ,MONSOONS - Abstract
Evapotranspiration (ET) accounts for over half of the moisture source of Asian monsoon rainfall, which has been significantly altered by anthropogenic forcings. However, how individual anthropogenic forcing affects the ET over monsoonal Asia is still elusive. In this study, we found a significant decline in ET over the Asian monsoon region during the period of 1950–2014 in Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The attribution analysis suggests that anthropogenic aerosol forcing is the primary cause of the weakening in ET in the historical simulation, while it is only partially compensated by the strengthening effect from GHGs, although GHGs are the dominant forcings for surface temperature increase. The physical mechanisms responsible for ET changes are different between aerosol and GHG forcings. The increase in aerosol emissions enhances the reflection and scattering of the downward solar radiation, which decreases the net surface irradiance for ET. GHGs, on the one hand, increase the moisture capability of the atmosphere and, thus, the ensuing rainfall; on the other hand, they increase the ascending motion over the Indian subcontinent, leading to an increase in rainfall. Both processes are beneficial for an ET increase. The results from this study suggest that future changes in the land–water cycle may mainly rely on the aerosol emission policy rather than the carbon reduction policy. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
4. Concurrent Asian monsoon strengthening and early modern human dispersal to East Asia during the last interglacial.
- Author
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Hong Ao, Jiaoyang Ruan, Martinón-Torres, María, Krapp, Mario, Liebrand, Diederik, Dekkers, Mark J., Caley, Thibaut, Jonell, Tara N., Zongmin Zhu, Chunju Huang, Xinxia Li, Ziyun Zhang, Qiang Sun, Pingguo Yang, Jiali Jiang, Xinzhou Li, Xiaoxun Xie, Yougui Song, Xiaoke Qiang, and Peng Zhang
- Subjects
MONSOONS ,RAINFALL ,HUMAN beings ,GREENHOUSE gases ,SOLAR radiation - Abstract
The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)--currently the largest monsoon system--remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy-and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
5. The Sino-Himalayan flora evolved from lowland biomes dominated by tropical floristic elements
- Author
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Liu, Yun, Lai, Yang-Jun, Ye, Jian-Fei, Hu, Hai-Hua, Peng, Dan-Xiao, Lu, Li-Min, Sun, Hang, and Chen, Zhi-Duan
- Published
- 2023
- Full Text
- View/download PDF
6. Sensitivities of the Asian Summer Monsoon Simulations to Physical Parameters for the Perturbed Parameter Ensemble of HadGEM3‐GC3.05.
- Author
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Zhang, Xiaoqi, He, Bian, Guo, Zhun, Sexton, David M. H., Rostron, John W., and Furtado, Kalli
- Subjects
MONSOONS ,SUMMER ,PERSONAL protective equipment ,STATISTICAL correlation - Abstract
The simulation skill of the perturbed parameter ensemble (PPE) of HadGEM3‐GC3.05 on the mean climate pattern of the Asian summer monsoon (ASM) is evaluated in this study. The sensitivities of the model bias to the perturbed parameters are investigated based on metrics. The results show that the PPE mean (PPE‐20M) could effectively capture the general ASM precipitation and wind patterns, with a correlation coefficient of 0.78. PPE‐20M mainly shows positive precipitation biases over the tropical western Pacific, southern slope of the Tibetan Plateau, Indochina Peninsula, and South China and negative precipitation biases over the Indian continent and Bay of Bengal. The magnitude of the precipitation biases is more sensitive than its pattern to the variation of the perturbed parameters. Four parameters (ent_fac_dp, qlmin, ps_cloud‐ph, and psm) are found to be crucial for simulating the ASM precipitation intensity, and their combined effects are related to the simulated precipitation biases. Plain Language Summary: The simulation of the Asian summer monsoon (ASM) has attracted much attention in recent decades. However, state‐of‐the‐art coupled models still show similar systematic biases when simulating monsoon precipitation from CMIP3 to CMIP6. Recently, a perturbed parameter ensemble (PPE) method has been applied in the development of HadGEM3‐GC3.05 with the aim of improving the overall simulation skill of the coupled model. The PPE can also be used to understand the related physical processes in the model simulations. Thus, in this study, we aim to evaluate the simulation skills of PPE on the mean climate distributions of ASM. Four parameters were found to be the most critical in the precipitation simulations, which could be potential tunable parameters to reduce the biases of precipitation intensity over the monsoon regions. This study provides possible pathways to reduce model bias that could benefit the model development community. Key Points: The perturbed parameter ensemble mean captures the climate pattern of the Asian summer monsoon (ASM) but mainly overestimates precipitation over the western PacificFour parameters (ent_fac_dp, qlmin, ps_cloud‐ph, and psm) are crucial for simulating ASM precipitation in coupled runThe joint effect of these parameters, especially the deep entrainment amplitude, are dominant control for the bias in the western Pacific [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
7. Wildland Fires in the Subtropical Hill Forests of Southeastern Bangladesh.
- Author
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Farukh, Murad A., Islam, Md. A., and Hayasaka, Hiroshi
- Subjects
WILDFIRES ,METEOROLOGICAL charts ,WEATHER ,SHIFTING cultivation ,ATMOSPHERIC temperature ,FOREST fires ,FIRE management - Abstract
The first ever comprehensive study on wildland fires in Bangladesh is carried out to develop a fire prevention and prediction method. The major causes of huge wildland fires (88%) in the subtropical Chittagong Hill forest (43% of total) of southern Bangladesh are reported as shifting cultivation, grazing and unauthorized settlement. We used satellite hotspot (HS) data from 2003 to 2021 (a total of 54,669 HSs) to clarify the spatio-temporal structure of wildland fires. Fire weather conditions were analyzed using various weather data and synoptic-scale weather maps at different air levels. Fires concentrated from March through April or a transitional period from the dry season, caused by the Asian winter monsoon, to the wet season, due to the Asian summer monsoon. Fire occurrence depended on dry conditions and pre-monsoon showers and their timing. The difference in 925 hPa heights of high and low pressure systems may be attributed to the different types of the Asian winter and summer monsoons. The average maximum air temperature and incident shortwave solar energy in April were the highest and strongest, contributing fire-prone weather conditions. Based on the analysis, a fire prevention and prediction method will be developed, and this report may also facilitate the establishment of future CO
2 reduction measures for Bangladesh. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
8. Model-based orbital-scale precipitation δ18O variations and distinct mechanisms in Asian monsoon and arid regions.
- Author
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Liu, Xiaodong, Xie, Xiaoxun, Guo, Zhengtang, Yin, Zhi-Yong, and Chen, Guangshan
- Subjects
ARID regions ,WATER vapor transport ,MILANKOVITCH cycles ,MONSOONS ,WATER vapor ,SOLAR radiation ,REGIONAL differences - Abstract
The past Asian precipitation δ
18 O (δ18 Op ) records from stalagmites and other deposits have shown significant orbital-scale variations, but their climatic implications and regional differences are still not fully understood. This study, as the first attempt of a 300-kyr transient stable isotope-enabled simulation, investigated the characteristics and mechanisms of the orbital-scale δ18 Op variations in three representative regions of Asia: arid Central Asia (CA), monsoonal South Asia (SA) and monsoonal East Asia (EA). The modelling results showed that the variations in the CA, SA and EA annual δ18 Op exhibited significant but asynchronous 23-kyr precession cycles. Further analyses revealed that although the precession-induced insolation variation was the ultimate cause of the δ18 Op variation in all three regions, the dominant mechanisms and the involved physical processes were distinct among them. For the CA region, the rainy-season (November–March) temperature effect and water vapour transport by the westerly circulation were identified as the key precession-scale processes linking the October–February boreal mid-latitude insolation to the rainy-season or annual δ18 Op . In the SA region, the rainy-season (June–September) precipitation amount effect and upstream depletion of the monsoonal water vapour δ18 O served as the main mechanisms linking the rainy-season or annual δ18 Op to the April–July insolation variation at the precession scale. For the EA region, however, the precession-scale annual δ18 Op was mainly controlled by the late-monsoon (August–September) and pre-monsoon (April–May) water vapour transport patterns, which were driven by the July–August insolation and the global ice volume, respectively. These results suggest that the climatic implications of the orbital-scale Asia δ18 Op variations are sensitive to their geographic locations as determined by the combined effects of insolation and regional circulation patterns associated with the respective rainy seasons. This study provides new insights into understanding the regional differences and formation mechanisms of the Asian orbital-scale δ18 Op variations. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
9. A 230-Year Summer Precipitation Variations Recorded by Tree-Ring δ 18 O in Heng Mountains, North China.
- Author
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Liu, Yu, Shi, Wenxin, Li, Qiang, Liu, Wentai, and Cai, Qiufang
- Subjects
ATLANTIC multidecadal oscillation ,EL Nino ,TREE-rings ,MONSOONS ,OXYGEN isotopes ,GLOBAL warming - Abstract
To explore the history of the changes in monsoon precipitation and their driving mechanisms in the context of global warming, climatology studies using tree-ring stable oxygen isotopes (δ
18 O) were carried out in Shanxi Province, China. Based on a tree-ring δ18 O series from Pinus tabulaeformis Carr. on Heng Mountain, a 230-year June–July precipitation sequence from 1784 to 2013 AD was reconstructed that explained 45% of the total variance (44% after adjusting the degrees of freedom). The reconstructed sequence captured the characteristics of the variations in precipitation. Periods of drought occurred mainly in 1820–1840 AD, 1855–1865 AD, 1895–1910 AD, 1925–1930 AD, and 1970–1995 AD, and wet periods occurred mainly in 1880–1895 AD, 1910–1925 AD, and 1935–1960 AD. The dry and wet years in the precipitation reconstruction corresponded well to the years in which disaster events were documented in historical records. A spatial correlation analysis with Climatic Research Unit (CRU)-gridded precipitation data indicated that the reconstructed precipitation provided good regional representation and reflected large-scale June–July precipitation changes in northern China. In addition, the reconstructed precipitation sequence was also significantly correlated with the dry and wet index (DWI) and other tree-ring dry/wet reconstructions from the surrounding areas. The correlation between the reconstructed precipitation and the Asian monsoon index showed that the precipitation can indicate the intensity of the Asian summer monsoon. Moreover, a significant negative correlation was found between the El Niño–Southern Oscillation (ENSO) and the reconstructed precipitation. At the decadal scale, the negative phase of the Pacific Decadal Oscillation (PDO) and the positive phase of the Atlantic Multidecadal Oscillation (AMO) may co-promote summer precipitation in the study area. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
10. Nocturnal Southerly Moist Surge Parallel to the Coastline Over the Western Bay of Bengal.
- Author
-
Fujinami, Hatsuki, Sato, Tomonori, Kanamori, Hironari, and Kato, Masaya
- Subjects
COASTS ,ATMOSPHERIC circulation ,JETS (Fluid dynamics) ,THERMOCYCLING ,SUBCONTINENTS ,WESTERLIES ,MONSOONS - Abstract
The role of the diurnal atmospheric circulation cycle around the eastern Indian subcontinent, leeward of the monsoon westerlies, on the hydroclimate of South Asia remains unknown. Here, we reveal that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB), and then flow onto the Gangetic Plain enhancing onshore moisture flux and nocturnal precipitation over the Himalayas and the Meghalaya Plateau. This nocturnal surge is strongly controlled by the diurnal cycle of dynamic and thermodynamic effects around the subcontinent. At night, nocturnal westerly low‐level jets appear over the subcontinent. Strong low‐level southwesterly flow with a low‐level jet structure also appears parallel to the coastline over the western BoB, extending from the west of Sri Lanka. The low‐level westerlies from the subcontinent and the low‐level southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge. Plain Language Summary: Nocturnal precipitation is a well‐known phenomenon around the Himalayas and the Meghalaya Plateau in South Asia in summer. Such precipitation is a major supply source for glaciers in the central–eastern Himalayas and the headwaters of major rivers such as the Ganges and the Brahmaputra. In this study, we show that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB) and then flow onto the Gangetic Plain, enhancing moisture transport toward land and nocturnal precipitation in South Asia. Here, we refer to the phenomenon as the nocturnal southerly moist surge. This nocturnal surge is strongly affected by the diurnal cycle of the thermal and topographic effects of the Indian subcontinent. At night, a strong low‐level westerly jet appears above the nocturnal stable layer over the Indian subcontinent. Strong low‐level southwesterlies with a low‐level jet structure also appear over the western BoB, extending from the strait between the southernmost tip of the Indian subcontinent and Sri Lanka. The low‐level westerlies flowing from the subcontinent and the southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge over the western BoB. Key Points: Nocturnal low‐level southerly moist surge occurs parallel to the western Bay of Bengal coastline and flows over the Gangetic PlainThe surge consists of strong low‐level westerlies from the Indian subcontinent and southwesterlies extending from the west of Sri LankaDynamic and thermodynamic effects of the Indian subcontinent likely play an important role in forming the nocturnal surge [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
11. Effect of the Asian monsoon on the northward migration of the brown planthopper to northern South China
- Author
-
Shi‐Jun Yang, Yun‐Xuan Bao, Xin‐Fei Zheng, and Juan Zeng
- Subjects
Asian monsoon ,brown planthopper (Nilaparvata lugens) ,composite analysis ,northern South China ,Polar low–Continental low–West Pacific subtropical high (P–C–W) pattern ,South China Sea subtropical high ,Ecology ,QH540-549.5 - Abstract
Abstract As wind‐borne migration of insects is strongly influenced by atmospheric circulation and weather systems, the relationships between insect population abundance and meteorological conditions are substantial. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major wind‐borne insects hampering rice production in Asia, and its migration is significantly influenced by the Asian monsoon, a main component of the Asian climate system. However, the degree and mechanisms of the effects of monsoon on BPH migration have been little studied. In this paper, the effect of the Asian monsoon on the northward migration of BPH from the Indochina Peninsula to northern South China (NSC) was investigated based on the BPH light‐trap data and meteorological data for 39 years. The results show that the level of BPH migration in May could indicate the degree of annual pest outbreaks in NSC and that the southeast monsoon was more critical in this northward migration than the previously recognized southwest monsoon. The significance of the southeast monsoon stemmed from the strong effect of South China Sea subtropical high on BPH migration under a unique weather system distribution, the Polar low–Continental low–West Pacific subtropical high pattern. Furthermore, based on the key areas of migration obtained from the composite analysis, the multivariable linear regression prediction model could effectively predict the occurrence of BPH in NSC. These results indicate the importance of interactions between monsoons during BPH northward migration, which reflects the complex relationship between BPH migration and atmospheric motion.
- Published
- 2022
- Full Text
- View/download PDF
12. Robust and Uncertain Sea-Level Pressure Patterns over Summertime East Asia in the CMIP6 Multi-Model Future Projections.
- Author
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Tomoaki OSE, Hirokazu ENDO, Yuhei TAKAYA, Shuhei MAEDA, and Toshiyuki NAKAEGAWA
- Subjects
SUMMER ,OCEAN temperature ,VERTICAL motion ,GLOBAL warming ,ORTHOGONAL functions - Abstract
Robust and uncertain sea-level pressure patterns over summertime East Asia in the future global warming projections and their causes are studied by applying the inter-model empirical orthogonal function (EOF) analysis to the multi-model experiments in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and focusing on common features with the previous CMIP5 analysis. The ensemble average and the first to third EOF modes associated with future pressure changes are similar to the corresponding modes from CMIP5. The first and second modes represent strengthened and weakened high-pressure systems in subtropical and northern East Asia, respectively. The third mode is the reverse anomaly of the climatological pressure pattern over summertime East Asia, which indicates weakened southerly monsoon winds. The second mode pattern makes positive contributions to almost all the CMIP6 future pressure changes, representing a robust future projection pattern. The robust mode is the result of surface warming over the northern continents and neighboring seas that is stronger than the global average. The first and third modes are considered to be uncertain (but major) patterns in the ensemble projections as the signs of their contributions to the future changes are dependent on the model used. Suppressed vertical motion over the equatorial (northern) Indian Ocean caused by the vertically stabilized atmosphere under the global warming scenario is the source of the first (third) mode, together with the counter vertical motion anomaly over the equatorial (northern) Pacific. The aforementioned characteristics of the modes are essentially similar to those identified in the CMIP5 analysis, whereas the different sea surface temperature anomalies are related to the secondary structures of the modes. Some uncertainties in the future projections can be attributed to the systematic differences in the model climatology of the present-day precipitation, which determines the distribution of the suppressed vertical motion under the future warmer climate. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
13. Decadal changes of the early summer Asian monsoon and the South China Sea tropical cyclones during 2001–2020
- Author
-
Cho, Yin-Min, Lu, Mong-Ming, Sui, Chung-Hsiung, Solis, Ana L. S., and Chen, Meng-Shih
- Published
- 2022
- Full Text
- View/download PDF
14. A New Perspective of Pacific-Japan Pattern: Estimated Percentage of the Cases Triggered by Rossby Wave Breaking.
- Author
-
Kazuto TAKEMURA and Hitoshi MUKOUGAWA
- Subjects
WATER waves ,ROSSBY waves ,OCEAN temperature ,MADDEN-Julian oscillation ,AIR masses ,PERCENTILES - Abstract
This study quantitatively examined the relative importance of Rossby wave breaking (RWB) east of Japan to a formation of the Pacific-Japan (PJ) pattern compared with that of tropical atmospheric and oceanographic variabilities. First, cases of the positive and negative PJ patterns are classified into those with and without the RWB occurrence. The result of the classification indicates that the cases of the positive PJ pattern triggered by the RWB account for approximately 20 % of the whole cases of the positive PJ pattern. The number of positive PJ cases with the RWB further accounts for approximately 80 % of those in the cases associated with the RWB. Results of a lag composite analysis and the related Q-vector diagnosis for the cases of the positive PJ pattern with the presence of RWB show that the RWB east of Japan promotes the formation of the PJ pattern through the southwestward intrusion of high potential vorticity air mass toward the subtropical western North Pacific (WNP) and the consequent dynamically induced enhanced convection over the region, consistent with results of previous studies. By contrast, the composite for the cases the negative PJ pattern accompanied by the RWB indicates that the RWB-related upper-tropospheric zonally elongated anomalous circulation and basin-wide sea surface temperature (SST) warming over the Indian Ocean can contribute suppressed convective activities over the subtropical WNP and the consequent formation of the negative PJ pattern although the RWB occurs. The composite for the cases of positive and negative PJ patterns with the absence of RWB further indicates that the convective activities over the subtropical WNP move northwestward with time, causing the formation of the PJ pattern. The formation of the PJ pattern with the absence of RWB is also closely associated with tropical SST and phase of the boreal summer intraseasonal oscillation, illuminating "pure" tropical impacts on the formation of a PJ pattern. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
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