The Asian Monsoons as a Unified System

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

scholarly journals Southern Hemisphere forcing of Plioceneδ18O and the evolution of Indo-Asian monsoons

2008 ◽  
Vol 23 (4) ◽  
pp. n/a-n/a ◽  
Author(s):  
Steven C. Clemens ◽  
Warren L. Prell ◽  
Youbin Sun ◽  
Zhengyu Liu ◽  
Guangshan Chen
Keyword(s):  
Southern Hemisphere ◽  
Asian Monsoons

scholarly journals Modeling upper tropospheric and lower stratospheric water vapor anomalies

2013 ◽  
Vol 13 (4) ◽  
pp. 9653-9679 ◽  
Author(s):  
M. R. Schoeberl ◽  
A. E. Dessler ◽  
T. Wang
Keyword(s):  
Water Vapor ◽  
Lower Stratosphere ◽  
Calculation Model ◽  
Vapor Concentration ◽  
Cold Temperatures ◽  
Tropical Tropopause Layer ◽  
Stratospheric Water Vapor ◽  
Tropical Tropopause ◽  
Minimum Displacement ◽  
Asian Monsoons

Abstract. The domain-filling, forward trajectory calculation model developed by Schoeberl and Dessler (2011) is used to further investigate processes that produce upper tropospheric and lower stratospheric water vapor anomalies. We examine the pathways parcels take from the base of the tropical tropopause layer (TTL) to the lower stratosphere. Most parcels found in the lower stratosphere arise from East Asia, the Tropical West Pacific (TWP) and the Central/South America. The belt of TTL parcel origins is very wide compared to the final dehydration zones near the top of the TTL. This is due to the convergence of rising air as a result of the stronger diabatic heating near the tropopause relative to levels above and below. The observed water vapor anomalies – both wet and dry – correspond to regions where parcels have minimal displacement from their initialization. These minimum displacement regions include the winter TWP and the Asian and American monsoons. To better understand the stratospheric water vapor concentration we introduce the water vapor spectrum and investigate the source of the wettest and driest components of the spectrum. We find that the driest air parcels that originate below the TWP, moving upward to dehydrate in the TWP cold upper troposphere. The wettest air parcels originate at the edges of the TWP as well as the summer American and Asian monsoons. The wet air parcels are important since they skew the mean stratospheric water vapor distribution toward higher values. Both TWP cold temperatures that produce dry parcels as well as extra-TWP processes that control the wet parcels determine stratospheric water vapor.

scholarly journals Precipitation <i>δ</i><sup>18</sup>O on the Himalaya–Tibet orogeny and its relationship to surface elevation

2019 ◽  
Vol 15 (1) ◽  
pp. 169-187 ◽  
Author(s):  
Hong Shen ◽  
Christopher J. Poulsen
Keyword(s):  
Climate Model ◽  
Surface Elevation ◽  
Lapse Rate ◽  
The Tibetan Plateau ◽  
Surface Elevation Change ◽  
Rayleigh Distillation ◽  
History Of ◽  
Dominant Process ◽  
Asian Monsoons ◽  
The Himalaya

Abstract. The elevation history of the Himalaya–Tibet orogen is central to understanding the evolution and dynamics of both the India–Asia collision and the Asian monsoons. The surface elevation history of the region is largely deduced from stable isotope (δ18O, δD) paleoaltimetry. This method is based on the observed relationship between the isotopic composition of meteoric waters (δ18Op, δDp) and surface elevation, and the assumption that precipitation undergoes Rayleigh distillation under forced ascent. Here we evaluate how elevation-induced climate change influences the δ18Op–elevation relationship and whether Rayleigh distillation is the dominant process affecting δ18Op. We use an isotope-enabled climate model, ECHAM-wiso, to show that the Rayleigh distillation process is only dominant in the monsoonal regions of the Himalayas when the mountains are high. When the orogen is lowered, local surface recycling and convective processes become important, as forced ascent is weakened due to weaker Asian monsoons. As a result, the δ18Op lapse rate in the Himalayas increases from around −3 to above −0.1 ‰ km−1, and has little relationship with elevation. On the Tibetan Plateau, the meridional gradient of δ18O decreases from ∼1 to ∼0.3 ‰ ∘−1 with reduced elevation, primarily due to enhanced sub-cloud reevaporation under lower relative humidity. Overall, we report that using δ18Op or δDp to deduce surface elevation change in the Himalayan–Tibetan region has severe limitations and demonstrate that the processes that control annual-mean precipitation-weighted δ18Op vary by region and with surface elevation. In summary, we determine that the application of δ18O paleoaltimetry is only appropriate for 7 of the 50 sites from which δ18O records have been used to infer past elevations.

A chemical investigation of microstructural changes in oyster (Magallana gigas) shells

2020 ◽  
Author(s):  
Linda K. Dämmer ◽  
Niels J. de Winter ◽  
Michaela Falkenroth ◽  
Gert-Jan Reichart ◽  
Simone Moretti ◽  
...  
Keyword(s):  
Trace Element ◽  
Oyster Shell ◽  
Isotopic Analysis ◽  
Isotopic Signature ◽  
Planetary Science ◽  
Chemical Variability ◽  
Porous Microstructure ◽  
Asian Monsoons ◽  
Clumped Isotope ◽  
Foliated Structure

&lt;p&gt;The shells of oysters (Family Ostreidae) are predominantly composed of two different calcite microstructures: A dense foliated structure consisting of sheet-like folia (&amp;#8220;foliated&amp;#8221; microstructure) and a more porous microstructure consisting of less well organized leaf-shaped crystals (&amp;#8220;chalky&amp;#8221; microstructure). These unique characteristics of oyster shells have been subject to a number of studies, with some authors hypothesizing that the chalky structures are mineralized by bacteria living in the shell (Vermeij, 2014). The formation of these microstructures is of great interest, because the phenomenon is unique in the mollusk phylum and because the shells of oysters are popular archives for paleoclimate and paleoenvironment reconstructions (e.g. Bougeois et al., 2018; de Winter et al., 2018). Previous authors have challenged the bacterially mediated mineralization hypothesis through microstructural observations of different parts of the oyster shell (Checa et al., 2018).&lt;/p&gt;&lt;p&gt;Here, we expand on this structural evidence by adding detailed observations of differences in chemical composition between the foliated and chalky microstructures. We combine information on trace element concentrations with stable carbon, oxygen, nitrogen and sulfur isotope ratios as well as carbonate clumped isotope analyses of samples from foliated and chalky structures in multiple modern specimens of Magallana gigas, the Pacific oyster. These analyses shed light on the chemical variability within the oyster shell and how it relates to the occurrence of various calcite microstructures. Given the unique isotopic signature of bacterially mediated calcite, our isotopic analysis results allow us to definitively conclude whether the chalky shell structure in modern oysters was precipitated via symbiotic microbes. Furthermore, the degree of intra-shell chemical variability has implications for paleoclimate and paleoenvirionmental reconstructions from fossil oyster shells, for which the applied trace element and isotope systems function as important proxies. The results of this study therefore yield important recommendations for sampling fossil oyster shells for reconstructions, and provide a baseline for the investigation of chemical variability between shell microstructures throughout the Ostreidae family and the mollusk phylum.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Bougeois, L., Dupont-Nivet, G., De Raf&amp;#233;lis, M., Tindall, J. C., Proust, J.-N., Reichart, G.-J., de Nooijer, L. J., Guo, Z. and Ormukov, C.: Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters, Earth and Planetary Science Letters, 485, 99&amp;#8211;110, 2018.&lt;/p&gt;&lt;p&gt;Checa, A. G., Harper, E. M. and Gonz&amp;#225;lez-Segura, A.: Structure and crystallography of foliated and chalk shell microstructures of the oyster Magallana: the same materials grown under different conditions, Scientific reports, 8(1), 7507, 2018.&lt;/p&gt;&lt;p&gt;Vermeij, G. J.: The oyster enigma variations: a hypothesis of microbial calcification, Paleobiology, 40(1), 1&amp;#8211;13, 2014.&lt;/p&gt;&lt;p&gt;de Winter, N., Vellekoop, J., Vorsselmans, R., Golreihan, A., Soete, J., Petersen, S., Meyer, K., Casadio, S., Speijer, R. and Claeys, P.: An assessment of latest Cretaceous Pycnodonte vesicularis (Lamarck, 1806) shells as records for palaeoseasonality: a multi-proxy investigation, Climate of the Past, 14(6), 725&amp;#8211;749, 2018.&lt;/p&gt;

scholarly journals Detecting Source Regions of Wave Activities in the Tropical Atmosphere by Applying Beamforming to Interpolated Data Grids

2009 ◽  
Vol 26 (2) ◽  
pp. 270-280
Author(s):  
Qi Hu ◽  
Zhaoning Liang ◽  
Michael W. Hoffman
Keyword(s):  
Intraseasonal Oscillation ◽  
Relevant Information ◽  
Tropical Pacific ◽  
Tropical Atmosphere ◽  
Pacific Region ◽  
Data Grids ◽  
Source Regions ◽  
Intraseasonal Oscillations ◽  
Tropical Weather ◽  
Asian Monsoons

Abstract Wave activities are primary sources of weather disturbances and cyclones in the tropical atmosphere. One such activity is the intraseasonal variations in wind, convection, and precipitation in the tropical Indian and western tropical Pacific region. These variations affect the intensity, break and reset, and rainfall in the Indian and the East Asian monsoons. Detecting the source regions of these wave activities is essential for understanding and for prediction of wave development. In this study, a fixed beamforming method is proposed to deduce source regions of some wave activities in the tropical atmosphere. This method is tested with simulations of single and distributed complex sources of waves and, then, fixed beamformers are applied to the ECMWF interpolated data grids to detect and identify source regions of the intraseasonal oscillations–waves in the tropical Indian and tropical Pacific Ocean region. Results show that the fixed beamforming technique can uniquely identify the source regions of the intraseasonal oscillations. Applications of this method have revealed various source regions of all major intraseasonal oscillation (ISO) events in the tropical Indian and western equatorial Pacific region during the 29 yr from 1974 to 2002. Knowing these source regions will make it possible to extract the relevant information and, thus, to better understand the development of the intraseasonal oscillations as well as their effects on the tropical weather and climate.

scholarly journals The Effect of ENSO on Tibetan Plateau Snow Depth: A Stationary Wave Teleconnection Mechanism and Implications for the South Asian Monsoons

2005 ◽  
Vol 18 (12) ◽  
pp. 2067-2079 ◽  
Author(s):  
Jeffrey Shaman ◽  
Eli Tziperman
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Snow Depth ◽  
Rossby Waves ◽  
Stationary Wave ◽  
The Tibetan Plateau ◽  
The South ◽  
Central Pacific ◽  
The North ◽  
Asian Monsoons

Abstract An atmospheric stationary wave teleconnection mechanism is proposed to explain how ENSO may affect the Tibetan Plateau snow depth and thereby the south Asian monsoons. Using statistical analysis, the short available record of satellite estimates of snow depth, and ray tracing, it is shown that wintertime ENSO conditions in the central Pacific may produce stationary barotropic Rossby waves in the troposphere with a northeastward group velocity. These waves reflect off the North American jet, turning equatorward, and enter the North African–Asian jet over the eastern Atlantic Ocean. Once there, the waves move with the jet across North Africa, South Asia, the Himalayas, and China. Anomalous increases in upper-tropospheric potential vorticity and increased wintertime snowfall over the Tibetan Plateau are speculated to be associated with these Rossby waves. The increased snowfall produces a larger Tibetan Plateau snowpack, which persists through the spring and summer, and weakens the intensity of the south Asian summer monsoons.

Pollen Evidence of Changing Holocene Monsoon Climate in Sichuan Province, China

1993 ◽  
Vol 39 (3) ◽  
pp. 325-337 ◽  
Author(s):  
Devra I. Jarvis
Keyword(s):  
Pollen Record ◽  
Monsoon Climate ◽  
Deciduous Species ◽  
Global Circulation ◽  
Warming Climate ◽  
Cold Tolerant ◽  
Monsoon System ◽  
Asian Monsoons ◽  
Sclerophyllous Vegetation ◽  
Warm Temperate

AbstractPollen evidence from Lake Shayema, Mianning County, was obtained to examine postglacial vegetation and climatic change in southwestern Sichuan, China. The sclerophyllous character of the region's warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the Asian monsoons. The pollen record displays several changes in the vegetation over the last 11,000 yr. From 11,000 to 9100 yr B.P., cold-tolerant species, such as Abies , Betula, and deciduous oaks, dominated the vegetation. Between 9100 and 7800 yr B.P., the abundance of deciduous oaks decreased and evergreen oaks increased, as did Tsuga and mesic deciduous species. This change suggests a warming climate with increased precipitation. From 7800 to 4000 yr B.P., sclerophyllous species increased at the expense of mesic deciduous species, an indication that precipitation was becoming more seasonal. Except for increased disturbance starting ca. 1000 yr B.P., the predominance of sclerophyllous vegetation continued until today. The pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid Holocene.

The Asian Monsoons and Zheng He's Voyages to the Western Ocean

2011 ◽  
Vol 64 (2) ◽  
pp. 207-218 ◽  
Author(s):  
Deng Hui ◽  
Li Xin
Keyword(s):  
Asian Monsoon ◽  
Careful Consideration ◽  
Historical Records ◽  
Close Attention ◽  
History Of ◽  
Changing Patterns ◽  
Geographical Perspective ◽  
Asian Monsoons ◽  
Rendezvous Points ◽  
History Of Navigation

The expedition of Zheng He's fleet to the Western Ocean1 in the first half of the 15th century is an important event in the history of navigation, which has attracted the broad attention of domestic and foreign scholars from different fields2. This paper reveals the relation between Zheng He's voyages and the Asian Monsoon from a geographical perspective. Historical records show that Zheng He's seven voyages to the Western Ocean were precisely organized and successfully carried out due to careful consideration of the conditions and periodical patterns of the Asian tropical and subtropical monsoon. Details such as fleet routes, sailing schedules, wind-waiting points, divergent and rendezvous points were painstakingly planned and arranged in advance by the organizers of the expedition, who all paid close attention to the changing patterns of the Asian Monsoon.

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