Seismic attenuation of regional phases in the northern Middle East and the Tibetan Plateau

2011 ◽  
Author(s):  
Xueyang Bao
Keyword(s):  
Middle East ◽  
Tibetan Plateau ◽  
Seismic Attenuation ◽  
The Tibetan Plateau ◽  
Regional Phases

Lateral variation of Pn and Lg attenuation at the CDSN station LSA

1999 ◽  
Vol 89 (1) ◽  
pp. 325-330
Author(s):  
C. C. Reese ◽  
R. R. Rapine ◽  
J. F. Ni
Keyword(s):  
Tibetan Plateau ◽  
Regional Scale ◽  
The Tibetan Plateau ◽  
Lateral Variation ◽  
Data Set ◽  
Southern Boundary ◽  
Recent Tectonics ◽  
Regional Phases ◽  
Southern Tibetan Plateau ◽  
Central Tibet

Abstract The propagation efficiencies of the regional phases Lg and Pn are indicative of how active and recent tectonics influence crust and uppermost mantle properties, respectively. In this study, regional scale lateral heterogeneity of Lg and Pn attenuation for the region in and around the southern Tibetan Plateau is investigated. The data set is comprised of seismograms recorded at the Chinese Digital Seismogram Network (CDSN) station LSA from regional events with epicentral distances within 11°. Attenuation of Lg and Pn is calculated using spectral methods and assuming constant QLg and QPn models for the frequency bands 0.3 to 3.0 Hz and 0.5 to 4.0 Hz, respectively. Lateral variation in attenuation is estimated by analyzing data on an event-by-event basis. Significant lateral variation is observed with QLg decreasing from about 520 for events south of LSA to about 340 for events north of LSA and QPn ∼ 670 for southern backazimuths, while QPn ∼ 240 for northern events. For Pn, this north-south variation is consistent with other observations, indicating partially melted upper mantle beneath north central Tibet. For Lg, the azimuthal variation in attenuation indicates that Lg propagation as observed at LSA is efficient for paths crossing the southern boundary of the Tibetan Plateau relative to paths within the plateau itself.

Modeling dust sources, transport, and radiative effects at different altitudes over the Tibetan Plateau

2020 ◽  
Author(s):  
Zhiyuan Hu ◽  
Jianping Huang ◽  
Chun Zhao ◽  
Qinjian Jin ◽  
Yuanyuan Ma ◽  
...  
Keyword(s):  
Middle East ◽  
Tibetan Plateau ◽  
Mass Flux ◽  
Radiation Budget ◽  
Dust Particles ◽  
The Tibetan Plateau ◽  
North African ◽  
The North ◽  
Dust Mass ◽  
Different Altitudes

<p>Mineral dust plays an important role in the climate of the Tibetan Plateau (TP) by modifying the radiation budget, cloud macro- and microphysics, precipitation, and snow albedo. Meanwhile, the TP with the highest topography in the word can affect intercontinental transport of dust plumes and induce typical distribution characteristics of dust at different altitudes. In this study, we conduct a quasi-global simulation to investigate the characteristics of dust source contribution and transport over the TP at different altitude by using a fully coupled meteorology-chemistry model (WRF-Chem) with a tracer-tagging technique. Generally, the simulation reasonably captures the spatial distribution of satellite retrieved dust aerosol optical depth (AOD) at different altitudes. Model results show that dust particles are emitted into atmosphere through updrafts over major desert regions, and then transported to the TP. The East Asian dust (mainly from Gobi and Taklamakan deserts) transports southward and is lifted up to the TP, contributing a mass loading of 50 mg/m<sup>2</sup> at 3 km height and 5 mg/m<sup>2</sup> at 12 km height over the northern slop of the TP. Dust from North Africa and Middle East are concentrated over both northern and southern slopes below 6 km, where mass loadings range from 10 to 100mg/m<sup>2</sup> and 1 to 10 mg/m<sup>2</sup> below 3 km and above 9 km, respectively. As the dust is transported to the north and over the TP, mass loadings are 5-10 mg/m<sup>2</sup> above 6 km.</p><p>The imported dust mass flux from East Asia to the TP is 7.9 Tg/year mostly occuring at the heights of 3–6 km. The North African and Middle East dust particles are transported eastward following the westerly jet, and then imported into the TP at West side with the dust mass flux of 7.8 and 26.6 Tg/year, respectively. The maximum mass flux of the North African dust mainly occurs in 0–3 km (3.9 Tg/year), while the Middle East within 6–9 km (12.3 Tg/year). The dust outflow occurs at East side (–17.89 Tg/year) and South side (–11.22 Tg/year) of the TP with a peak value (8.7 Tg/year) in 6–9 km . Moreover, the dust mass is within the size range of 1.25~5.0</p>

scholarly journals Seasonal Responses of Indian Summer Monsoon to Dust Aerosols in the Middle East, India, and China

2016 ◽  
Vol 29 (17) ◽  
pp. 6329-6349 ◽  
Author(s):  
Qinjian Jin ◽  
Zong-Liang Yang ◽  
Jiangfeng Wei
Keyword(s):  
Water Vapor ◽  
Middle East ◽  
Tibetan Plateau ◽  
The Tibetan Plateau ◽  
Heating Effect ◽  
Anthropogenic Aerosols ◽  
Dust Aerosols ◽  
Northern India ◽  
Monsoon Flow ◽  
Seasonal Responses

Abstract The seasonal responses of the Indian summer monsoon (ISM) to dust aerosols in local (the Thar Desert) and remote (the Middle East and western China) regions are studied using the WRF Model coupled with online chemistry (WRF-Chem). Ensemble experiments are designed by perturbing model physical and chemical schemes to examine the uncertainties of model parameterizations. Model results show that the dust-induced increase in ISM total rainfall can be attributed to the remote dust in the Middle East, while the contributions from local and remote dust are very limited. Convective rainfall shows a spatially more homogeneous increase than stratiform rainfall, whose responses follow the topography. The magnitude of dust-induced increase in rainfall is comparable to that caused by anthropogenic aerosols. The Middle East dust aerosols tend to enhance the southwesterly monsoon flow, which can transport more water vapor to southern and northern India, while the anthropogenic aerosols tend to enhance the southeasterly monsoon flow, resulting in more water vapor and rainfall over northern India. Both dust and anthropogenic aerosol-induced rainfall responses can be attributed to their heating effect in the mid-to-upper troposphere, which enhances monsoon circulations. The heating effect of dust over the Iranian Plateau seems to play a bigger role than that over the Tibetan Plateau, while the heating of anthropogenic aerosols over the Tibetan Plateau is more important. Moreover, dust aerosols can decrease rainfall over the Arabian Sea through their indirect effect. This study addresses the relative roles of dust and anthropogenic aerosols in altering the ISM rainfall and provides insights into aerosol–ISM interactions.

scholarly journals Seismic attenuation of regional phases in the northern Middle East and eastern Tibetan plateau

2017 ◽  
Author(s):  
◽  
Wenfei Ku
Keyword(s):  
Middle East ◽  
Tibetan Plateau ◽  
Continental Collision ◽  
Seismic Attenuation ◽  
Eastern Tibetan Plateau ◽  
Uppermost Mantle ◽  
Iranian Plateau ◽  
High Attenuation ◽  
Attenuation Structure ◽  
Q Values

Temperature and composition are two major causes for subsurface seismic anomalies. Positive temperature anomalies will lead to a reduction in both attenuation and velocity; however, compositional anomalies should not necessarily produce a strong correlation in attenuation and velocity. As a result, by combining velocity and attenuation structure we can distinguish between compositional and temperature anomalies. Using efficiency tomography and Q tomography, I have constructed Sn attenuation models for two continental-continental collision zones, the northern Middle East and the eastern Tibetan Plateau. The Tibetan Plateau was formed by the continental collision between Indian and Eurasian plates that has been going on at least since [about]50Ma. Two tomographic techniques have been used to determine the attenuation structure of the uppermost mantle beneath the eastern Tibetan Plateau. I observe lateral heterogeneity of Sn attenuation beneath the southern Tibetan Plateau that indicates a complex geometry of the underthrusting Indian continental lithosphere (UICL). Sn is blocked with relative low Q values across the Qiangtang block and Songpan-Ganzi block indicating a hot and weak lithosphere. This observation can be caused by mantle upwellings induced by the sinking slab detached from the UICL. The Turkish-Iranian plateau and Zagros, the main tectonic feature of the northern Middle East, was formed as a result of the continental collision between the Arabian and Eurasian plates since Early Cenozoic (23-35Ma). I have collected a large Sn waveform data set in the northern Middle East that I have quality controlled using both automated and manual approaches. Two tomographic techniques have been used to determine the attenuation structure of the uppermost mantle. I observe inefficient/blocked Sn and low Q values in the Turkish-Iranian plateau indicating a hot and thin mantle lithosphere. Intrinsic attenuation is the dominant uppermost mantle shear wave attenuation mechanism beneath the eastern Anatolian plateau and Lesser Caucasus. Partial melting appears to be the main cause of high attenuation in two of the regions. Scattering attenuation appears to be the dominant mechanism in the Zagros. The high attenuation in the Iranian plateau is likely not caused by partial melting thus the seismic anomalies in the uppermost mantle are likely compositional. Data censorship is a common problem in seismic attenuation studies. Discarding blocked Sn paths will cause left censored data problem and the resulting model will be biased to high Q values. Using Level of Detection Divided by Two (LOD/2) technique, I am able to obtain lower Q values and smoother variations in the resulting models comparing with censored models.

scholarly journals Upstream Subtropical Signals Preceding the Asian Summer Monsoon Circulation

2004 ◽  
Vol 17 (21) ◽  
pp. 4213-4229 ◽  
Author(s):  
Song Yang ◽  
K-M. Lau ◽  
S-H. Yoo ◽  
J. L. Kinter ◽  
K. Miyakoda ◽  
...  
Keyword(s):  
Middle East ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Large Scale ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Jet Stream ◽  
The Tibetan Plateau ◽  
Physical Processes ◽  
Asian Summer

Abstract In this study, the authors address several issues with respect to the antecedent signals of the large-scale Asian summer monsoon that were earlier identified by Webster and Yang. In particular, they revisit the changes in the subtropical upper-tropospheric westerlies preceding the monsoon, depict the detailed structure of the monsoon's antecedent signals, and investigate the physical processes from the signals to the monsoon. They also explore the teleconnection of these signals to various large-scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the Tibetan Plateau and the monsoon. Before a strong (weak) Asian summer monsoon, the 200-mb westerlies over subtropical Asia are weak (strong) during the previous winter and spring. A significant feature of these signals is represented by the variability of the Middle East jet stream whose changes are linked to the Arctic Oscillation, North Atlantic Oscillation, El Niño–Southern Oscillation, and other climate phenomena. When this jet stream intensifies and shifts southeastward, cold air intrudes frequently from eastern Europe into the Middle East and southwestern Asia. As a result, in subtropical Asia, snow and precipitation increase, the ground wetness increases, and surface temperature decreases. A strengthening Middle East jet stream is also accompanied by increases in both stationary wave activity flux and higher-frequency eddy activities. The Tibetan Plateau acts to block these westerly activities propagating eastward and increase the persistence of the low-temperature anomalies, which in turn prolongs the atmospheric signals from winter to spring. A strong link is found between the persistent low-temperature anomalies and the decrease in geopotential height over southern Asia, including the Tibetan Plateau, in spring. The latter indicates a late establishment of the South Asian high, and implies a delay in the atmospheric transition from winter to summer conditions and in the development of the summer monsoon. The preceding scenario for a strong Middle East jet stream and a weaker Asian monsoon can be applied accordingly for the discussion of the physical processes from a weak jet stream to a strong monsoon. The current results of the relationship between the extratropical process and Asian monsoon resemble several features of the tropical–extratropical interaction mechanism for the tropospheric biennial oscillation (TBO). While the role of tropical heating is emphasized in the TBO mechanism, compared to the variability of the sea surface temperature related to El Niño–Southern Oscillation, the extratropical process examined in this study is more strongly linked to the Asian summer monsoon.

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