Gravity Observations and Apparent Density Changes before the 2017 Jiuzhaigou Ms7.0 Earthquake and Their Precursory Significance

An Ms7.0 earthquake struck Jiuzhaigou (China) on 8 August 2017. The epicenter was in the eastern margin of the Tibetan Plateau, an area covered by a dense time-varying gravity observation network. Data from seven repeated high-precision hybrid gravity surveys (2014–2017) allowed the microGal-level time-varying gravity signal to be obtained at a resolution better than 75 km using the modified Bayesian gravity adjustment method. The “equivalent source” model inversion method in spherical coordinates was adopted to obtain the near-crust apparent density variations before the earthquake. A major gravity change occurred from the southwest to the northeast of the eastern Tibetan Plateau approximately 2 years before the earthquake, and a substantial gravity gradient zone was consistent with the tectonic trend that gradually appeared within the focal area of the Jiuzhaigou earthquake during 2015–2016. Factors that might cause such regional gravitational changes (e.g., vertical crustal deformation and variations in near-surface water distributions) were studied. The results suggest that gravity effects contributed by these known factors were insufficient to produce gravity changes as big as those observed, which might be related to the process of fluid material redistribution in the crust. Regional change of the gravity field has precursory significance for high-risk earthquake areas and it could be used as a candidate precursor for annual medium-term earthquake prediction.

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Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

Climate of the Past ◽

10.5194/cp-10-91-2014 ◽

2014 ◽

Vol 10 (1) ◽

pp. 91-106 ◽

Cited By ~ 61

Author(s):

E. Dietze ◽

F. Maussion ◽

M. Ahlborn ◽

B. Diekmann ◽

K. Hartmann ◽

...

Keyword(s):

Grain Size ◽

Sediment Transport ◽

Tibetan Plateau ◽

Transport Processes ◽

The Tibetan Plateau ◽

Dust Deposition ◽

Northerly Wind ◽

Near Surface ◽

Depositional Processes ◽

End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

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Investigation of the Variability of Near‐Surface Temperature Anomaly and Its Causes Over the Tibetan Plateau

Journal of Geophysical Research Atmospheres ◽

10.1029/2020jd032800 ◽

2020 ◽

Vol 125 (19) ◽

Author(s):

Ye Liu ◽

Yongkang Xue ◽

Qian Li ◽

Dennis Lettenmaier ◽

Ping Zhao

Keyword(s):

Tibetan Plateau ◽

Surface Temperature ◽

Temperature Anomaly ◽

The Tibetan Plateau ◽

Near Surface

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A numerical process study on the rapid transport of stratospheric air down to the surface over western North America and the Tibetan Plateau

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-6535-2019 ◽

2019 ◽

Vol 19 (9) ◽

pp. 6535-6549 ◽

Cited By ~ 2

Author(s):

Bojan Škerlak ◽

Stephan Pfahl ◽

Michael Sprenger ◽

Heini Wernli

Keyword(s):

Boundary Layer ◽

Tibetan Plateau ◽

Surface Ozone ◽

Vertical Transport ◽

The Tibetan Plateau ◽

Near Surface ◽

Air Mass ◽

Ozone Concentrations ◽

Rapid Transport ◽

Upper Level

Abstract. Upper-level fronts are often associated with the rapid transport of stratospheric air along tilted isentropes to the middle or lower troposphere, where this air leads to significantly enhanced ozone concentrations. These plumes of originally stratospheric air can only occasionally be observed at the surface because (i) stable boundary layers prevent an efficient vertical transport down to the surface, and (ii) even if boundary layer turbulence were strong enough to enable this transport, the originally stratospheric air mass can be diluted by mixing, such that only a weak stratospheric signal can be recorded at the surface. Most documented examples of stratospheric air reaching the surface occurred in mountainous regions. This study investigates two such events, using a passive stratospheric air mass tracer in a mesoscale model to explore the processes that enable the transport down to the surface. The events occurred in early May 2006 in the Rocky Mountains and in mid-June 2006 on the Tibetan Plateau. In both cases, a tropopause fold associated with an upper-level front enabled stratospheric air to enter the troposphere. In our model simulation of the North American case, the strong frontal zone reaches down to 700 hPa and leads to a fairly direct vertical transport of the stratospheric tracer along the tilted isentropes to the surface. In the Tibetan Plateau case, however, no near-surface front exists and a reservoir of high stratospheric tracer concentrations initially forms at 300–400 hPa, without further isentropic descent. However, entrainment at the top of the very deep boundary layer (reaching to 300 hPa over the Tibetan Plateau) and turbulence within the boundary layer allows for downward transport of stratospheric air to the surface. Despite the strongly differing dynamical processes, stratospheric tracer concentrations at the surface reach peak values of 10 %–20 % of the imposed stratospheric value in both cases, corroborating the potential of deep stratosphere-to-troposphere transport events to significantly influence surface ozone concentrations in these regions.

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Impact of topography on black carbon transport to the southern Tibetan Plateau during the pre-monsoon season and its climatic implication

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-5923-2020 ◽

2020 ◽

Vol 20 (10) ◽

pp. 5923-5943 ◽

Cited By ~ 2

Author(s):

Meixin Zhang ◽

Chun Zhao ◽

Zhiyuan Cong ◽

Qiuyan Du ◽

Mingyue Xu ◽

...

Keyword(s):

Tibetan Plateau ◽

Black Carbon ◽

Radiative Forcing ◽

Monsoon Season ◽

Radiative Heating ◽

The Tibetan Plateau ◽

Complex Topography ◽

Meridional Transport ◽

Near Surface ◽

Mass Volume

Abstract. Most previous modeling studies about black carbon (BC) transport and its impact over the Tibetan Plateau (TP) conducted simulations with horizontal resolutions coarser than 20 km that may not be able to resolve the complex topography of the Himalayas well. In this study, the two experiments covering all of the Himalayas with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) at the horizontal resolution of 4 km but with two different topography datasets (4 km complex topography and 20 km smooth topography) are conducted for pre-monsoon season (April 2016) to investigate the impacts of topography on modeling the transport and distribution of BC over the TP. Both experiments show the evident accumulation of aerosols near the southern Himalayas during the pre-monsoon season, consistent with the satellite retrievals. The observed episode of high surface BC concentration at the station near Mt. Everest due to heavy biomass burning near the southern Himalayas is well captured by the simulations. The simulations indicate that the prevailing upflow across the Himalayas driven by the large-scale westerly and small-scale southerly circulations during the daytime is the dominant transport mechanism of southern Asian BC into the TP, and it is much stronger than that during the nighttime. The simulation with the 4 km topography resolves more valleys and mountain ridges and shows that the BC transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is more efficient. The complex topography results in stronger overall cross-Himalayan transport during the simulation period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. This results in 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the TP from the simulation with the 4 km complex topography than that with the 20 km smoother topography. The different topography also leads to different distributions of snow cover and BC forcing in snow. This study implies that the relatively smooth topography used by the models with resolutions coarser than 20 km may introduce significant negative biases in estimating light-absorbing aerosol radiative forcing over the TP during the pre-monsoon season. Highlights. The black carbon (BC) transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is much more efficient during the pre-monsoon season. The complex topography results in stronger overall cross-Himalayan transport during the study period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. The complex topography generates 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the Tibetan Plateau (TP) than the smoother topography, which implies that the smooth topography used by the models with relatively coarse resolution may introduce significant negative biases in estimating BC radiative forcing over the TP during the pre-monsoon season. The different topography also leads to different distributions of snow cover and BC forcing in snow over the TP.

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Recent Trends in Land Surface Temperature on the Tibetan Plateau

Journal of Climate ◽

10.1175/jcli3811.1 ◽

2006 ◽

Vol 19 (12) ◽

pp. 2995-3003 ◽

Cited By ~ 29

Author(s):

Yuichiro Oku ◽

Hirohiko Ishikawa ◽

Shigenori Haginoya ◽

Yaoming Ma

Keyword(s):

Tibetan Plateau ◽

Surface Temperature ◽

Air Temperature ◽

Land Surface Temperature ◽

Land Surface ◽

Precipitation Amount ◽

Surface Air Temperature ◽

The Tibetan Plateau ◽

Near Surface ◽

Diurnal Range

Abstract The diurnal, seasonal, and interannual variations in land surface temperature (LST) on the Tibetan Plateau from 1996 to 2002 are analyzed using the hourly LST dataset obtained by Japanese Geostationary Meteorological Satellite 5 (GMS-5) observations. Comparing LST retrieved from GMS-5 with independent precipitation amount data demonstrates the consistent and complementary relationship between them. The results indicate an increase in the LST over this period. The daily minimum has risen faster than the daily maximum, resulting in a narrowing of the diurnal range of LST. This is in agreement with the observed trends in both global and plateau near-surface air temperature. Since the near-surface air temperature is mainly controlled by LST, this result ensures a warming trend in near-surface air temperature.

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Modeling the Effects of Lakes in the Tibetan Plateau on Diurnal Variations of Regional Climate and Their Seasonality

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0091.1 ◽

2020 ◽

Vol 21 (11) ◽

pp. 2523-2536

Author(s):

Lingjing Zhu ◽

Jiming Jin ◽

Yimin Liu

Keyword(s):

Tibetan Plateau ◽

Regional Climate ◽

Wrf Model ◽

Surface Air Temperature ◽

Diurnal Variations ◽

The Tibetan Plateau ◽

Near Surface ◽

Local Climate ◽

Lake Model ◽

Physically Based

AbstractIn this study, we investigated the effects of lakes in the Tibetan Plateau (TP) on diurnal variations of local climate and their seasonal changes by using the Weather Research and Forecasting (WRF) Model coupled with a one-dimensional physically based lake model. We conducted WRF simulations for the TP over 2000–10, and the model showed excellent performance in simulating near-surface air temperature, precipitation, lake surface temperature, and lake-region precipitation when compared to observations. We carried out additional WRF simulations where all the TP lakes were replaced with the nearest land-use types. The differences between these two sets of simulations were analyzed to quantify the effects of the TP lakes on the local climate. Our results indicate that the strongest lake-induced cooling occurred during the spring daytime, while the most significant warming occurred during the fall nighttime. The cooling and warming effects of the lakes further inhibited precipitation during summer afternoons and evenings and motivated it during fall early mornings, respectively. This study lays a solid foundation for further exploration of the role of TP lakes in climate systems at different time scales.

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Isostatic Crustal Thickness Under The Tibetan Plateau And Himalayas From Satellite Gravity Gradiometry Data

Earth Sciences Research Journal ◽

10.15446/esrj.v19n2.44574 ◽

2015 ◽

Vol 19 (2) ◽

pp. 97-106 ◽

Cited By ~ 4

Author(s):

Robert Tenzer ◽

Mohammad Bagherbandi ◽

Lars E Sjöberg ◽

Pavel Novák

Keyword(s):

Tibetan Plateau ◽

Spherical Harmonic ◽

Crustal Thickness ◽

Moho Depth ◽

Gravity Gradient ◽

The Tibetan Plateau ◽

Systematic Bias ◽

Font Size ◽

Isostatic Gravity ◽

Vening Meinesz

The global gravity and crustal models are used in this study to determine the regional Moho model. For this purpose, we solve the Vening Meinesz-Moritz’s (VMM) inverse problem of isostasy de ned in terms of the isostatic gravity gradient. The functional relation between the Moho depth and the second-order radial derivative of the VMM isostatic potential is formulated by means of the (linearized) Fredholm integral equation of the rst kind. Methods for a spherical harmonic analysis and synthesis of the gravity eld and crustal structure models are applied to evaluate the gravity gradient corrections and the respective corrected gravity gradient, taking into consideration major known density structures within the Earth’s crust (while mantle heterogeneities are disregarded). The resulting gravity gradient is compensated isostatically based on applying the VMM scheme. The VMM inverse problem for finding the Moho depths is solved iteratively. The regularization is applied to stabilize the ill-posed solution. The global geopotential model GOCO-03s, the global topographic/bathymetric model DTM2006.0 and the global crustal model CRUST1.0 are used to generate the VMM isostatic gravity gradient with a spectral resolution complete to a spherical harmonic degree of 250. The VMM inverse scheme is used to determine the regional isostatic crustal thickness beneath the Tibetan Plateau and Himalayas (compiled on a 1x1 arc-deg grid). The differences between the isostatic and seismic Moho models are modeled and subsequently corrected for by applying the non-isostatic correction. Our results show that the regional gravity gradient inversion can model realistically the relative Moho geometry, while the solution contains a systematic bias. We explain this bias by more localized information on the Earth’s inner structure in the gravity gradient eld compared to the potential or gravity fields. Espesor isostático de la corteza bajo la meseta tibetana y los Himalayas a partir de datos satelitales de gradiente gravitatoria ResumenEste estudio utiliza los modelos globales de gravedad y de espesor de la corteza para determinar un modelo regional de la discontinuidad de Mohorovičić (Moho). Con este fin se resolvió el problema inverso de isostasia Vening Meinesz-Moritz (VMM) de nido en términos de gradiente gravitatoria isostática. La relación funcional entre la profundidad de la Moho y la derivación radial de segundo orden del potencial isostático VMM fue formulado a través de la ecuación integral Fredholm de primera clase. Se aplicaron métodos para el análisis esférico armónico y para la síntesis del campo gravitacional, y los modelos de estructura de corteza para evaluar las correcciones de gradiente gravitatoria y el respectivo gradiente gravitatorio corregido, considerando el conocimiento de las principales densidades de la estructura al interior de la corteza de la Tierra (las heterogenidades del manto fueron ignoradas). El gradiente gravitatorio resultante se compensó isostáticamente con la aplicación del esquema VVM. Se resolvió reiterativamente el problema inverso VVM para encontrar las profundidades de la discontinuidad Moho. Se aplicó la regularización para estabilizar la solución planteada. El modelo geopotencial global GOCO-03s, el modelo global topográfico/batimetrico DTM2006.0 y el modelo global de la corteza CRUST 1.0 permitieron generar el gradiente gravitacional isostático VVM con una resolución espectral completa a un grado esférico armonioso de 250. A través del esquema inverso VMM se determinó el espesor isostático regional bajo la meseta Tibetana y los Himalayas (compilada en una cuadrícula de 1x1 grados sexagesimales). Las diferencias entre los modelos isostático y sísmico de la Moho fueron modeladas y corregidas con la aplicación de la corrección no isostática. Los resultados muestran que la inversión del gradiente gravitatorio puede modelar realísticamente la geometría de la Moho, a pesar que la solución contiene una desviación sistemática. Esta inclinación se explica por la información estructural interna de la Tierra en el campo del gradiente gravitatorio comparado con el potencial gravitatorio.

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A Teleconnection Pattern over Eurasian Continent in early Spring and its Impact on Bay of Bangle Monsoon Onset

10.5194/egusphere-egu2020-8951 ◽

2020 ◽

Author(s):

Yaoxian Yang ◽

Yimin Liu ◽

Guoxiong Wu ◽

Yongkun Xie ◽

Jinxiao Li

Keyword(s):

Tibetan Plateau ◽

Rossby Wave ◽

Numerical Test ◽

Stationary Wave ◽

Early Spring ◽

Teleconnection Pattern ◽

Monsoon Onset ◽

The Tibetan Plateau ◽

Near Surface ◽

Eurasian Continent

A teleconnection pattern over the Eurasian continent in early spring and its impact on Bay of Bangle Monsoon onset, is investigated on the basis of reanalysis datasets and numerical test. It is revealed that this pattern shows Rossby wave activities that excited by the forcing feedback of the transient eddies over the exit region of the North Atlantic jet. The anomalous centers can manifest themselves as Rossby wave dividing into two branches and propagating towards Lake Baikal and south flank of the Tibetan Plateau.&#160;Meanwhile, asymmetric atmospheric response to vorticity forcing is characterized by weaker amplitude during positive phase than negative phase, which is caused by weaker positive vorticity forcing. Moreover, the anomalous cold cyclone locates on the Tibetan Plateau can bring more snowfall and correspond to anomalously wet soil condition, thereby decreasing surface heat flux and near-surface temperatures, leading to an anomalous cold cyclone can be maintained until April. Therefore, it can postpone Bay of Bangle Monsoon onset. Subsequently, the interannual variations of stationary wave can give a better explanation for late Monsoon onset under neutral ENSO condition. The simulated response to vorticity forcing also can reproduce the pattern of this stationary wave in Linear Baroclinic Model (LBM).

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