scholarly journals The effect of low density over the “roof of the world” Tibetan Plateau on the triggering of convection

2019 ◽  
Author(s):  
Yinjun Wang ◽  
Xiangde Xu ◽  
Mingyu Zhou ◽  
Donald H. Lenschow ◽  
Xueliang Guo ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Tibetan Plateau ◽  
Thermal Structure ◽  
Cloud Formation ◽  
The Tibetan Plateau ◽  
Climate Data ◽  
Eddy Simulation ◽  
Thermal Turbulence ◽  
Air Density ◽  
Low Cloud

Abstract. We study the relationships between convective characteristics and air density over the Tibetan Plateau (TP) from the perspective of both climate statistics and large eddy simulation (LES). First, based on climate data, we found that there is stronger thermal turbulence and higher frequency of low cloud formation for the same surface relative humidity over the eastern and central TP compared with the eastern monsoon region of China. Second, we focus on the dynamical and thermal structure of the atmospheric boundary layer (ABL) with low air density. With the same surface heat flux, a decrease in air density enhances the buoyancy flux, which increases the ABL depth and moisture transport from the subcloud layer into the cloud layer. With the same low cloud cover for different air densities, the greater ABL depth for lower air density means that the average mixed-layer relative humidity with higher air density will be greater than that with low air density. Results from a subcloud convective velocity scaling scheme were compared with LES results, which indicated that the original fixed parameter values in this scheme may not adequate in case of lower relative humidity and weaker thermal turbulence in the subcloud layer.

scholarly journals Evaluating the streamflow simulation capability of PERSIANN-CDR daily rainfall products in two river basins on the Tibetan Plateau

2016 ◽  
Author(s):  
Xiaomang Liu ◽  
Tiantian Yang ◽  
Koulin Hsu ◽  
Changming Liu ◽  
Soroosh Sorooshian
Keyword(s):  
Tibetan Plateau ◽  
River Basin ◽  
Yangtze River ◽  
Yellow River ◽  
Yangtze River Basin ◽  
Information Source ◽  
Hydrologic Model ◽  
The Tibetan Plateau ◽  
Climate Data ◽  
Streamflow Simulation

Abstract. On the Tibetan Plateau, the limited ground-based rainfall information owing to a harsh environment has brought great challenges to hydrological studies. Satellite-based rainfall products, which allow a better coverage than both radar network and rain gauges on the Tibetan Plateau, can be suitable observation alternatives for investigating the hydrological processes and climate change. In this study, a newly developed daily satellite-based precipitation product, termed Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Climate Data Record (PERSIANN-CDR), is used as input of a hydrologic model to simulate streamflow in the upper Yellow and Yangtze River Basin on the Tibetan Plateau. The results show that the simulated streamflow using PERSIANN-CDR precipitation is closer to observation than that using limited gauge-based precipitation interpolation in the upper Yangtze River Basin. The simulated streamflow using gauge-based precipitation are higher than the streamflow observation during the wet season. In the upper Yellow River Basin, PERSIANN-CDR precipitation and gauge-based precipitation have similar good performance in simulating streamflow. The evaluation of streamflow simulation capability in this study partly indicates that PERSIANN-CDR rainfall product has good potentials to be a reliable dataset and an alternative information source besides the sparse gauge network for conducting long term hydrological and climate studies on the Tibetan Plateau.

scholarly journals Observational evidence of particle hygroscopic growth in the upper troposphere–lower stratosphere (UTLS) over the Tibetan Plateau

2019 ◽  
Vol 19 (13) ◽  
pp. 8399-8406 ◽  
Author(s):  
Qianshan He ◽  
Jianzhong Ma ◽  
Xiangdong Zheng ◽  
Xiaolu Yan ◽  
Holger Vömel ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Tibetan Plateau ◽  
Lower Stratosphere ◽  
Fine Particles ◽  
Asian Summer Monsoon ◽  
Radiative Properties ◽  
Aerosol Layer ◽  
The Tibetan Plateau ◽  
Hygroscopic Growth ◽  
Upper Troposphere

Abstract. We measured the vertical profiles of backscatter ratio (BSR) using the balloon-borne, lightweight Compact Optical Backscatter AerosoL Detector (COBALD) instruments above Linzhi, located in the southeastern Tibetan Plateau, in the summer of 2014. An enhanced aerosol layer in the upper troposphere–lower stratosphere (UTLS), with BSR (455 nm) > 1.1 and BSR (940 nm) > 1.4, was observed. The color index (CI) of the enhanced aerosol layer, defined as the ratio of aerosol backscatter ratios (ABSRs) at wavelengths of 940 and 455 nm, varied from 4 to 8, indicating the prevalence of fine particles with a mode radius of less than 0.1 µm. We find that unlike the very small particles (mode radius smaller than 0.04 µm) at low relative humidity (RHi < 40 %), the relatively large particles in the aerosol layer were generally very hydrophilic as their size increased dramatically with relative humidity. This result indicates that water vapor can play a very important role in increasing the size of fine particles in the UTLS over the Tibetan Plateau. Our observations provide observation-based evidence supporting the idea that aerosol particle hygroscopic growth is an important factor influencing the radiative properties of the Asian Tropopause Aerosol Layer (ATAL) during the Asian summer monsoon.

scholarly journals Spatio-Temporal Variation of Reference Evapotranspiration and Its Climatic Drivers over the Tibetan Plateau during 1970–2018

2021 ◽  
Vol 11 (17) ◽  
pp. 8013
Author(s):  
Shanshan Hu ◽  
Ruyi Gao ◽  
Tao Zhang ◽  
Peng Bai ◽  
Rui Zhang
Keyword(s):  
Wind Speed ◽  
Relative Humidity ◽  
Tibetan Plateau ◽  
Reference Evapotranspiration ◽  
Climatic Factors ◽  
Kendall Test ◽  
The Tibetan Plateau ◽  
Variation Characteristics ◽  
Climatic Drivers ◽  
Spatio Temporal

Reference evapotranspiration (ET0) is a key component of hydrologic cycle and it is important for water resources management. Analysis of ET0 changes is particularly critical for understanding the impacts of climatic change on hydrology in ecologically fragile regions. In this study, using the Penman–Monteith method and the Mann–Kendall test, the variation characteristics of ET0 on the Tibetan Plateau (TP) from 1970 to 2018 was analyzed, and the dominant climatic factors controlling the change of ET0 was also explored. The result shows that in TP region: (1) there was an abrupt change in the trend of ET0 around 1997, and the ET0 declined at a rate of −25.9 mm/decade during 1970–1996 but increased by 31.1 mm/decade during 1997–2018; (2) ET0 is most sensitive to solar radiation, then relative humidity, wind speed and mean temperature; (3) the decrease of ET0 before 1997 was mainly due to the decline of wind speed and the increase of relative humidity, while the increase of ET0 after 1997 was mainly due to the decrease of relative humidity. The results of this study can provide data reference for the research of water balance on the TP.

Vegetation and ocean feedbacks on the Asian climate response to the uplift of the Tibetan Plateau

2020 ◽  
Author(s):  
Ran Zhang ◽  
Dabang Jiang ◽  
Zhongshi Zhang
Keyword(s):  
Tibetan Plateau ◽  
Thermal Structure ◽  
Winter Monsoon ◽  
Annual Precipitation ◽  
The Tibetan Plateau ◽  
Climate Response ◽  
Vegetation Feedback ◽  
Asian Winter Monsoon ◽  
Community Earth System Model ◽  
Monsoon Winds

&lt;p&gt;The growth of the Tibetan Plateau (TP) is one of the important forcings acting on the evolution of the Asian climate during the Cenozoic. However, whether vegetation and ocean feedbacks play a specific role in the Asian climate response to TP uplift remains unclear. Here we investigate this issue through a set of numerical experiments with the Community Earth System Model. The results indicate that vegetation and ocean feedbacks have important but different effects on the Asian climate change in association with TP uplift, which are intrinsically related to the adjustment of thermal structure. The vegetation feedback leads to excess annual precipitation in East China and South Asia and a weakening of the Asian winter monsoon winds. By comparison, the ocean feedback induces a deficit of annual precipitation particularly in most areas of the Bay of Bengal and the South China Sea and a weakening of the Asian summer and winter monsoon winds. These results highlight the importance of vegetation and ocean feedbacks and further facilitate a better understanding of the paleoclimatic response to the uplift of the TP.&lt;/p&gt;

Observed Linkage between Tibetan Plateau Soil Moisture and South Asian Summer Precipitation and the Possible Mechanism

2021 ◽  
Vol 34 (1) ◽  
pp. 361-377
Author(s):  
Waheed Ullah ◽  
Wang Guojie ◽  
Zhiqiu Gao ◽  
Daniel Fiifi Tawia Hagan ◽  
Asher Samuel Bhatti ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Linear Method ◽  
Summer Precipitation ◽  
Moisture Flux ◽  
Thermal Processes ◽  
The Tibetan Plateau ◽  
Climate Data ◽  
Thermal Profile ◽  
Near Surface

AbstractUnderstanding the Tibetan Plateau (TP) thermal processes is of utmost significance in changing climate. This study investigates the effect of soil moisture in changing the TP thermal profile and consequently summer precipitation in South Asia (SA). Soil moisture from Special Sensor Microwave Imager (SSM/I) developed from the F-08, F-11, and F-13 fundamental climate data record and atmospheric reanalysis from ERA-Interim, MERRA-2, and NCEP/CFSR during 1988–2008 are used. A generalized linear method that assesses the reciprocal forcing between two connected fields, named the coupled manifold technique (CMT), is applied to TP soil moisture and SA summer precipitation. It is revealed that interannual variations of SA precipitation are significantly (confidence level = 99%) impacted by TP soil moisture and the explained ratio of variance in SA is 0.3–0.4. Composite analysis indicates that SA summer precipitation has positive anomalies in response to dry TP soil moisture in the previous spring and vice versa. For understanding the possible mechanism, thermal processes, relative humidity, wind components, and moisture flux anomalies were calculated for dry and wet TP soil moisture and summer precipitation. The results suggested that TP soil moisture is likely to regulate near-surface energy balance and diabatic heating profile over TP. As a result, the surrounding lower-level westerlies (easterlies) (at 850 hPa) converge (diverge), associated with divergence (convergence) at the upper troposphere (200 hPa). The westerlies (easterlies) are usually moisture-rich (moisture-deficient) and thus cause more (less) precipitation in western (eastern) SA. It is thus suggested that the spring soil moisture may affect the thermal profile of TP, affecting the summer precipitation in SA as a consequence.

scholarly journals Tree growth and its climate signal along latitudinal and altitudinal gradients: comparison of tree rings between Finland and the Tibetan Plateau

2017 ◽  
Vol 14 (12) ◽  
pp. 3083-3095 ◽  
Author(s):  
Lixin Lyu ◽  
Susanne Suvanto ◽  
Pekka Nöjd ◽  
Helena M. Henttonen ◽  
Harri Mäkinen ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Tree Ring ◽  
Tree Growth ◽  
Latitudinal Gradient ◽  
Ring Width ◽  
Growing Season ◽  
The Tibetan Plateau ◽  
Climate Variables ◽  
Climate Data ◽  
Altitudinal Gradients

Abstract. Latitudinal and altitudinal gradients can be utilized to forecast the impact of climate change on forests. To improve the understanding of how these gradients impact forest dynamics, we tested two hypotheses: (1) the change of the tree growth–climate relationship is similar along both latitudinal and altitudinal gradients, and (2) the time periods during which climate affects growth the most occur later towards higher latitudes and altitudes. To address this, we utilized tree-ring data from a latitudinal gradient in Finland and from two altitudinal gradients on the Tibetan Plateau. We analysed the latitudinal and altitudinal growth patterns in tree rings and investigated the growth–climate relationship of trees by correlating ring-width index chronologies with climate variables, calculating with flexible time windows, and using daily-resolution climate data. High latitude and altitude plots showed higher correlations between tree-ring chronologies and growing season temperature. However, the effects of winter temperature showed contrasting patterns for the gradients. The timing of the highest correlation with temperatures during the growing season at southern sites was approximately 1 month ahead of that at northern sites in the latitudinal gradient. In one out of two altitudinal gradients, the timing for the strongest negative correlation with temperature at low-altitude sites was ahead of treeline sites during the growing season, possibly due to differences in moisture limitation. Mean values and the standard deviation of tree-ring width increased with increasing mean July temperatures on both types of gradients. Our results showed similarities of tree growth responses to increasing seasonal temperature between latitudinal and altitudinal gradients. However, differences in climate–growth relationships were also found between gradients due to differences in other factors such as moisture conditions. Changes in the timing of the most critical climate variables demonstrated the necessity for the use of daily-resolution climate data in environmental gradient studies.

scholarly journals Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ<sup>18</sup>O of tree-ring cellulose

2015 ◽  
Vol 11 (2) ◽  
pp. 327-337 ◽  
Author(s):  
J. Wernicke ◽  
J. Grießinger ◽  
P. Hochreuther ◽  
A. Bräuning
Keyword(s):  
Relative Humidity ◽  
Tibetan Plateau ◽  
Tree Ring ◽  
Summer Season ◽  
Ice Age ◽  
Transfer Model ◽  
The Tibetan Plateau ◽  
The Past ◽  
Dry Conditions ◽  
Hydroclimatic Variables

Abstract. We present an 800-year δ18O chronology from the eastern part of the Tibetan Plateau (TP). The chronology dates back to AD 1193 and was sampled in AD 1996 from living Juniperus tibetica trees. This first long-term tree-ring-based δ18O chronology for eastern Tibet provides a reliable archive for hydroclimatic reconstructions. Highly significant correlations were obtained with hydroclimatic variables (relative humidity, vapour pressure, and precipitation) during the summer season. We applied a linear transfer model to reconstruct summer season relative humidity variations over the past 800 years. More moist conditions prevailed during the termination of the Medieval Warm Period while a systematic shift during the Little Ice Age is not detectable. A distinct trend towards more dry conditions since the 1870s is apparent. The moisture decline weakened around the 1950s but still shows a negative trend. The mid-19th century humidity decrease is in good accordance with several multiproxy hydroclimate reconstructions for south Tibet. However, the pronounced summer relative humidity decline is stronger on the central and eastern TP. Furthermore, the relative humidity at our study site is significantly linked to the relative humidity at large parts of the TP. Therefore, we deduce that the reconstructed relative humidity is mostly controlled by local and mesoscale climatic drivers, although significant connections to the higher troposphere of west-central Asia were observed.

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