scholarly journals Cumulus over the Tibetan Plateau in the Summer Based on CloudSat–CALIPSO Data

2016 ◽  
Vol 29 (3) ◽  
pp. 1219-1230 ◽  
Author(s):  
Yunying Li ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Climate Models ◽  
Surface Wind ◽  
Lower Atmosphere ◽  
The Tibetan Plateau ◽  
Shallow Convection ◽  
Free Atmosphere ◽  
Northern Summer ◽  
Static Energy ◽  
Fine Resolution

Abstract Cumulus (Cu) can transport heat and water vapor from the boundary layer to the free atmosphere, leading to the redistribution of heat and moist energy in the lower atmosphere. This paper uses the fine-resolution CloudSat–CALIPSO product to characterize Cu over the Tibetan Plateau (TP). It is found that Cu is one of the dominant cloud types over the TP in the northern summer. The Cu event frequency, defined as Cu occurring within 50-km segments, is 54% over the TP in the summer, which is much larger over the TP than in its surrounding regions. The surface wind vector converging at the central TP and the topographic forcing provide the necessary moisture and dynamical lifting of convection over the TP. The structure of the atmospheric moist static energy shows that the thermodynamical environment over the northern TP can be characterized as having weak instability, a shallow layer of instability, and lower altitudes for the level of free convection. The diurnal variation of Cu with frequency peaks during the daytime confirms the surface thermodynamic control on Cu formation over the TP. This study offers insights into how surface heat is transported to the free troposphere over the TP and provides an observational test of climate models in simulating shallow convection over the TP.

scholarly journals The Tibetan Plateau Uplift is Crucial for Eastward Propagation of Madden-Julian Oscillation

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Young-Min Yang ◽  
June-Yi Lee ◽  
Bin Wang
Keyword(s):  
Tibetan Plateau ◽  
Information Science ◽  
The Tibetan Plateau ◽  
Maritime Continent ◽  
Free Atmosphere ◽  
Plateau Uplift ◽  
Tibetan Plateau Uplift ◽  
The Indian Ocean ◽  
Upward Transport ◽  
Static Energy

Abstract The Tibetan Plateau (TP) and Himalayas have been treated as an essential external factor in shaping Asian monsoon and mid-latitude atmospheric circulation. In this study we perform numerical experiments with different uplift altitudes using the Nanjing University of Information Science and Technology Earth System Model to examine potential impacts of uplift of the TP and Himalayas on eastward propagation of the MJO and the associated mechanisms. Analysis of experimental results with dynamics-based MJO diagnostics indicates two potential mechanisms. First, the uplift considerably enhances low-level mean westerlies in the Indian Ocean and convection in the Maritime Continent, which in turn strengthens boundary layer moisture convergence (BLMC) to the east of the MJO convective center. The increased BLMC reinforces upward transport of moisture and heat from BL to free atmosphere and increases lower tropospheric diabatic heating by shallow and congestus clouds ahead of the MJO center, enhancing the Kelvin-Rossby wave feedback. Second, the uplift increases upper tropospheric mean easterlies and stratiform heating at the west of the MJO center, which contributes to eastward propagation of MJO by generating positive moist static energy at the east of MJO center. This study will contribute to a better understanding of the origin of the MJO and improvement in simulation of MJO propagation.

scholarly journals Assessing Impacts of PBL and Surface Layer Schemes in Simulating the Surface–Atmosphere Interactions and Precipitation over the Tropical Ocean Using Observations from AMIE/DYNAMO

2016 ◽  
Vol 29 (22) ◽  
pp. 8191-8210 ◽  
Author(s):  
Yun Qian ◽  
Huiping Yan ◽  
Larry K. Berg ◽  
Samson Hagos ◽  
Zhe Feng ◽  
...  
Keyword(s):  
Surface Layer ◽  
Climate Models ◽  
Deep Convection ◽  
Surface Wind ◽  
Wrf Model ◽  
Surface Fluxes ◽  
Shallow Convection ◽  
Free Atmosphere ◽  
Tropical Ocean ◽  
Surface Atmosphere

Abstract Accuracy of turbulence parameterization in representing planetary boundary layer (PBL) processes and surface–atmosphere interactions in climate models is critical for predicting the initiation and development of clouds. This study 1) evaluates WRF Model–simulated spatial patterns and vertical profiles of atmospheric variables at various spatial resolutions and with different PBL, surface layer, and shallow convection schemes against measurements; 2) identifies model biases by examining the moisture tendency terms contributed by PBL and convection processes through nudging experiments; and 3) investigates the main causes of these biases by analyzing the dependence of modeled surface fluxes on PBL and surface layer schemes over the tropical ocean. The results show that PBL and surface parameterizations have surprisingly large impacts on precipitation and surface moisture fluxes over tropical oceans. All of the parameterizations tested tend to overpredict moisture in the PBL and free atmosphere and consequently result in larger moist static energy and precipitation. Moisture nudging tends to suppress the initiation of convection and reduces the excess precipitation. The reduction in precipitation bias in turn reduces the surface wind and latent heat (LH) flux biases, which suggests the positive feedback between precipitation and surface fluxes is responsible, at least in part, for the model drifts. The updated Kain–Fritsch cumulus potential (KF-CuP) shallow convection scheme tends to suppress the deep convection, consequently decreasing precipitation. The Eta Model surface layer scheme predicts more reasonable LH fluxes and LH–wind speed relationship than those for the MM5 scheme. The results help us identify sources of biases of current parameterization schemes in reproducing PBL processes, the initiation of convection, and intraseasonal variability of precipitation.

Weakening Trend in the Atmospheric Heat Source over the Tibetan Plateau during Recent Decades. Part II: Connection with Climate Warming

2009 ◽  
Vol 22 (15) ◽  
pp. 4197-4212 ◽  
Author(s):  
Anmin Duan ◽  
Guoxiong Wu
Keyword(s):  
Twentieth Century ◽  
Wind Speed ◽  
Tibetan Plateau ◽  
General Circulation ◽  
Climate Models ◽  
Surface Wind ◽  
Sensible Heat Flux ◽  
Surface Wind Speed ◽  
The Tibetan Plateau ◽  
Coupled Climate Models

Abstract In Part I the authors have shown that heating sources in spring over the Tibetan Plateau (TP), and in particular the sensible heat flux (SHF), exhibit a significant weakening trend since the mid-1980s that is induced mainly by decreased surface wind speed. The possible reason of such a change is further investigated in Part II by analyzing historical observations and the NCEP/Department of Energy (DOE) reanalysis. The steady declining trend in the surface wind speed over the TP after the 1970s arises mainly from the zonal component. Since the mean altitude of the TP is about 600 hPa and the surface flow is controlled by the East Asian subtropical westerly jet (EASWJ) for most parts of the year, the substantial tropospheric warming in the mid- and high latitudes to the north of the plateau results in a decrease of the meridional pressure gradient in the subtropics. As a result, the EASWJ and the surface winds over the TP are decelerated. Moreover, changes of the general circulation in the twentieth century simulated by 16 coupled climate models driven by natural and anthropogenic forcings are examined. Intercomparison results suggest that sulfate aerosol indirect effects and ozone may be important in reproducing the weakening trend in EASWJ. Although nearly half of the models can successfully reproduce the observed trends in the EASWJ during the last two decades, there is an obvious spread in simulation of the spatial patterns of twentieth-century tropospheric temperatures, suggesting significant room still exists for improvement of the current state-of-the-art coupled climate models.

scholarly journals The Role of Shallow Convection over the Tibetan Plateau

2017 ◽  
Vol 30 (15) ◽  
pp. 5791-5803 ◽  
Author(s):  
Yunying Li ◽  
Minghua Zhang
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Diabatic Heating ◽  
Middle Atmosphere ◽  
Atmospheric Environment ◽  
Monsoon Circulation ◽  
The Tibetan Plateau ◽  
Shallow Convection ◽  
Sensitivity Experiment ◽  
Stratiform Clouds

Cumulus (Cu) from shallow convection is one of the dominant cloud types over the Tibetan Plateau (TP) in the summer according to CloudSat– CALIPSO observations. Its thermodynamic effects on the atmospheric environment and impacts on the large-scale atmospheric circulation are studied in this paper using the Community Atmospheric Model, version 5.3 (CAM5.3). It is found that the model can reasonably simulate the unique distribution of diabatic heating and Cu over the TP. Shallow convection provides the dominant diabatic heating and drying to the lower and middle atmosphere over the TP. A sensitivity experiment indicates that without Cu over the TP, large-scale condensation and stratiform clouds would increase dramatically, which induces enhanced low-level wind and moisture convergence toward the TP, resulting in significantly enhanced monsoon circulation with remote impact on the areas far beyond the TP. Cu therefore acts as a safety valve to modulate the atmospheric environment that prevents the formation of superclusters of stratiform clouds and precipitation over the TP.

scholarly journals Assessing the Performance of CMIP5 Global Climate Models for Simulating Future Precipitation Change in the Tibetan Plateau

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1771 ◽  
Author(s):  
Kun Jia ◽  
Yunfeng Ruan ◽  
Yanzhao Yang ◽  
Chao Zhang
Keyword(s):  
Tibetan Plateau ◽  
Climate Models ◽  
Global Climate ◽  
Precipitation Change ◽  
Multiple Criteria ◽  
Global Climate Models ◽  
The Tibetan Plateau ◽  
Spatial Distributions ◽  
Near Term ◽  
Far Future

In this study, the performance of 33 Coupled Model Intercomparison Project 5 (CMIP5) global climate models (GCMs) in simulating precipitation over the Tibetan Plateau (TP) was assessed using data from 1961 to 2005 by an improved score-based method, which adopts multiple criteria to achieve a comprehensive evaluation. The future precipitation change was also estimated based on the Delta method by selecting the submultiple model ensemble (SMME) in the near-term (2006–2050) and far future (2051–2095) periods under Representative Concentration Pathways (RCP) scenarios RCP4.5 and RCP8.5. The results showed that most GCMs can reasonably simulate the precipitation pattern of an annual cycle; however, all GCMs overestimated the precipitation over TP, especially in spring and summer. The GCMs generally provide good simulations of the temporal characteristics of precipitation, while they did not perform as well in reproducing its spatial distributions. Different assessment criteria lead to inconsistent results; however, the improved rank score method, which adopts multiple criteria, provided a robust assessment of GCMs performance. The future annual precipitation was projected to increase by ~6% in the near-term with respect to the period 1961–2005, whereas increases of 12.3% and 16.7% are expected in the far future under RCP4.5 and RCP8.5 scenarios, respectively. Similar spatial distributions of future precipitation changes can be seen in the near-term and far future periods under the two scenarios, and indicate that the most predominant increases occurred in the north of TP. The results of this study are expected to provide valuable information on climate change, and for water resources and agricultural management in TP.

Remote Sources of Surface Temperature Cold Bias over the Tibetan Plateau: Role of Tropical SST Climatological Bias

2020 ◽  
Author(s):  
Yuting Wu ◽  
Xiaoming Hu ◽  
Ziqian Wang ◽  
Zhenning Li ◽  
Song Yang
Keyword(s):  
Tibetan Plateau ◽  
Surface Temperature ◽  
Distribution Pattern ◽  
Climate Models ◽  
Cmip5 Models ◽  
Cold Bias ◽  
The Tibetan Plateau ◽  
Sst Bias ◽  
Hypothesis Model

<p>The surface temperature cold bias over the Tibetan Plateau (TP) is a long-lasting problem in both reanalysis data and climate models. While previous studies have mainly focused on local processes for this bias, the TP surface temperature is also closely related to tropical SST in both observations and Coupled Model Inter-comparison Project (CMIP5) models. This study investigates the role of tropical SST climatological bias in the TP surface temperature cold bias, and analysis of CMIP5 models suggests that the surface temperature cold bias over the TP is more obvious (about 4 K) in winter, with an east-west distribution pattern, than in summer (about 1 K), with a south-north distribution pattern. Considering that the tropical SST bias in CMIP5 models may be an important source of the TP surface temperature cold bias, a series of model experiments were conducted by the NCAR CAM4 to test the hypothesis. Model experiment results show that the tropical SST bias can reproduce cold bias over the TP, with 2 K in winter and about 0.5 K in summer. The mechanisms for TP surface temperature cold bias are different in winter and summer. In winter, tropical SST bias influences the TP surface temperature mainly by anomalous snow cover, while anomalous precipitation and clouds are more important for the temperature bias in summer.</p>

Extending the paleoglaciological record of the southeastern Tibetan Plateau by combining geochronological and high-resolution remote sensing techniques

2020 ◽  
Author(s):  
Arjen P. Stroeven ◽  
Ramona A.A. Schneider ◽  
Robin Blomdin ◽  
Natacha Gribenski ◽  
Marc W. Caffee ◽  
...  
Keyword(s):  
High Resolution ◽  
Tibetan Plateau ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models ◽  
Luminescence Dating ◽  
The Tibetan Plateau ◽  
Exposure Dating ◽  
Southeastern Margin ◽  
Downstream Communities

<p>Paleoglaciological data is a crucial source of information towards insightful paleoclimate reconstructions by providing vital boundary conditions for regional and global climate models. In this context, the Third Pole Environment is considered a key region because it is highly sensitive to global climate change and its many glaciers constitute a diminishing but critical supply of freshwater to downstream communities in SE Asia. Despite its importance, extents of past glaciation on the Tibetan Plateau remain poorly documented or controversial largely because of the lack of well define glacial chronostratigraphies and reconstructions of former glacier extent. This study contributes to a better documentation of the extent and improved resolution of the timing of past glaciations on the southeastern margin of the Tibetan Plateau. We deploy a high-resolution TanDEM-X Digital Elevation Model (12 m resolution) to produce maps of glacial and proglacial fluvial landforms in unprecedented detail. Geomorphological and sedimentological field observations complement the mapping while cosmogenic nuclide exposure dating of quartz samples from boulders on end moraines detail the timing of local glacier expansion. Additionally, samples for optically stimulated luminescence dating were taken from extensive and distinct terraces located in pull-apart basins downstream of the end moraines to determine their formation time. We compare this new dataset with new and published electron spin resonance ages from terraces. Temporal coherence between the different chronometers strengthens the geochronological record while divergence highlights limitations in the applicability of the chronometers to glacial research or in our conceptual understanding of landscape changes in tectonic regions. Results highlight our current understanding of paleoglaciation, landscape development, and paleoclimate on the SE Tibetan Plateau.</p>

scholarly journals High-resolution ensemble projections and uncertainty assessment of regional climate change over China in CORDEX East Asia

2018 ◽  
Vol 22 (5) ◽  
pp. 3087-3103 ◽  
Author(s):  
Huanghe Gu ◽  
Zhongbo Yu ◽  
Chuanguo Yang ◽  
Qin Ju ◽  
Tao Yang ◽  
...  
Keyword(s):  
Climate Change ◽  
Tibetan Plateau ◽  
Model Uncertainty ◽  
Climate Models ◽  
Southern China ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Internal Variability ◽  
Northeastern China ◽  
The Tibetan Plateau

Abstract. An ensemble simulation of five regional climate models (RCMs) from the coordinated regional downscaling experiment in East Asia is evaluated and used to project future regional climate change in China. The influences of model uncertainty and internal variability on projections are also identified. The RCMs simulate the historical (1980–2005) climate and future (2006–2049) climate projections under the Representative Concentration Pathway (RCP) RCP4.5 scenario. The simulations for five subregions in China, including northeastern China, northern China, southern China, northwestern China, and the Tibetan Plateau, are highlighted in this study. Results show that (1) RCMs can capture the climatology, annual cycle, and interannual variability of temperature and precipitation and that a multi-model ensemble (MME) outperforms that of an individual RCM. The added values for RCMs are confirmed by comparing the performance of RCMs and global climate models (GCMs) in reproducing annual and seasonal mean precipitation and temperature during the historical period. (2) For future (2030–2049) climate, the MME indicates consistent warming trends at around 1 ∘C in the entire domain and projects pronounced warming in northern and western China. The annual precipitation is likely to increase in most of the simulation region, except for the Tibetan Plateau. (3) Generally, the future projected change in annual and seasonal mean temperature by RCMs is nearly consistent with the results from the driving GCM. However, changes in annual and seasonal mean precipitation exhibit significant inter-RCM differences and possess a larger magnitude and variability than the driving GCM. Even opposite signals for projected changes in average precipitation between the MME and the driving GCM are shown over southern China, northeastern China, and the Tibetan Plateau. (4) The uncertainty in projected mean temperature mainly arises from the internal variability over northern and southern China and the model uncertainty over the other three subregions. For the projected mean precipitation, the dominant uncertainty source is the internal variability over most regions, except for the Tibetan Plateau, where the model uncertainty reaches up to 60 %. Moreover, the model uncertainty increases with prediction lead time across all subregions.

scholarly journals Evaluation of the Global Climate Models in the CMIP5 over the Tibetan Plateau

2013 ◽  
Vol 26 (10) ◽  
pp. 3187-3208 ◽  
Author(s):  
Fengge Su ◽  
Xiaolan Duan ◽  
Deliang Chen ◽  
Zhenchun Hao ◽  
Lan Cuo
Keyword(s):  
Tibetan Plateau ◽  
Radiative Forcing ◽  
Climate Models ◽  
Seasonal Pattern ◽  
Global Climate Models ◽  
First Century ◽  
The Tibetan Plateau ◽  
Twenty First Century ◽  
Near Term

Abstract The performance of 24 GCMs available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated over the eastern Tibetan Plateau (TP) by comparing the model outputs with ground observations for the period 1961–2005. The twenty-first century trends of precipitation and temperature based on the GCMs’ projections over the TP are also analyzed. The results suggest that for temperature most GCMs reasonably capture the climatological patterns and spatial variations of the observed climate. However, the majority of the models have cold biases, with a mean underestimation of 1.1°–2.5°C for the months December–May, and less than 1°C for June–October. For precipitation, the simulations of all models overestimate the observations in climatological annual means by 62.0%–183.0%, and only half of the 24 GCMs are able to reproduce the observed seasonal pattern, which demonstrates a critical need to improve precipitation-related processes in these models. All models produce a warming trend in the twenty-first century under the Representative Concentration Pathway 8.5 (rcp8.5) scenario; in contrast, the rcp2.6 scenario predicts a lower average warming rate for the near term, and a small cooling trend in the long-term period with the decreasing radiative forcing. In the near term, the projected precipitation change is about 3.2% higher than the 1961–2005 annual mean, whereas in the long term the precipitation is projected to increase 6.0% under rcp2.6 and 12.0% under the rcp8.5 scenario. Relative to the 1961–2005 mean, the annual temperature is projected to increase by 1.2°–1.3°C in the short term; the warmings under the rcp2.6 and rcp8.5 scenarios are 1.8° and 4.1°C, respectively, for the long term.

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