scholarly journals Variations of surface roughness on inhomogeneous underlying surface at Nagqu Area over the Tibetan Plateau

2020 ◽  
Author(s):  
Maoshan Li ◽  
Lei Shu ◽  
Xiaoran Liu ◽  
Shucheng Yin ◽  
Lingzhi Wang ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Tibetan Plateau ◽  
Satellite Data ◽  
Underlying Surface ◽  
Surface Model ◽  
Model Parameters ◽  
Observation Data ◽  
The Tibetan Plateau ◽  
Northern Tibetan Plateau ◽  
Variation Characteristics

Abstract. Using the MODIS satellite data and station atmospheric turbulence observation data in Nagqu area of northern Tibetan plateau in 2008, 2010 and 2012, with the Massman retrieved model and an independent method to determine aerodynamic surface roughness, the temporal and spatial variation characteristics of the surface roughness was analyzed. The results show that the surface roughness has obvious seasonal variation characteristics. From February to August, Z0m increases constantly with the ablation of snow and vegetation growth, and the maximum value reaches 4–5 cm at BJ site. From September to February, Z0m gradually decreased because of the post-monsoon over the plateau, and the values decreased to about 1–2 cm. The snowfall in abnormal years is the main reason why Z0m is obviously lower than that in normal. The underlying surface can be divided into four categories according to the different values of Z0m: snow and ice, sparse grassland, lush grassland and town. Among them, lush grassland and sparse grassland account for 62.49 % and 33.74 % respectively in the region, which are the main categories, and their Z0m annual changes are between 2–6 cm and 1–4 cm. The correlation between the two methods are positively related to each other, and the retrieved data are smaller than the measured results due to the average sliding action. On the whole, Z0m calculated by satellite data retrieved algorithm is feasible, it can be applied to improve the model parameters of land surface model parameters and the accuracy of model simulation, better reveal the heat flux exchange.

scholarly journals Variations in surface roughness of heterogeneous surfaces in the Nagqu area of the Tibetan Plateau

2021 ◽  
Vol 25 (5) ◽  
pp. 2915-2930
Author(s):  
Maoshan Li ◽  
Xiaoran Liu ◽  
Lei Shu ◽  
Shucheng Yin ◽  
Lingzhi Wang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Tibetan Plateau ◽  
Sensible Heat Flux ◽  
Underlying Surface ◽  
The Tibetan Plateau ◽  
Vegetation Growth ◽  
Northern Tibetan Plateau ◽  
Roughness Lengths ◽  
Aerodynamic Roughness

Abstract. Temporal and spatial variations of the surface aerodynamic roughness lengths (Z0 m) in the Nagqu area of the northern Tibetan Plateau were analysed in 2008, 2010 and 2012 using MODIS satellite data and in situ atmospheric turbulence observations. Surface aerodynamic roughness lengths were calculated from turbulent observations by a single-height ultrasonic anemometer and retrieved by the Massman model. The results showed that Z0 m has an apparent characteristic of seasonal variation. From February to August, Z0 m increased with snow ablation and vegetation growth, and the maximum value reached 4–5 cm at the BJ site. From September to February, Z0 m gradually decreased and reached its minimum values of about 1–2 cm. Snowfall in abnormal years was the main reason for the significantly lower Z0 m compared with that in normal conditions. The underlying surface can be divided into four categories according to the different values of Z0 m: snow and ice, sparse grassland, lush grassland and town. Among them, lush grassland and sparse grassland accounted for 62.49 % and 33.74 %, and they have an annual variation of Z0 m between 1–4 and 2–6 cm, respectively. The two methods were positively correlated, and the retrieved values were lower than the measured results due to the heterogeneity of the underlying surface. These results are substituted into the Noah-MP (multi-parameterisation) model to replace the original parameter design numerical simulation experiment. After replacing the model surface roughness, the sensible heat flux and latent heat flux were simulated with a better diurnal dynamics.

scholarly journals Analysis of Long-Term Meteorological Observation for Weather and Climate Fundamental Data over the Northern Tibetan Plateau

2016 ◽  
Vol 2016 ◽  
pp. 1-10
Author(s):  
Fangfang Huang ◽  
Weiqiang Ma
Keyword(s):  
Tibetan Plateau ◽  
Land Surface ◽  
Critical Role ◽  
Diurnal Variations ◽  
Observation Data ◽  
The Tibetan Plateau ◽  
Meteorological Observation ◽  
Homogeneous Surface ◽  
Northern Tibetan Plateau ◽  
Weather And Climate

Meteorological observation plays a critical role in climatic study, and in situ measurements are the foundation of meteorological observation, especially in the Tibetan Plateau, the surface of which is fairly complex. Several field stations in the Northern Tibetan Plateau, which features relatively homogeneous surface, were selected as the study area. A detailed description on the significance of site observation for climate prediction was given in this paper. Data from weather stations can be used to verify satellite data and provide parameters for initial mode field in the study of weather and climate changes. The field observation data in the Northern Tibetan Plateau from 2001 to 2013 is analyzed. The results show that in El Nino year, values of land surface temperature (Ts), air temperature (Ta) and wind speed are all greater than their mean values and that soil moisture values are lower than the averaged, while the opposite is the case in La Nina year. The warming rate in the Northern Tibetan Plateau is greater than that in global areas. The diurnal variations ofTsandTaare various in different seasons and underlying surfaces, with the diurnal variations greater in spring, and less in summer and autumn. Furthermore, the diurnal variation in the area with drier underlying surface is more obvious than that in area with moist surface.

L'apport de la télédétection spatiale à la modélisation des surfaces continentales

2020 ◽  
pp. 052
Author(s):  
Jean-Christophe Calvet ◽  
Jean-Louis Champeaux
Keyword(s):  
Satellite Data ◽  
Land Surface ◽  
Land Surface Model ◽  
Static Model ◽  
Geographic Information ◽  
Surface Model ◽  
Model Parameters

Cet article présente les différentes étapes des développements réalisés au CNRM des années 1990 à nos jours pour spatialiser à diverses échelles les simulations du modèle Isba des surfaces terrestres. Une attention particulière est portée sur l'intégration, dans le modèle, de données satellitaires permettant de caractériser la végétation. Deux façons complémentaires d'introduire de l'information géographique dans Isba sont présentées : cartographie de paramètres statiques et intégration au fil de l'eau dans le modèle de variables observables depuis l'espace. This paper presents successive steps in developments made at CNRM from the 1990s to the present-day in order to spatialize the simulations of the Isba land surface model at various scales. The focus is on the integration in the model of satellite data informative about vegetation. Two complementary ways to integrate geographic information in Isba are presented: mapping of static model parameters and sequential assimilation of variables observable from space.

scholarly journals Surface ozone at Nam Co (4730 m a.s.l.) in the inland Tibetan Plateau: variation, synthesis comparison and regional representativeness

2017 ◽  
Author(s):  
Xiufeng Yin ◽  
Shichang Kang ◽  
Benjamin de Foy ◽  
Zhiyuan Cong ◽  
Jiali Luo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Surface Ozone ◽  
Early Morning ◽  
Photochemical Reactions ◽  
Transport Processes ◽  
The Tibetan Plateau ◽  
Nam Co ◽  
Mixing Ratios ◽  
Northern Tibetan Plateau ◽  
Ozone Levels

Abstract. Ozone is an important pollutant and greenhouse gas, and tropospheric ozone variations are generally associated with both natural and anthropogenic processes. As one of the most pristine and inaccessible regions in the world, the Tibetan Plateau has been considered as an ideal region for studying processes of the background atmosphere. Due to the vast area of the Tibetan Plateau, sites in the southern, northern and central regions exhibit different patterns of variation in surface ozone. Here, we present long-term measurements for ~ 5 years (January 2011 to October 2015) of surface ozone mixing ratios at Nam Co Station, which is a regional background site in the inland Tibetan Plateau. An average surface ozone mixing ratio of 47.6 ± 11.6 ppb was recorded, and a large annual cycle was observed with maximum ozone mixing ratios in the spring and minimum ratios during the winter. The diurnal cycle is characterized by a minimum in the early morning and a maximum in the late afternoon. Nam Co Station represents a background region where surface ozone receives negligible local anthropogenic emissions. Surface ozone at Nam Co Station is mainly dominated by natural processes involving photochemical reactions and potential local vertical mixing. Model results indicate that the study site is affected by the surrounding areas in different seasons and that air masses from the northern Tibetan Plateau lead to increased ozone levels in the summer. In contrast to the surface ozone levels at the edges of the Tibetan Plateau, those at Nam Co Station are less affected by stratospheric intrusions and human activities which makes Nam Co Station representative of vast background areas in the central Tibetan Plateau. By comparing measurements at Nam Co Station with those from other sites in the Tibetan Plateau and beyond, we aim to expand the understanding of ozone cycles and transport processes over the Tibetan Plateau. This work may provide a reference for model simulations in the future.

scholarly journals Diachronous Tibetan Plateau landscape evolution derived from lava field geomorphology

2020 ◽  
Author(s):  
Mark Allen ◽  
Robert Law
Keyword(s):  
Tibetan Plateau ◽  
Landscape Evolution ◽  
Tectonic Geomorphology ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Lava Field ◽  
Northern Tibetan Plateau ◽  
Tectonic Processes ◽  
Stepwise Evolution

<p><strong>Evolution of the Tibetan Plateau is important for understanding continental tectonics because of its exceptional elevation (~5 km above sea level) and crustal thickness (~70 km). Patterns of long-term landscape evolution can constrain tectonic processes, but have been hard to quantify, in contrast to established datasets for strain, exhumation and paleo-elevation. This study analyses the relief of the bases and tops of 17 Cenozoic lava fields on the central and northern Tibetan Plateau. Analyzed fields have typical lateral dimensions of 10s of km, and so have an appropriate scale for interpreting tectonic geomorphology. Fourteen of the fields have not been deformed since eruption. One field is cut by normal faults; two others are gently folded with limb dips <6<sup>o</sup></strong><strong>. </strong><strong>Relief of the bases and tops of the fields is comparable to modern, internally-drained, parts of the plateau, and distinctly lower than externally-drained regions. The lavas preserve a record of underlying low relief bedrock landscapes at the time they were erupted, which have undergone little change since. There is an overlap in each area between younger published low-temperature thermochronology ages and the oldest eruption in each area, here interpreted as the transition </strong><strong>between the end of significant (>3 km) exhumation and plateau landscape development. </strong><strong>This diachronous process took place between ~32.5<sup>o</sup> - ~36.5<sup>o</sup> N between ~40 and ~10 Ma, advancing northwards at a long-term rate of ~15 km/Myr. Results are consistent with incremental northwards growth of the plateau, rather than a stepwise evolution or synchronous uplift.</strong></p>

scholarly journals Numerical study of surface energy partitioning on the Tibetan Plateau: comparative analysis of two biosphere models

2009 ◽  
Vol 6 (6) ◽  
pp. 10849-10881
Author(s):  
J. Hong ◽  
J. Kim
Keyword(s):  
Comparative Analysis ◽  
Tibetan Plateau ◽  
Surface Energy ◽  
Summer Monsoon ◽  
Numerical Study ◽  
Asian Summer Monsoon ◽  
Energy Partitioning ◽  
In Situ Observation ◽  
Observation Data ◽  
The Tibetan Plateau

Abstract. The Tibetan Plateau is a critical region in the research of biosphere-atmosphere interactions on both regional and global scales due to its relation to Asian summer monsoon and El Niño. The unique environment on the Plateau provides valuable information for the evaluation of the models' surface energy partitioning associated with the summer monsoon. In this study, we investigated the surface energy partitioning on this important area through comparative analysis of two biosphere models constrained by the in-situ observation data. Indeed, the characteristics of the Plateau provide a unique opportunity to clarify the structural deficiencies of biosphere models as well as new insight into the surface energy partitioning on the Plateau. Our analysis showed that the observed inconsistency between the two biosphere models was mainly related to: 1) the parameterization for soil evaporation; 2) the way to deal with roughness lengths of momentum and scalars; and 3) the parameterization of subgrid velocity scale for aerodynamic conductance. Our study demonstrates that one should carefully interpret the modeling results on the Plateau especially during the pre-monsoon period.

scholarly journals Microphysical Properties of Convective Clouds in Summer over the Tibetan Plateau from SNPP/VIIRS Satellite Data

2019 ◽  
Vol 33 (3) ◽  
pp. 433-445
Author(s):  
Zhiguo Yue ◽  
Xing Yu ◽  
Guihua Liu ◽  
Jin Dai ◽  
Yannian Zhu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Satellite Data ◽  
The Tibetan Plateau ◽  
Convective Clouds ◽  
Microphysical Properties

scholarly journals Developing a novel hybrid model for the estimation of surface 8 h ozone (O<sub>3</sub>) across the remote Tibetan Plateau during 2005–2018

2020 ◽  
Vol 20 (10) ◽  
pp. 6159-6175 ◽  
Author(s):  
Rui Li ◽  
Yilong Zhao ◽  
Wenhui Zhou ◽  
Ya Meng ◽  
Ziyu Zhang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Hybrid Model ◽  
Additive Model ◽  
World Health ◽  
The Tibetan Plateau ◽  
The Novel ◽  
Slow Increase ◽  
Potential Health ◽  
Generalised Additive Model ◽  
Northern Tibetan Plateau

Abstract. We developed a two-stage model called the random-forest–generalised additive model (RF–GAM), based on satellite data, meteorological factors, and other geographical covariates, to predict the surface 8 h O3 concentrations across the remote Tibetan Plateau. The 10-fold cross-validation result suggested that RF–GAM showed excellent performance, with the highest R2 value (0.76) and lowest root-mean-square error (RMSE) (14.41 µg m−3), compared with other seven machine-learning models. The predictive performance of RF–GAM showed significant seasonal discrepancy, with the highest R2 value observed in summer (0.74), followed by winter (0.69) and autumn (0.67), and the lowest one in spring (0.64). Additionally, the unlearning ground-observed O3 data collected from open-access websites were applied to test the transferring ability of the novel model and confirmed that the model was robust in predicting the surface 8 h O3 concentration during other periods (R2=0.67, RMSE = 25.68 µg m−3). RF–GAM was then used to predict the daily 8 h O3 level over the Tibetan Plateau during 2005–2018 for the first time. It was found that the estimated O3 concentration displayed a slow increase, from 64.74±8.30 µg m−3 to 66.45±8.67 µg m−3 from 2005 to 2015, whereas it decreased from the peak to 65.87±8.52 µg m−3 during 2015–2018. Besides this, the estimated 8 h O3 concentrations exhibited notable spatial variation, with the highest values in some cities of the northern Tibetan Plateau, such as Huangnan (73.48±4.53 µg m−3) and Hainan (72.24±5.34 µg m−3), followed by the cities in the central region, including Lhasa (65.99±7.24 µg m−3) and Shigatse (65.15±6.14 µg m−3), and the lowest O3 concentration occurred in a city of the southeastern Tibetan Plateau called Aba (55.17±12.77 µg m−3). Based on the 8 h O3 critical value (100 µg m−3) provided by the World Health Organization (WHO), we further estimated the annual mean nonattainment days over the Tibetan Plateau. It should be noted that most of the cities on the Tibetan Plateau had excellent air quality, while several cities (e.g. Huangnan, Haidong, and Guoluo) still suffered from more than 40 nonattainment days each year, which should be given more attention in order to alleviate local O3 pollution. The results shown herein confirm that the novel hybrid model improves the prediction accuracy and can be applied to assess the potential health risk, particularly in remote regions with few monitoring sites.

scholarly journals Long-term snow disasters during 1982–2012 in the Tibetan Plateau using satellite data

2016 ◽  
Vol 8 (2) ◽  
pp. 466-477 ◽  
Author(s):  
Hang Yin ◽  
Chunxiang Cao ◽  
Min Xu ◽  
Wei Chen ◽  
Xiliang Ni ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Satellite Data ◽  
The Tibetan Plateau
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