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Hong-Hai Zhang, Gui-Peng Yang, Chun-Ying Liu, and Lu-Ping Su

Abstract

The total suspended particulate (TSP) samples over the Yellow Sea and the East China Sea were collected to determine the major compositions of water-soluble ionic species during two cruises in autumn 2007. The aerosol compositions exhibited an obvious regional variation between the two cruises, with higher concentrations (except Na+ and Mg2+) over the northern Yellow Sea during the first cruise. The concentrations of the secondary ions [non–sea salt sulfate (nss-), , and ] were 11 ± 4.9, 3.1 ± 2.1, and 3.7 ± 2.6 μg m−3, respectively, which together contributed over 72% of the total determined ion concentrations. Significant correlations between these secondary ions were found within each sampling period, while nss-K+ and nss-Ca2+ showed strong correlation with each other. The calculated results of equivalent concentrations of anions (nss- and ) and cations ( and Ca2+) showed that the acidic species were mostly neutralized with the alkaline species over the study areas. The mass ratio of nss-/ was 1.4 during the investigation period. In addition, the concentrations of MSA were 0.011 ± 0.044 and 0.0081 ± 0.0047 μg m−3 during the two cruises, respectively. Based on the measured MSA, nss-, and their ratios, the relative biogenic sulfur contribution to the total nss- was estimated to be only 2.0% during the two cruises, further suggesting the major contribution of anthropogenic source to sulfur budget over the marginal seas of China.

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Yang Lu, Susan C. Steele-Dunne, and Gabriëlle J. M. De Lannoy

Abstract

Surface heat fluxes are vital to hydrological and environmental studies, but mapping them accurately over a large area remains a problem. In this study, brightness temperature (TB) observations or soil moisture retrievals from the NASA Soil Moisture Active Passive (SMAP) mission and land surface temperature (LST) product from the Geostationary Operational Environmental Satellite (GOES) are assimilated together into a coupled water and heat transfer model to improve surface heat flux estimates. A particle filter is used to assimilate SMAP data, while a particle smoothing method is adopted to assimilate GOES LST time series, correcting for both systematic biases via parameter updating and for short-term error via state updating. One experiment assimilates SMAP TB at horizontal polarization and GOES LST, a second experiment assimilates SMAP TB at vertical polarization and GOES LST, and a third experiment assimilates SMAP soil moisture retrievals along with GOES LST. The aim is to examine if the assimilation of physically consistent TB and LST observations could yield improved surface heat flux estimates. It is demonstrated that all three assimilation experiments improved flux estimates compared to a no-assimilation case. Assimilating TB data tends to produce smaller bias in soil moisture estimates compared to assimilating soil moisture retrievals, but the estimates are influenced by the respective bias correction approaches. Despite the differences in soil moisture estimates, the flux estimates from different assimilation experiments are in general very similar.

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Yuan Yang, Ming Pan, Peirong Lin, Hylke E. Beck, Zhenzhong Zeng, Dai Yamazaki, Cédric H. David, Hui Lu, Kun Yang, Yang Hong, and Eric F. Wood

Abstract

Better understanding and quantification of river floods for very local and flashy events calls for modeling capability at fine spatial and temporal scales. However, long-term discharge records with a global coverage suitable for extreme events analysis are still lacking. Here, grounded on recent breakthroughs in global runoff hydrology, river modeling, high resolution hydrography, and climate reanalysis, we developed a 3-hourly river discharge record globally for 2.94 million river reaches during the 40-year period of 1980-2019. The underlying modeling chain consists of the VIC land surface model (0.05°, 3-hourly) that is well calibrated and bias corrected and the RAPID routing model (2.94 million river and catchment vectors), with precipitation input from MSWEP and other meteorological fields downscaled from ERA5. Flood events (above 2-year return) and their characteristics (number, spatial distribution, and seasonality) were extracted and studied. Validations against 3-hourly flow records from 6,000+ gauges in CONUS and daily records from 14,000+ gauges globally show good modeling performance across all flow ranges, good skills in reconstructing flood events (high extremes), and the benefit of (and need for) sub-daily modeling. This data record, referred as Global Reach-level Flood Reanalysis (GRFR), is publicly available at https://www.reachhydro.org/home/records/grfr.

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Jian Lu, Koichi Sakaguchi, Qing Yang, L. Ruby Leung, Gang Chen, Chun Zhao, Erik Swenson, and Zhangshuan J. Hou

Abstract

Building on the recent advent of the concept of finite-amplitude wave activity, a contour-following diagnostics for column water vapor (CWV) is developed and applied to a pair of aquaplanet model simulations to understand and quantify the higher moments in the global hydrological cycle. The Lagrangian nature of the diagnostics leads to a more tractable formalism for the transient, zonally asymmetric component of the hydrological cycle, with a strong linear relation emerging between the wave activity and the wave component of precipitation minus evaporation (). The dry-versus-wet disparity in the transient hydrological cycle is measured by , and it is found to increase at a super-Clausius–Clapeyron rate at the poleward side of the mean storm track in response to a uniform sea surface temperature (SST) warming and the meridional structure of the increase can be largely attributed to the change of the meridional stirring scale of the midlatitude Rossby waves. Further scaling for indicates that the rate of the wavy hydrological cycle, measured by the ratio of to the CWV wave activity, is subdued almost everywhere in the extratropics, implying an overall weakening of the transient circulation. Extending the CWV wave activity analysis to the transient moist regions helps reveal some unique characteristics of atmospheric rivers in terms of transport function, minimum precipitation efficiency, and maximum hydrological cycle rate, as well as an overall weakening of the hydrological cycle rate in the atmospheric river regions under SST warming.

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Yiquan Jiang, Xiu-Qun Yang, Xiaohong Liu, Yun Qian, Kai Zhang, Minghuai Wang, Fang Li, Yong Wang, and Zheng Lu

Abstract

Aerosols emitted from wildfires could significantly affect global climate through perturbing global radiation balance. In this study, the Community Earth System Model with prescribed daily fire aerosol emissions is used to investigate fire aerosols’ impacts on global climate with emphasis on the role of climate feedbacks. The total global fire aerosol radiative effect (RE) is estimated to be −0.78 ± 0.29 W m−2, which is mostly from shortwave RE due to aerosol–cloud interactions (REaci; −0.70 ± 0.20 W m−2). The associated global annual-mean surface air temperature (SAT) change ∆T is −0.64 ± 0.16 K with the largest reduction in the Arctic regions where the shortwave REaci is strong. Associated with the cooling, the Arctic sea ice is increased, which acts to reamplify the Arctic cooling through a positive ice-albedo feedback. The fast response (irrelevant to ∆T) tends to decrease surface latent heat flux into atmosphere in the tropics to balance strong atmospheric fire black carbon absorption, which reduces the precipitation in the tropical land regions (southern Africa and South America). The climate feedback processes (associated with ∆T) lead to a significant surface latent heat flux reduction over global ocean areas, which could explain most (~80%) of the global precipitation reduction. The precipitation significantly decreases in deep tropical regions (5°N) but increases in the Southern Hemisphere tropical ocean, which is associated with the southward shift of the intertropical convergence zone and the weakening of Southern Hemisphere Hadley cell. Such changes could partly compensate the interhemispheric temperature asymmetry induced by boreal forest fire aerosol indirect effects, through intensifying the cross-equator atmospheric heat transport.

Open access
Yan Wang, Kun Yang, Zhengyang Pan, Jun Qin, Deliang Chen, Changgui Lin, Yingying Chen, Lazhu, Wenjun Tang, Menglei Han, Ning Lu, and Hui Wu

Abstract

The southern Tibetan Plateau (STP) is the region in which water vapor passes from South Asia into the Tibetan Plateau (TP). The accuracy of precipitable water vapor (PWV) modeling for this region depends strongly on the quality of the available estimates of water vapor advection and the parameterization of land evaporation models. While climate simulation is frequently improved by assimilating relevant satellite and reanalysis products, this requires an understanding of the accuracy of these products. In this study, PWV data from MODIS infrared and near-infrared measurements, AIRS Level-2 and Level-3, MERRA, ERA-Interim, JRA-55, and NCEP final reanalysis (NCEP-Final) are evaluated against ground-based GPS measurements at nine stations over the STP, which covers the summer monsoon season from 2007 to 2013. The MODIS infrared product is shown to underestimate water vapor levels by more than 20% (1.84 mm), while the MODIS near-infrared product overestimates them by over 40% (3.52 mm). The AIRS PWV product appears to be most useful for constructing high-resolution and high-quality PWV datasets over the TP; particularly the AIRS Level-2 product has a relatively low bias (0.48 mm) and RMSE (1.83 mm) and correlates strongly with the GPS measurements (R = 0.90). The four reanalysis datasets exhibit similar performance in terms of their correlation coefficients (R = 0.87–0.90), bias (0.72–1.49 mm), and RMSE (2.19–2.35 mm). The key finding is that all the reanalyses have positive biases along the PWV seasonal cycle, which is linked to the well-known wet bias over the TP of current climate models.

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Wenli Wang, Kun Yang, Long Zhao, Ziyan Zheng, Hui Lu, Ali Mamtimin, Baohong Ding, Xin Li, Lin Zhao, Hongyi Li, Tao Che, and John C. Moore

Abstract

Snow depth on the interior of Tibetan Plateau (TP) in state-of-the-art reanalysis products is almost an order of magnitude higher than observed. This huge bias stems primarily from excessive snowfall, but inappropriate process representation of shallow snow also causes excessive snow depth and snow cover. This study investigated the issue with respect to the parameterization of fresh snow albedo. The characteristics of TP snowfall were investigated using ground truth data. Snow in the interior of the TP is usually only some centimeters in depth. The albedo of fresh snow depends on snow depth, and is frequently less than 0.4. Such low albedo values contrast with the high values (~0.8) used in the existing snow schemes of land surface models. The SNICAR radiative transfer model can reproduce the observations that fresh shallow snow has a low albedo value, based on which a fresh snow albedo scheme was derived in this study. Finally, the impact of the fresh snow albedo on snow ablation was examined at 45 meteorological stations on TP using the land surface model Noah-MP which incorporated the new scheme. Allowing albedo to change with snow depth can produce quite realistic snow depths compared with observations. In contrast, the typically assumed fresh snow albedo of 0.82 leads to too large snow depths in the snow ablation period averaged across 45 stations. The shallow snow transparency impact on snow ablation is therefore particularly important in the TP interior, where snow is rather thin and radiation is strong.

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Koichi Sakaguchi, L. Ruby Leung, Chun Zhao, Qing Yang, Jian Lu, Samson Hagos, Sara A. Rauscher, Li Dong, Todd D. Ringler, and Peter H. Lauritzen

Abstract

This study presents a diagnosis of a multiresolution approach using the Model for Prediction Across Scales–Atmosphere (MPAS-A) for simulating regional climate. Four Atmospheric Model Intercomparison Project (AMIP) experiments were conducted for 1999–2009. In the first two experiments, MPAS-A was configured using global quasi-uniform grids at 120- and 30-km grid spacing. In the other two experiments, MPAS-A was configured using variable-resolution (VR) mesh with local refinement at 30 km over North America and South America and embedded in a quasi-uniform domain at 120 km elsewhere. Precipitation and related fields in the four simulations are examined to determine how well the VRs reproduce the features simulated by the globally high-resolution model in the refined domain. In previous analyses of idealized aquaplanet simulations, characteristics of the global high-resolution simulation in moist processes developed only near the boundary of the refined region. In contrast, AMIP simulations with VR grids can reproduce high-resolution characteristics across the refined domain, particularly in South America. This finding indicates the importance of finely resolved lower boundary forcings such as topography and surface heterogeneity for regional climate and demonstrates the ability of the MPAS-A VR to replicate the large-scale moisture transport as simulated in the quasi-uniform high-resolution model. Upscale effects from the high-resolution regions on a large-scale circulation outside the refined domain are observed, but the effects are mainly limited to northeastern Asia during the warm season. Together, the results support the multiresolution approach as a computationally efficient and physically consistent method for modeling regional climate.

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Shasha Shang, Gaofeng Zhu, Jianhui Wei, Yan Li, Kun Zhang, Ruolin Li, Joël Arnault, Zhenyu Zhang, Patrick Laux, Qianya Yang, Ningpeng Dong, Lu Gao, and Harald Kunstmann

Abstract

Precipitation in the Three-River Headwater (TRH) region has undergone significant changes as a result of global warming, which can affect water resources in downstream regions of Asia. However, the underlying mechanisms of the precipitation variability during the cold season (October to April), are still not fully understood. In this study, the daily China gridded precipitation product of CN05.1 as well as the NCEP-NCAR reanalysis are used to investigate the characteristics of the cold season precipitation variability over the TRH region and associated atmospheric mechanisms. The cold season precipitation shows an increasing trend (5.5 mm decade-1) from 1961 to 2014, with a dry-to-wet shift in around the late 1980s. The results indicate that the increased precipitation is associated with the enhanced easterly anomalies over the Tibetan Plateau (TP) and enhanced southeasterly water vapor transport. The enhanced Walker circulations, caused by the gradients of sea surface temperature between the equatorial central-eastern Pacific and Indo-western Pacific in tropical oceans, resulted in strengthened easterly anomalies over the TP and the westward expansion of the anticyclone in the western North Pacific. Meanwhile, the changed Walker circulation is accompanied by a strengthened local Hadley circulation which leads to enhanced meridional water vapor transport from tropical oceans and the South China Sea toward the TRH region. Furthermore, the strengthened East Asia Subtropical Westerly jet may contribute to the enhanced divergence at upper level and anomalous ascending motion above the TRH region leading to more precipitation.

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Fan Yang, Qing He, Jianping Huang, Ali Mamtimin, Xinghua Yang, Wen Huo, Chenglong Zhou, Xinchun Liu, Wenshou Wei, Caixia Cui, Minzhong Wang, Hongjun Li, Lianmei Yang, Hongsheng Zhang, Yuzhi Liu, Xinqian Zheng, Honglin Pan, Lili Jin, Han Zou, Libo Zhou, Yongqiang Liu, Jiantao Zhang, Lu Meng, Yu Wang, Xiaolin Qin, Yongjun Yao, Houyong Liu, Fumin Xue, and Wei Zheng

Abstract

As the second-largest shifting sand desert worldwide, the Taklimakan Desert (TD) represents the typical aeolian landforms in arid regions as an important source of global dust aerosols. It directly affects the ecological environment and human health across East Asia. Thus, establishing a comprehensive environment and climate observation network for field research in the TD region is essential to improve our understanding of the desert meteorology and environment, assess its impact, mitigate potential environmental issues, and promote sustainable development. With a nearly 20-yr effort under the extremely harsh conditions of the TD, the Desert Environment and Climate Observation Network (DECON) has been established completely covering the TD region. The core of DECON is the Tazhong station in the hinterland of the TD. Moreover, the network also includes 4 satellite stations located along the edge of the TD for synergistic observations, and 18 automatic weather stations interspersed between them. Thus, DECON marks a new chapter of environmental and meteorological observation capabilities over the TD, including dust storms, dust emission and transport mechanisms, desert land–atmosphere interactions, desert boundary layer structure, ground calibration for remote sensing monitoring, and desert carbon sinks. In addition, DECON promotes cooperation and communication within the research community in the field of desert environments and climate, which promotes a better understanding of the status and role of desert ecosystems. Finally, DECON is expected to provide the basic support necessary for coordinated environmental and meteorological monitoring and mitigation, joint construction of ecologically friendly communities, and sustainable development of central Asia.

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