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104 result(s) for "Lin, Changgui"
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Impact of model resolution on simulating the water vapor transport through the central Himalayas: implication for models’ wet bias over the Tibetan Plateau
Current climate models commonly overestimate precipitation over the Tibetan Plateau (TP), which limits our understanding of past and future water balance in the region. Identifying sources of such models’ wet bias is therefore crucial. The Himalayas is considered a major pathway of water vapor transport (WVT) towards the TP. Their steep terrain, together with associated small-scale processes, cannot be resolved by coarse-resolution models, which may result in excessive WVT towards the TP. This paper, therefore, investigated the resolution dependency of simulated WVT through the central Himalayas and its further impact on precipitation bias over the TP. According to a summer monsoon season of simulations conducted using the weather research forecasting (WRF) model with resolutions of 30, 10, and 2 km, the study found that finer resolutions (especially 2 km) diminish the positive precipitation bias over the TP. The higher-resolution simulations produce more precipitation over the southern Himalayan slopes and weaker WVT towards the TP, explaining the reduced wet bias. The decreased WVT is reflected mostly in the weakened wind speed, which is due to the fact that the high resolution can improve resolving orographic drag over a complex terrain and other processes associated with heterogeneous surface forcing. A significant difference was particularly found when the model resolution is changed from 30 to 10 km, suggesting that a resolution of approximately 10 km represents a good compromise between a more spatially detailed simulation of WVT and computational cost for a domain covering the whole TP.
Simulation of summer precipitation diurnal cycles over the Tibetan Plateau at the gray-zone grid spacing for cumulus parameterization
The Tibetan Plateau (TP) is often referred to as the “water tower of Asia” or the “Third Pole”. It remains a challenge for most global and regional models to realistically simulate precipitation, especially its diurnal cycles, over the TP. This study focuses on evaluating the summer (June–August) precipitation diurnal cycles over the TP simulated by the Weather Research and Forecasting (WRF) model. The horizontal resolution used in this study is 9 km, which is within the gray-zone grid spacing that a cumulus parameterization scheme (CU) may or may not be used. We conducted WRF simulations with different cumulus schemes (CU experiments) and a simulation without CU (No_CU experiment). The selected CUs include the Grell-3D Ensemble (Grell), New Simplified Arakawa-Schubert (NSAS), and Multiscale Kain-Fritsch (MSKF). These simulations are compared with both the in-situ observations and satellite products. Results show that the scale-aware MSKF outperforms the other CUs in simulating precipitation in terms of both the mean intensity and diurnal cycles. In addition, the peak time of precipitation intensity is better captured by all the CU experiments than by the No_CU experiment. However, all the CU experiments tend to overestimate the mean precipitation and simulate an earlier peak of precipitation frequency when compared to observations. The frequencies and initiation timings for short-duration (1–3 h) and long-duration (> 6 h) precipitation events are well captured by the No_CU experiment, while these features are poorly reproduced by the CU experiments. The results demonstrate simulation without a CU outperforms those with a CU at the gray-zone spatial resolution in regard to the precipitation diurnal cycles.
Observed Coherent Trends of Surface and Upper-Air Wind Speed over China since 1960
Previous studies indicated that surface wind speed over China declined during past decades, and several explanations exist in the literature. This study presents long-term (1960–2009) changes of both surface and upper-air wind speeds over China and addresses observed evidence to interpret these changes. It is found that surface wind over China underwent a three-phase change over the past 50 yr: (i) it step changed to a strong wind level at the end of the 1960s, (ii) it declined until the beginning of the 2000s, and (iii) it seemed to be steady and even recovering during the very recent years. The variability of surface wind speed is greater at higher elevations and less at lower elevations. In particular, surface wind speed over the elevated Tibetan Plateau has changed more significantly. Changes in upper-air wind speed observed from rawinsonde are similar to surface wind changes. The NCEP–NCAR reanalysis indicates that wind speed changes correspond to changes in geopotential height gradient at 500 hPa. The latter are further correlated with the changes of latitudinal surface temperature gradient, with a correlation coefficient of 0.88 for the past 50 yr over China. This strongly suggests that the spatial gradient of surface global warming or cooling may significantly change surface wind speed at a regional scale through atmospheric thermal adaption. The recovery of wind speed since the beginning of the 2000s over the Tibetan Plateau might be a precursor of the reversal of wind speed trends over China, as wind over high elevations can respond more rapidly to the warming gradient and atmospheric circulation adjustment.
Superflexible Inorganic Ag2Te0.6S0.4 Fiber with High Thermoelectric Performance
Fiber‐based inorganic thermoelectric (TE) devices, owing to the small size, light‐weight, flexibility, and high TE performance, are promising for applications in flexible thermoelectrics. Unfortunately, current inorganic TE fibers are strictly constrained by limited mechanical freedom because of the undesirable tensile strain, typically limited to a value of 1.5%, posing a strong obstacle for further application in large‐scale wearable systems. Here, a superflexible Ag2Te0.6S0.4 inorganic TE fiber is demonstrated that provides a record tensile strain of 21.2%, such that it enables various complex deformations. Importantly, the TE performance of the fiber shows high stability after ≈1000 cycles of bending and releasing processes with a small bending radius of 5 mm. This allows for the integration of the inorganic TE fiber into 3D wearable fabric, yielding a normalized power density of 0.4 µW m−1 K−2 under the temperature difference of 20 K, which is approaching the high‐performance Bi2Te3‐based inorganic TE fabric and is nearly two orders of magnitude higher than the organic TE fabrics. These results highlight that the inorganic TE fiber with both superior shape‐conformable ability and high TE performance may find potential applications in wearable electronics. Inorganic Ag2Te0.6S0.4 fiber with both superb flexibility and high thermoelectric performance is successfully fabricated by a molten core approach. The resulting Ag2Te0.6S0.4 fiber provides a record tensile strain of 21.2%, such that it enables various complex deformations. The 3D wearable fabric made from Ag2Te0.6S0.4 fiber demonstrates its potential for flexible thermoelectric devices.
Erratum: wet bias of summer precipitation in the northwestern Tibetan Plateau in ERA5 is linked to overestimated lower-level southerly wind over the Plateau
We sincerely apologize for a technical error revealed in this article, published in 2023: the spectral nudging process at the upper levels was not functioning as intended. Consequently, the final results presented in the original work are based on WRF downscaling without active spectral nudging. To assess the potential impact of this error on the study’s main conclusion, we conducted two additional experiments using the same WRF version 3.7.1. Results show that the technical error does not alter the main conclusion of the study: the ERA5 overestimation of summer precipitation over the northwestern Tibetan Plateau is associated with an overestimated lower-level southerly wind.
Can aerosol loading explain the solar dimming over the Tibetan Plateau?
Solar radiation over the Tibetan Plateau has declined over recent three decades, whereas total cloud cover has a decreasing trend. A likely explanation to this paradox is the increase in aerosols over this clean region. However, this study shows that the radiation extinction due to aerosol loading is of one order lower in magnitude than the observed dimming, and the solar dimming is also seen in a satellite product that was produced without considering temporal variations of aerosols. Instead, the inter‐annual variability and decadal change in solar radiation is contrasting to that in water vapor amount and deep cloud cover (but not total cloud cover). Therefore, we suggest that the solar dimming over the Plateau is mainly due to the increase in water vapor amount and deep cloud cover, which in turn are related to the rapid warming and the increase in convective available potential energy. Key Points Solar dimming and total cloud cover decreasing co‐existed Aerosol impact on solar dimming was not significant over TP Deep cloud cover and water vapor content increased
Unlocking body-surface physiological evolution via IR-temperature dual sensing with single chalcogenide fiber
Improvements to body-surface physiological monitoring ability including real-time, accuracy and integration, are essential to meet the expansive demands for personal healthcare. As part of this, simultaneous monitoring of sweat metabolites and body temperature offers an exciting path to maximizing diagnostic precision and minimizing morbidity rates. Herein, we report a high-performance biomarker-temperature sensor made of a single As 3 Se 5 Te 2 chalcogenide glass fiber to monitor physiology evolution on body-surface. The sensor integrates efficient thermal resistance and fiber evanescent wave effects, permitting the independent sensing of temperature and biomarkers with an ultrahigh temperature coefficient of resistance (−5.84% K –1 ), rapid temperature response (0.3 s) and excellent IR sensing sensitivity. Moreover, by attaching a fiber to the wrist, we demonstrate simultaneous observation of both sweat metabolite (urea and lactate) and temperature changes during exercise. This illuminating sensing method will provide crucial capabilities in physiological monitoring and pave the way for advanced personalized diagnostic. The article introduces a single chalcogenide glass fiber enables simultaneous and efficient sensing of body-surface temperature and sweat biomarkers for real-time physiological monitoring.
A MULTISCALE SOIL MOISTURE AND FREEZE–THAW MONITORING NETWORK ON THE THIRD POLE
Multisphere interactions over the Tibetan Plateau directly impact its surrounding climate and environment at a variety of spatiotemporal scales. Remote sensing and modeling are expected to provide hydrometeorological data needed for these process studies, but in situ observations are required to support their calibration and validation. For this purpose, we have established a dense monitoring network on the central Tibetan Plateau to measure two state variables (soil moisture and temperature) at three spatial scales (1.0°, 0.3°, and 0.1°) and four soil depths (0–5, 10, 20, and 40 cm). The experimental area is characterized by low biomass, high soil moisture dynamic range, and typical freeze–thaw cycle. The network consists of 56 stations with their elevation varying over 4470–4950 m. As auxiliary parameters of this network, soil texture and soil organic carbon content are measured at each station to support further studies. To guarantee continuous and high-quality data, tremendous efforts have been made to protect the data-logger from soil water intrusion, to calibrate soil moisture sensors, and to upscale the point measurements. As the highest soil moisture network above sea level in the world, our network meets the requirement for evaluating a variety of soil moisture products and for soil moisture scaling analyses. It also directly contributes to the soil–water–ice–air–ecosystem interaction studies on the third pole. The data will be publicized via the International Soil Moisture Network and the recent 2-yr data will become accessible soon.
Enhanced third-order optical nonlinearity and photon luminescence of Sn2+ in gold nanoparticles embedded chalcogenide glasses
In this work, we successfully prepared gold nanoparticles (AuNPs) within a germanium–tin–sulfur (Ge–Sn–S, GSS) chalcogenide glass (ChG). The formation of AuNPs in the GSS ChG relies on the reduction capacity of Sn2+ ions, which we found their existence in the glass matrix by the characteristic emissions at nearly 450 nm. The AuNPs exhibit strong optical activity which caused a significant enhancement of third-order optical nonlinearity of the GSS ChG as well as photon luminescence of the Sn2+ ions. In addition, optical properties the AuNPs-embedded GSS ChGs can be modified by further gold doping and one-step heat-treatment process.