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The Tibetan Plateau (TP), also called the Third Pole, is considered to be "the world water tower". The northwestern TP (NWTP), which has an average elevation higher than 4800 m, is an arid region where the summer precipitation is largely overestimated by the ERA5 global reanalysis product. We hypothesize that this wet bias is mainly caused by unrealistic lower-level winds that trigger strong convection over the region; it can be reduced by using a high-resolution regional climate model with a large domain that allows realistically representing interactions between the Westerlies and Asian summer monsoons. Here, downscaling using the Weather Research and Forecasting (WRF) model driven by ERA5 was conducted with a large domain (8°‒50° N, 65°‒125° E) at 9 km for the period 1979‒2019 (WRF9km). Precipitation values from WRF9km and ERA5 were evaluated against satellite observations; compared with ERA5, WRF9km captured the climatological summer precipitation over the NWTP with a much-reduced wet bias. The ERA5 overestimation is mainly caused by excessive convective precipitation, likely linked to strong vertical motions over the NWTP induced by an overestimated lower-level southerly wind. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Sub-grid orographic drag directly acts on wind and impacts the regional water cycle through control of atmospheric water vapor (AWV) transport. The effect of turbulent orographic form drag (TOFD) on wind and precipitation is investigated in this study using the WRF model for a winter month over the western Tibetan Plateau (TP), where solid precipitation supplies large amounts of water resources. The diurnal cycle of wind components and atmospheric circulation simulated with TOFD are consistent with observations and ERA-Interim data, whereas stronger westerlies exist in the simulation without the TOFD scheme. The latter results in more zonal AWV transport from the west and more precipitation over the western TP and surroundings. The implementation of the TOFD scheme leads to reduced biases, when evaluated with two observation-based precipitation products. It is therefore concluded that this scheme has a clear dynamical control on the regional atmospheric water recharge and thus the parameterization of the small-scale orographic drag in the model helps to improve the prediction of wintertime precipitation in the western TP region. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A series of GeSbSe ( x = 5, 10, 15, 20, 25, and 30 mol%) chalcogenide glasses were prepared by traditional melt-quenching method. The refractive indexes, infrared transmissions, and spontaneous Raman spectra of the glass samples were measured. Based on the spontaneous Raman scattering theory and considering the measured Raman spectral data, we calculated the Raman gain coefficients of the chalcogenide glasses. The effect of Sb on the structures and Raman gain coefficients of the glass samples was then systematically investigated to understand the role of chemical composition in glass structure and Raman gain coefficient. In the GeSbSe glasses, the number of heteropolar Ge-Se, Sb-Se bonds increased, whereas that of homopolar Se-Se bonds decreased at increased Sb concentration. The Raman gain coefficients increased until it reached a maximum value (290 × 10 m/W at GeSbSe) and then decreased when the Sb concentration further increased. These results showed that the Raman gain coefficients of Ge-Sb-Se chalcogenide glasses without poisonous elements were over 300 times of that of commonly fused silica and closely correlated with the structures of the glasses, suggesting that the Raman gain coefficient can be adjusted by modifying the structures of the glasses. This work provides a new possibility for environment-friendly Raman fiber laser and amplifier materials. [ABSTRACT FROM AUTHOR]

A 488 nm continuous wave (CW) laser was employed in Raman spectrometer to both induce and characterize phase transformation in chalcogenide glasses. Laser-induced Raman inactive changes, structural evolution, and crystallization were observed at laser-irradiated region in GeS-SbS glasses. The composition dependence of laser-induced phase transformation was discussed in terms of thermal stability and microstructural modification. It is strongly suggested from these results that fabrication of passive and active chalcogenide glass waveguides, such as refractive index change and nonlinear optical crystal line, is controllable by selecting appropriate glass composition, and convenient by using common CW lasers. [ABSTRACT FROM AUTHOR]

65GeS⋅25InS⋅10CsCl chalcohalide glass-ceramics containing β-InS crystallites in the glassy matrix were prepared by traditional melt-quenching and subsequent heat-treatment at a fairly low temperature ( T+10 C) for different durations. The transmission spectra show that the cut-off edge of short wavelength is red-shifted with the prolongation of annealing time, but remains an excellent transmittance in the mid-IR region. Meanwhile, its crystallization behavior was investigated systematically. The results show that the precipitation of β-InS crystal phase is responsible for the first crystallization peak, and the second crystal phase is GeS, which precipitated in the interior after a heat treatment at a high temperature ( T+70 C). Furthermore, the crystallization mechanism was investigated using the non-isothermal method. The crystallization rate constant K value of 6.08×10 s at 346 C for the β-InS phase is about three times larger than that of the GeS phase, indicating a much easier crystallization mechanism of β-InS phase. Therefore, it is easy to control the precipitation of sole β-InS crystallite, and to avoid interference of the second crystal phase GeS. [ABSTRACT FROM AUTHOR]

Transparent 90GeS⋅10GaS(G10) chalcogenide glass-ceramics containing β-GeS nanocrystals was successfully fabricated through controllable crystallization based on the knowledge of its nucleation-rate-like curve. Using the conventional Z-scan method, both large spectral dependence and crystallinity dependence of optical nonlinear parameters were learned under the excitation of different wavelengths that in proximity of the half-bandgap. In particular, a large value of figure of merit (FOM≈11.64) was obtained in the crystallized sample after the heat-treatment at 466°C for 40 h. Although it is not a straightforward process to select an appropriate medium for a specific application, this work opens a new way to construct suitable optical nonlinear properties (e.g., large FOM) though modifying the microstructure of chalcogenide glass-ceramics. [ABSTRACT FROM AUTHOR]

CdSe quantum dots (QDs) doped glasses have been widely investigated for optical filters, LED color converter and other optical emitters. Unlike CdSe QDs in solution, it is difficult to passivate the surface defects of CdSe QDs in glass matrix, which strongly suppress its intrinsic emission. In this study, surface passivation of CdSe quantum dots (QDs) by Cd1−xZnxSe shell in silicate glass was reported. An increase in the Se/Cd ratio can lead to the partial passivation of the surface states and appearance of the intrinsic emission of CdSe QDs. Optimizing the heat-treatment condition promotes the incorporation of Zn into CdSe QDs and results in the quenching of the defect emission. Formation of CdSe/Cd1−xZnxSe core/graded shell QDs is evidenced by the experimental results of TEM and Raman spectroscopy. Realization of the surface passivation and intrinsic emission of II-VI QDs may facilitate the wide applications of QDs doped all inorganic amorphous materials. [ABSTRACT FROM AUTHOR]

Gallium-based Ga-Sb-S sulfide glasses was elaborated and studied. A relationship between the structure, composition, and optical properties of the glass has been established. The effects of the introduction of Ga on the structure using infrared and Raman spectroscopies and on the Er3+-doped IR emission have been discussed. The results show that incorporation of Ga induced the dissociation of [SbS3] pyramids units and the formation of tetrahedral [GaS4] units. The dissolved rare earth ions are separated around the Ga-S bonding and the infrared emission quenching are controlled. Moreover, continuous introduction of Er ions into the glass forms more Er-S bonds through the further aggregation surrounding the [GaS4] units. In return, the infrared emission intensity decreased with excessive Er ion addition. This phenomenon is correlated with the recurrence concentration quenching effect induced by the increase of [GaS4] units. [ABSTRACT FROM AUTHOR]

Chalcogenide glass has been considered as a promising host for the potential laser gain and amplifier media operating in near- and mid-IR spectral region. In this work, the IR luminescence spectra of rare earth ions (Tm3+, Er3+, and Dy3+) doped 65GeS2-25In2S3-10CsI chalcogenide glasses were measured under the excitation of an 808 nm laser diode. To the best of our knowledge, it firstly provides the luminescence spectra of a full near- and mid-IR spectral range from 1 to 4 μm in rare earth ions doped chalcogenide glasses. The results of absorption spectra, luminescence spectra, and fluorescence decay curves were obtained in these samples with singly-, co- and triply-doping behaviors of Tm3+, Er3+, and Dy3+ ions. In order to search possible efficient IR emissions, the luminescence behavior was investigated specifically with the variation of doping behaviors and dopant ions, especially in the samples co- and triply-doped active ions. The results suggest that favorable near- and mid-IR luminescence of rare earth ions can be further modified in chalcogenide glasses through an elaborated design of doping behavior and optically active ions. [ABSTRACT FROM AUTHOR]