| 1. |
- Cai, Ziyi, et al.
(författare)
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Assessing Arctic wetting: Performances of CMIP6 models and projections of precipitation changes
- 2024
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Ingår i: Atmospheric Research. - 0169-8095. ; 297
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic region is experiencing a notable increase in precipitation, known as Arctic wetting, amidst the backdrop of Arctic warming. This phenomenon has implications for the Arctic hydrological cycle and numerous socio-ecological systems. However, the ability of climate models to accurately simulate changes in Arctic wetting has not been thoroughly assessed. In this study, we analyze total precipitation in the Arctic using station data, multiple reanalyses, and 35 models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). By employing the moisture budget equation and an evaluation method for model performance with ERA5 reanalysis as a reference, we evaluated the models' capability to reproduce past Arctic wetting patterns. Our findings indicate that most reanalyses and models are able to replicate Arctic wetting. However, the CMIP6 models generally exhibit an overestimation of Arctic wetting during the warm season and an underestimation during the cold season from 1979 to 2014 when compared to the ERA5 reanalysis. Further investigation reveals that the overestimation of wetting during the warm season is largest over the Arctic Ocean's northern part, specifically the Canadian Arctic Archipelago, and is associated with an overestimation of atmospheric moisture transport. Conversely, the models significantly underestimate wetting over the Barents-Kara Sea during the cold season, which can be attributed to an underestimation of evaporation resulting from the models' inadequate representation of sea ice reduction in that region. The models with the best performance in simulating historical Arctic wetting indicate a projected intensification of Arctic wetting, and optimal models significantly reduce uncertainties in future projections compared to the original models, particularly in the cold season and oceanic regions. Our study highlights significant biases in the CMIP6 models' simulation of Arctic precipitation, and improving the model's ability to simulate historical Arctic precipitation could reduce uncertainties in future projections.
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| 2. |
- Cai, Z. Y., et al.
(författare)
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Interdecadal variability of the warm Arctic-cold Eurasia pattern linked to the Barents oscillation
- 2023
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Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- Observed winter near-surface air temperature anomalies in the Northern Hemisphere have exhibited a warm Arctic-cold Eurasia (WACE) pattern with interdecadal variation in recent decades, but the exact mechanism behind WACE is still under debate. This study used reanalysis data and climate model simulations to investigate the interdecadal variability of the WACE pattern on a centennial scale, as well as the role of atmospheric circulations. It is found that the second mode of atmospheric variability over the North Atlantic-Arctic region, known as the Barents oscillation (BO), played a dominant role in regulating the interdecadal variability of WACE. The atmospheric circulation associated with the positive phase of the BO corresponds to an anomalous enhancement of the quasi-barotropic anticyclone near the southern Barents-Kara Seas (BKS) and the North Atlantic, as well as a weakening of the mid-latitude westerly jet. This atmospheric circulation anomaly favors the northward transport of atmospheric heat and moisture to the BKS from the mid-latitudes, resulting in an increased air temperature through downward longwave radiation. Concurrently cold air is transported from the polar region to Central Eurasia (CE), decreasing air temperature over CE. The amplified temperature anomaly dipole results in the decadal enhancement of the WACE pattern. The atmospheric circulation anomalies related to the negative phase of the BO are the opposite, which in turn leads to the decadal weakening of the WACE pattern. Our results further support the important role of internal atmospheric variability in the formation of WACE and emphasize that the atmospheric circulation associated with the BO is the main driver of WACE decadal variability over the past century.
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| 3. |
- Zhang, Yuelan, et al.
(författare)
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Two-Step Grain-Growth Kinetics of Sub-7 nm SnO2 Nanocrystal under Hydrothermal Condition
- 2015
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Ingår i: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 119:33, s. 19505-19512
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the grain growth kinetics of SnO2 quantum dots under hydrothermal conditions was investigated. By varying the reaction temperature and duration, SnO2 particle sizes were tuned from 2 to 7 nm. It is demonstrated that the growth behavior of subnanometer-sized SnO2 underwent two distinct processes: below the critical size of 5.5 nm, about double of Bohr radius, the grain growth kinetics obeys an Ostwald ripening mechanism, while above that, an oriented attachment process governs the particle growth. For the former cases, the activation energies were Ea1 = 61.94 kJ/mol at 200 °C and Ea1′ = 62.84 kJ/mol at 160 °C, which greatly differs from that of Ea2 = 131.32 kJ/mol for the latter case. High-resolution transmission electron microscope, X-ray diffraction as well as UV–vis diffuses reflectance, photoluminescence, Fourier transmission infrared, and Raman spectra were employed to reveal the size-dependent properties. As the particle size of SnO2 reduces, there occurred a lattice expansion, band gap broadening, and an abnormal blue shift. All these characteristics are closely related to the size changing in a narrow range from quantum dots to several nanometers. The findings reported here may shed light on further understanding the unique behaviors of quantum dots.
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