ABSTRACT
The effective temperature (ET) is employed to investigate observed changes of thermal comfort conditions over China during the late decades of the historical observational period. ET ...considers the aggregate effects of temperature, relative humidity, and wind speed to describe the human thermal sensitivity to weather and climate. The data used in the study is the recently produced gridded daily scale dataset CN05.1, which covers the period of 1961–2014 at a resolution of 0.25° latitude by 0.25° longitude. Results show a general increase of ET in both December‐January‐February (DJF) and June‐July‐August (JJA). The increase is mostly caused by an increase of temperature and a decrease of wind speed, while the contribution from relative humidity is small. As measured by ET, China is a cold country with many more cold days than hot days. Large decreases of cold days and increases of hot days are found following the increase of ET. The number of comfortable days shows larger values in the warm areas and during the warm seasons. During the analysis period, the number of annual comfortable days shows an increasing trend when considering the China‐wide average. However, the number of annual comfortable days during JJA decreases over warm areas.
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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.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
For current-fed dual active bridge bidirectional dc-dc converters, all the possible switching patterns are summarized in view of the combinations of both side pulse-width modulation duty cycles and ...phase-shift angle. A control strategy is proposed for the current-fed dual active bridge converter to operate with the optimized patterns. The equivalent duty cycle of the secondary side is smaller than that of the primary side by a fixed value, which is optimized based on the soft-switching achievement and the circulating current minimization. The closed-loop control is easy to be implemented since there are only two independent variables, one-side duty cycle and the phase-shift angle. With the proposed control, zero-voltage switching can be achieved for all power switches throughout full range of load even at no-load condition. The typical working modes with the proposed control are given. The optimal design of the system parameters including the fixed time delta and dead time is illustrated. The converter has a very good performance, not only under steady states but also in transients. The conversion efficiency is high. The effectiveness of the proposed control is verified by the experimental results of a 1-kW laboratory prototype.
Black carbon (BC) in snow/ice induces enhanced snow and glacier melting. As over 60% of atmospheric BC is emitted from anthropogenic sources, which directly impacts the distribution and concentration ...of BC in snow/ice, it is essential to assess the origin of anthropogenic BC transported to the Tibetan Plateau (TP) where there are few direct emissions attributable to local human activities. In this study, we used a regional climate‐atmospheric chemistry model and a set of BC scenarios for quantitative evaluation of the impact of anthropogenic BC from various sources and its climate effects over the TP in 2013. The results showed that the model performed well in terms of climatology, aerosol optical properties, and near‐surface concentrations, which indicates that this modeling framework is appropriate to characterize anthropogenic BC source‐receptor relationships over the TP. The simulated surface concentration associated with the anthropogenic sources showed seasonal differences. In the monsoon season, the contribution of anthropogenic BC was less than in the nonmonsoon season. In the nonmonsoon season, westerly winds prevailed and transported BC from central Asia and north India to the western TP. In the monsoon season, BC aerosol was transported to the middle‐upper troposphere over the Indo‐Gangetic Plain and crossed the Himalayas via southwesterly winds. The majority of anthropogenic BC over the TP was transported from South Asia, which contributed to 40%–80% (mean of 61.3%) of surface BC in the nonmonsoon season, and 10%–50% (mean of 19.4%) in the monsoon season. For the northeastern TP, anthropogenic BC from eastern China accounted for less than 10% of the total in the nonmonsoon season but can be up to 50% in the monsoon season. Averaged over the TP, the eastern China anthropogenic sources accounted for 6.2% and 8.4% of surface BC in the nonmonsoon and monsoon seasons, respectively. The anthropogenic BC induced negative radiative forcing and cooling effects at the near surface over the TP.
Key Points
The impact of anthropogenic BC from various sources and its climate effects over the Tibetan Plateau (TP) were quantitatively evaluated
The majority of anthropogenic BC over the TP was transported from South Asia
Anthropogenic BC aerosol was transported to the middle‐upper troposphere over the Indo‐Gangetic Plain and crossed the Himalayas via southwesterly winds to the TP
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This open access book provides a comprehensive, up-to-date picture of the current state of knowledge covering climate change, surface water change, arsenic pollution, water utilization, ...water-food-energy nexus, water related hazards, water management, and water governance in the Lancang-Mekong River Basin. Considering the widely concerned fact that the climate change and human intervention induced impacts on water will bring unprecedented threats to human societies and ecosystems, the book intends to support UN’s sustainable development goals through sustainable use of water by providing the most accurate and updated information on climate and water changes in a consistent way. Underlying all aspects of the book is a strong commitment to assessing the science comprehensively, without bias and in a way that is relevant to policy but not policy prescriptive. It can provide implications to support decision-makers and stakeholders for integrated water resources management and sustainable development at all levels.
To develop a finescale dataset for the purpose of analyzing historical climatic change over the Tibet Plateau (TP), a high-resolution regional climate simulation for 1979–2011 was conducted using the ...Weather Research and Forecasting (WRF) Model driven by the ERA-Interim (ERA-Int). This work evaluates the high-resolution (30 km) WRF simulation in terms of annual variation, spatial structure, and 33-yr temporal trends of surface air temperature (Tair) and precipitation (Prec) over the TP, with reference to station observations. Another focus is on the examination of the height–temperature relationship. Inheriting from its forcing, the WRF simulation presents an apparent cold bias in the TP. The cold bias is largely reduced by a lapse rate correction of the simulated surface air temperature with help of the station and model elevations. ERA-Int presents the same sign of Tair and Prec trends as the observations, but with smaller magnitude, especially in the dry season. Compared to its forcing, the WRF simulation improves the simulation of the annual cycles and temporal trends of Tair and Prec in the wet season. In the dry season, however, there is hardly any improvement. The observed Tair presents a downward linear trend in the lapse rate. This feature is examined in the WRF simulation in comparison to ERA-Int. The WRF simulation captures the observed lapse rate and its temporal trend better than ERA-Int. The decreasing lapse rate over time confirms that Tair change in the TP is elevation dependent.
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Na+ plays a vital role in numerous physiological processes across humans and animals, necessitating a comprehensive understanding of Na+ transmembrane transport. Among the various Na+ pumps and ...channels, light-driven Na+-pumping rhodopsin (NaR) has emerged as a noteworthy model in this field. This review offers a concise overview of the structural and functional studies conducted on NaR, encompassing ground/intermediate-state structures and photocycle kinetics. The primary focus lies in addressing key inquiries: (1) unraveling the translocation pathway of Na+; (2) examining the role of structural changes within the photocycle, particularly in the O state, in facilitating Na+ transport; and (3) investigating the timing of Na+ uptake/release. By delving into these unresolved issues and existing debates, this review aims to shed light on the future direction of Na+ pump research.
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Unprecedented heatwave-drought concurrences in the past two decades have been reported over inner East Asia. Tree-ring-based reconstructions of heatwaves and soil moisture for the past 260 years ...reveal an abrupt shift to hotter and drier climate over this region. Enhanced land-atmosphere coupling, associated with persistent soil moisture deficit, appears to intensify surface warming and anticyclonic circulation anomalies, fueling heatwaves that exacerbate soil drying. Our analysis demonstrates that the magnitude of the warm and dry anomalies compounding in the recent two decades is unprecedented over the quarter of a millennium, and this trend clearly exceeds the natural variability range. The "hockey stick"-like change warns that the warming and drying concurrence is potentially irreversible beyond a tipping point in the East Asian climate system.
Near-surface (10 m) wind speed (NWS) plays a crucial role in many areas, including hydrological cycles, wind energy production, and air pollution, but what drives its multidecadal changes is still ...unclear. Using reanalysis datasets and model simulations from phase 6 of the Coupled Model Intercomparison Projection (CMIP6), this study investigates recent trends in the annual mean NWS. The results show that the Northern Hemisphere (NH) terrestrial NWS experienced significant (p < 0.1) decreasing trends during 1980–2010, when the Southern Hemisphere (SH) ocean NWS was characterized by significant (p < 0.1) upward trends. However, during 2010–19, global NWS trends shifted in their sign: NWS trends over the NH land became positive, and trends over the SH tended to be negative. We propose that the strengthening of SH NWS during 1980–2010 was associated with an intensified Hadley cell over the SH, while the declining of NH land NWS could have been caused by changes in atmospheric circulation, alteration of vegetation and/or land use, and the accelerating Arctic warming. The CMIP6 model simulations further demonstrate that the greenhouse gas (GHG) warming plays an important role in triggering the NWS trends over the two hemispheres during 1980–2010 through modulating meridional atmospheric circulation. This study also points at the importance of anthropogenic GHG forcing and the natural Pacific decadal oscillation to the long-term trends and multidecadal variability in global NWS, respectively.
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The performance of 24 GCMs available in the fifth phase of the Coupled Model Intercomparison Project (CMIP5) is evaluated over the eastern Tibetan Plateau (TP) by comparing the model outputs with ...ground observations for the period 1961–2005. The twenty-first century trends of precipitation and temperature based on the GCMs’ projections over the TP are also analyzed. The results suggest that for temperature most GCMs reasonably capture the climatological patterns and spatial variations of the observed climate. However, the majority of the models have cold biases, with a mean underestimation of 1.1°–2.5°C for the months December–May, and less than 1°C for June–October. For precipitation, the simulations of all models overestimate the observations in climatological annual means by 62.0%–183.0%, and only half of the 24 GCMs are able to reproduce the observed seasonal pattern, which demonstrates a critical need to improve precipitation-related processes in these models. All models produce a warming trend in the twenty-first century under the Representative Concentration Pathway 8.5 (rcp8.5) scenario; in contrast, the rcp2.6 scenario predicts a lower average warming rate for the near term, and a small cooling trend in the long-term period with the decreasing radiative forcing. In the near term, the projected precipitation change is about 3.2% higher than the 1961–2005 annual mean, whereas in the long term the precipitation is projected to increase 6.0% under rcp2.6 and 12.0% under the rcp8.5 scenario. Relative to the 1961–2005 mean, the annual temperature is projected to increase by 1.2°–1.3°C in the short term; the warmings under the rcp2.6 and rcp8.5 scenarios are 1.8° and 4.1°C, respectively, for the long term.
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