The Arctic warming, especially during winter, has been almost twice as large as the global average since the late 1990s, which is known as the Arctic amplification. Yet linkage between the amplified ...Arctic warming and the midlatitude change is still under debate. This study examines the decadal changes of wintertime poleward heat and moisture transports between two 18-year epochs (1999–2016 and 1981–1998) with five atmospheric reanalyses. It is found that the wintertime Arctic warming induces an amplification of the high latitude stationary wave component of zonal wavenumber one but a weakening of the wavenumber two. These stationary wave changes enhance poleward heat and moisture transports, which are conducive to further Arctic warming and moistening, acting as a positive feedback onto the Arctic warming. Meanwhile, the Arctic warming reduces atmospheric baroclinicity and thus weakens synoptic eddy activities in the high latitudes. The decreased transient eddy activities reduce poleward heat and moisture transports, which decrease the Arctic temperature and moisture, acting as a negative feedback onto the Arctic warming. Since the increased poleward heat transport by stationary waves is nearly cancelled by the decreased transport by transient eddies, the total poleward heat transport contributes little to the Arctic warming. However, the total poleward moisture transport increases over most areas of the high latitudes that is dominated by the increased transport by stationary waves, which provides a significant net positive feedback onto the Arctic warming and moistening. Such a poleward moisture transport feedback may be particularly crucial to the amplified Arctic warming during winter when the ice-albedo feedback vanishes.
North Atlantic Oscillation (NAO) has a significant impact on surrounding winter weather and climate. However, the causes of its occasional reversal between early and late winter remain unclear. This ...study proposes a mechanism for the mid‐winter reversal of NAO from the perspective of local midlatitude air‐sea interaction. Strong sea surface temperature (SST) tripole events, which are defined by empirical orthogonal function of winter‐mean interannual North Atlantic SST anomalies, are primarily induced by NAO in early winter and peak in January. In late winter, the persistent SST tripole exerts active feedback on atmosphere through diabatic heat and transient eddy forcing. The resulting atmospheric circulation anomalies exhibit an almost reversed NAO pattern in February, which forms a wavetrain originating above the Gulf Stream and propagating to the Middle East and weakens the former SST tripole. Consequently, significant reversals of air temperature anomalies occur in Europe and the Caspian Sea area between February and December.
Plain Language Summary
The North Atlantic Oscillation (NAO) is a crucial atmospheric system that significantly impacts the weather and climate of the surrounding regions during winter. However, it often reverses between early and late winter, and the reasons for its mid‐winter reversal remain unclear. The NAO behavior can be influenced by multiple factors, such as atmospheric internal processes, underlying surface, and remote climate system, which makes the issue more complex. This study highlights the role of underlying sea surface temperature anomalies (SSTAs) in the mid‐winter reversal of NAO. The North Atlantic SSTAs are closely associated with the NAO and exhibit a tripole pattern. For strong sea surface temperature (SST) tripole events, the NAO primarily induces the early winter North Atlantic SST tripole. The SSTAs develop in early winter, peak in January, and feedback on the atmospheric circulation in late winter. The atmospheric circulation anomalies exhibit an almost reversed NAO pattern in February, forming a wavetrain that propagates above the Gulf Stream to the Middle East. As a result, during the warm phase of the SST tripole, Europe experiences colder temperatures, and the Caspian Sea experiences warmer temperatures in February than usual, as opposed to the positive NAO’s control over warm Europe and cold Caspian Sea in December.
Key Points
In early winter, North Atlantic Oscillation (NAO) forces a North Atlantic sea surface temperature (SST) tripole, which persists and tends to induce a nearly reversed NAO pattern in February
SST tripole induces a wavetrain over the Gulf Stream to the Middle East via diabatic heating and transient eddy forcing in February
As a result, there are remarkable reversals of air temperature anomalies in Europe and Caspian Sea area between February and December
The long‐term memory of the ocean makes sea surface temperature anomalies (SSTAs) become a significant predictor for the subsequent atmosphere, and the tropical ocean is primarily regarded as a major ...source of atmospheric anomalies. While in North Pacific, the local midlatitude SSTAs also have large contributions but have not been adequately considered yet. We discover a strong connection between the Kuroshio‐Oyashio Extension (KOE) SSTAs in spring and the local atmospheric circulation anomalies in following summer at interannual timescale, wherein, the spring KOE SSTAs are generally independent of tropical ocean, and they are primarily induced by the concurrent atmospheric anomalies via surface heat flux and ocean dynamic processes. The spring KOE SSTAs can persist to summer, and then generate nearly reversed whole‐layer atmospheric circulation anomalies in their north side through both diabatic heating and atmospheric transient eddy forcing. Consequently, precipitation anomalies in Pan‐Pacific regions are distinctly modulated from spring to summer.
Plain Language Summary
Because of the vast heat‐holding capacity and the long‐term memory of ocean, sea surface temperature anomalies (SSTAs) are usually taken as the significant factors to understand and predict climate anomalies. On interannual timescale, attentions have primarily centered on the tropical SSTAs, but recent studies indicated that the SSTAs in mid‐to‐high latitudes, especially in the Kuroshio‐Oyashio Extension (KOE) could have important feedbacks on the atmosphere. In this study, the KOE SSTAs in spring are discovered to have large interannual variability, and they are independent of the tropical SSTAs but closely linked to the subsequent summer atmospheric anomalies. It is found that the spring KOE SSTAs are mainly forced by the atmosphere via the surface heat flux and the ocean dynamic processes. In turn, they can persist to summer, and then play a dominant role in the air‐sea interaction in North Pacific, inducing remarkable geopotential height anomalies in north side. Consequently, in terms of the KOE SSTAs evolving from spring to summer, the Pan‐Pacific precipitation anomalies are distinctly modulated due to the opposite air‐sea interaction processes in the two seasons. These findings advocate for the use of springtime KOE SSTAs as a predictive indicator for following summer atmospheric and precipitation conditions.
Key Points
The spring Kuroshio‐Oyashio Extension (KOE) sea surface temperature anomalies (SSTAs) are independent of tropical ocean and primarily forced by the concurrent local atmosphere at interannual timescale
The spring KOE SSTAs can persist to summer and exert a delayed cross‐season impact on the subsequent summer atmosphere
Associated with the spring KOE SSTAs, precipitation anomalies in Pan‐Pacific regions are distinctly modulated from spring to summer
Interaction between synoptic eddy and mean flow plays a crucial role in maintaining midlatitude westerly jet. In this study, climatologies of synoptic eddy activities and their feedback onto ...midlatitude jet for 1980–2016 are evaluated and compared through analyzing daily data from five atmospheric reanalyses with different resolutions including one coarse-resolution reanalysis (NCEP2) and four fine-resolution reanalyses (ERA-Interim, JRA-55, MERRA-2, and CFSR). Horizontal resolutions of the atmospheric models generating those reanalyses are approximately equivalent to 210, 79, 60, 50, and 38 km, respectively. Results show that the eddy activities and their feedback onto the midlatitude jet in those fine-resolution reanalyses are consistently and significantly stronger than those in the coarse-resolution reanalysis (NCEP2). The maximal relative increases that are found to occur primarily in the midlatitudes of the Southern Hemisphere are estimated to be up to 55% for the baroclinicity, 53% for the eddy energetics, 59% for the eddy forcing, and even 85% for the eddy feedback onto the mean flow. Those increases are reasonably conjectured to be related to increased model resolutions, since the synoptic eddy genesis is proportional to the low-level atmospheric meridional temperature gradient which is sensitive to the meridional resolution of atmospheric models. Although the coarse-resolution reanalysis resolves synoptic eddies insufficiently and thus underestimates their feedback onto the mean flow, the magnitudes of eddy-driven jets are almost the same among five reanalyses, implying a mismatch between the eddy feedback and the eddy-driven jet in the coarse-resolution reanalysis. Therefore, the results of this study imply the importance of using fine-resolution reanalyses in accurately understanding the midlatitude synoptic eddy–mean flow interaction.
Enabling robots to provide effective assistance yet still accommodating the operator’s commands for telemanipulation of an object is very challenging because robot’s assistance is not always ...intuitive for human operators and human behaviors and preferences are sometimes ambiguous for the robot to interpret. Due to the difference in hand structures, some motion assistance from the robot may surprise the operator with counter-intuitive movements, which could introduce more burden to the human to correct the actions and/or reduce the operator’s sense of system control. To address these problems, we developed a novel preference-aware assistance knowledge learning approach. An assistance preference model learns what assistance is preferred by a human, and a stage-wise model updating method ensures the learning stability while dealing with the ambiguity of human preference data. Such a preference-aware assistance knowledge enables a teleoperated robot hand to provide more active yet preferred assistance toward manipulation success. We also developed knowledge transfer methods to transfer the preference knowledge across different robot hand structures to avoid extensive robot-specific training. Experiments to telemanipulate a 3-finger hand and 2-finger hand, respectively, to use, move, and hand over a cup have been conducted. Results demonstrated that the methods enabled the robots to effectively learn the preference knowledge and allowed knowledge transfer between robots with less training effort.
A record-breaking extreme Meiyu rainfall occurred along the Yangtze River valley (YRV) in 2020 since 1961, persisting from 11 June to 31 July with the largest amount and the highest intensity. From ...the aspect of water vapor, the causes of its formation are revealed in this study. The 2020 Meiyu rainfall amount is directly attributed to the greatly enhanced vertically integrated water vapor transport (IVT) convergence, which is in turn primarily determined by the mean circulation dynamic (MCD) contribution associated with anomalous East Asian summer monsoon (EASM) and the thermodynamic component (TH) contribution due to water vapor anomaly. The MCD contribution is mainly responsible for the extreme Meiyu rainfall amount and abundant water vapor convergence in the YRV, whereas the TH contribution tends to shift Meiyu rain belt northward to the Yangtze-Huaihe River valley, extending the Meiyu rainfall coverage area. Furthermore, the excessive moist static energy (MSE) associated with the largest water vapor anomaly could substantially increase the atmospheric instability, favoring the extreme 2020 Meiyu rainfall intensity. In terms of the tremendous IVT to the YRV from both the South China Sea and Bay of Bengal during the 2020 Meiyu period, the low-level anticyclone anomalies over the western North Pacific (WNP) and Bay of Bengal provide appropriate atmospheric circulation conditions, and they are generated by the super suppressed WNP convective activities as a Matsuno-Gill type response, which are further attributed to the combined warm SST anomalies in both the tropical western Indian Ocean (TWIO) and tropical Atlantic Ocean (TAO) eventually.
Factor models provide a cornerstone for understanding financial asset pricing; however, research on China’s stock market risk premia is still limited. Motivated by this, this paper proposes a ...four-factor model for China’s stock market that includes a market factor, a size factor, a value factor, and a liquidity factor. We compare our four-factor model with a set of prominent factor models based on newly developed likelihood-ratio tests and Bayesian methods. Along with the comparison, we also find supporting evidence for the alternative t-distribution assumption for empirical asset pricing studies. Our results show the following: (1) distributional tests suggest that the returns of factors and stock return anomalies are fat-tailed and therefore are better captured by t-distributions than by normality; (2) under t-distribution assumptions, our four-factor model outperforms a set of prominent factor models in terms of explaining the factors in each other, pricing a comprehensive list of stock return anomalies, and Bayesian marginal likelihoods; (3) model comparison results vary across normality and t-distribution assumptions, which suggests that distributional assumptions matter for asset pricing studies. This paper contributes to the literature by proposing an effective asset pricing factor model and providing factor model comparison tests under non-normal distributional assumptions in the context of China.
This paper investigates the impact of haze on China's stock markets and the intermediary role of investor attention. We propose that haze attracts investor attention through direct physical and ...psychological experiences of haze, haze-related news and government regulations, and thereby affects stock markets through investor attention. Using novel data collected from a leading Internet stock forum in China, our empirical analysis reveals that: (1) the aggravation of haze, increase in the amount of haze-related news, and reinforcement of regulations lead investors to pay more attention to haze-related issues; (2) the increased investor attention on haze decreases stock market returns.
Abstract
El Niño–Southern Oscillation (ENSO) is the strongest interannual signature in the tropical air–sea system and can affect global atmospheric variables, but ENSO’s climatic impact on land ...surface variables such as skin temperature, snow cover, and soil moisture that can serve as seasonal climate predictors remains relatively little known. Here we examine ENSO’s impact on the three land surface variables in Northern Hemisphere extratropics by regression analysis, using a combination of ERA5 reanalysis, GLDAS, satellite-based observations, and CESM2 simulations. Our results show that during El Niño winters anomalous land surface warming occurs in Northern Hemisphere midlatitudes, accompanied by snow cover reduction, especially in northern North America and eastern Europe, while anomalous cooling occurs in southern North America and the Tibetan Plateau, accompanied by increased snow cover. Meanwhile, increased soil moisture is observed in southern North America, central Asia, and southeast China. Further analysis indicates that atmospheric moisture processes dominate the formation of the land surface anomalies, for which the changes in water vapor and precipitation induced by the ENSO-related large-scale atmospheric teleconnection are critical. The anomalous land surface warming in midlatitudes mainly results from the increased downward longwave radiation due to the increase of water vapor, whereas the physical pathway causing water vapor anomalies is different over North America and Eurasia. Controlled by ENSO-induced changes in atmospheric circulation and moisture transport, anomalous precipitation explains most of the snow cover and soil moisture anomalies, which play a certain role in shaping the skin temperature anomalies in some regions through snow–albedo feedback and evaporation, respectively.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Tibetan Plateau (TP) has experienced an accelerated wintertime warming in recent decades under global warming, but consensus on its causes has not yet been reached. This study quantifies the ...processes of the warming through analyzing surface temperature budget and surface energy balance. It is found that increased diabatic heating (73%) and warm advection (27%) by an anomalous anticyclone southeast of TP are two primary processes determining the surface air warming. The former is caused by a significant increase of the TP skin temperature which warms the near surface atmosphere through increasing upward surface sensible heat flux. The land surface warming is attributed to increased absorbed radiation fluxes in which three processes are identified to be major contributors. While outside forcing which is primarily due to increased anthropogenic emissions of greenhouse gases contributes to the warming by 25% through increasing downward longwave radiation, two types of local positive feedbacks which are triggered by the land surface warming are found to contribute to most of the warming. One is the snow-albedo feedback which accounts for 47% of the surface warming by increasing surface absorption of incident solar radiation. The other is the moisture process feedback which accounts for 28% of the surface warming. The surface warming which works with increased soil water due to increased precipitation in the preceding seasons tends to promote surface evaporation and moisten the atmosphere aloft over the eastern TP, which, in turn, tends to increase downward longwave radiation and cause a further surface warming.
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