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.[1] Decadal changes in surface air temperature (SAT) variability and cold surge characteristics over Northeast Asia during late winter (January-March) are analyzed for the past three decades. Power spectrum analysis of SAT reveals that the low-frequency variabilities with a period longer than 10 days are significantly enhanced, while the high-frequency variabilities with a period shorter than 10 days are weakened in the 1980s and 2000s. Moreover, cold surges were stronger and lasted longer during the 1980s and 2000s compared to those that occurred in the 1990s. Here, we propose that large-scale atmospheric conditions manifested by a different phase of the Arctic Oscillation (AO) provide preconditioning for a cold surge event, which showed a prominent decadal fluctuation. The more (less) frequent strong and long-lasting cold surge occurrences in the 1980s and 2000s (1990s) are preceded by the more dominant negative (positive) phase of the AO. Lag-composite analyses for cold surge events categorized by the AO phases indicate that stronger and longer-lasting cold air advection dominates at the lower-level, when upper-level wave train and coastal trough are developed over East Asia under the strong negative AO phase. These results suggest that the decadal changes in SAT variability and cold surge characteristics are strongly associated with the decadal changes in the phase distribution of the AO.

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The present study examines the impacts of snow initialization on surface air temperature by a number of ensemble seasonal predictability experiments using the NCAR Community Atmosphere Model version 3 (CAM3) AGCM with and without snow initialization. The study attempts to isolate snow signals on surface air temperature. In this preliminary study, any effects of variations in sea ice extent are ignored and do not explicitly identify possible impacts on atmospheric circulation. The Canadian Meteorological Center (CMC) daily snow depth analysis was used in defining initial snow states, where anomaly rescaling was applied in order to account for the systematic bias of the CAM3 snow depth with respect to the CMC analysis. Two suites of seasonal (3 months long) ensemble hindcasts starting at each month in the colder part of the year (September–April) with and without the snow initialization were performed for 12 recent years (1999–2010), and the predictability skill of surface air temperature was estimated. Results show that considerable potential predictability increases up to 2 months ahead can be attained using snow initialization. Relatively large increases are found over East Asia, western Russia, and western Canada in the later part of this period. It is suggested that the predictability increases are sensitive to the strength of snow–albedo feedback determined by given local climate conditions; large gains tend to exist over the regions of strong snow–albedo feedback. Implications of these results for seasonal predictability over the extratropical Northern Hemisphere and future direction for this research are discussed.

The authors investigate the circulation change during the life cycle of a weak stratospheric polar vortex (WSV) event and its impact on temperature variation over East Asia. The lower-tropospheric temperature over East Asia strongly fluctuates despite the slow decay of stratospheric circulation and the continuously negative Arctic Oscillation (AO) pattern during the WSV event. The temperature fluctuation is critically influenced by the variation of the East Asian upper-level coastal trough (EAT), which may be coupled to the stratospheric circulation during the WSV events. The EAT is deepened anomalously during the Peak phase (from lag −5 to lag 5 day) of the WSV, and East Asian temperature is lowest during this phase. During the next period (Decay-1 phase: from lag 6 to lag 16 day), in spite of the slowly decaying WSV condition, the cold temperature anomaly over East Asia is suddenly weakened; this change is caused by a westward-propagating signal of an anticyclonic anomaly from the North Pacific to East Asia. After about two weeks (Decay-2 phase: from lag 17 to lag 27 day), the cold conditions over East Asia are restrengthened by an intensification of EAT, which is related to the eastward propagation of a large-scale wave packet originating from a negative North Atlantic Oscillation (NAO)-type structure in the Decay-1 phase and its delayed influence on the East Asia region.

The 2015 Paris Agreement led to a number of studies that assessed the impact of the 1.5 °C and 2.0 °C increases in global temperature over preindustrial levels. However, those assessments have not actively investigated the impact of these levels of warming on fire weather. In view of a recent series of high-profile wildfire events worldwide, we access fire weather sensitivity based on a set of multi-model large ensemble climate simulations for these low-emission scenarios. The results indicate that the half degree difference between these two thresholds may lead to a significantly increased hazard of wildfire in certain parts of the world, particularly the Amazon, African savanna and Mediterranean. Although further experiments focused on human land use are needed to depict future fire activity, considering that rising temperatures are the most influential factor in augmenting the danger of fire weather, limiting global warming to 1.5 °C would alleviate some risk in these parts of the world.

It is well-known in motor control literature that a response time (RT) increases as a logarithmic function of the number of response alternatives (NA) (Hick's law). In this study, we identified neural correlates for this relationship using event-related functional MRI and a choice finger-movement task. Behaviorally, average RTs of all subjects increased as a logarithmic function of the NA in accordance with the law. From a voxel-wise search for brain areas where the activity was correlated with NA and thence the RT, a positive correlation was found at the posterior cingulate and left superior frontal gyri, whereas a negative correlation was observed at areas in bilateral inferior parietal lobules. This differential modulation by the task context, namely, the NA available for a choice response with identical stimulus and response, indicates that these regions are involved in various aspects of response selection, intentional retrieval of motor program, or spatial expectancy.

It has been demonstrated that recalibrations of audio-visual asynchrony are likely to occur in sensory processing rather than in the higher domains of cognition in the brain. The aim of the present study was to investigate recalibration of time perception to judge auditory and visual input simultaneity using a virtual environment (VE). A virtual corridor built for this experiment has depth of field, and includes six light sources (light-emitting diodes, LEDs) affixed on a computer monitor, which appear to be situated at different distances. Subjects in the VE were presented with both the flashes of LEDs and associated bursts of white noise with random stimulus onset asynchrony (SOA). Even though the auditory and visual stimuli were presented from the same distance on the display device, the subjects showed different time recalibration effects (TREs) depending on subjects' tendencies of immersion in VE. The results suggest that the differences in the TREs can be explained by subject-specific tendencies such as absorption to stimuli, which can construct subjective reality in top-down processing. Future research on neural substrates of recalibration for simultaneity will contribute toward understanding of how the brain creates the representation of spatiotemporal coherence. IntroductionOur everyday lives require constant processing of auditory and visual signals to establish coherent audiovisual images from the physical environment. These two signals stemming from a single source, however, reach our ears and eyes at different moments and trigger neural activities in separate sensory pathways and then are processed with different temporal windows in various brain regions. For instance, we see a glass fall down and smash into pieces on the floor and hear the cracking noise simultaneously without sensing any temporal disparity between the two signals. Actually, the visual and auditory signals have different conduction speeds in terms of physical characteristics. The sound signal takes more time to strike our ear drums than the light signal takes to hit the retina. The physical disparity in the speed of sound and light must be recalibrated by neural mechanisms for coherent perception of the audiovisual events.The neural mechanisms with which we integrate information from our sensory pathways to ensure a coherent world should possess a degree of plasticity in temporal processing. The mechanisms should reduce relevant temporal disparities