[1] The 2010 summer heat wave in western Russia was extraordinary, with the region experiencing the warmest July since at least 1880 and numerous locations setting all-time maximum temperature records. This study explores whether early warning could have been provided through knowledge of natural and human-caused climate forcings. Model simulations and observational data are used to determine the impact of observed sea surface temperatures (SSTs), sea ice conditions and greenhouse gas concentrations. Analysis of forced model simulations indicates that neither human influences nor other slowly evolving ocean boundary conditions contributed substantially to the magnitude of this heat wave. They also provide evidence that such an intense event could be produced through natural variability alone. Analysis of observations indicate that this heat wave was mainly due to internal atmospheric dynamical processes that produced and maintained a strong and long-lived blocking event, and that similar atmospheric patterns have occurred with prior heat waves in this region. We conclude that the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability. Slowly varying boundary conditions that could have provided predictability and the potential for early warning did not appear to play an appreciable role in this event.
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Control of nanocrystal (NC) crystallinity currently raises great interest because of its potential benefits in both physics modeling and technological applications. Advances in methods for synthesizing perfect single-crystalline NCs are recent, so that the effect of crystallinity on NC properties has received only limited study and still needs to be properly investigated. Here, we report that crystallinity of gold NCs dramatically modifies their vibrations. Using low-frequency Raman scattering, we clearly demonstrate that single-domain NCs vibrate differently than their multiply twinned counterparts, through the splitting of the quadrupolar vibrations, which is only observed for the former. Using the resonant ultrasound approach, we calculate the vibrational frequencies of a gold sphere and show that elastic anisotropy induces a lift of degeneracy of the quadrupolar mode in good agreement with our experimental measurements. These findings open up challenging perspectives on using Raman spectroscopy to characterize nanocrystallinity.crystallinity ͉ elastic anisotropy ͉ quadrupolar mode ͉ Raman spectroscopy C rystallinity was recently shown to have an effect on the reactivity, the electron-phonon interaction, and the mechanical properties of silver nanocrystals (NCs), in this way demonstrating perfect nanocrystallinity to be a relevant issue in tailoring NCs' properties (1). From a theoretical point of view, atomistic simulations have pointed out some specific effects of morphology on phonons in nanoscopic metal grains (2), showing that realistic nanograin models display complex vibrational properties. As a counterpart to the simulations, very few experimental investigations have been reported that attempt to demonstrate such a dependence of vibrational properties on the degree of crystallinity of metal NCs (1, 3). This is partially due to the difficulty in tailoring the crystallinity of NCs, as mentioned above, but also to the technical limitation in detecting and identifying the related experimental features. The present article reports that vibrational properties of noble-metal NCs dramatically depend on their nanocrystallinity and clearly demonstrates the relevance of elastic anisotropy in small NCs. These findings make it possible to use vibrational spectroscopy as an alternative or complementary nondestructive tool to the electron microscopy techniques for characterizing nanocrystallinity and also provide interesting insights for understanding, at the nanoscale, how vibrations are affected by the presence of twinning planar defects in metal NCs. Results and DiscussionIn this work, we use a one-step one-phase synthetic route (4) to produce colloidal solutions containing gold NCs. Several samples are synthesized by depositing the NCs on a substrate of highly oriented pyrolitic graphite (HOPG). These samples mainly contain single-domain gold NCs with a size distribution slightly varying from one sample to the other. In these samples, NCs tend to spontaneously self-organize because of their very narrow size dist...
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