Since the late 1990s, surface temperature has been higher than (near or lower than) normal for summer/autumn (winter/spring) over Japan, indicating that the seasonal temperature contrast has become enhanced. In order to relate this to global-scale variability on decadal timescale, atmospheric re-analysis and ocean assimilation datasets were analyzed. It is suggested that the La Niña-like conditions which have been frequently observed in the tropical Pacific oceanic and atmospheric fields in the last decade have contributed to these temperature tendencies observed in Japan. These global characteristics are consistent with the global warming hiatus. The results presented here indicate that not only interannual variability and century-scale long-term trends but also decadal variability in global oceanic and atmospheric fields significantly affect Japan's temperature.(Citation: Urabe, Y., and S. Maeda, 2014: The relationship between Japan's recent temperature and decadal variability. SOLA, 10, 176−179,

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Clathrate hydrates preserve active species more stably than the other icy materials and investigation of the behavior of the active species elucidates the physicochemical properties of clathrate hydrates like guest-guest interaction. Color of the tert-butylamine clathrate hydrate changes to blue after gamma irradiation and is bleachable with visible light. The electron spin resonance (ESR) spectrum at 120 K mainly consists of a triplet signal of the C-centered radical NH2C(CH3)2CH2• together with a single signal at g = 2.0008. The latter signal disappears after light exposure. These results indicate that both the blue color and the single ESR signal are derived from trapped electrons in the hydrate. They thermally decay around 140-160 K by the first-order reaction, and the activation energy is 27 kJ/mol. Since tert-butylamine molecules can capture protons due to the high proton affinity, electrons may remain in the hydrate without reacting with protons, making the hydrate blue after gamma irradiation. The long-lived trapped electrons in the tert-butylamine hydrate have an advantage to investigate those in icy materials because tert-butylamine hydrate is nonionic and has a tetra-coordinated host water network like crystalline ice without any substitution for water molecules.

We investigated features of the atmosphere and ocean to seek a possible candidate that suppressed the growth of the El Niño event in 2014. In the boreal summer-fall season, equatorially antisymmetric sea surface temperature (SST) anomalies with a positive (negative) sign to the north (south) of the equator prevailed in the central and eastern tropical Pacific. In association with the SST anomalies, cumulus convective activity was enhanced in the region of the climatological Intertropical Convergence Zone (ITCZ). Anomalous southerly surface winds flowing across the equator toward the ITCZ induced upward latent heat flux anomalies and lowered SST in the near-equatorial region. These coherent spatial patterns between SST, wind, and latent heat flux anomalies suggested that the wind-evaporation-SST (WES) feedback sustained the suppression of the El Niño growth. A linear baroclinic model experiment indicated that the enhanced convective heating in the ITCZ also contributed to sustain the anomalous surface southerlies across the equator by the intense meridional atmospheric circulation over the equator. These results indicate that the anomalous southerlies across the equator sustained by the WES feedback and intense convective heating in the ITCZ contributed to the suppression of the El Niño growth.(Citation: Maeda, S., Y. Urabe, K. Takemura, T. Yasuda, and Y. Tanimoto, 2016: Active role of the ITCZ and WES feedback in hampering the growth of the expected full-fledged El Niño in

Since around 2013, the globally averaged sea surface temperature has rapidly warmed up and reached its highest on record. During this time, there was an intensifying El Niño event that caused positive temperature anomalies in the tropical Pacific Ocean. Compared with the conditions observed in 1997/98, when the previous highest record was marked associated with strong El Niño event, there were notable differences detected in the recent conditions. In the tropical Pacific, remarkable warming near sea surface associated with strong El Niño event in 2015/16 started from significantly warmed conditions along with positive temperature anomaly redistributed from the western part since early 2014, resulting in positive anomalies in the central to eastern part remaining for more than two years, much longer than 1997/98 event. In addition, substantial warming was observed in the North Pacific around 2013 and contribution of the North Pacific region to the global averaged SST anomaly marked significantly large value and was comparable to that of the tropical Pacific.(Citation: Urabe, Y., T. Yasuda, and S. Maeda, 2017: Rapid warming in global sea surface temperature since around 2013. SOLA, 13, 25−30,