Chiharu Takahashi

Over 5,000 Years of Ensemble Future Climate Simulations by 60-km Global and 20-km Regional Atmospheric Models

AbstractAn unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the a...

Vehicle-dependent Effects of Sphingosine 1-phosphate on Plasminogen Activator Inhibitor-1 Expression

Aim: Sphingosine 1-phosphate (S1P) has been suggested to be a positive regulator of plasminogen activator inhibitor 1 (PAI-1) in adipocytes, while some studies are not consistent with this prothrombotic property of S1P. Since S1P is bound to apolipoprotein M (apoM) on HDL or to albumin in plasma, we compared the properties of these two forms on the PAI-1 induction. Methods: We investigated the associations of S1P, apoM, and PAI-1 concentrations in the plasma of normal coronary artery (NCA), stable angina pectoris (SAP), and acute coronary syndrome (ACS) subjects (n = 32, 71, and 38, respectively). Then, we compared the effects of S1P with various vehicles on the PAI-1 expression in 3T3L1 adipocytes. We also investigated the modulation of the PAI-1 levels in mice infected with adenovirus coding apoM. Results: Among ACS subjects, the PAI-1 level was positively correlated with the S1P level, but not the apoM level. In adipocytes, S1P bound to an apoM-rich vehicle induced PAI-1 expression to a lesser extent than the control vehicle, while S1P bound to an apoM-depleted vehicle induced PAI-1 expression to a greater extent than the control vehicle in 3T3L1 adipocytes. Additionally, apoM overexpression in mice failed to modulate the plasma PAI-1 level and the adipose PAI-1 expression level. S1P bound to albumin increased PAI-1 expression through the S1P receptor 2-Rho/ROCK-NFκB pathway. Conclusion: S1P bound to albumin, but not to apoM, induces PAI-1 expression in adipocytes, indicating that S1P can exert different properties on the pathogenesis of vascular diseases, depending on its vehicle.

Climate Change Increased the Likelihood of the 2016 Heat Extremes in Asia

Introduction. Analyses of the observed monthly temperature record from the Goddard Institute for Space Studies (GISS) Surface Temperature Analysis (GISTEMP; Hansen et al. 2010) indicate that the total area that experienced extreme warmth over the global land surface in 2016 was record-breaking, exceeding the previous highest record in 2010 (Fig. 19.1a, fraction of area that experiences extremely high temperature). This frequent occurrence of warm events is particularly remarkable over the Asian region (Fig. 19.1a). Many parts of Southeast Asia, southern India, and northern Eurasia experienced extremely high temperature by the end of 2016 (Fig. 19.1b). In India, at least 580 people were killed by the heat waves from March to May (India’s government; European Commission). The record-breaking high temperature had been persistent more than 10 months in the Maritime Continent. In Thailand, the heat wave also caused a new record for energy consumption because of the nationwide usage of air conditioners (Gecker and Chuwiruch 2016). Generally, Southeast Asia experiences warm and dry conditions during El Niño, being in the region of anomalously downward motion associated with the weakened Walker Circulation. Also, the global surface warms up with a lag of several months following an El Niño event through persistent changes in atmospheric circulation (Trenberth et al. 2002). In this report, we investigate to what extent the 2016 extreme warmth across Asia was attributable to anthropogenic warming or to the major El Niño episode in 2015/16. Many studies have concluded that heat waves over the global land area have become more frequent due to human-induced global warming (e.g., Jones et al. 2008; Christidis and Stott 2014; Shiogama et al. 2016). To separate the influences of anthropogenic warming and natural variability on the 2016 heat events in Asia, we analyzed large ensembles of atmospheric general circulation model (AGCM) simulations with and without anthropogenic warming and ENSO effects.

Significant Aerosol Influence on the Recent Decadal Decrease in Tropical Cyclone Activity Over the Western North Pacific

Over the past two decades, the number of tropical cyclones (TCs) has decreased markedly in the southeastern part of the western North Pacific (WNP) as a component of the interdecadal variation. This decrease has partially been explained by an internal low-frequency variability of sea surface temperature (SST) in the Pacific, but influences of external forcing remain unclear. Here we show that past changes in sulfate aerosol emissions contributed approximately 60% of the observed decreasing trends in TC genesis frequency in the southeastern WNP for 1992–2011, using multiple simulations by a global climate model. This decrease was mainly attributed to the increased vertical wind shear and decreased low-level vorticity, associated with a trans-basin multidecadal SST change driven by aerosol forcing. The near-future projection shows that the aerosol forcing still has some potential influence on decadal TC change, but the projected decreasing frequency is mainly due to increasing greenhouse gases forcing.

A Persistent Japanese Heat Wave in Early August 2015: Roles of Natural Variability and Human-Induced Warming

Introduction. A prolonged heat wave hit Japan in early August 2015. Daily maximum surface air temperature (SAT) exceeded 35°C for eight consecutive days and the 8-day mean anomaly was greater than 4°C at several observation sites, causing over 10 000 people to suffer from heatstroke. This heat wave was particularly unusual because an ongoing extreme El Niño of 2015 was expected to lead to a cooler summer in Japan. A primary cause of this heat wave was an intraseasonal tropical disturbance (Fig. 21.1). A tropical cyclone (TC), TC1513, was generated in the western North Pacific (WNP) during the convectively active phase of the intraseasonal oscillation (ISO) in the western Pacific (Fig. 21.1c and Supplemental Fig. S21.3c), followed by another TC (TC1514). Li and Zhou (2013) demonstrated that the two major components of the ISO, the 30–60 day Madden–Julian oscillation (MJO, Madden and Julian 1971) and the 10–20 day quasi-biweekly oscillation (QBWO, Chen and Sui 2010) can affect the genesis and intensity of TCs in the WNP during the summer. It appears that the TCs in this study likewise formed in association with the ISO. The diabatic heating associated with the TCrelated precipitation induced a Rossby wave train, which is characterized by cyclonic circulation and anticyclonic circulation anomalies in the WNP and East Asia, respectively (Figs. 21.1b,d). This pattern is similar to the so-called Pacific–Japan (PJ) teleconnection pattern (Nitta 1987; Wakabayashi and Kawamura 2004) in July and August, accompanying a meridional tripolar pattern in precipitation, vorticity, and temperature anomalies (Supplemental Fig. S21.1a). Several studies have also reported that TCs can generate the PJ pattern over the WNP (Kawamura and Ogasawara 2006; Yamada and Kawamura 2007). In early August 2015, the positive PJ pattern gave rise to the abnormally persistent hot and dry days over Japan. The El Niño conditions climatologically had a cooling impact on Japan in July–August (Supplemental Fig. S21.1a), yet the 2015 summer was still unexpectedly hot (Supplemental Fig. S21.1b). Anthropogenic warming can change the likelihood of specific extreme events, although the odds of an event occurring may vary from year to year depending on the regional sea surface temperature (SST) pattern (Christidis and Stott 2014). In this study, we investigate the possible influences of the intraseasonal variability, the 2015 strong El Niño, and anthropogenic warming on the Japanese heat wave in August 2015 using an atmospheric general circulation model (AGCM).