Masahiro Watanabe

Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIR

Abstract In this article, it is examined whether a positive atmosphere‐ocean feedback is found over the North Atlantic through a series of general circulation model (GCM) experiments. A 60‐year integration of an atmospheric GCM (AGCM) coupled with a 50 m deep motionless ocean was conducted. The coupled run was compared with two uncoupled runs, one with prescribed mid‐latitude climato‐logical sea surface temperatures (SSTs) and the other with daily SSTs derived from the coupled experiment. The un

Abstract Anomalous atmospheric fields associated with the North Atlantic Oscillation (NAO) are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the NAO is a regional phenomenon. Analyses on the interannual time scale reveal that the NAO signal is relatively confined to the Euro–Atlantic sector in December while it extends toward East Asia and the North Pacific in February. The difference is most clearly seen in the meridional wind anomaly, which shows

The anomalous, low‐level anticyclone near the Philippines and suppressed convection over the western Pacific associated with the mature warm phase of El Niño–Southern Oscillation (ENSO) have been suggested as important elements in the interaction between ENSO and the East Asian monsoon. We examined the causes of these anomalies in the circulation and convection using a newly developed, linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fl

This study attempts to investigate decadal-scale climate changes in the mid- and high latitudes of the Northern Hemisphere in winter 1989 by using various observational data for atmospheric parameters, sea surface temperature (SST), and snow cover. Decadal-scale changes in the winter atmosphere after 1989 are characterized as follows: a dipole pattern of height anomalies between midlatitudes and polar regions with an equivalent barotropic structure, temperature changes with cooling in the polar

A newly developed, linear baroclinic model (LBM) and its application to the tropical ENSO teleconnection is described. The model, based on primitive equations linearized about the observed, zonally varying basic state in northern winter, involves linear schemes for the cumulus convection, and surface sensible and latent heat fluxes, referred to as the moist LBM. This enables us to solve a steady-state response of the coupled dynamicalconvective system to a given SST anomaly, which is fairly diff

Abstract The rate of increase of global‐mean surface air temperature (SAT g ) has apparently slowed during the last decade. We investigated the extent to which state‐of‐the‐art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SAT g linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11‐me

Abstract The high sensitivity of the El Niño–Southern Oscillation (ENSO) to cumulus convection is examined by means of a series of climate simulations using an updated version of the Model for Interdisciplinary Research on Climate (MIROC), called MIROC5. Given that the preindustrial control run using MIROC5 shows a realistic ENSO, the integration is repeated with four different values of the parameter, λ, which affects the efficiency of the entrainment rate in cumuli. The ENSO amplitude is found

The interdecadal basin-wide warming and cooling cycle of the North Atlantic Ocean, known as the Atlantic multidecadal variability (AMV), influences not only the Euro-Atlantic climatic conditions, but also tropical storms and monsoons remotely. However, controversy still remains on the relative importance of external forcing and internal processes for the past AMV. Here, we use three attribution experiments, consisting of five-member ensemble for each, for 1931–2014 by a climate model and show th

Historical wintertime sea surface temperature (SST) data show that a sandwich pattern dominates on the decadal timescales in the North Atlantic, at least after the 1970s. The authors investigated how such decadal SST anomalies can survive against local thermal feedback, which acts to dampen them rapidly. At the surface, winter SST anomalies have a negligible projection with the subsequent summer anomalies while they show a significant projection with the SST anomalies in the next winter. On the

Changes in the sea surface temperature (SST) pattern in the tropical Pacific modulate radiative feedbacks to greenhouse gas forcing, the pace of global warming and regional climate impacts. Therefore, elucidating the drivers of the pattern is critically important for reducing uncertainties in future projections. However, the causes of observed changes over recent decades, an enhancement of the zonal SST contrast coupled with a strengthening of the Walker circulation, are still debated. Here we f

Due to errors in complex coupled feedbacks that compensate differently in different global climate models, as well as nonlinear nature of El Niño‐Southern Oscillation (ENSO), there remain difficulties in detecting and evaluating the reason for the past and future changes in the ENSO amplitude, σ niño . Here we use physics parameter ensembles, in which error compensation was eliminated by perturbing model parameters, to explore relationships between mean climate and variability. With four such en