Research Institute for Global Change

Yokohama-shi, Japan

Research Institute for Global Change

Yokohama-shi, Japan
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Feely R.A.,National Oceanic and Atmospheric Administration | Sabine C.L.,National Oceanic and Atmospheric Administration | Byrne R.H.,University of South Florida | Millero F.J.,University of Miami | And 5 more authors.
Global Biogeochemical Cycles | Year: 2012

Based on measurements from the WOCE/JGOFS global CO2 survey, the CLIVAR/CO2 Repeat Hydrography Program and the Canadian Line P survey, we have observed an average decrease of 0.34% yr-1 in the saturation state of surface seawater in the Pacific Ocean with respect to aragonite and calcite. The upward migrations of the aragonite and calcite saturation horizons, averaging about 1 to 2 m yr-1, are the direct result of the uptake of anthropogenic CO2 by the oceans and regional changes in circulation and biogeochemical processes. The shoaling of the saturation horizon is regionally variable, with more rapid shoaling in the South Pacific where there is a larger uptake of anthropogenic CO2. In some locations, particularly in the North Pacific Subtropical Gyre and in the California Current, the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon. If CO2 emissions continue as projected over the rest of this century, the resulting changes in the marine carbonate system would mean that many coral reef systems in the Pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole, and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival. © 2012 American Geophysical Union. All Rights Reserved.

Ratnam J.V.,Research Institute for Global Change | Ratnam J.V.,Application Laboratory | Behera S.K.,Research Institute for Global Change | Behera S.K.,Application Laboratory | And 5 more authors.
Climate Dynamics | Year: 2012

The main aim of this paper is to evaluate the Advanced Research Weather Research and Forecasting (WRF) regional model in simulating the precipitation over southern Africa during austral summer. The model's ability to reproduce the southern African mean climate and its variability around this mean state was evaluated by using the two-tier approach of specifying sea surface temperature (SST) to WRF and by using the one-tier approach of coupling the WRF with a simple mixed-layer ocean model. The boundary conditions provided by the reanalysis-II data were used for the simulations. Model experiments were conducted for twelve austral summers from DJF1998-99 to DJF2009-10. The experiments using both the two-tier and one-tier approaches simulated the spatial and temporal distributions of the precipitation realistically. However, both experiments simulated negative biases over Mozambique. Furthermore, analysis of the wet and dry spells revealed that the one-tier approach is superior to the two-tier approach. Based on the analysis of the surface temperature and the zonal wind shear it is noted that the simple mixed-layer ocean model coupled to WRF can be effectively used in place of two-tier WRF to simulate the climate of southern Africa. This is an important result because specification of SST at higher temporal resolutions in the subtropics is the most difficult task in the two-tier approach for most regional prediction models. The one-tier approach with the simple mixed-layer model can effectively reduce the complicacy of finding good SST predictions. © 2011 Springer-Verlag.

Ratnam J.V.,Research Institute for Global Change | Ratnam J.V.,Application Laboratory | Behera S.K.,Research Institute for Global Change | Behera S.K.,Application Laboratory | And 6 more authors.
Climate Dynamics | Year: 2012

The winter months from December 2009 to February 2010 witnessed extreme conditions affecting lives of millions of people around the globe. During this winter, the El Niño Modoki in the tropical Pacific was a dominant climatic mode. In this study, exclusive impacts of the El Niño Modoki are evaluated with an Atmospheric General Circulation Model. Sensitivity experiments are conducted by selectively specifying anomalies of the observed sea surface temperature in the tropical Pacific. Observed data are also used in the diagnostics to trace the source of forced Rossby waves. Both the observational results and the model simulated results show that the heating associated with the El Niño Modoki in the central tropical Pacific accounted for most of the anomalous conditions observed over southern parts of North America, Europe and over most countries in the Southern Hemisphere viz. Uruguay. Unlike those, the model-simulated results suggest that the anomalously high precipitation observed over Australia and Florida might be associated with the narrow eastern Pacific heating observed during the season. © 2011 Springer-Verlag.

Ratna S.B.,University of Pune | Sikka D.R.,Indian Institute of Tropical Meteorology | Dalvi M.,University of Pune | Venkata Ratnam J.,Research Institute for Global change | Venkata Ratnam J.,Application Laboratory
International Journal of Climatology | Year: 2011

This paper discusses the simulations of Indian summer monsoon (ISM) using a high-resolution National Center for Environmental Prediction (NCEP) T170/L42 model for a 20-year period (1985-2004) with observed Sea Surface Temperature (SSTs) as boundary conditions and using five initial conditions in the first week of May. Good agreement is found between the observed and simulated climatologies. Interannual variability (IAV) of the ISM rainfall as simulated in individual ensemble members and as provided by ensemble average shows that the two series are found to agree well; however, the simulation of the actual observed year-to-year variability is poor. The model simulations do not show much skill in the simulation of drought and excess monsoon seasons. One aspect which has emerged from the study is that where dynamical seasonal prediction has specific base for the large areal and temporal averages, the technique is not to be stretched for application on short areal scale such as that of a cluster of a few grid point. Monsoon onset over Kerala (MOK) coast of India and advance from Kerala coast to northwest India is discussed based on ensemble average and individual ensemble member basis. It is suggested that the model is capable of realistically simulating these processes, particularly if ensemble average is used, as the intermember spread in the ensemble members is large. In short, the high-resolution model appears to provide better climatology and its magnitude of IAV, which compares favourably with observations, although year-to-year matching of the observed and simulated seasonal/monthly rainfall totals for India as a whole is not good. © 2010 Royal Meteorological Society.

Richards K.J.,Pacific University in Oregon | Natarov A.,Hawaii Pacific University | Firing E.,University of Hawaii at Manoa | Kashino Y.,Research Institute for Global Change | And 5 more authors.
Journal of Geophysical Research C: Oceans | Year: 2015

We investigate the characteristics of shear-generated turbulence in the natural environment by considering data from a number of cruises in the western equatorial Pacific. In this region, the vertical shear of the flow is dominated by flow structures that have a relatively small vertical scale of O(10 m). Combining data from all cruises, we find a strong relationship between the turbulent dissipation rate, ε{lunate}, vertical shear, S, and buoyancy frequency, N. Examination of ε{lunate} at a fixed value of Richardson number, Ri=N2/S2, shows that ε{lunate}∝ut2N for a wide range of values of N, where ut is an appropriate velocity scale which we assume to be the horizontal velocity scale of the turbulence. The implied vertical length scale, ℓv=ut/N, is consistent with theoretical and numerical studies of stratified turbulence. Such behavior is found for Ri<0.4. The vertical diffusion coefficient then scales as κv∝ut2/N at a fixed value of Richardson number. The amplitude of ε{lunate} is found to increase with decreasing Ri, but only modestly, and certainly less dramatically than suggested by some parameterization schemes. Provided the shear generating the turbulence is resolved, our results point to a way to parameterize the unresolved turbulence. © 2015. American Geophysical Union. All Rights Reserved.

Hargreaves J.C.,Research Institute for Global Change | Annan J.D.,Research Institute for Global Change | Yoshimori M.,Atmosphere and Ocean Research Institute | Abe-Ouchi A.,Atmosphere and Ocean Research Institute
Geophysical Research Letters | Year: 2012

We investigate the relationship between the Last Glacial Maximum (LGM) and climate sensitivity across the PMIP2 multi-model ensemble of GCMs, and find a correlation between tropical temperature and climate sensitivity which is statistically significant and physically plausible. We use this relationship, together with the LGM temperature reconstruction of Annan and Hargreaves (2012), to generate estimates for the equilibrium climate sensitivity. We estimate the equilibrium climate sensitivity to be about 2.5C with a high probability of being under 4C, though these results are subject to several important caveats. The forthcoming PMIP3/CMIP5 models were not considered in this analysis, as very few LGM simulations are currently available from these models. We propose that these models will provide a useful validation of the correlation presented here. © 2012. American Geophysical Union. All Rights Reserved.

Ratnam J.V.,Research Institute for Global Change | Behera S.K.,Research Institute for Global Change | Masumoto Y.,Research Institute for Global Change | Masumoto Y.,University of Tokyo | And 2 more authors.
Monthly Weather Review | Year: 2012

Remote effects due to the tropical disturbances in the north Indian Ocean are investigated by analyzing long-lasting ($5 days) tropical disturbances, which reached at least the strength of tropical storms. The present analysis is carried out for both the pre- and postmonsoon periods. The spatial and temporal distribution of the outgoing longwave radiation (OLR) during the premonsoon disturbances over the Bay of Bengal reveals several interesting features. Temporal distribution of the OLR anomalies shows that the intraseasonal oscillations play an important role in the formation of those disturbances. The spatial distribution of the OLR anomalies shows a dipole with negative OLR anomalies over the bay and positive OLR anomalies over the Indonesian region. The atmospheric response to the negative OLR anomalies results in positive temperature anomalies over northwest India, Pakistan, Afghanistan, Iran, and Saudi Arabia, remote from the disturbance; and the response to the positive anomalies causes slight increase in the sea surface temperature of the Arabian Sea. NegativeOLRanomalies are also seen over western Japan due to the Rossby waves generated by the heating over the Bay of Bengal besides the enhancement of the so-called "Pacific-Japan" teleconnection pattern. However, the analysis shows that the postmonsoon disturbances over the Bay of Bengal and the disturbances formed over the Arabian Sea in both pre- and postmonsoon seasons do not develop remote teleconnections associated with the above type of Rossby wave mechanism. These results are significant for the short- to medium-range weather forecast over a wide range covering Japan, Pakistan, Afghanistan, Iran, and Saudi Arabia. ©2012 American Meteorological Society.

Annan J.D.,Research Institute for Global Change | Hargreaves J.C.,Research Institute for Global Change | Tachiiri K.,Research Institute for Global Change
Geophysical Research Letters | Year: 2011

Comparison of model outputs with observations of the climate system forms an essential component of model assessment and is crucial for building our confidence in model predictions. Methods for undertaking this comparison are not always clearly justified and understood. Here we show that the popular approach of comparing the ensemble spread to a so-called "observationally- constrained pdf" can be highly misleading. Such a comparison will almost certainly result in disagreement, but in reality tells us little about the performance of the ensemble. We present an alternative approach, and show how it may lead to very different, and rather more encouraging, conclusions. We additionally present some necessary conditions for an ensemble (or more generally, a probabilistic prediction) to be challenged by an observation. Copyright 2011 by the American Geophysical Union.

Annan J.D.,Research Institute for Global Change | Hargreaves J.C.,Research Institute for Global Change
Climate of the Past | Year: 2013

Some recent compilations of proxy data both on land and ocean (MARGO Project Members, 2009; Bartlein et al., 2011; Shakun et al., 2012), have provided a new opportunity for an improved assessment of the overall climatic state of the Last Glacial Maximum. In this paper, we combine these proxy data with the ensemble of structurally diverse state of the art climate models which participated in the PMIP2 project (Braconnot et al., 2007) to generate a spatially complete reconstruction of surface air (and sea surface) temperatures. We test a variety of approaches, and show that multiple linear regression performs well for this application. Our reconstruction is significantly different to and more accurate than previous approaches and we obtain an estimated global mean cooling of 4.0 ± 0.8 C (95% CI). © Author(s) 2013. CC Attribution 3.0 License.

Annan J.D.,Research Institute for Global Change | Hargreaves J.C.,Research Institute for Global Change
Geophysical Research Letters | Year: 2010

We consider paradigms for interpretation and analysis of the CMIP3 ensemble of climate model simulations. The dominant paradigm in climate science, of an ensemble sampled from a distribution centred on the truth, is contrasted with the paradigm of a statistically indistinguishable ensemble, which has been more commonly adopted in other fields. This latter interpretation (which gives rise to a natural probabilistic interpretation of ensemble output) leads to new insights about the evaluation of ensemble performance. Using the well-known rank histogram method of analysis, we find that the CMIP3 ensemble generally provides a rather good sample under the statistically indistinguishable paradigm, although it appears marginally over-dispersive and exhibits some modest biases. These results contrast strongly with the incompatibility of the ensemble with the truth-centred paradigm. Thus, our analysis provides for the first time a sound theoretical foundation, with empirical support, for the probabilistic use of multi-model ensembles in climate research. © Copyright 2010 by the American Geophysical Union.

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