Multi-model Projection of Global Warming Impact on Tropical Cyclone Genesis Frequency over the Western North Pacific

Climatologically, an abrupt enhancement of convection occurs in mid-July over the western North Pacific (WNP) around 20°N, 150°E known as a convection jump (CJ), which is associated with a rapid diminishment of the Baiu rainband over central Japan through excitation of stationary Rossby wave. In view of the subtropical-origin teleconnection, we examined a projected future delay of the Baiu withdrawal under global warming conditions with relevance to future changes in seasonal evolution over the WNP. Based on reproducibility evaluation of the Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model outputs with respect to seasonal evolution of summertime precipitation over central Japan, we computed weighted multi-model ensembles, which are used for diagnosis of the projected future CJ changes. The result shows that CJ under global warming will occur more southeastward. In the future projection, increases in sea surface temperature (SST) over the equatorial Pacific and subtropical North Pacific are larger than those in the adjacent regions. Sensitivity experiments with a general circulation model (MJ98 AGCM) utilizing these salient warm SST anomalies also show the southeastward shift of CJ in comparison with a control simulation. These results indicate that the change in the location of subtropical convections associated with the spatial distribution of warm SST anomalies could be an important factor for the late termination of the Baiu season over central Japan under global warming conditions.

Section: Summary and Discussionmentioning

confidence: 99%

Delay of the Baiu Withdrawal in Japan under Global Warming Condition with Relevance to Warming Patterns of SST

Inoue

Ueda

2012

“…Therefore, the threshold values of criteria for detecting simulated TCs should be more lenient than those for real TCs. Furthermore, because model specifications such as resolution and parameterization schemes are different for each model, it is necessary to optimize different threshold values of the criteria for each model in order to appropriately detect simulated TCs (e.g., Yokoi and Takayabu 2009;Murakami et al 2012). The thresholds are optimized for each model to ensure that the present-day (PD) annual mean TC number in the WNP basin matches that observed (approximately 27 per year for the period 1979̶2007).…”

Section: Detection Algorithm For Tropical Cyclonesmentioning

confidence: 99%

Hindcast Prediction and Near-Future Projection of Tropical Cyclone Activity over the Western North Pacific Using CMIP5 Near-Term Experiments with MIROC

Mori

Kimoto

Ishii³

et al. 2013

Self Cite

In line with the experimental design for near-term climate prediction toward the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, we perform ensembles of initialized decadal hindcast and near-future projection using three versions of the coupled atmosphere̶ocean model MIROC. In the present study, we explore interannual and multiyear predictability of tropical cyclone (TC) activity in the western North Pacific (WNP) using the initialized hindcasts and examine global warming impacts on TC activity in the near-future on the basis of near-future projections up to 2035.The hindcasts of year-to-year variation in TC number capture the observed values reasonably well. Moreover, interannual variability of TC genesis and occurrence frequency associated with the El Niño Southern Oscillation are found to be predictable, mainly through better prediction of sea surface temperature (SST) and large-scale vorticity anomalies in the lower troposphere. These results indicate that the models can reproduce the major basic mechanisms that link TC genesis with large-scale circulation. Skillful prediction of TC number is likely difficult on multiyear timescales, at least based on our hindcasts, but through initializations, the three-year-mean hindcasts from 1998 onward reasonably capture observed major characteristics of TC activity associated with Pacific climate shift during the late 1990s.Near-future projections (2016̶2035) suggest significant reductions (approximately 14%) in TC number, particularly over the western part of the WNP, even under scenarios in which projected global warming is less prominent than that at the end of this century. This reduction is likely due to the suppression of large-scale lower tropospheric vorticity and relative humidity and the enhancement of vertical wind shear. The projected SST exhibits a more pronounced warming over the eastern tropical Pacific than over the western region and accompanies the weakening of Walker circulation via redistribution of tropical convection activity, which appears to be responsible for the change in the large-scale fields in the WNP.

“…Several studies applied process-oriented performance metrics to the CMIP3 models (e.g. Yokoi and Takayabu 2009;Nishii et al 2009). Especially, Kosaka and Nakamura (2011) found that models with better reproducibility of the climatological-mean fields tend to show better reproducibility of the most dominant summertime anomaly pattern over the western North Pacific.…”

Section: Discussionmentioning

confidence: 99%

Relationship of the Reproducibility of Multiple Variables among Global Climate Models

Nishii

Miyasaka

Nakamura

et al. 2012

Self Cite

Numerous e¤orts have been made for evaluating the performance of global climate models with such expectation that those models with higher reproducibility of the current climate should provide more reliable projections of climate changes into the future. Attempts have been made to define a single general metric through which the overall performance of a global climate model can be assessed. On the basis of general metrics defined through several techniques of multivariate analysis, the present study compares global climate models from a viewpoint of their reproducibility of climatological-mean fields of multiple variables. The analyses indicate that a reproducibility of a particular variable is not necessarily independent of that of others, which may bring redundant information into a general metric. The model reproducibility in upper and mid-tropospheric temperature and lower-tropospheric humidity, for example, tends to be anti-correlated with that in upper and mid-tropospheric humidity. It is argued that attention has to be paid to this kind of trade-o¤ relationships among some variables and resultant redundancy in synthesizing multiple metrics. A possibility is suggested that an arbitrary selection of variables can yield some redundant information of variables. The redundancy is, however, found to exert no serious influence on the quality of a general metric as long as it is based on the su‰cient number of variables. In our attempt to evaluate the climate models by introducing general performance metrics with reduced redundancy of variables, the overall model ranking is found rather insensitive to the specific definition of the metric.