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Published byErnest Colver Modified over 10 years ago
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Detecting decadal climate phase reversal in near past: implications of recent North Pacific climate variability Shoshiro Minobe (Graduate School of Hokkaido University, Sapporo, Japan) It is difficult to predict Pacific Decadal Variability, then how about nowcast?
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Mechanisms of PDV Two different views –Stochastically forced variations, with short damping time (e.g., Newman 2003; 2007). –Oscillatory phenomena due to coupled air-sea mode or extraterrestrial forcing, suggested by several models (e.g., Zhong et al 2009; Tanaka et al. 2012; Meehl et al. 2009).
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Air-sea coupled multidecadal mode Zhong et al. (2009) Salinity signal propagating in the subarctic region reaches the northwestern North Pacific, influence on Kuroshio-Oyashio extensions, from which feedback to the atmosphere making a oscillation. Lag correlation of salinity(contour) & dynamic height(color) onto KEO SST. 0-500 m average, along 50N, 25-80 year band-pass filter. Rossby wave due to salinity!
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18.6-yr tidal modulation causes oscillation in the ocean & atmosphere. Tanaka et al. (2012) 430-yr AOGCM integration with & without 18.6-yr tide modulation. Spectra of Aleutian low strength (NPI) SST: clim (contour), composite (color) Tidal modulation no uniform only Kuril SLP: clim (contour), composite (color)
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11-yr solar cycle Meehl et al. (2009 Science) Composite of four 11 solar peak years. for precipitation Stippling indicates significance at the 5% level, and dashed lines indicate position of climatological precipitation maxima.
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Most of CMIP5 models underperform persistency prediction Predictability of PDO by CMIP5 models are generally low. Only MIROC5 outperform persistency prediction. Decadal prediction is difficult, then a decadal nowcast is possible? Kim et al. 2012 GRL
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Good new for Atlantic researchers. IPCC-class models can be useful for predictions with 3-6 year lead time. But many of them do not update their results operationally (only for AR5 and AR6). Kim et al. 2012 GRL
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1998/99 shift? “Pacific Ocean Showing Signs of Major Shifts in the Climate” JPL Bill Patzert 20, Jan, 1999.
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Chavez et al. (2003 Science) 3-yr running mean
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A more recent change? Bromirski, Miller et. al 2011 (JGR-O) 3-yr running mean
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Motivation, cont. The decadal nowcast is not easy, because a basic method is to extract decadal variability is low-pass filtering, which needs not only past data but also future information for a data point to be filtered. Thus, decadal nowcast cannot avoid uncertainty from future. It should be useful to know decadal variability including explicit estimation of the uncertainty, using a method as possible as simple. This can gives a measure how extraordinary or just ordinary phenomena are going on.
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Approach To do so, we generate 1,000 future data of climate indices (NPI and PDO index) using AR-1 model, and each time series, consist of observed past data and AR-1 future estimation, is filtered. The resultant 1,000 filtered data allow us to estimate uncertainty of decadal variability in near past. Filtering: decadal filter & bidecadal filter (10 & 30-yr half power point) This method is tentatively called End-Effect Estimate Filter (EEE-Filter).
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AR-1 (first-order autoregressive) model This is equivalent to Manu’s process oriented model Data are seasonally sampled (one for year) and lag is one year.
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EEE-Filter for 1 st Atmos & Ocean modes Phase reversal probability: NPI: 100% PDO: 100% Consistent with Bromirski, Miller, et al. (2011)
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SLP Epoch difference Pattern of SLP diff. of the recent change is similar to that of the 70s shift. color: SLP diff., contour: confidence limit (95% solid, 90% dashed)
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EEE-Filter, end yr 2008-2011 50%, 5 & 95%, 5-yr running The phase reversal was detected in 2009.
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EEE-Filter, end yr 1990-1993 5-year running average detected phase reversal for 1998/99 minor shift at the end year 1991-1993, but EEE-Filter shows no significant phase reversal. 50%, 5 & 95%, 5-yr running
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A decadal prediction speculation In 1999 it was suggested that the next phase- reversal of bidecadal variability may occur from 2000 to 2007. Roughly consistent! (Minobe 1999 GRL)
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EEE-Bidecadal Filter Hypothesis of Yasuda (2005, 2009) for Tidal mixing influence on climate. Bidecadal-filter (10 & 30-yr half power point) 50%, 5 & 95%, Tide+lag4 yr
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Chhak et al. (2009) NPGO (Annual mean) EEE-Filter for 2 nd Ocean & Atmos modes SLP
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Conclusions End-Effect Estimate Filter (EEE-Filter) is proposed. EEE-Filter detects decadal phase reversal of Aleutian Low/PDO around 2006/07 in 2009, –consistent with a decade-ago speculation by Minobe (1999 GRL). NPGO may be going to change its phase soon. Any suggestions for improvements are welcomed!
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