detecting decadal climate phase reversal in near past: implications of recent north pacific climate...
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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 precipitationmaxima.
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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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1998/99shift? “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
'dy
y n sdt
er oi
( 1) ( )y n y nr noise
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 1st 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 2008-201150%, 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 2nd 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!