A Diagnostic Risk A Diagnostic Risk Assessment for Pattern Assessment for Pattern

FlipsFlips

Kevin LiptonKevin Lipton

Gordon StrassbergGordon Strassberg

April 29, 2003April 29, 2003

Overview of DiscussionOverview of Discussion

• Definition of Pattern Flip as used in Definition of Pattern Flip as used in this study.this study.

• Data collection and methodology.Data collection and methodology.

• Formulation of the diagnostic risk Formulation of the diagnostic risk index.index.

• March 2003 results.March 2003 results.

• Conclusions and future research.Conclusions and future research.

What is a “pattern flip?”What is a “pattern flip?”

• In this study, a significant change in In this study, a significant change in the longwave pattern (500 mb the longwave pattern (500 mb Heights) over North America.Heights) over North America.

• Each segment of the flip remained in Each segment of the flip remained in place for more than 2 weeks, in order place for more than 2 weeks, in order to reflect in monthly indices.to reflect in monthly indices.

Example of Pattern FlipExample of Pattern Flip

• Oct 1989 VS Nov 1989: 500 mb Height Oct 1989 VS Nov 1989: 500 mb Height AnomaliesAnomalies

Data Collection and Data Collection and MethodologyMethodology

• Months/Years of pattern flips were Months/Years of pattern flips were determined by memory and then verified determined by memory and then verified with NCEP Reanalysis Data.with NCEP Reanalysis Data.

• Monthly values of several atmospheric Monthly values of several atmospheric indices/teleconnection patterns of known indices/teleconnection patterns of known importance to N. American weather were importance to N. American weather were used.used.

• NAO, PNA, SOI, and EP were the relevant NAO, PNA, SOI, and EP were the relevant indices.indices.

Data Collection and Data Collection and MethodologyMethodology

• NAO, PNA, EP monthly values from NAO, PNA, EP monthly values from the CPC website.the CPC website.

• SOI data obtained from Long SOI data obtained from Long Paddock (Australian Gov’t Service).Paddock (Australian Gov’t Service).

• Data examined for the month Data examined for the month preceding the flip AND the month of preceding the flip AND the month of the flip itself.the flip itself.

Formulation of the Diagnostic Formulation of the Diagnostic IndexIndex

• Most obvious elements to use were Most obvious elements to use were monthly sign changes in certain monthly sign changes in certain indices before/during the pattern flip.indices before/during the pattern flip.

• SOI, NAO, and EP all changed signs in SOI, NAO, and EP all changed signs in 50% or more of the cold season 50% or more of the cold season cases (Nov-Mar).cases (Nov-Mar).

Procedure ErrorProcedure Error

• SOI sign changes were weighted SOI sign changes were weighted most heavily since it appeared to be most heavily since it appeared to be the most frequent change of sign.the most frequent change of sign.

• However, after adding several more However, after adding several more cases, this was no longer accurate.cases, this was no longer accurate.

• Heavy weighting of SOI may be Heavy weighting of SOI may be overdone.overdone.

Formulation of the Diagnostic Formulation of the Diagnostic IndexIndex

• Data review showed significance in Data review showed significance in the sum of the NAO+PNA+EP values the sum of the NAO+PNA+EP values for the month preceding the flip.for the month preceding the flip.

Final Risk Index WeightingFinal Risk Index Weighting

• SOI sign change 35%SOI sign change 35%

• NAO/PNA/EP sum 30%NAO/PNA/EP sum 30%

• Any 2 indices change sign 15%Any 2 indices change sign 15%

• NAO sign change 10%NAO sign change 10%

• EP sign change 10%EP sign change 10%

• If “yes” to above, full weighting applied; if If “yes” to above, full weighting applied; if “no” then 0 weighting applied.“no” then 0 weighting applied.

Cold Season ResultsCold Season Results

Month/Month/YearYear

SOI SOI Sign Sign Change Change 35%35%

NAO/PNA/EP NAO/PNA/EP Sum “-” 30%Sum “-” 30%

2 Ind. 2 Ind. Change Change Sign 15%Sign 15%

NAO Sign NAO Sign Change Change 10%10%

EP Sign EP Sign Change Change 10%10%

Risk Risk %%

Dec 84Dec 84 YY 1.41.4 YY YY YY 7070

Nov 89Nov 89 YY -1.2-1.2 YY YY YY 100100

Jan 90Jan 90 NN -1.9-1.9 YY YY YY 6565

Mar 92Mar 92 NN 0.60.6 NN NN NN 00

Jan 93Jan 93 NN -1.8-1.8 NN NN NN 3030

Jan 96Jan 96 YY -1.1-1.1 YY NN YY 9090

March 2003 ResultsMarch 2003 Results

• Average % Risk: 59%Average % Risk: 59%

• Mar 2003 Risk: 65% (Above Average)Mar 2003 Risk: 65% (Above Average)

MonthMonth/Year/Year

SOI SOI Sign Sign ChangChange 35%e 35%

NAO/NAO/PNA/PNA/EP EP Sum Sum “-” “-” 30%30%

2 Ind. 2 Ind. ChangChange Sign e Sign 15%15%

NAO NAO Sign Sign ChangChange 10%e 10%

EP EP Sign Sign ChangChange 10%e 10%

Risk %Risk %

Mar Mar 0303

NN -2.9-2.9 YY YY YY 6565

More ResultsMore Results

• Several “stable” months (no flip) Several “stable” months (no flip) were tested using the diagnostic were tested using the diagnostic index.index.

• The average risk of a flip for those 4 The average risk of a flip for those 4 months was only 34%.months was only 34%.

ConclusionsConclusions

• Atmospheric Indices can be used to Atmospheric Indices can be used to diagnose the risk of a pattern flip in diagnose the risk of a pattern flip in past months.past months.

• There is a clear difference in this There is a clear difference in this index between months that had a index between months that had a pattern flip and months that did not.pattern flip and months that did not.

Future ResearchFuture Research

• Develop Prognostic Index for assessing the Develop Prognostic Index for assessing the risk of pattern flipsrisk of pattern flips– Decrease the temporal scale and use weekly or Decrease the temporal scale and use weekly or

bi-weekly data and apply a similar risk bi-weekly data and apply a similar risk assessment study.assessment study.

– Include other known indices (SST Anomalies, Include other known indices (SST Anomalies, QBO, MJO, PDO). QBO, MJO, PDO).

– Develop technique for Different Types of Develop technique for Different Types of Pattern Changes/Flips (I.E. Ridge E/Trough Pattern Changes/Flips (I.E. Ridge E/Trough W/vice versa).W/vice versa).

ReferencesReferences

• <ftp://ftpprd.ncep.noaa.gov/pub/cpc/wd52dg/data/indices/<ftp://ftpprd.ncep.noaa.gov/pub/cpc/wd52dg/data/indices/

tele_index.nh>tele_index.nh>

• <http://www.longpaddock.qld.gov.au/<http://www.longpaddock.qld.gov.au/SeasonalClimateOutlook/SouthernOscillationIndex/SeasonalClimateOutlook/SouthernOscillationIndex/

SOIDataFiles/>SOIDataFiles/>