Large-Scale Regime Transition and Its Large-Scale Regime Transition and Its Relationship to Significant Cool Season Relationship to Significant Cool Season

Precipitation Events in the NortheastPrecipitation Events in the Northeast

Heather ArchambaultHeather Archambault

Advisors: Lance Bosart and Daniel KeyserAdvisors: Lance Bosart and Daniel Keyser

NWS Focal Point: Rich GrummNWS Focal Point: Rich Grumm

Department of Earth and Atmospheric Sciences, Department of Earth and Atmospheric Sciences,

University at Albany, State University of New YorkUniversity at Albany, State University of New York

  

Research MotivationResearch Motivation

• Meteorological wisdom: increased threat of major storm Meteorological wisdom: increased threat of major storm during large-scale regime changeduring large-scale regime change

• Past research points to a possible connection between Past research points to a possible connection between synoptic-scale cyclogenesis and reconfiguration of the synoptic-scale cyclogenesis and reconfiguration of the planetary-scale flowplanetary-scale flow

• Dave Groenert (CSTAR, 2002) documented an apparent Dave Groenert (CSTAR, 2002) documented an apparent tendency for an increased number of precipitation events in tendency for an increased number of precipitation events in the Northeast during phase transitions of the NAOthe Northeast during phase transitions of the NAO

Presentation OverviewPresentation Overview

• Research goalsResearch goals

• Climatology of PNA/NAO tendencyClimatology of PNA/NAO tendency

• Time series of NAO/PNA tendency [d(Time series of NAO/PNA tendency [d(INDEXINDEX)/dt])/dt]– Correlations with NE domain-average daily precipitationCorrelations with NE domain-average daily precipitation– Correlations with 1000 hPa NE Height Anomaly Index (HAI)Correlations with 1000 hPa NE Height Anomaly Index (HAI)

• Major regime change / NE precipitation correlationMajor regime change / NE precipitation correlation

• Major regime change / NE height anomaly correlationMajor regime change / NE height anomaly correlation

• Future workFuture work

Focus of Research:Focus of Research:

• Review literature that documents individual cases of Review literature that documents individual cases of reconfiguration of the planetary-scale flow in association reconfiguration of the planetary-scale flow in association with major precipitation events in the Northeastern United with major precipitation events in the Northeastern United StatesStates  

• Relate previous work to modern definitions of regime Relate previous work to modern definitions of regime changechange

• Determine and quantify an objective definition for a Determine and quantify an objective definition for a significant large-scale regime change significant large-scale regime change

– Phase change of teleconnection index (PNA, NAO) greater than 2 Phase change of teleconnection index (PNA, NAO) greater than 2 standard deviations over a 7-day periodstandard deviations over a 7-day period

Focus (cont):Focus (cont):

• Determine whether more storms/precipitation can be Determine whether more storms/precipitation can be expected during regime changes as compared to expected during regime changes as compared to climatology in the Northeastclimatology in the Northeast

• Construct composite analyses to identify characteristic Construct composite analyses to identify characteristic signatures of significant large-scale regime changessignatures of significant large-scale regime changes

• Use composite analyses and results from case studies to Use composite analyses and results from case studies to determine whether possible regime change/precipitation determine whether possible regime change/precipitation relationships are associative or cause and effectrelationships are associative or cause and effect

Positive PNA – Thickness AnomaliesPositive PNA – Thickness Anomalies

Courtesy: Courtesy: Anantha Aiyyer Anantha Aiyyer & Eyad Atallah& Eyad Atallah

Negative PNA – Thickness AnomaliesNegative PNA – Thickness Anomalies

Courtesy: Courtesy: Anantha Aiyyer Anantha Aiyyer & Eyad Atallah& Eyad Atallah

Positive NAO – Thickness AnomaliesPositive NAO – Thickness Anomalies

Courtesy: Courtesy: Anantha Aiyyer Anantha Aiyyer & Eyad Atallah& Eyad Atallah

Negative NAO – Thickness AnomaliesNegative NAO – Thickness Anomalies

Courtesy: Courtesy: Anantha Aiyyer Anantha Aiyyer & Eyad Atallah& Eyad Atallah

NAO TendenciesNAO Tendencies

Climatology of Teleconnection TendenciesClimatology of Teleconnection Tendencies

PNA Tendencies (1948-2001, 7 Day Interval)PNA Tendencies (1948-2001, 7 Day Interval)

Daily Index Tendency / NE Precipitation Daily Index Tendency / NE Precipitation Time Series CorrelationsTime Series Correlations

• Daily time series of NAO/PNA tendency were createdDaily time series of NAO/PNA tendency were created– Seven-day tendency: Index on Day (t + 3) – Index on Day (t - 3)Seven-day tendency: Index on Day (t + 3) – Index on Day (t - 3)

• Correlated with time series of daily NE precipitationCorrelated with time series of daily NE precipitation– Standardized domain-average precipitation values calculated from Standardized domain-average precipitation values calculated from

the Unified Precipitation Dataset (UPD) from 1954 - 1998the Unified Precipitation Dataset (UPD) from 1954 - 1998

• Seven-day NAO tendency / precipitation correlation:Seven-day NAO tendency / precipitation correlation:– Correlation Coefficient: -0.04, RCorrelation Coefficient: -0.04, R22 value: 0.0 value: 0.0

• Seven-day PNA tendency / precipitation correlation:Seven-day PNA tendency / precipitation correlation:– Correlation Coefficient: 0.04, RCorrelation Coefficient: 0.04, R22 value: 0.0 value: 0.0

• Conclusion: No correlation between daily teleconnection Conclusion: No correlation between daily teleconnection index tendency and Northeast daily precipitation valuesindex tendency and Northeast daily precipitation values

1000 hPa Height Anomaly Index (HAI)1000 hPa Height Anomaly Index (HAI)

• Purpose: correlate with daily NAO/PNA tendency as an Purpose: correlate with daily NAO/PNA tendency as an alternative to daily precipitation valuesalternative to daily precipitation values

• 1000 hPa height anomalies calculated from NCEP/NCAR 1000 hPa height anomalies calculated from NCEP/NCAR Reanalysis (1951 – 2001)Reanalysis (1951 – 2001)

• Height anomalies are normalized according to climatology Height anomalies are normalized according to climatology of the 15-day period centered around each day of the 15-day period centered around each day

• This accounts for the higher mean/smaller standard This accounts for the higher mean/smaller standard deviation in the height field that exists in summer vs. deviation in the height field that exists in summer vs. winterwinter

• 48.2 % of days had HAI < 0 (8,970 of 18,628 days)48.2 % of days had HAI < 0 (8,970 of 18,628 days)

Daily Index Tendency / NE Height Anomaly Daily Index Tendency / NE Height Anomaly Time Series CorrelationsTime Series Correlations

• Time series of daily tendency of the NAO/PNA were Time series of daily tendency of the NAO/PNA were correlated with time series of daily 1000 hPa Northeast correlated with time series of daily 1000 hPa Northeast Height Anomaly Index (HAI)Height Anomaly Index (HAI)

• Seven-day NAO tendency / HAI correlation:Seven-day NAO tendency / HAI correlation:– Correlation Coefficient: -0.06, RCorrelation Coefficient: -0.06, R22 value: 0.00 value: 0.00

• Seven-day PNA tendency / HAI correlation:Seven-day PNA tendency / HAI correlation:– Correlation Coefficient: -0.23, RCorrelation Coefficient: -0.23, R22 value: 0.05 value: 0.05

• Conclusion: No significant correlation between daily index Conclusion: No significant correlation between daily index tendency and daily Northeast 1000 hPa height anomaly tendency and daily Northeast 1000 hPa height anomaly indexindex

Major Regime Change / NE Precipitation Major Regime Change / NE Precipitation CorrelationsCorrelations

• Based on definition of major regime change: created a Based on definition of major regime change: created a subset of days for further correlations with precipitationsubset of days for further correlations with precipitation

• Index change during major regime transition was correlated Index change during major regime transition was correlated with daily precipitation with daily precipitation – Major regime transition: phase change of greater than 2 standard Major regime transition: phase change of greater than 2 standard

deviationsdeviations

• Overall NAO regime change / precipitation correlation: Overall NAO regime change / precipitation correlation: Correlation CoefficientCorrelation Coefficient: -0.07, : -0.07, RR22 value value: 0.01: 0.01

Major NAO Swing / Northeast Precipitation Correlation 1954 - 1998

0.05 0.06

0.020.04

0.050.03

0.050.03

0.01 0.01 0.00

0.15

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Co

rre

lati

on

Co

eff

icie

nt

/ R

-Sq

ua

red

Va

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Correlation CoefficientR-Squared Value

Major PNA Swing / Northeast Precipitation Correlation1954 - 1998

0.11

0.01

0.29

0.18

0.07 0.09

0.030.01 0.00 0.00

0.13

0.03

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECCo

rre

lati

on

Co

eff

icie

nt

/ R

-Sq

ua

red

Va

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Correlation Coefficient

R-Squared Value

• Overall PNA regime change / precipitation correlation: Overall PNA regime change / precipitation correlation: Correlation CoefficientCorrelation Coefficient: 0.11, : 0.11, RR22 value value: 0.01: 0.01

Major Regime Change / Major Regime Change / 1000 hPa NE Height Anomaly Correlations1000 hPa NE Height Anomaly Correlations

• Index tendency for the days where a major regime change Index tendency for the days where a major regime change was ongoing was correlated with daily 1000 hPa height was ongoing was correlated with daily 1000 hPa height anomaliesanomalies

• Overall NAO regime change / HAI correlation: Overall NAO regime change / HAI correlation: Correlation CoefficientCorrelation Coefficient: -0.15, : -0.15, RR22 value value: 0.02: 0.02

Major NAO Swing / Northeast HAI Correlation 1951 - 2001

0.00 0.000.03

0.05

0.130.10

0.06 0.07

0.000.01 0.01 0.00

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Co

rre

lati

on

Co

eff

icie

nt

/ R

-Sq

ua

red

Va

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Correlation Coefficient

R-Squared Value

Major PNA Swing / Northeast HAI Correlation1951 - 2001

0.04 0.05

0.01 0.000.03

0.08

0.19

0.08

0.00 0.00 0.00 0.00

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Co

rrel

atio

n C

oef

fici

ent

/R

-Sq

uar

ed V

alu

e

Correlation Coefficient

R-Squared Value

• Overall PNA regime change / HAI correlation: Overall PNA regime change / HAI correlation: Correlation CoefficientCorrelation Coefficient: 0.0, : 0.0, RR22 value value: 0.0: 0.0

Preliminary ResultsPreliminary Results

• No correlation between daily time series of index tendency No correlation between daily time series of index tendency & NE precipitation / 1000 hPa height anomalies& NE precipitation / 1000 hPa height anomalies

• Major NAO swings / NE precipitation: Major NAO swings / NE precipitation: – Weakening jet (+NAO to Weakening jet (+NAO to –NAO) –NAO) : possible enhanced precipitation : possible enhanced precipitation

in winterin winter– Strengthening jet (Strengthening jet (–NAO to +NAO)–NAO to +NAO): possible enhanced : possible enhanced

precipitation in summerprecipitation in summer

• For major swings in the NAO, a slight negative correlation For major swings in the NAO, a slight negative correlation with 1000 hPa height anomalies can be found in the summer with 1000 hPa height anomalies can be found in the summer months:months:– negative height anomalies are correlated with a strengthening of negative height anomalies are correlated with a strengthening of

the North Atlantic jet (negative to positive NAO)the North Atlantic jet (negative to positive NAO)– approximately 10% of height anomaly variability can be attributed approximately 10% of height anomaly variability can be attributed

to major swings in the NAO during summer monthsto major swings in the NAO during summer months

Preliminary Results (cont.)Preliminary Results (cont.)

• For major swings in the PNA, the largest correlation with For major swings in the PNA, the largest correlation with precipitation can be found in March (Rprecipitation can be found in March (R2 2 = 0.29) and April= 0.29) and April– Ridge building in west/troughing in SE: enhanced precipitationRidge building in west/troughing in SE: enhanced precipitation

• No overall correlation between major swings in the PNA No overall correlation between major swings in the PNA and 1000 hPA height anomaliesand 1000 hPA height anomalies– Slight positive correlation is found in May-JuneSlight positive correlation is found in May-June

• PNA change from positive to negative corresponds with heights PNA change from positive to negative corresponds with heights lowering in western Canada/Pacific NW, ridge amplification lowering in western Canada/Pacific NW, ridge amplification over SE USover SE US

– Slight negative correlation is found in July-AugustSlight negative correlation is found in July-August

• PNA change from negative to positive corresponds with PNA change from negative to positive corresponds with building ridge in western Canada/Pacific NW and lower heights building ridge in western Canada/Pacific NW and lower heights in the southeastern USin the southeastern US

What’s NextWhat’s Next

• Determine whether a “significant” precipitation event is Determine whether a “significant” precipitation event is more likely during a major PNA or NAO swing as more likely during a major PNA or NAO swing as compared to climatologycompared to climatology

– Lag correlations: storm at end, beginning of regime change?Lag correlations: storm at end, beginning of regime change?

• Create correlation maps using top NAO and PNA Create correlation maps using top NAO and PNA transitionstransitions

– Find best correlation between transitions and 1000 hPa height Find best correlation between transitions and 1000 hPa height anomalies/precipitation for the United Statesanomalies/precipitation for the United States