Rossby wave breaking (RWB)• Definition • Detection / Measurement • Climatology• Dynamics

– Impact on internal variability (NAO / NAM) – Impact on surface turbulent heat flux (PDO)

Definition

350 K Potential Vorticity, 1-8 July 1998

- Wave amplitude reaches critical level - Irreversible overturning of isentropic potential vorticity

PVUData: NCEP / NCAR Reanalysis

PVU

Anticyclonic RWB Cyclonic RWB

Detection / measurement

Centroid of low-P lobe

Climatology: DJF 1958-2006

Antic

Cycl

contours are relative frequency shading is zonal extent

Climatology 1958-2008

Relative frequency:

Rossby wave breaking (RWB)• Definition • Detection / measurement • Climatology• Dynamics

– Impact on internal variability (NAO / NAM) – Impact on surface turbulent heat flux (PDO)

Dynamics• Impact on internal variability (NAO / NAM)

– Forces the background flow via, primarily, eddy momentum flux convergence

– Generates surface pressure anomalies

• Impact on surface turbulent heat flux (PDO) – Generates coherent, 3D circulations associated

with temperature and moisture anomalies

Forcing of background flow

€

∂u

∂t=∇ ⋅

r E + ...

r E ≡ (v '2 −u'2 ,−u'v')

• Look at composite divergence of E fields around hundreds of RWB centroids

Hoskins et al. (1983)

€

∇⋅ r

E

SLP

Regions where RWB forces NAO

Pos.

Neg.

Dynamics• Impact on internal variability (NAO / NAM)

– Forces the background flow via, primarily, eddy momentum flux convergence

– Generates surface pressure anomalies

• Impact on surface turbulent heat flux (PDO) – Generates coherent, 3D circulations associated

with temperature and moisture anomalies

Pacific Decadal Oscillation

Leading pattern of extratropical Pacific sea surface temperature variability

Data: NOAA ESRL SST V2

“warm”

“cool”

Pacific Decadal Oscillation

Alexander et al. (2002) Journal of Climate

Anticyclonic and cyclonic RWB

DD

Negative indicatesinto the ocean

Anticyclonic RWB Composite of 200 randomly

Selected winter cases

UU

Negative indicatesinto the ocean

Cyclonic RWB Composite of 200 randomly

selected winter cases

RWB Variability (EOFs)

Relative frequency:

All four patterns are significantly correlated with the

current and future PDO (e.g., January)

Effect of Cyclonic Dec-Jan RWB

Effect of Cyclonic Dec-Jan RWB

200 randomly selected cases

Effect of Cyclonic Dec-Jan RWB

200 randomly selected cases

Effect of Anticyclonic Jul-Aug RWB

200 randomly selected cases

RWB Variability (EOFs)

Relative frequency:

All four patterns are significantly correlated with the

current and future PDO (e.g., January)

Statistical Model of PDO using RWB WWSSJan CACAPDO 4321

•Cross validation•Stepwise bootstrapping•Model any month

Rossby wave breaking (RWB)• Definition • Detection / Measurement • Climatology• Dynamics

– Impact on internal variability (NAO / NAM) – Impact on surface turbulent heat flux (PDO)

Rossby wave breaking

PVU

350 K, July 1998, NCEP / NCAR Reanalysis data

- Wave amplitude reaches critical level - Irreversible overturning of isentropic potential vorticity

PVU

Cyclonic Rossby wave breaking

PVU

Potential vorticity on the 350-K surface, January 2003

PVU