Variability of Mass Transport into Polar Stratosphere and Winter Cold Air

Outbreaks in Mid-latitudes

Variability of Mass Transport into Polar Stratosphere and Winter Cold Air

Outbreaks in Mid-latitudes

Ming CaiDepartment of Earth, Ocean, and Atmospheric Science,

Florida State University

Ming CaiDepartment of Earth, Ocean, and Atmospheric Science,

Florida State University

Acknowledgement: Huug M. van den Dool, Y-Y Yu, R-C Ren

Grant Support: NOAA CPO: NA10OAR4310168

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• Prognostic component: Dynamical prediction for (extratropic) stratospheric anomalies using CFS.

Status: Zhang et al. (2013): Evaluation of CFSv2 Predictions for the Stratospheric Circulation Anomalies (see the poster on Wednesday and Thursday).

• Diagnostic component: Statistical “instantaneous” relations between stratospheric and surface temperature anomalies (downscaling)

Status: This presentation (manuscript under preparation)

• Development of prototype forecast toolsStatus: waiting for availability of DAILY forecasts or

reforecasts with lead time > 2 weeks and new funding

• Prognostic component: Dynamical prediction for (extratropic) stratospheric anomalies using CFS.

Status: Zhang et al. (2013): Evaluation of CFSv2 Predictions for the Stratospheric Circulation Anomalies (see the poster on Wednesday and Thursday).

• Diagnostic component: Statistical “instantaneous” relations between stratospheric and surface temperature anomalies (downscaling)

Status: This presentation (manuscript under preparation)

• Development of prototype forecast toolsStatus: waiting for availability of DAILY forecasts or

reforecasts with lead time > 2 weeks and new funding 22

A hybrid forecasting strategy for intraseasonal cold season climate predictions (14 - 60? days)A hybrid forecasting strategy for intraseasonal cold season climate predictions (14 - 60? days)

Mean meridional mass circulation in winter hemisphere (Cai and Shin 2014)

3333

44

Vertical and meridional couplings by baroclinically amplifying (westward tilting)

waves (Johnson 1989)

Vertical and meridional couplings by baroclinically amplifying (westward tilting)

waves (Johnson 1989)

• A net poleward (adiabatic) transport of warm air mass aloft and a net equatorward (adiabatic) transport of cold air mass transport below.

• A net poleward (adiabatic) transport of warm air mass aloft and a net equatorward (adiabatic) transport of cold air mass transport below.

• Stronger poleward air mass transport in the warm air branch aloft is coupled with stronger air mass transport in the cold air branch near the surface and vice versa.

• Stronger poleward air mass transport in the warm air branch aloft is coupled with stronger air mass transport in the cold air branch near the surface and vice versa.

60N

25N

90NStronger Meridional Mass Circulation near surface

Mass circulation variability and cold air outbreaks in the mid-latitudes

Warmair

Cold air

60N

25N

90NWeaker Meridional Mass Circulation near surface

WarmairCold

air

Less cold air outbreaks in mid-latitudesColdness in high latitudes

More cold air outbreaks in mid-latitudesWarmness in high latitudes 55

6666

Indices of mass circulation crossing the polar circleIndices of mass circulation crossing the polar circle

The results with n = 0 are representative

• WB60N: the total air mass transported into the polar region

• CB60N: the total air mass out of the polar region

WB60N and CB60N are nearly perfectly positively correlated.

WB60N is representative mass circulation crossing 60N

The constant of 0.3085 corresponds to the fractional area of a given domain occupied by SATA exceeding/below 0.5LSD. 7777

Indices of coldness and warmnessIndices of coldness and warmness

The results with n = 0 are representative

CH(t) and CM(t): Percentage of area occupied by negative temperature anomalies below 0.5*standard_deviation (local) in high latitude zone (60 N poleward) and mid-latitudes (between 25 and 60N).

WH(t) and WM(t): Percentage of area occupied by positive temperature anomalies exceeding 0.5*standard_deviation (local) in high latitude zone (60 N poleward) and mid-latitudes (between 25 and 60N).

• ERA Interim Daily fields of T_surf, p_surf, 3D air temperature and winds in winters from 1979-2011 (33 winters): winter = Nov. 1 – Feb. 28 (120 days)

• Anomaly field = departure of the total field from the daily annual cycle.

• 6 WB60N threshold values: (1) WB60N’ < -1.0SD (weaker circulation), (2) WB60N’ < -0.5SD (weak circulation); (3) -0.5SD WB60N’ < 0 (Neutral-); (4) 0<WB60N’< 0.5SD (Neutral+); WB60N’> 0.5SD (strong); and WB60N’> 1.0SD (Stronger)

• Unless specified otherwise, all statistics of T_surf anomalies are obtained in the period of 1-10 days after WB50N reaches one of the threshold values.

• ERA Interim Daily fields of T_surf, p_surf, 3D air temperature and winds in winters from 1979-2011 (33 winters): winter = Nov. 1 – Feb. 28 (120 days)

• Anomaly field = departure of the total field from the daily annual cycle.

• 6 WB60N threshold values: (1) WB60N’ < -1.0SD (weaker circulation), (2) WB60N’ < -0.5SD (weak circulation); (3) -0.5SD WB60N’ < 0 (Neutral-); (4) 0<WB60N’< 0.5SD (Neutral+); WB60N’> 0.5SD (strong); and WB60N’> 1.0SD (Stronger)

• Unless specified otherwise, all statistics of T_surf anomalies are obtained in the period of 1-10 days after WB50N reaches one of the threshold values. 88

Data and Analysis ProceduresData and Analysis Procedures

9999

Lead

/Lag

Cor

rela

tions

bet

wee

n W

B60

N a

nd

war

mne

ss/c

oldn

ess

Indi

ces

Amp.

Masscirculation

High latitudes

Mid-latitudes

Coldness Warmness

1010

Shift of PDFs of temperature indices with WB60N Shift of PDFs of temperature indices with WB60N

Coldness

Warmness

Weaker Stronger Weaker Stronger

Weaker Stronger Weaker Stronger

Whigh Wmid-lat

Coldness

Warmness

Chigh Cmid-lat

Strong Circulation

Weak Circulation

Map

s of

Pro

babi

lity

of

T >

0.5

LS

D o

r T

< -

0.5L

SD

T > 0.5LSD T < -0.5LSD

T < -0.5LSDT > 0.5LSD

1111

Strong Circulation

Neutral-

Com

posi

te M

ean

Sur

face

Tem

pera

ture

Ano

mal

ies

Neutral+

Stronger Circulation

Weak Circulation

Weaker Circulation

1212

EOF113.1%

EO

F m

odes

of

Sur

face

Tem

pera

ture

Ano

mal

ies

EOF38.4%

EOF55.4%

EOF211.3%

EOF47.6%

EOF64.8%

Sum=50.3% 1313

Strong Circulation

Neutral-

Con

trib

utio

n to

the

mea

n co

mpo

site

pat

tern

Neutral+

Stronger Circulation

Weak Circulation

Weaker Circulation

1414

15151515

Com

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te M

eans

of

Tim

e S

erie

s of

EO

Fs

Amp.

Masscirculation

16161616

Con

trib

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Var

ianc

e of

EO

Fs

Amp.

Masscirculation

EOF1

EOF5

EOF2

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EOF3 EOF4_______Strong

Circulation

_______Climatology

________Weak

Circulation

Survey of mass circulation crossing 60N in winter of 2013-14Survey of mass circulation crossing 60N in winter of 2013-14

Stratosphere

Warm Branch

Cold Branch

climatology

1SD

-1SD

12/9/13 1/1/14 1/18/14

1717

18181818

Com

posi

te M

eans

of

Tsu

rf d

ay 1

-7 a

fter

Amp.

Masscirculation

Mean Ts 12/10-12/16 Mean Ts 1/2-1/7

Mean Ts 1/19-1/25 Mean of the three cases

• Variability of mass flux warm air branch is synchronized with that of cold air branch.

• Lack of warm air into polar region is accompanied by weaker equatorward advancement of cold air near the surface. As a result, the cold air mass is largely imprisoned within polar circle, responsible for general warmness in mid-latitudes and below climatology temperature in high latitudes.

• Stronger warm air into polar stratosphere is accompanied by stronger equatorward advancement of cold air near the surface, resulting in massive cold air outbreaks in mid-latitudes and warmth in high latitudes.

• EOF1 and EOF4 of T_surf correspond to warm Arctic and cold over the two major continents after a stronger mass circulation (PDF shift in response to mass circulation).

• Positive phase of EOF2 represents warm Eurasian and cold N. America or vice versa. Amplitude of both positive and negative phases of EOF2 tends to increase after a stronger mass circulation (var. increase in response to mass circulation).

• Variability of mass flux warm air branch is synchronized with that of cold air branch.

• Lack of warm air into polar region is accompanied by weaker equatorward advancement of cold air near the surface. As a result, the cold air mass is largely imprisoned within polar circle, responsible for general warmness in mid-latitudes and below climatology temperature in high latitudes.

• Stronger warm air into polar stratosphere is accompanied by stronger equatorward advancement of cold air near the surface, resulting in massive cold air outbreaks in mid-latitudes and warmth in high latitudes.

• EOF1 and EOF4 of T_surf correspond to warm Arctic and cold over the two major continents after a stronger mass circulation (PDF shift in response to mass circulation).

• Positive phase of EOF2 represents warm Eurasian and cold N. America or vice versa. Amplitude of both positive and negative phases of EOF2 tends to increase after a stronger mass circulation (var. increase in response to mass circulation). 1919

SummarySummary