Variability of Mass Transport into Polar Stratosphere and Winter

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Transcript Variability of Mass Transport into Polar Stratosphere and Winter

Variability of Mass Transport into Polar
Stratosphere and Winter Cold Air
Outbreaks in Mid-latitudes
Ming Cai
Department 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
1
A hybrid forecasting strategy for intraseasonal
cold season climate predictions (14 - 60? days)
• 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 tools
Status: waiting for availability of DAILY forecasts or
reforecasts with lead time > 2 weeks and new funding2
Mean meridional mass circulation in winter
hemisphere (Cai and Shin 2014)
3
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.
• 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.
4
Mass circulation variability and cold air outbreaks
in the mid-latitudes
Weaker Meridional Mass
Circulation near surface 90N
Cold
air
Warm
air
Stronger Meridional Mass 90N
Circulation near surface
Warm
air
60N
60N
Cold
air
25N
25N
Less cold air outbreaks in
mid-latitudes
Coldness in high latitudes
More cold air outbreaks in
mid-latitudes
Warmness in high latitudes
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Indices of mass circulation crossing the polar circle
WB60N(t) =
Q max
å
Fm (l , f = 60 N, Q n , t)
l
Q n =Q n* (t )
CB60N(t) =
Q n*-1 (t )
å
- Fm (l , f = 60 N, Q n , t)
l
Q n =Q min(t )
• 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.
The results with n = 0 are representative
WB60N is representative mass circulation crossing 60N
6
Indices of coldness and warmness
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).
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).
The constant of
H ((SATA - SATA
) - 0.5LSD)dA
0.3085 corresponds
ò
A
WH (t) =
- 0.3085
to the fractional
dA
òA
area of a given
120-day
domain
occupied
H
(-(SATA
SATA
)
0.5LSD)
dA
ò
SATA
CH (t) = A
- 0.3085 by
The results with
exceeding/below
òA dA n = 0 are representative
7
0.5LSD.
120-day
Data and Analysis Procedures
• 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.
8
Lead/Lag Correlations between WB60N and
warmness/coldness Indices
High
latitudes
Coldness
Warmness
Amp.
Midlatitudes
Mass
circulation
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Shift of PDFs of temperature indices with WB60N
Coldness
Chigh
Cmid-lat
Warmness
Weaker
Warmness
Stronger
Weaker
Stronger
Wmid-lat
Stronger
Weaker
Stronger
Whigh
Coldness
Weaker
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Maps of Probability of T > 0.5LSD or T < -0.5LSD
T > 0.5LSD
T < -0.5LSD
Weak
Circulation
T > 0.5LSD
T < -0.5LSD
Strong
Circulation
11
Composite Mean Surface Temperature Anomalies
Neutral-
Neutral+
Weak
Circulation
Strong
Circulation
Weaker
Circulation
Stronger
Circulation
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EOF modes of Surface Temperature Anomalies
EOF1
13.1%
EOF2
11.3%
EOF3
8.4%
EOF4
7.6%
EOF5
5.4%
EOF6
4.8%
Sum=50.3%
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Contribution to the mean composite pattern
Neutral-
Neutral+
Weak
Circulation
Strong
Circulation
Weaker
Circulation
Stronger
Circulation
14
Composite Means of Time Series of EOFs
Amp.
Mass
circulation
15
Contribution to Variance of EOFs
EOF1
EOF2
_______
Climatology
EOF3
EOF5
EOF4
EOF6
_______
Strong
Circulation
Amp.
________
Weak
Mass
Circulation
circulation
16
Survey of mass circulation crossing 60N in winter of 2013-14
Stratosphere
Warm Branch
12/9/13
1/18/14
1/1/14
Cold Branch
1SD
climatology
-1SD
17
Composite Means of Tsurf day 1-7 after
Mean Ts 12/10-12/16
Mean Ts 1/19-1/25
Mean Ts 1/2-1/7
Mean of the three Amp.
cases
Mass
circulation
18
Summary
• 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). 19