Data denial experiments
for extratropical transition
forecasts
Doris Anwender, Carla Cardinali, Sarah Jones
Acknowledgements: Roberto Buizza, Carsten Maas, ECMWF
Forschungszentrum Karlsruhe
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ET impacts predictability
500 hPa geopot. (556 gpdam) fcst 10 Sep. 12 UTC - 12 Sep. 12 UTC
Typhoon
Maemi 2003
500 hPa geopot. (556 gpdam) fcst 10 Sep. 12 UTC - 13 Sep. 12 UTC
500 hPa geopot. (556 gpdam) fcst 10 Sep. 12 UTC - 14 Sep. 12 UTC
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Schematic of 4D-Var data assimilation
Experiments with IFS (ECMWF)
Analysis
Observation
Truth
0
-12
12 h
12 h
12
12 h
24
time
12 h
assimilation window
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Data denial experiments
In regions around the TC
(orange box) : ETout
In sensitiv regions (extratropical
singular vector 1): SVout
In sensitiv regions on TC
(singular vector 1 targeted on
TC): TSVout
Verification region:
large
Verification region:
Europe
ET events
Data denial
cases
ET time
Cristobal
18
09.08.2002 00 UTC
Fabian
14
08.09.2003 18 UTC
Irene
18
18.08.2005 18 UTC
Maria
16
10.09.2005 12 UTC
Helene
9
24.09.2006 18 UTC
Chantal
12
01.08.2007 06 UTC
Gabrielle
16
11.09.2007 12 UTC
Noel
11
03.11.2007 00 UTC
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Measure of degradation
500 hPa geopotential:
(RMSEA-FCtr - RMSEA-Fden)
SVout / Etout / TSVout
Ex. forecast 1
Ex. forecast 2
m2 / s 2
m2 / s 2
1
2
3
4
5
day
1
2
3
4
5
day
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Cumulative impact
Time dependent average impact of denial in 8 storms
500 hPa Geopotential
m2 / s 2
8
6
Impact over large domain
m2 / s 2
ETout
SVout
4
2
2
0
0
-2
-2
-4
-4
-6
-6
-8
-8
24
ETout
SVout
6
4
12
Impact over Europe
8
36
48
60
72
84
96 108 120
12
24
36
48
60
72
84
96 108 120
forecast time (hours)
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ETout : Highest degradation for each forecast
m2 / s 2
0
av: -35
Magnitude of neg.
impact on large area
80
120
160
highest negative
impact SVout
SVout: Highest degradation for each forecast
200
m2 / s 2
0
av: -27
40
impact
impact
40
80
120
highest
negative
160
impact ETout
200
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ETout : Highest improvement for each forecast
2
200
2
av: 26.8
m /s
Magnitude of pos.
impact
highest
positive on large area
120
80
impact SVout
40
0
SVout: Highest improvement for each forecast
2
m /s
200
2
av: 28.6
160
impact
impact
160
120
80
40
highest positive
impact ETout
0
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ETout : Highest impact for each forecast
2
m /s
2
0
av: -59
Magnitude of neg.
impact on Europe
-200
-300
SVout: Highest impact for each forecast
-400
2
m /s
2
0
av: -49
-100
impact
impact
-100
-200
-300
-400
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Denial regions for Helene
Helene: 21 September 2006 00 UTC
ETout
SVout
TSVout
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Distribution of denial regions
ECMWF Analysis 00Z21SEP2006
ECMWF Analysis 12Z21SEP2006
ECMWF Analysis 00Z22SEP2006
ECMWF Analysis 12Z22SEP2006
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Distribution of denial regions
ECMWF Analysis 00Z23SEP2006
ECMWF Analysis 12Z23SEP2006
ECMWF Analysis 00Z24SEP2006
ECMWF Analysis 12Z24SEP2006
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How does denial in targeted SV
regions affect the forecast?
Strongest impact of 500 hPa geopotential over Europe
300
200
100
m2 / s 2 0
-100
-200
-300
-400
2100
2112
2200 2212 2300 2312 2400 2412
Initialization dates
TSVout
ETout
SVout
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Impact due to ET
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 21.09.08 00 UTC Verification 23.09.08 00 UTC
Control - ETout
Control - TCSVout
AnCtr - AnETout
AnCtr - AnTCSVout
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Impact due to ET
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 21.09.08 00 UTC Verification 24.09.08 00 UTC
Control - ETout
Control - TCSVout
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Impact due to ET
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 21.09.08 00 UTC Verification 25.09.08 00 UTC
Control - ETout
Control - TCSVout
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Impact due to ET
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 21.09.08 00 UTC Verification 26.09.08 00 UTC
Control - ETout
Control - TCSVout
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Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 22.09.08 00 UTC Verification 24.09.08 00 UTC
Control - ETout
Control - TCSVout
AnCtr - AnETout
AnCtr - AnTCSVout
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Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 22.09.08 00 UTC Verification 25.09.08 00 UTC
Control - ETout
Control - TCSVout
Forschungszentrum Karlsruhe
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Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 22.09.08 00 UTC Verification 26.09.08 00 UTC
Control - ETout
Control - TCSVout
Forschungszentrum Karlsruhe
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Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe
Ini. time 22.09.08 00 UTC Verification 27.09.08 00 UTC
Control - ETout
Control - TCSVout
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Results for 8 denial cases:
• Cumulative impact shows both for the large domain and Europe:
 higher degradation for SVout up to 3 days
 higher degradation for ETout after 3 days
but impact is small
• Strongest degradations both for the large domain and for
Europe are distinctly stronger for ETout than for SVout
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Results for Helene:
• Degradation for TCSVout is much stronger than both for ETout and SVout for
almost every denial case
• Denial in ETout region important for degradation for very early forecast time
and for times when TC was embedded in midlatitude flow
• Strong variability is seen in the impact of the denial from case to case
• For some cases inner structure of ET played important role for downstream
propagation of errors, for others it played no role
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Outlook:
Which other ingredients of an ET may play also an important role?
Inner structure
Upstream trough
Outflow
Subtropical high pressure
system
Strongest impact of 500 hPa geopotential over Europe
300
200
2
100
m / s02
-100
-200
-300
-400
2100
2112
2200 2212 2300 2312 2400 2412
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