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Data denial experiments for extratropical transition forecasts

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Presentation on theme: "Data denial experiments for extratropical transition forecasts"— Presentation transcript:

1 Data denial experiments for extratropical transition forecasts
Doris Anwender, Carla Cardinali, Sarah Jones contribute to both the investigation areas Rossby wave triggering and propagation and ensembles and adaptivity Acknowledgements: Roberto Buizza, Carsten Maas, ECMWF

2 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 ET events can excite Rossby wave trains by their interaction with the midlatitudes ET can reduce predictability reduction of predictability spreads downstream data denial experiments  which processes are sensitive to modified initial conditions what would be the best observing strategy and how can the impact spread downstream

3 Schematic of 4D-Var data assimilation
Experiments with IFS (ECMWF) Background Analysis Observation Truth time -12 12 24 analysis at specifiy time t=0 is calculated from background from t=-12h and observations observations are taken, go through quality contol, are assimilated within time inverval of 6 hours my experiments consist of denying observations in certain regions denial should yield an upper bound of influence that adding observations can have under the assumption that the effect of denying data is symmetric to the effect to adding those data investigate which regions yield highest impact 12 h 12 h 12 h 12 h assimilation window

4 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: Europe ET events Data denial cases ET time Cristobal 18 UTC Fabian 14 UTC Irene UTC Maria 16 UTC Helene 9 UTC Chantal 12 UTC Gabrielle UTC Noel 11 UTC Verification region: large

5 Measure of degradation
500 hPa geopotential: (RMSEA-FCtr - RMSEA-Fden) SVout / Etout / TSVout Ex. forecast 1 Ex. forecast 2 measure of degradation: rmse control minus rmse denial ctr forecast started from analysis with the observations denial forecast started from analysis without the respective observations normalized by rmse ctr for each denial case we get rmses for 5 days forecast time often below zero  degradation but sometimes above zero  improvement day day 5

6 Cumulative impact Time dependent average impact of denial in 8 storms
500 hPa Geopotential Impact over large domain Impact over Europe 8 6 4 2 -2 -4 -6 -8 ETout 8 6 4 2 -2 -4 -6 -8 ETout SVout SVout forecast time (hours)

7 Magnitude of neg. impact on large area
ETout : Highest degradation for each forecast 40 80 120 160 200 av: -35 Magnitude of neg. impact on large area impact highest negative impact SVout highest negative impact ETout SVout: Highest degradation for each forecast Cristobal Fabian Irene Maria Helene Chantal 40 80 120 160 200 av: -27 impact positive impacts less strong than negative ETout much higher impacts than SVout; especially strong TCs like Fabian and Helene Fabian Cristobal Maria Helene Chantal Gabrielle Irene Noel 7

8 Magnitude of pos. impact on large area
ETout : Highest improvement for each forecast 200 160 120 80 40 av: 26.8 Magnitude of pos. impact on large area impact highest positive impact ETout highest positive impact SVout SVout: Highest improvement for each forecast Cristobal Fabian Irene Maria Helene Chantal 200 160 120 80 40 av: 28.6 impact positive impacts less strong than negative ETout much higher impacts than SVout; especially strong TCs like Fabian and Helene Cristobal Fabian Maria Helene Chantal Gabrielle Irene Noel 8

9 Magnitude of neg. impact on Europe
ETout : Highest impact for each forecast -100 -200 -300 -400 av: -59 Magnitude of neg. impact on Europe impact Cristobal Fabian Irene Maria Helene Chantal SVout: Highest impact for each forecast -100 -200 -300 -400 av: -49 impact positive impacts less strong than negative ETout much higher impacts than SVout; especially strong TCs like Fabian and Helene Fabian Cristobal Maria Helene Chantal Gabrielle Irene Noel

10 Denial regions for Helene
Helene: 21 September UTC ETout SVout TSVout in situ measurements, temps and buoys we see first problem: very different amount and quality in regions where data are denied, especially between targSVout and the other two however: keep in mind that ETout region for this denial case is much smaller than the others and very few in situ data inside 10

11 Distribution of denial regions
ECMWF Analysis 00Z21SEP2006 ECMWF Analysis 12Z21SEP2006 ECMWF Analysis 00Z22SEP2006 ECMWF Analysis 12Z22SEP2006 Degradation over Europe: bevore interaction with midlats deterioration of fcst due to data in ETout (not on UTC) This is true also for large verification area Europe: When TC embedded in midlat flow improvement due to data in ETout For large area: partly deterioration partly improvement

12 Distribution of denial regions
ECMWF Analysis 00Z23SEP2006 ECMWF Analysis 12Z23SEP2006 ECMWF Analysis 00Z24SEP2006 ECMWF Analysis 12Z24SEP2006

13 How does denial in targeted SV regions affect the forecast?
Strongest impact of 500 hPa geopotential over Europe 300 200 100 -100 -200 -300 -400 From 2312 not downstream impact but impact of ET system itself Only for 2200 and 2212: midlatitudes play dominant role for downstream propagation of errors / ET system plays no role In all the other cases: ET system plays a dominant role TSVout ETout SVout Initialization dates 13

14 Ini. time 21.09.08 00 UTC Verification 23.09.08 00 UTC
Impact due to ET Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout AnCtr - AnETout AnCtr - AnTCSVout

15 Ini. time 21.09.08 00 UTC Verification 24.09.08 00 UTC
Impact due to ET Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

16 Ini. time 21.09.08 00 UTC Verification 25.09.08 00 UTC
Impact due to ET Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

17 Ini. time 21.09.08 00 UTC Verification 26.09.08 00 UTC
Impact due to ET Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

18 Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout AnCtr - AnETout AnCtr - AnTCSVout

19 Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

20 Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

21 Impact due to midlatitude flow
Difference between control and denial forecast of 500 hPa geopotential over Europe Ini. time UTC Verification UTC Control - ETout Control - TCSVout

22 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

23 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

24 Strongest impact of 500 hPa geopotential over Europe
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 300 200 100 -100 -200 -300 -400

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