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

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

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

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 09.08.2002 00 UTC Fabian 14 08.09.2003 18 UTC Irene 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 11.09.2007 12 UTC Noel 11 03.11.2007 00 UTC Verification region: large

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 1 2 3 4 5 day 1 2 3 4 5 day 5

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 12 24 36 48 60 72 84 96 108 120 12 24 36 48 60 72 84 96 108 120 forecast time (hours)

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

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

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

Denial regions for Helene Helene: 21 September 2006 00 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

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 21. 00 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

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

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 2100 2112 2200 2212 2300 2312 2400 2412 TSVout ETout SVout Initialization dates 13

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 21.09.08 00 UTC Verification 23.09.08 00 UTC Control - ETout Control - TCSVout AnCtr - AnETout AnCtr - AnTCSVout

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 21.09.08 00 UTC Verification 24.09.08 00 UTC Control - ETout Control - TCSVout

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 21.09.08 00 UTC Verification 25.09.08 00 UTC Control - ETout Control - TCSVout

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 21.09.08 00 UTC Verification 26.09.08 00 UTC Control - ETout Control - TCSVout

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

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

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

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

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

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

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 2100 2112 2200 2212 2300 2312 2400 2412 300 200 100 -100 -200 -300 -400