WMO workshop on Impact Studies 9-12 March 2004
(Some) surface data impact studies at ECMWF
Jean-Noël Thépaut, Graeme KellyECMWF
WMO workshop on Impact Studies 9-12 March 2004
Outline
• Background and rationale• Experimental framework• “Low resolution” OSEs• “High resolution” OSES• Concluding remarks
WMO workshop on Impact Studies 9-12 March 2004
Background and Rationale
• Request from EUMETSAT to ECMWF• MSG and METOP follow-up: scope of measuring surface
pressure from space?
• Goal: Assess through Observing System Experiments (OSE) the relative merits of the current surface pressure Observing System versus the current surface wind Observing System.
• Further interest expressed internally (and by EUCOS) on the impact of the surface network in a heavily space-based constrained NWP system
WMO workshop on Impact Studies 9-12 March 2004
Experimental framework (4D-Var)
WMO workshop on Impact Studies 9-12 March 2004
Elements of 4D-Var (CY25R1)• Temporal window: 12 hour
• Observations binned in hourly slots
• Trajectory run: TL511 (40 km) L60
• Minimization run: TL159 (120 km) L60
• Two minimizations:– 1st minimization: – 30 iterations– 2nd minimization: – 25 iterations (improved physics)
WMO workshop on Impact Studies 9-12 March 2004
Observations used at ECMWF (CY25R1)
• Conventional:• Synop surface pressure• Ship surface pressure and wind• Buoy surface pressure and wind• PAOB surface pressure• Radiosonde temperature wind and humidity• Pilot wind• Aircraft temperature and wind• American and European profiler winds
• Satellite:• AMSU-A radiances from NOAA-15/16• HIRS-12 radiances from NOAA-14• SSM/I wind speed and TCWV from DMSP-13/14• Seawinds wind vectors from Quikscat• Atmospheric Motion Vectors from GOES/Meteosat/GMS• CSR WV radiances from Meteosat 7• Ozone total column and profiles from GOME/ERS and
SBUV/NOAA16
WMO workshop on Impact Studies 9-12 March 2004
Observational errors used at ECMWF (CY25R1)
• Synop surface pressure: 0.7 hPa• Ship surface pressure: 1.2 hPa• Buoy surface pressure: 0.8 hPa• PAOB surface pressure: 3.0 hPa
• Ship winds: 2.0 m/s• Buoy winds: 1.8 m/s• Scatterometer winds: 2.0 m/s• SSM/I winds: 2.4 m/s
NB: background errors are:Surface wind: ~ 0.9 m/sSurface pressure:~ 0.8 hPa
WMO workshop on Impact Studies 9-12 March 2004
“Low resolution” OSES
• Data assimilation system:– Light version of the CY25R1 operational system
• 4D-VAR over 6 hour• Resolution T319/T63• Current operational cycle at that time (data usage, QC,
physics)• More or less consistent with Bouttier and Kelly (1999)
• Period under investigation– 20020201-20020317 (~6-7 weeks) : winter– 20010615-20010801 (~7 weeks) : summer
• Denial type experiments
WMO workshop on Impact Studies 9-12 March 2004
“Low resolution” OSEs
• The questions the OSEs have been designed to provide guidance to are:1. Merits today of the current surface pressure
Observing System versus the current surface wind Observing System
2. What is the impact of a modification in accuracy of the surface pressure Observing System?
3. Are surface pressure over land+surface winds over sea able to control the surface pressure field?
4. What is the impact of reducing the current surface pressure Observing System over sea?
WMO workshop on Impact Studies 9-12 March 2004
“Low resolution” OSEs (ctd)
• WINTER OSEs:1. CTL: control (all observations in)2. NOSURF: no surface data3. NOSURFWIND: no surface wind observations (Quikscat,
buoys, Ships, SSMI)4. NOSURFWIND2hPa: no surface wind observations and
all observational errors for surface pressure observations set to 2 hPa
5. NOSP: no surface pressure data6. NOSPSEA: no surface pressure data over sea7. NOSPBUOYSEA: no buoy surface pressure data (only
Ship surface pressure data left)
WMO workshop on Impact Studies 9-12 March 2004
“Low resolution” OSEs (ctd)
• SUMMER OSEs (PAOBS systematically removed):
1. CTL: control (all observations in)2. NOSURFWIND: no surface wind observations (Quikscat,
buoys, Ships, SSMI)3. NOSPSEA: no surface pressure data over sea4. NOSPBUOYSEA: no buoy surface pressure data (only
Ship surface pressure data left)
WMO workshop on Impact Studies 9-12 March 2004
Numerical Results: WINTER
WMO workshop on Impact Studies 9-12 March 2004
Winter Mean Z1000 hPa analysis field
(20020204-20020317)
WMO workshop on Impact Studies 9-12 March 2004
CTL / NOSURF / NOSPLarge biases in case of no surface pressure observations
Small compensation by surface wind observations
Surface winds alone have a detrimental impact in SH (not shown)
WMO workshop on Impact Studies 9-12 March 2004
NOSURF versus CTLLarge RMS forecast errors (including large biases) in case of nosurface Observing System.
WMO workshop on Impact Studies 9-12 March 2004
CTL versus NOSPSEA ?Significant degradation of the scores when surface pressure observations over sea are removed
Sea Surface winds + Land Surface Pressure are not sufficient
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSPSEA ?
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSPSEA ?
surface pressure observations (ships, buoys, paobs) have a (marginally) larger impact than surface winds (ships, buoys, SSM/I and QuikScat) in the Northern Hemisphere (large scatter)
Similar importance in Southern Hemisphere (1000 hPa)
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSPSEA?
NH
SH
Fc+48 Fc+96
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSPSEA?
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSURFWIND2hPa
• Proxy to a degraded surface pressure Observing System in Northern Hemisphere, and improved in the Southern Hemisphere
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSURFWIND2hPa
NH
SH
Fc+48 Fc+96
WMO workshop on Impact Studies 9-12 March 2004
NOSURFWIND versus NOSURFWIND2hPa
• Conclusions:
• Northern Hemisphere: Specification of 2 hPa observation errors for Surface Pressure Data has a negative impact (degradation of the Observing system)
• Overall, impact of surface pressure observations smaller than in Bouttier and Kelly (2002)
– Sign of an improved and better constrained assimilation system?
WMO workshop on Impact Studies 9-12 March 2004
CTL versus NOSPBUOYSEA?
NH
SH
Fc+48 Fc+96
WMO workshop on Impact Studies 9-12 March 2004
CTL versus NOSPBUOYSEA?
Europe
N. America
Fc+48 Fc+96
WMO workshop on Impact Studies 9-12 March 2004
CTL versus NOSPBUOYSEA?
Northern Hemisphere: Slight degradation of the scores when surface pressure buoys are removed
Southern Hemisphere: neutral impact (PAOB+SHIP sp + surface winds able to compensate?)
WMO workshop on Impact Studies 9-12 March 2004
NOSPSEA versus NOSPBUOYSEA?
Surface pressure Ships (+ surface winds) manage to recover a substantial part of the quality of the CTL
WMO workshop on Impact Studies 9-12 March 2004
Concluding remarks (1)
• With the precautions required due to the limits of the OSEs, the main findings of the WINTER OSEs (44 cases) are:
• Surface data are an essential element of the current Observing System
• Surface pressure observations are absolutely essential to anchor the surface pressure field
• Surface winds assimilated in isolation can have a detrimental impact
WMO workshop on Impact Studies 9-12 March 2004
Concluding remarks (2)
• More specifically, the WINTER OSEs provide some guidance to the original questions:
1. In isolation, surface wind Observing System (1/3 buoys, Ships, QuikScat and SSM/I) have a similar impact as surface pressure Observing System (buoys, Ships, PAOBs) in the Southern Hemisphere
2. Larger impact of surface pressure Observing System in the Northern Hemisphere
3. A degradation of the accuracy of the current surface pressure observing system has a clear detrimental impact
WMO workshop on Impact Studies 9-12 March 2004
Concluding remarks (3)
4. In presence of surface winds, a limited number of (accurate) surface pressure observations – Ships -manage to recover most of the forecast error
SUMMER OSES (48 cases):1. In boring anticyclonic regimes, the scatter of the impact
from surface pressure observations is very large2. Impact for the forecaster questionable?3. If at all, positive impact of surface pressure observation
from buoys (but it is hard to be conclusive)!
WMO workshop on Impact Studies 9-12 March 2004
“High resolution” OSES
• Data assimilation system:– CY25R4 operational system
• 4D-VAR over 12 hour• Resolution T511/T159
– Consistent with Kelly et al. (2004)
• Period under investigation– Winter 2002-2003 (2 months)– Summer 2002 (2 months)
• Reduced set of denial type experiments– NOSHIPBUOY (both seasons)– NOSHIP (summer)– NOBUOY (summer)
WMO workshop on Impact Studies 9-12 March 2004
ECMWF system (25R4)
• 3xAMSUA (NOAA 15/16/17) - radiances• 3 SSMI (F-13/14/15) - radiances• 2xHIRS (NOAA-16/17) - radiances• Radiances from 2xGEOS (Met-7 GOES-10)• Winds from 3xGEOS (Met-7/5 GOES-10) and
MODIS/TERRA • SeaWinds on QuiKSCAT• ERS-2 Altimeter / SAR• SBUV (NOAA-16)
Do surface observations still matter?
WMO workshop on Impact Studies 9-12 March 2004
The answer is yes!NH
SH
Europe
N.Am
WMO workshop on Impact Studies 9-12 March 2004
Winter
Summer
Larger impact in Winter than in Summer
WMO workshop on Impact Studies 9-12 March 2004
NH
EUROPE
SH
60 summer cases
- positive impact of both buoys and ships
WMO workshop on Impact Studies 9-12 March 2004
Northern Hemisphere: Forecast error day 1/2/3
WMO workshop on Impact Studies 9-12 March 2004
Southern Hemisphere: Forecast error day 1/2/3
WMO workshop on Impact Studies 9-12 March 2004
Europe: Forecast error day 1/2/3
WMO workshop on Impact Studies 9-12 March 2004
Case study: 20020809 12Z
NOSHIPBUOY
3day forecast
CONTRL
3day forecast
NOSHIPBUOY 3day
forecast diff.
Verifying
Analysis
(ops)
WMO workshop on Impact Studies 9-12 March 2004
Where does it come from?
buoys
Ships
NOSHIPBUOY – CONTRL MSL diff
WMO workshop on Impact Studies 9-12 March 2004
Time evolution of the MSL difference
WMO workshop on Impact Studies 9-12 March 2004
NOBUOY - CONTRL
NH SH
EUROPE
WMO workshop on Impact Studies 9-12 March 2004
NH SH
EUROPE
NOSHIP - CONTRL
WMO workshop on Impact Studies 9-12 March 2004
Conclusions from “high resolution” OSEs
• The Sea surface observation network is important despite the growing impact of satellite observations– Results are statistically significant (not shown)– Larger impact in the Northern Hemisphere (specially in
winter)
• Buoys and Ships seem to be equally important– Perhaps a slight advantage to the Ships
• Buoys and Ships can have a crucial impact synoptically• Complementarity of the Space and Terrestrial network
for global NWP
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