Downscaling of ECMWF seasonal integrations by RegCM
Transcript of Downscaling of ECMWF seasonal integrations by RegCM
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Downscaling of ECMWF seasonalintegrations by RegCM
Čedo Branković and Mirta Patarčić
Croatian Meteorological and Hydrological ServiceGrič 3, 10000 Zagreb, Croatia
(Thanks to Paul Dando and Manuel Fuentes for help in data retrieval)
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Outline of the talk
1. Introduction
2. Downscaling of ECMWF operational seasonal forecasts (an attempt)
3. Downscaling of ECWMF experimental seasonalforecasts (ENSEMBLES)
4. Some conclusions
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Precipitation (mm/day)
JAS (mean 1991-2001)
Observed (mm/day)
Zagreb 2.9Split 1.5
ECMWF (ENSEMBLES)
CRU
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CRU
Precipitation (mm/day)
JFM(mean 1992-2002)
Observed (mm/day)
Zagreb 1.3Split 1.7
ECMWF (ENSEMBLES)
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Orography in global and limited area models
RegCM 50 km
ECMWF 1.875°
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Outline of the talk
1. Introduction
2. Downscaling of ECMWF operational seasonal forecasts (an attempt)
3. Downscaling of ECWMF experimental seasonalforecasts
4. Some conclusions
![Page 7: Downscaling of ECMWF seasonal integrations by RegCM](https://reader030.fdocuments.us/reader030/viewer/2022012915/61c5ec26cdb4b84f677716e5/html5/thumbnails/7.jpg)
* TL95 global spectral model (1.875°)
* 40 members, JJA 2003
* 6 pressure levels (1000, 925, 850, 700, 500, 200)
* Frequency of LBCs every 12 hours
Big ensemble, but poor input for a viable downscaling.
Do we have to downscale the whole ensemble?
RegCM (Giorgi et al. 1993, MWR): 50 km, 14 levels
(only one season tested)
ECMWF operational seasonal forecasts
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How to select a sub-ensemble?
* From short- and medium-range forecasting experience:
Objectively select representative members that characterise all possible evolution scenarios of the global model ensemble.
(Molteni et al. 2001 QJ, Montani et al. 2001 Nonlin. Proc. Geophys.)
* If resources allow, downscale all members and then manipulate
Representative members from a global model may not be representative in a regional model.
(Experiments at CMHS: downscaling of ECMWF EPS by usingAladin-HR; Branković et al. 2007 ECMWF Tech Memo 507)
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Z500June 2003 July 2003
Most populated clusters
ECMWF operational analysis
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Z500 JJA 2003
Ensemble mean(12 members)
ECMWF
RegCM
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T2m JJA 2003ECMWF RegCMEn
semble
mea
nVa
rian
ce
Zagreb 24.0Split 28.4
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Precipitation JJA 2003ECMWF RegCMEn
semble
mea
nVa
rian
ce
Zagreb 1.6Split 0.5
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Outline of the talk
1. Introduction
2. Downscaling of ECMWF operational seasonal forecasts (an attempt)
3. Downscaling of ECWMF experimental seasonalforecasts
4. Some conclusions
![Page 14: Downscaling of ECMWF seasonal integrations by RegCM](https://reader030.fdocuments.us/reader030/viewer/2022012915/61c5ec26cdb4b84f677716e5/html5/thumbnails/14.jpg)
* Part of ENSEMBLES project
* TL95 global spectral model (1.875°), 40 model levels
* Frequency of LBCs every 6 hours
* 6-month f/c (May, November), 9 members, 1991-2001
Much better input for downscaling, but smaller ensembles.
No sub-ensembles!
RegCM: 50 km, 18 levels; JAS and JFM seasons
ECMWF experimental seasonal forecasts
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ACC T850 JFM
-1-0.8-0.6-0.4-0.2
00.20.40.60.8
1
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
year
AC
C
RegCM ECMWF
ACC T850 JAS
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
RegCMECMWF
ACC T850 wrt ERA
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T2m anomaly JFM
-3.0
-2.5-2.0
-1.5-1.0
-0.50.0
0.51.0
1.52.0
2.5
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
ECMWF ensm RegCM ensm CRU ERA40
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T2m anomaly JAS
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
ECMWF ensm RegCM ensm CRU ERA40
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JFM JAS
T2m error (11 years)
RegCM
ECMWF
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RegCM CRU verifPrecipitation (11 years)
JAS
JFM
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Skill scores (accuracy measures)
Contingency tables and quantities (Wilks 1995)
dcN
baY
NY
Fcst
Observed
nd a HR +=
n = a+b+c+d total number of fcst/event pairs
Hit rate [0,1]
b ab FAR+
= False alarm ratio[1,0]
c baaTS++
= Threat score [0,1]
d) (b b) (a d) (c c) (abc) - (ad 2 HSS
+++++=
Heidke score [1 perfect, 0 random f/c, HSS < 0 worse than random f/c]
d) (b c) (abc - ad KSS++
=Kuipers score
cab a B
++=Bias [1 unbiased,
B > 1 overforecasting,B < 1 underforecasting]
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T2m > +20°CJAS
Hit rate (wrt CRU)
nd a HR +=
dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
ECMWF
RegCM
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T2m > +20°CJAS
Hit rate (wrt ERA)
dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
nd a HR +=
ECMWF
RegCM
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T2m > +20°CJAS
False alarm ratio
b ab FAR+
=
dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
ECMWF
RegCM
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T2m anom > +0°C Threat score
ECMWF
RegCM
JAS JFMcba
aTS++
=
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T2m anom < -0°CJFM
Kuipers score
dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
d) (b c) (abc - ad KSS++
=
ECMWF
RegCM
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dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
c b aaTS++
=
ECMWF
RegCM
Average for Zagreb270 mm
Precip>2.0 mm/dayJAS
Threat score
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Precip>2.0 mm/dayJAS
Bias
cab a B
++=
dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
ECMWF
RegCM
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dcN
baY
NY
Fcst
Observed
dcN
baY
NY
Fcst
Observed
c b aaTS++
=
ECMWF
Precip>2.0 mm/dayJFM
Threat score
RegCM
Average for Split156 mm
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Some thoughts on verification statistics:
* No clear overall winner, but RM tends to be better forhigher thresholds and over mountains(results may improve in favour of RM with a higher resolution)
* Need to know better systematic biases of RM(“climate” of 1990’s is biased)
* How to best verify results of downscaling ?
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... and some thoughts on dynamical downscaling:
* Probably not worth the trouble for upper-air fields (?)
* Improves the structure of surface fields
* If GCM forecast is good, a significant benefit of downscaling in orography-related fields (need for ever improved orography)
* Won’t improve bad global forecast
* It is as good as RM is good