WORLD METEOROLOGICAL ORGANIZATION
_________________
CBS ET/EPS/Doc. 3(4) Add.1
(16.VI.2003)
_______
COMMISSION FOR BASIC SYSTEMS
OPAG ON DPFS
EXPERT TEAM ON
ENSEMBLE PREDICTION SYSTEMS
Item: 3
Original: ENGLISH
Geneva, Switzerland, 27-31 October 2003
IMPROVEMENT OF ENSEMBLE PREDICTION SYSTEM AT
KOREA METEOROLOGICAL ADMINISTRATION
(Submitted by Woo-Jin LEE)
____________________________________________________
Summary and purpose of document
The status and prospects of ensemble prediction system at Korea
Meteorological Administration is summarized.
_____________________________________________________
Action proposed
The expert team is invited to take into account the information given in this
document.
1.
Problem Noted
1.1
An ensemble prediction system (EPS) based on the breeding approach with global
spectral model (T106L21) has been on test operation at Korea Meteorological Administration
(KMA) since March 2001. The EPS runs for 10 days projection once a day at 12 UTC with 16
bred vectors (BVs), which are updated at every 12 hours. A global mean enstrophy is used to
maintain the magnitude of BVs within the range of tangent linear approximation.
1.2
The standard verification scores are regularly evaluated with WMO standards. Even
though the EPS mean is slightly better than the deterministic one in terms of RMSE errors in
500 hPa geopotential heights, the EPS has a weak spread in Northern Hemisphere,
particularly at summer. This weakness is also confirmed in comparison of spaghetti diagram
and time series of model variables with Japan Meteorological Agency counterparts.
2.
Attempt for Trouble Shooting
2.1
It has been noted that the BVs tend to grow more rapidly in the southern
hemisphere, where baroclinicity is strong, than in the northern hemisphere, which hamper
the spread of error growth in the northern hemisphere during the early stage of evolution.
2.2
To avoid the problem, the BVs are spatially filtered at each breeding cycle such that
its magnitude is set to zero in the southern hemisphere. It is intended to artificially activate the
secondary optimal modes with local instability associated with Northern hemisphere Jet
streams. An example of filtered bred vector is shown in Fig. 1.
3.
Improvement Accessed
3.1
Sensitivity experiment on the revised BVs (RBVs) with T106L30 version was
conducted against control (old BVs with T106L21 version) during August 2003 once a day.
3.2
The various measures indicate that RBVs shows consistent improvement in terms of
skill and spread (Figs 2,3,4, and 5).
4.
Implication to Severe weather
4.1
The heavy rain episode has been examined in terms of potential for early warning
during the experiment period. The case shows that RBVs produce better probability of
precipitation than the old one (Fig. 6).
4.2
For the tropical cyclone MAEMI case, the ensemble of tracks from RBVs has more
spread, while retaining the comparable mean track, than the old one (Fig. 7). However, it is
noted that the ensemble tracks for both BVs are RBVs are slightly located south of the best
track. It indicates that BVs and RBVs could not well capture uncertainty associated with the
subtropical Pacific High which partially control the track on the ridge.
5.
Plan for the Future
5.1
Selected EPS products with RBVs will be open through Internet with standard
verification scores recommended by WMO.
5.2
Extreme forecast index is under development, and will be distributed to local
forecasters for evaluation of its potential. The objective identification of outliers from bundle
of scenarios continues to be explored.
5.3
The spatial filtering applied to RBVs will be refined further to accommodate with the
analysis error and to take the local instability at upwind region into account.
Acknowledgements
The figures are prepared by Ms. Seon-Ok Moon who is a leading researcher for the
improvement of EPS at KMA.
Fig. 1. An example of bred vector (left), and revised bred vector with spatial filter (right)
Fig. 2. RMSE of mean ensemble and spread of ensemble for revised 16 bred vectors with
T106L30 (red), and for original 16 bred vectors with T106L21 (white) in terms of geopotential
meter at 500 hPa in northern hemisphere during August 2003. The spread is measured with
standard deviation among members in ensemble. The revised bred vector shows more
spread and less RMSE errors than the original bred vectors. It is noted that the spread and
RMSE are comparable which is expected for a sound ensemble.
200308 섭동장 개선후 120시간 예보
500hPa 고도 테라그랜드 (북반구)
10
10
8
8
Percentage
Percentage
200308 현업 120시간 예보
500hPa 고도 테라그랜드 (북반구)
6
4
6
4
2
2
0
0
1
2
3
4
5
6
7
8
9
10
11 12
13 14
1
15
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Interval
Interval
Fig. 3. Talagrand for geopotential meter at 500 hPa in the northern hemisphere at +5 days in
advance during August 2003. Left panel is for the original 16 bred vectors with T106L21, and
right panel is for the revised 16 bred vectors with T106L30, which indicates improvements
with revised bred vectors.
2003년 8월 앙상블 예보 현업 5일쩨 Reliability Diagram
500hPa 고도 > | NCEP기후값 + 50m | (북반구)
1
Obseved Relative Frequency
0.9
0.8
0.4
0.7
0.3
0.6
0.5
0.2
0.4
0.1
0.3
0
0.2
0
0.2
0.4
0.6
0.8
1
re l F C d is trib u tio n
0.1
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Forecast Probability
2003년 8월 앙상블 예보 개선시 5일쩨 Reliability Diagram
500hPa 고도 > | NCEP기후값 + 50m | (북반구)
1
O bseved Relative Frequency
0.9
0.8
0.4
0.7
0.6
0.3
0.5
0.2
0.4
0.1
0.3
0
0.2
0
0.2
0.4
0.6
0.8
1
re l F C d is trib u tio n
0.1
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Forecast Probability
Fig. 4. Reliability diagram for geopotential meter exceeding 50 meters with reference to
NCEP climatology at 500 hPa in the northern hemisphere at +5 days in advance during
August 2003. Upper panel is for the original 16 bred vectors with T106L21, and lower panel
is for the revised 16 bred vectors with T106L30, which indicates improvements with revised
bred vectors.
T106L30 2003년 8월 북반구영역
500hP a 고도 anom aly < -50m
1
1
0.8
0.8
0.6
0.6
적중률
적중률
T106L30 2003년 8월 북반구영역
500hP a 고도 anom aly > +50m
24시간 예보
72시간 예보
120시간 예보
168시간 예보
y =x
0.4
0.2
24시간 예보
72시간 예보
120시간 예보
168시간 예보
y =x
0.4
0.2
0
0
0
0.2
0.4
0.6
0.8
1
0
0.2
비적중률
1
0.8
0.8
0.6
0.6
적중률
적중률
0.8
1
T106L21 2003년 8월 북반구영역
500hP a 고도 anom aly < -50m
1
24시간 예보
72시간 예보
120시간 예보
168시간 예보
y =x
0.2
0.6
비적중률
T106L21 2003년 8월 북반구영역
500hP a 고도 anom aly > +50m
0.4
0.4
24시간 예보
72시간 예보
120시간 예보
168시간 예보
y =x
0.4
0.2
0
0
0
0.2
0.4
0.6
비적중률
0.8
1
0
0.2
0.4
0.6
0.8
1
비적중률
Fig. 5. ROC curve for geopotential meter above 50 meters (two left panels) and below
50 meters (two right panels) with reference to NCEP climatology at 500 hPa in the northern
hemisphere at different leading time (in days) during August 2003. Upper two panels are for
the revised 16 bred vectors with T106L30, and lower two panels are for the original 16 bred
vectors with T106L21, which indicates improvements with revised bred vectors.
Fig. 6. Probability of precipitation exceeding 1mm/12hrs at +5days in advance with initial
state of 12UTC 7th September 2003 with revised 16 bred vectors (middle), and with original
16 bred vectors (right). The observed 12 hour rainfall distribution is shown in the left panel for
comparison, which indicates improvements with revised bred vectors.
Fig. 7. Typhoon tracks from revised 16 bred vectors with T106L30 (upper right) and original
16 bred vectors with T106L21 (lower right), compared with the best track (upper left) for the
typhoon MAEMI (14th) with initial state of 12UTC 9th 2003.