Upload
seoras
View
27
Download
1
Embed Size (px)
DESCRIPTION
Satellite Winds Superobbing. Hurricane Opal October 1995. Image Courtesy of UW - CIMSS. Howard Berger Mary Forsythe John Eyre Sean Healy. Outline. Background/Problem Superob Methodology Method Observation Error Results Conclusions/Future Work. Problem:. - PowerPoint PPT Presentation
Citation preview
1
Satellite Winds Superobbing
Howard BergerMary Forsythe
John EyreSean Healy
ImageCourtesyof UW - CIMSS
Hurricane OpalOctober 1995
2
Outline
•Background/Problem
•Superob Methodology•Method•Observation Error
•Results
•Conclusions/Future Work
Problem:• High - Resolution satellite wind data sets showed negative impact (Butterworth and Ingleby, 2000) Why?
•Suspected that observations errors were spatially correlated
•To account for this negative impact, wind data were/are thinned to 2º x 2º x 100 hPa boxes
4
•Bormann et al. (2002) compared wind data to co-located radiosondes showing statistically significant spatial error correlations up to 800 km.
Cor
rela
tion
Met-7 W V NH Correlations
Graphic fromBormann et al.2002
5
Question:
Can we lower the data volume to reduce the effect of correlated error while making some use of the high-resolution data?
6
Proposed Solution:
Average the observation - background
(innovations) within a prescribed 3-d box to create
a superobservation.
7
Advantages:
•Data volume is reduced to same resolution that resulted from thinning.
•Averaging removes some of the random, uncorrelated error within the data.
8
SuperobbingMethod:
9
1) Sort observations into 2º x 2º x 100 hPa boxes.
28 N
16 W
26 N
18 W
10
2) Within each box: Average u and v component innovations, latitude, longitude and pressures.
28 N
26 N
16 W18 W
11
3) Find observation that is closest to average position and add averaged innovation to thebackground value at that observation location.
26 N
28 N
16 W18 W
12
Superob Observation Error
13
•Superobbing removes some of the random observation error.
•This new error can be approximated by making a few assumptions about the errors within the background and the observation.
Superob Observation Error
14
Superob Observation Error
Assume that within a box:
•Observation and background errors not correlated with each other.
•Background errors fully correlated.
•Background errors have the same magnitude.
15
Assumptions (cont):
•All of the innovations weighted equally.
•Constant observation error correlation.
Superob Observation Error
Token Evil Math Slide
2 ( )Tse W DED W=
2se = Superob Observation Error
W =Vector of Weights (1xN)
D =Diagonal matrix of component observation errors (N x N)
E =Observation Error Correlation Matrix (NxN)
1
1
a a
aE
a
a a
=
L
O O M
M O O
L
Observation Correlation Matrix
a =Correlation within box. Value calculated from correlation function in Bormann et al., 2002
1 1 1 2 1
2 1
1
n
n n n
c c c c c c
c cE
c c c c
=
L
O O M
M O O M
L L
i jc c =Correlation of ith observation with jth observation
18
00z 10 June, 2003.(20 N - 40 N) (0E 30 E)
Old Observation Error Superob Error
19
Experimental Design
•Control Run:•Operational Set up plus GOES BUFR VIS/IR/WV winds•GOES-9 is still Satob format
•Thinning to 2˚ x 2˚ x 100 hPa boxes
•Superob Experiment•Same as control run, except winds are superobbed to 2˚ x 2˚ x 100 hPa boxes
20
• Trial Period: 24 Jan -17 Feb 2004
• 4 Analyses and 6-hr forecasts• 00z,06z,12z,18z
• 1 analysis and 5-day forecast (12z)
Experimental Design (cont)
21
Token Model Info Slide
• Grid – point model (288 E-W x 217 N-S)
• Staggered Arakawa C-Grid
• Approx 100 km horizontal resolution (one-half operational resolution)
• 38 levels hybrid-eta configuration
• 3D-Var Data Assimilation
22
Results
• % normalized root mean square (rms) error against control rms differences calculated for:
•Mean sea-level pressure (PMSL) •500 hPa height (H500) •850 hPa wind (W850) •250 hPa wind (W250)
• In regions:•Northern Hemisphere (NH) •Tropics (TR) •Southern Hemisphere (SH)
•For forecast periods of:•T+24, T+48, T+72 ,T+96 , T+120
Trial Statistics
24
-2
-1
0
1
2
3
4
PM
SL T
+2
4
PM
SL T
+4
8
PM
SL T
+7
2
PM
SL T
+9
6
PM
SL T
+1
20
H500 T
+24
H500 T
+48
H500 T
+72
W250 T
+24
W850 T
+24
W850 T
+48
W850 T
+72
W250 T
+24
PM
SL T
+2
4
PM
SL T
+4
8
PM
SL T
+7
2
PM
SL T
+9
6
PM
SL T
+1
20
H500 T
+24
H500 T
+48
H500 T
+72
W250 T
+24
Exp
erim
ent –
Con
trol
RM
S E
rror
(%
)
TP – ObservationsTP – Analysis
NH – ObservationsNH – Analysis
SH – ObservationsSH – Analysis
25
Anomaly Correlations
Vs. Forecast RangeCompared to
Analysis500 hPa Height
NH
SH
TR
26
T+24 Forecast – Sonde
RMS Vector Error 250 hPa Wind
NH
TR
SH
27
250 hPa u-componentAnalysis Increments
28
250 hPa u-componentAnalysis Increments
29
Results Summary
•Superobbing experiment results are small and mixed
•Generally more positive in the northern hemisphere than in the southern hemisphere or tropics
•Time series results are mixed: Some forecasts better than control, some worse
30
Implications
•Mixed results suggest either:•Random Error not most significant error component of AMVs
•Superobbing set up not ideal to treat random error
31
Future Work
•Back to basics approach•Re-calculate observation errors from innovation statistics
•Experiment with “model independent” quality indicators and “model independent” components in Bufr file
32
• Stripped down impact experiment (i.e no ATOVS radiances)
• Experiment using simulated AMV’s in Met Office System
• Ideas from IWW!!!!!
Future Work (cont)