A new implementation of TC-detect program with CCAM's output A new implementation of TC-detect...
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Transcript of A new implementation of TC-detect program with CCAM's output A new implementation of TC-detect...
A new implementation of TC-detect program with CCAM's
outputBui Hoang Hai
Faculty of Meteorology, Hydrology and Oceanography, Hanoi University of Science, Vietnam
Aspendale, 10th December, 2012
Downscaled Vietnam Climate Projections workshop and training program
Outlines
• Tropical cyclone detections in High-resolution data
• The previous TC-detect program• Some changes • Some initial results• Conclusion and remark
Tropical cyclone detections in High-resolution data
• Pros: – TCs are well resolved!
• Cons:– More local maximas– Takes longer time to run
Characteristics of a Tropical cyclones
• Large negative sea level pressure deficit• Warm cored structure – positive temperature
anomaly through out the troposphere.• Large (tangential) wind speed (Vm>17ms-1) • Large vorticity
Our last TC detect procedure
1 Compute U, V, T, H at specific pressure level (850hPa, 700hPa, 500hPa, 300hPa and Sea Level Pressure)
Check each grid point for TC candidate: A vorticity maxima at 850hPa that has value greater than a prescribed criteria (e.g. 10-4 s-1) (10-5 s-1)
2
3Search for the SLP minimum center using birational interpolation (within 2 degree radius circle from Candidate center)
Our last TC detect procedure (cont.)
4 Check Criteria to determine a Tropical Cyclone
1o2.5o Outer Core Streng (OCS) at 850hPa > OCSCrit (10 ms-1) (5 ms-1)
2.5o
SLP Anomaly < SLPCrit (-2 hPa)Core Temperature Anomaly > TcoreCrit (1 K)
Geopotential Height Anomaly at 500hPa < H500Crit (-10m)
Core Temperature Anomaly is calculated by weighted averaging (0.1, 0.2, 0.3, 0.4)
Tracking procedure:
Is the dectected TC a new born one or a previous one?
t0 - 12h
t0 - 6h
300km
Final processing: only vortices that lasts at least two days are considered to be model TCs.
Some thoughts
• The detection time is quite long (mainly because of the costly interpolation procedure)
• Higher resolutions lead to more small-scale spatial variation of vorticity, these maxima are not located at the centers
• Sea level pressure is somewhat more reliable because its variation is quite small
• Is the searching for vorticity maxima at the first place necessary?
• Or is it necessary at all in the whole procedure?
Criteria?
Vorticity?
- At 850 hPa, 900 hPa- Threshold: >1 × 10-5, 2.0 × 10-5, 3.5 × 10-5, 3.5 × 10-5, 7 × 10-5,
For more detail, see Walsh et al. (2006)
Others
- Latitude < 30o ,40o
- Cannot genesis on land
Wind speed?
- At 850 hPa, at 10m- Area-averaged, OCS- Threshold: >5ms-1, 10ms-1, 15ms-1, 17ms-1,
Warm cored structure?
- T’250 > 0.5K- T’700 + T’500 + T’300 > 0 K, 1.5K, 3K-T’850 +T’700 + T’500 + T’300 > 3
Minimum lifespan
1, 2, 3 days
Our new procedure
• Detection phase• Search for SLP centers using a downhill method: The
first guess centers is located every 3 degree: (~330km) and calculate SLP anomaly
• Calculate some characteristics based on the closed gridpoints (Without costly interpolation)• OCS
• Tcore anomaly (Tano)
• Maximum Vorticiy (Vort)• Maximum windspeed (Vmax)• Sea level presure
Our new procedure
• Tracking phase• If two centers are close (e.g. less than 400km), only
the one with lower SLPano is chosen.• The tracking procedure is similar to the previous
one.
Sample run’s outputTC#; 45YYYY;MM;DD;HH; LON; LAT; Tano; slpano; ocs; Vort; Vmax; Slp ----------------------------------TC#; 1Num_Obs: 31982; 9; 1; 0; 145.36; 27.33; 0.96; -6.07; 11.77; 144.18; 19.92; 996.021982; 9; 1; 6; 143.41; 27.33; 0.96; -6.23; 11.93; 143.69; 20.67; 994.121982; 9; 1;12; 143.11; 27.33; 0.92; -6.33; 12.04; 143.10; 21.51; 995.04 ----------------------------------TC#; 2Num_Obs: 111982; 9; 1;18; 142.94; 27.34; 0.92; -6.73; 12.72; 145.46; 20.24; 993.041982; 9; 2; 0; 141.93; 27.33; 1.02; -6.97; 12.72; 151.32; 20.81; 993.961982; 9; 2; 6; 141.36; 27.74; 1.03; -7.19; 13.50; 157.04; 20.37; 992.401982; 9; 2;12; 140.21; 27.70; 1.13; -7.36; 13.37; 150.56; 20.65; 993.351982; 9; 2;18; 139.92; 28.53; 1.14; -6.72; 13.03; 153.60; 21.93; 993.791982; 9; 3; 0; 139.14; 28.94; 1.18; -6.56; 12.41; 144.50; 24.12; 994.801982; 9; 3; 6; 138.94; 28.96; 1.21; -7.18; 14.01; 161.81; 24.08; 992.211982; 9; 3;12; 139.33; 29.51; 1.19; -7.11; 13.57; 169.89; 23.91; 993.371982; 9; 3;18; 140.34; 29.65; 1.19; -7.33; 13.96; 195.96; 25.59; 992.551982; 9; 4; 0; 140.54; 30.28; 1.44; -8.34; 15.86; 216.92; 30.01; 993.271982; 9; 4; 6; 142.03; 31.47; 1.74; -9.32; 17.37; 218.11; 32.14; 991.55
Tracking time: ~3 minites compares to ~3 hours as the old procedure
Some initial results
• Simulation data: CCAM simulation for 09/1982.• Stretching grid, highest resolution: ~20km over
the region of Vietnam• Spectral nudging from ERA-interim
SLP vs Maximum Vorticity
0
100
200
300
400
500
600
700
800
900
1000
-20 -15 -10 -5 0
TC
Non TC
x10-6s-1
SLPmin vs OCS and Vmax
0
5
10
15
20
25
30
35
40
45
50
980 990 1000 1010 1020
Vmax
Vmax
0
5
10
15
20
25
30
35
40
45
50
980 990 1000 1010 1020
OCS
OCS
Correl = -0.85 Correl = -0.71
Conclusion and remarks
• High resolution’s data has some challenges for Tropical cyclone detection procedures
• Vorticity doesn’t seem to be a good criteria for Tropical cyclone detection
• OCS in the model is highly correlated with intensity (SLV), not like in observation. The reason may be model TCs are broader.
• Future works: • Have some case studies with ‘regular’ 50-km or
possibly higher resolution.• Improve the tracking precedure