A new implementation of TC-detect program with CCAM's output A new implementation of TC-detect program with CCAM's output Bui Hoang Hai Faculty of Meteorology, Hydrology and Oceanography, Hanoi University of Science, Vietnam Aspendale, 10 th 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 (V m >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 s -1 ) (10 -5 s -1 ) 2 3 Search 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 Outer Core Streng (OCS) at 850hPa > OCSCrit (10 ms -1 ) (5 ms -1 ) 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? t h t 0 - 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 < 30 o,40 o - 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’ T’ T’ 300 > 0 K, 1.5K, 3K -T’ 850 +T’ T’ 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 T core anomaly (T ano ) 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 output TC#; 45 YYYY;MM;DD;HH; LON; LAT; Tano; slpano; ocs; Vort; Vmax; Slp TC#; 1 Num_Obs: ; 9; 1; 0; ; 27.33; 0.96; -6.07; 11.77; ; 19.92; ; 9; 1; 6; ; 27.33; 0.96; -6.23; 11.93; ; 20.67; ; 9; 1;12; ; 27.33; 0.92; -6.33; 12.04; ; 21.51; TC#; 2 Num_Obs: ; 9; 1;18; ; 27.34; 0.92; -6.73; 12.72; ; 20.24; ; 9; 2; 0; ; 27.33; 1.02; -6.97; 12.72; ; 20.81; ; 9; 2; 6; ; 27.74; 1.03; -7.19; 13.50; ; 20.37; ; 9; 2;12; ; 27.70; 1.13; -7.36; 13.37; ; 20.65; ; 9; 2;18; ; 28.53; 1.14; -6.72; 13.03; ; 21.93; ; 9; 3; 0; ; 28.94; 1.18; -6.56; 12.41; ; 24.12; ; 9; 3; 6; ; 28.96; 1.21; -7.18; 14.01; ; 24.08; ; 9; 3;12; ; 29.51; 1.19; -7.11; 13.57; ; 23.91; ; 9; 3;18; ; 29.65; 1.19; -7.33; 13.96; ; 25.59; ; 9; 4; 0; ; 30.28; 1.44; -8.34; 15.86; ; 30.01; ; 9; 4; 6; ; 31.47; 1.74; -9.32; 17.37; ; 32.14; 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

Some initial results

Observation (ibtracs)

Case 1 SLP Crit = -3hPa Min life span = 8 OCS Crit = 3 m/sTcore Crit = 0

Case 1 SLP Crit = -3hPa Min life span = 1 OCS Crit = 3 m/sTcore Crit = 0

SLP vs Tcore_anom K

SLP vs Maximum Vorticity x10 -6 s -1

SLP vs OCS ms -1

SLPmin vs OCS and Vmax Correl = -0.85Correl = -0.71

Increasing the OCS criteria OCSCrit = 3m/sOCSCrit = 6m/s

Increasing the OCS criteria OCSCrit = 3m/sOCSCrit = 6m/s

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

Thanks for your attention!