1. Tropical cyclone activity in the Minerva T1279 seasonal forecasts. Preliminary analysis Julia Manganello 1, Kevin Hodges 2 1 COLA, USA 2 NERC Centre for Earth Observation, University of Reading, UK Minerva Workshop, 16-17 Sept. 2013, GMU

2. Outline: Data. TC Identification methods. Seasonal mean TC frequencies:  interannual variability,  seasonal cycle,  climatological means. Genesis and Tracks. Intensity distributions. Summary and conclusions Outline: Data. TC Identification methods. Seasonal mean TC frequencies:  interannual variability,  seasonal cycle,  climatological means. Genesis and Tracks. Intensity distributions. Summary and conclusions Page 2

3. Minerva Workshop, 16-17 Sept. 2013, GMU Data: Minerva T1279 seasonal forecasts. 2000-2011 period, 15 ensemble members. MJJASON season. Analysis for the Northern Hemisphere (NH) only. OBS:  IBTrACS version v02r01.  Processed imposing conditions 1 and 4 of the TC Identification Criteria. Data: Minerva T1279 seasonal forecasts. 2000-2011 period, 15 ensemble members. MJJASON season. Analysis for the Northern Hemisphere (NH) only. OBS:  IBTrACS version v02r01.  Processed imposing conditions 1 and 4 of the TC Identification Criteria. Page 3

4. Minerva Workshop, 16-17 Sept. 2013, GMU Page 4 Tracking and Identification of TCs TC Ident ITC Ident II 1. Surface (10-m) wind speed threshold, m/s.15.4 1 2. Difference in vorticity 2 between 850 hPa and 250 hPa (a warm core condition). larger than zero 3. Vorticity 2 max at each level (6 levels) between 850 hPa and 250 hPa (a coherent vertical structure condition). satisfied for both 4. Number of consequtive time steps when criteria 1-3 are satisfied. 4 (24 hours) 3 (18 hours) 5. Cyclogenesis (first identification) occurs between 0- 20°N over land and 0-30°N over oceans. satisfied for both 2. TC Identification Criteria: 1. Hodges Method for detection and tracking of tropical vortices:  Relative vorticity max of 5x10 -6 s -1 at T63 (relative vorticity is averaged over 850, 700 and 600-hPa before detection and tracking),  Lifetime  2 days.  Displacement distance filter (displacement distance of the selected vortices should satisfy a min of 10° (~1,000 km) over their lifetime). 1 Observed “tropical storm” threshold for 10-min max. sustained wind. U 10min = 0.88 * U 1min 2 Vorticity is truncated at T319 (N160).

5. Clim. Means: 51.8 46.3* Clim. Means: 53.7 55.7 * difference wrt OBS is statistically significant at the 95% confidence level Minerva Workshop, 16-17 Sept. 2013, GMU TC frequency: interannual variability Northern Hemisphere TC Ident. I TC Ident. II Page 5

6. Clim. Means: 54.0 68.1 53.5* Clim. Means: 49.9 59.1 48.9 # * difference between Athena and ensm. mean Minerva values is statistically significant at the 95% confidence level. The same applies to each Minerva ensmeble member. # same as *, except for one ensemble member the one-tailed p value is 0.0279. Minerva Workshop, 16-17 Sept. 2013, GMU Comparison with Athena Northern Hemisphere MJJASON JJASON Page 6

7. North Atlantic TC frequency: interannual variability Minerva Workshop, 16-17 Sept. 2013, GMU Page 7 TC Ident. I TC Ident. II Clim. Means: 12.8 9.8 Clim. Means: 13.3 11.5 * difference wrt OBS is statistically significant at the 95% confidence level

8. TC frequency: interannual variability Minerva Workshop, 16-17 Sept. 2013, GMU Page 8 Northeast Pacific Northwest Pacific Clim. Means: 15.0 10.1* Clim. Means: 20.9 27.2* * difference wrt OBS is statistically significant at the 95% confidence level

9. TC frequency: interannual variability Minerva Workshop, 16-17 Sept. 2013, GMU Page 9 North Indian Ocean Clim. Means: 4.4 6.6* * difference wrt OBS is statistically significant at the 95% confidence level

10. TC frequency: seasonal cycle Minerva Workshop, 16-17 Sept. 2013, GMU Page 10 North Indian Ocean North Atlantic Northeast Pacific Northwest Pacific

11. ExperimentNHNAtlEPacWPacNInd IBTrACS 51.853.712.8 13. 3 14.515.020.420.94.14.4 Scaling I Scaling II Minerva T1279 46.3*55.79.8 11. 5 8.2* 10.1 * 23.0* 27.2 * 5.2 6.6 * Scaling I Scaling II Athena T1279 (13-mo. hndcst, 1990-2008) 62.3*9.2*12.731.2*8.7* Mean TC frequency, MJJASON, 2000-2011 Minerva Workshop, 16-17 Sept. 2013, GMU Page 11 * difference wrt OBS is statistically significant at the 95% confidence level

12. Correlation of the ensemble mean PDI with the OBS ExperimentNHNAtlEPacWPacNInd Minerva T1279, Scaling I0.010.510.19 0.61 # (p=0.03) -0.09 Minerva T1279, Scaling II 0.030.510.18 0.61 # (p=0.03) -0.09 ♯ - indicates statistical significance using one-sided Student’s t-test and assuming serial correlation in the time series. Brackets include one-tailed p-value. ExperimentNHNAtlEPacWPacNInd Minerva T1279, Scaling I0.18 0.76 ♯ (p=0.006 ) 0.52 0.60 ♯ (p=0.02) -0.48 Minerva T1279, Scaling II 0.12 0.74 ♯ (p=0.01) 0.330.49-0.35 Correlation of the ens. mean TC frequency with the OBS Minerva Workshop, 16-17 Sept. 2013, GMU Page 12

13. Genesis and Track Densities North Atlantic Minerva Workshop, 16-17 Sept. 2013, GMU Page 13 TC Ident. II OBS T1279 (truncated )

14. Minerva Workshop, 16-17 Sept. 2013, GMU Page 14 Genesis and Track Densities Northeast Pacific TC Ident. II OBS T1279 (truncated )

15. Minerva Workshop, 16-17 Sept. 2013, GMU Page 15 Genesis and Track Densities Northwest Pacific TC Ident. II OBS T1279 (truncated )

16. Minerva Workshop, 16-17 Sept. 2013, GMU Page 16 Genesis and Track Densities North Indian Ocean TC Ident. II OBS T1279 (truncated )

17. Minerva Workshop, 16-17 Sept. 2013, GMU Page 17 Intensity Distribution TC Ident. II OBS T1279

18. Page 18 Summary and Conclusions Seasonal mean TC activity is best forecast in the North Atlantic and, to a lesser degree, the western North Pacific, although there are biases in the mean TC counts, intensity distribution and geographical distribution of genesis locations and tracks. TC activity in the eastern North Pacific is under-predicted. Simulation of TC activity in the North Indian Ocean has large errors. In all basins, the most intense storms (equivalent to CAT 2 and higher) are under-predicted. The maximum intensities simulated are about 55-60 m/s which is equivalent to at most a CAT 4 system. Minerva Workshop, 16-17 Sept. 2013, GMU