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Tropical cyclone activity in the Minerva T1279 seasonal forecasts. Preliminary analysis

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. Outline: Data. TC Identification methods.

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Tropical cyclone activity in the Minerva T1279 seasonal forecasts. Preliminary analysis

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  1. Tropical cyclone activity in the Minerva T1279 seasonal forecasts. Preliminary analysis Julia Manganello1, Kevin Hodges2 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 Minerva Workshop, 16-17 Sept. 2013, GMU Page 2

  3. 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. Minerva Workshop, 16-17 Sept. 2013, GMU Page 3

  4. Tracking and Identification of TCs • 1. Hodges Method for detection and tracking of tropical vortices: • Relative vorticitymax 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). 2. TC Identification Criteria: 1 Observed “tropical storm” threshold for 10-min max. sustained wind. U10min = 0.88 * U1min 2Vorticity is truncated at T319 (N160). Minerva Workshop, 16-17 Sept. 2013, GMU Page 4

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

  6. Comparison with Athena Northern Hemisphere MJJASON Clim. Means: 54.0 68.1 53.5* JJASON 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 Page 6

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

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

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

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

  11. Mean TC frequency, MJJASON, 2000-2011 * difference wrt OBS is statistically significant at the 95% confidence level Minerva Workshop, 16-17 Sept. 2013, GMU Page 11

  12. Correlation of the ens. mean TC frequency with the OBS Correlation of the ensemble mean PDI with the OBS ♯ - indicates statistical significance using one-sided Student’s t-test and assuming serial correlation in the time series. Brackets include one-tailed p-value. Minerva Workshop, 16-17 Sept. 2013, GMU Page 12

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

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

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

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

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

  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 Page 18

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