Seasonal forecasts of the tropical cyclone activity in … · Seasonal forecasts of the tropical cyclone activity in an ECMWF coupled operational prediction system!! Julia Manganello1,

Seasonal forecasts of the tropical cyclone activity in an ECMWF coupled operational prediction

system

Julia Manganello1, Kevin Hodges2 and the Minerva Project Team

1 COLA, USA 2 NERC Centre for Earth Observation, University of Reading, UK

S2S Interna*onal Conference, Feb. 2014

ECMWF coupled ensemble systems (1)

System atmosphere model cycle

atmosphere spectral trunca2on

atmosphere ver2cal levels ocean model ocean horizontal res,

equatorial refinement ocean

ver2cal levels

MINERVA IFS cy 38r1 T319 / T639 / T1279 91 levels, top = 1 hPa NEMO v 3.0/3.1 1 degree,

~ 0.3 deg. Lat. 42 levels

System 4 IFS cy 36r4 T255 91 levels, top = 1 hPa NEMO v 3.0/3.1 1 degree, ~ 0.3 deg. Lat. 42 levels

EPS (previous) IFS cy 38r2 T639 (d 0-‐10),

T319 62 levels, top = 5 hPa NEMO v 3.0/3.1 1 degree, ~ 0.3 deg. Lat. 42 levels

ENS (current) IFS cy 40r1 T639 (d 0-‐10),

T319 91 levels, top = 1 hPa NEMO v 3.4 1 degree, ~ 0.3 deg. Lat. 42 levels

S2S Interna*onal Conference, Feb. 2014 Page 1

Courtesy of Franco Molteni (ECMWF)

ECMWF coupled ensemble systems (2)

System coupler

2me range of ocean-‐

atmosphere coupling

coupling frequency

unperturbed ini2al cond. for re-‐forecasts

atmospheric perturba2ons

ocean perturba2ons

stochas2c model

perturba2ons

MINERVA OASIS-‐3 from start 3 hours ERA-‐Interim + ORA-‐S4

SV, EDA from 2011 dates

5 ocean analyses + SST perturba*ons

3-‐*mescale SPPT + KE backsca[er

System 4 OASIS-‐3 from start 3 hours ERA-‐Interim + ORA-‐S4 SV

5 ocean analyses + SST perturba*ons


EPS (previous) OASIS-‐3 from day 10 3 hours ERA-‐Interim +

ORA-‐S4

SV, EDA from current or recent date

generated by ENS member fluxes during day 1 to 10


ENS (current)

sequen*al, single executable code

from start 3 hours ERA-‐Interim + ORA-‐S4

SV, EDA from current or recent date

5 ocean analyses 2-‐*mescale SPPT + KE backsca[er

ORA-‐S4 : Ocean Re-‐Analysis for ECMWF System-‐4 EDA : Ensemble of Data Assimila*ons (low-‐res 4D-‐var)

SV : Singular Vectors of 48-‐hour linear propagator SPPT : Stochas*c Perturba*on of Physical Tendencies scheme


Courtesy of Franco Molteni (ECMWF)

Minerva Catalog: Base Experiments

Resolu2on Start Dates Ensembles Length Period of Integra2on

T319 (65 km) May 1, Nov 1 51 7 months 1980-‐2013




For more information, please see a poster “Project Minerva: Towards Seamless High-Resolution Climate Prediction” by Ben Cash (COLA) – Feb. 12 – 13, Session D

•  May-November (MJJASON) mean tropical cyclone (TC) frequency and the accumulated cyclone energy (ACE);

•  Northern Hemisphere: North Atlantic and the western North Pacific;

•  Analysis periods are 2000-2011 and 1980-2011;

•  OBS – International Best Track Archive for Climate Stewardship (IBTrACS).

Tracking and Identification of TCs

T1279 T639 T319

1. Surface (10-m) wind speed threshold, m/s (intensity threshold)

15.41 14.41,2 13.41,2

2. Difference in vorticity3 between 850 hPa and 250 hPa (a warm core condition).

larger than zero

3. Vorticity3 max at each level (6 levels) between 850 hPa and 250 hPa (a coherent vertical structure condition).

applied

4. Number of consecutive time steps when criteria 1-3 are satisfied.

4 (24 hours)

5. Cyclogenesis (first identification) occurs between 0-20°N over land and 0-30°N over oceans.

applied

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.

1 Observed “tropical storm” threshold for 10-min max. sustained wind. U10min = 0.88 * U1min 2 Surface speed threshold is further adjusted for model resolution. 3 Vorticity is truncated at T319 (N160). IBTrACS data are filtered using criteria 1 and 4.


RMS Error1 (wrt OBS mean in %) / Mean ensemble spread1

TC Freq. ACE

2000-2011

IFS T1279 0.77# 0.60

IFS T639 0.86# 0.71#

IFS T319 -0.18 0.61#

1980-2011

IFS T639 0.48# 0.65#

IFS T319 -0.37 0.43#

Genesis (2000-2011)

North Atlantic

Correlation with OBS

TC Freq. ACE

2000-2011

IFS T1279 2.85 (22.2%) / 3.40 39.9 (34.2%) / 39.1

IFS T639 2.66 (20.8%) / 3.21 35.9 (30.8%) / 40.9

IFS T319 4.51 (35.1%) / 3.43 42.0 (36.1%) / 38.6

1980-2011

IFS T639 3.76 (37.7%) / 2.72 43.4 (48.7%) / 33.2

IFS T319 4.77 (47.8%) / 2.92 51.3 (57.6%) / 30.3

OBS

T1279

T639

T319

mean=12.8

mean=10.7

mean=9.8

mean=11.5

# (bold) - statistical significance at the 95% (90%) confidence level. 1 - after mean bias correction


RMS Error1 (wrt OBS mean in %) / Mean ensemble spread1

TC Freq. ACE

2000-2011

IFS T1279 0.56 0.69#

IFS T639 0.70# 0.84#

IFS T319 0.75# 0.70#

1980-2011

IFS T639 0.46# 0.76#

IFS T319 0.52# 0.68#

Genesis (2000-2011)

Western North Pacific

Correlation with OBS

TC Freq. ACE

2000-2011

IFS T1279 2.36 (11.5%) / 3.46 34.9 (18.9%) / 40.4

IFS T639 2.01 (9.8%) / 3.31 28.4 (15.4%) / 35.4

IFS T319 1.88 (9.2%) / 3.37 35.5 (19.2%) / 32.2

1980-2011

IFS T639 3.41 (15.2%) / 3.45 43.2 (20.9%) / 40.2

IFS T319 3.27 (14.5%) / 3.68 47.9 (23.2%) / 35.2

OBS

T1279

T639

T319

mean=20.4

mean=26.3#

mean=28.9#

mean=30.1#


# (bold) - statistical significance at the 95% (90%) confidence level. 1 - after mean bias correction

TC frequency (North Atlantic, 1980-2011)

IBTrACS T639 (bias-corrected) T639

r = 0.48

25-75 percentile

10-90 percentile

r = -0.28 r = 0.74

r = 0.86

Corr.: 0.48 RMSE: 3.76 SPRD: 2.72 Ratio: 1.38


ACE (North Atlantic, 1980-2011)

r = 0.65

r = 0.34 r = 0.79

r = 0.71


25-75 percentile

10-90 percentile



Biases wrt ERA-Interim (2000-2010)

VWS

SST OBS

T1279

T639

T319

Genesis (2000-2011)

Mid-trop.

RH

500-hPa

Neg. Omega


mean=12.8

mean=10.7

mean=9.8

mean=11.5

North Atlantic T639 Biases wrt ERA-I (1980-2010)

Δ (TC frequency) Δ (SSTMDR – SSTGlobTrop) -1.0*Δ(VWSMDR)

Time series smoothed, mean bias subtracted

OBS T639

SSTMDR – SSTGlobTrop

0.66# 0.86#

-1.0*VWSMDR 0.65# 0.87#

Correlation of the TC frequency with climatological indices

MDR – (80°W-20°W, 7.5°N-22.5°N)

Bias Corr.

w/ ERA-I

Trend*

T639 ERA-I

SSTMDR -0.12 °C 0.86# 0.13# 0.16#

SSTGlobTrop -0.22 °C 0.84# 0.086# 0.076#

SSTMDR – SSTGlobTrop 0.10°C 0.83# 0.045 0.086

VWSMDR -0.38 m/s 0.69# -0.082 -0.52

* Units are °C/decade and m/s/decade ♯ - statistical significance at the 95% confidence level.

Comparison of T639 climatological indices with ERA-I


TC frequency (Western North Pacific, 1980-2011)


25-75 percentile

10-90 percentile

r = 0.46

r = 0.22 r = 0.54

r = 0.70



ACE (Western North Pacific, 1980-2011)


25-75 percentile

10-90 percentile

r = 0.76

r = 0.52 r = 0.85

r = 0.84



Summary and Conclusions

•  Overall, the forecast skill of the seasonal mean TC frequency and the ACE in Minerva can be considered as good, particularly for the western North Pacific basin. •  The largest errors in the North Atlantic are associated with the inability of the model to reproduce decadal scale changes (inactive/active periods or a trend). They appear to be primarily driven by errors in the MDR VWS which also shows no trend, rather than the relative SSTs. This suggests a possible connection to the tropical Pacific, although the actual mechanism is not clear.


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Seasonal forecasts of the tropical cyclone activity in … · Seasonal forecasts of the tropical cyclone activity in an ECMWF coupled operational prediction system!! Julia Manganello1,