Extra-tropical Cyclones in Recent Re-Analyses Kevin Hodges Lennart Bengtsson and Robert Lee 1

Motivation 2 Extra-tropical cyclones:- 1. Important components of the general circulation. 2. How should they be verified for distribution and properties? a) Observations are highly inhomogeneous. b) No long term observational record. Re-analyses:- 1. Best available, 4D, homogeneous data sets constrained by observations. 2. What are the uncertainties?

New Re-Analyses ERA-Interim (ECMWF) ERA-Interim (ECMWF) –T255L60 (~80km) spectral, 4D Var., Modern Era Retrospective Re-Analysis (MERRA) Modern Era Retrospective Re-Analysis (MERRA) –0.5 0 x L72(~74km) finite volume, Grid-point Statistical Interpolation (GSI, 3D Var.), Japanese 25 Year Re-Analysis (JRA25) Japanese 25 Year Re-Analysis (JRA25) –T106L40 (~125km) spectral, 3D Var., NCEP Coupled Re-analysis NCEP Coupled Re-analysis –T382L64 (~38km), GSI, th Century Re-Analysis 20 th Century Re-Analysis –Surface only observations, , ensemble kalmen filter, T63. 3

Comparison Methodology Identify and track cyclones – synoptic. Identify and track cyclones – synoptic. –MSLP – T63. –ξ 850 – T42. Compare using:- Compare using:- –INTERIM as base ( ). –Spatial statistics. –Intensity pdf’s. –Cyclone matching. –Composites. 4

Spatial Statistics NH, DJF SH, JJA Track DensityGenesis Density 5

Older Re-analyses Track Density Differences ( ) NHSH NCEP-ERA40 JRA25-ERA40

General Results 7 Number per month

INTERIM-JRA25 NH, DJF SH, JJA Track DensityGenesis Density 8

INTERIM-MERRA NH, DJF SH, JJA Track DensityGenesis Density 9

INTERIM-NCEP 10 NH, DJF SH, JJA Track DensityGenesis Density

Intensity-MSLP NH, DJFSH, JJA 11

Intensity Winds, Vorticity 12 NHSH 925hPa Winds 850hPa Vorticity

Cyclone Matching Vorticity,T42 Intensities Mean seperation ≤ 4 0 Time overlap > 60% points 13

Separation, Vorticity NH DJFSH JJA 14 JRA25-ERA40,

Intensity 15

Observations-Quickscat 16 Max. IntensitiesInstantaneous Differences

Lifecycles 17

ATHENA-Intensities 18 T159 Intensities

ATHENA-Distributions 19

Future Work Apply same methods directly to satellite data to verify cyclone structure in NWP (directly) and climate models (statistically). Apply same methods directly to satellite data to verify cyclone structure in NWP (directly) and climate models (statistically). Apply to other weather system types, e.g. TC including examining the transition of EW to TC; the extra-tropical transition of TC and polar lows. Apply to other weather system types, e.g. TC including examining the transition of EW to TC; the extra-tropical transition of TC and polar lows. Extend to energetics. Extend to energetics. 20