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Changes in extra-tropical and tropical storms in the 21st century

Changes in extra-tropical and tropical storms in the 21st century. Professor Lennart Bengtsson ESSC, University of Reading, UK. Changes in extra-tropical and tropical storm tracks in the 21st century.

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Changes in extra-tropical and tropical storms in the 21st century

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  1. Changes in extra-tropical and tropical storms in the 21st century Professor Lennart Bengtsson ESSC, University of Reading, UK Storm tracks and Climate change Lennart Bengtsson

  2. Changes in extra-tropical and tropical storm tracks in the 21st century • The change of storm tracks in the 21st century has been calculated by the ECHAM5 model using the IPCC-A1B scenario. For the present climate comparisons have been undertaken with the ERA-40 reanalyses. • Thanks to Kevin Hodges and Erich Roeckner • Joint paper submitted to J of Climate (April 2005) Storm tracks and Climate change Lennart Bengtsson

  3. Transient extra-tropical weather systems and climate • Determine the local weather • Regulate global transport of heat, water and momentum • Interact strongly with large scale circulation anomalies( e.g. blocking) Storm tracks and Climate change Lennart Bengtsson

  4. Transient tropical weather systems and climate • Transient easterly waves dominate the weather in the Tropics • During late summer and autumn some of the waves are transformed into hurricanes Storm tracks and Climate change Lennart Bengtsson

  5. Typical cyclone storm tracks Tracks Intensities Storm tracks and Climate change Lennart Bengtsson

  6. Changes in extra-tropical and tropical storm tracks in the 21st century • Identification of storm tracks • Models • Storm track validation ( ERA40) • Climate change scenario • Extra-tropical storm tracks • Tropical storm tracks • General conclusions Storm tracks and Climate change Lennart Bengtsson

  7. From Geng and Sugi, 2002, J. of Clim. Storm tracks and Climate change Lennart Bengtsson

  8. How are transient eddies identified? • Date sets are needed at least every 6 hour • We use a method proposed by Hodges (Hodges, 1999, MWR) • We use the vorticity at 850hPa • A transient eddy must exist for >48hours and be extended over at least1000km Storm tracks and Climate change Lennart Bengtsson

  9. Storm tracks DJF 2002/03 at 850 hPaERA 40 Storm tracks and Climate change Lennart Bengtsson

  10. ECHAM 5 • Roeckner et al., (2003), MPI-Report 349 • Resolution used T63L31 (top at 10hPa) • Water vapour, cloud liquid water and cloud ice in semi-Lagrangian flux form-scheme Storm tracks and Climate change Lennart Bengtsson

  11. Modelling error as a function of horisontal and vertical resolution (ECHAM climate model 2005) Storm tracks and Climate change Lennart Bengtsson

  12. Simulation of climateKöppen climate zones Main groups • A: Tropical rainy climate, all months > +18 C • B: Dry climate, Evaporation > Precipitation • C: Mild humid climate, coldest month +18 C - -3 C • D: Snowy - forest climate, coldest month < -3C but warmest > +10 • E: Polar climate , warmest month < +10 C • ET: Tundra climate, warmest month > 0 C • Subgroups • f : Moist, no dry seasons • w: Dry season in winter • s : Dry season in summer Storm tracks and Climate change Lennart Bengtsson

  13. Köppen climate zones ECHAM5 simulated ERA40 determined from analyses. Storm tracks and Climate change Lennart Bengtsson

  14. Validation using ERA40 • 3 AMIP-type experiments 1979-1999 using observed SST and sea-ice ( with AMIP-2 protocol ( WGNE,1996) • ERA40 1979-2002 Storm tracks and Climate change Lennart Bengtsson

  15. Storm track diagnostic • The full storm track cycle has been calculated including cyclogenesis, storm track density, storm track intensity and cyclolysis • Calculations has been done for the NH extra-tropics ( 30N-90N), SH extra-tropics (30S-90S) and for the NH tropical belt ( 0-30N) • Storm tracks have been ordered as a function of the maximum intensity obtained for each individual track. Storm tracks and Climate change Lennart Bengtsson

  16. ERA40 Cyclogenesis, 850 hPa (DJF) Storm tracks and Climate change Lennart Bengtsson

  17. ERA 40 storm track density and intensityDJF Storm tracks and Climate change Lennart Bengtsson

  18. Storm tracks ERA40 (left)ECHAM5 ( right) NH(DJF) Storm tracks and Climate change Lennart Bengtsson

  19. Number of vortices ( max. intensity)ERA 40 and ECHAM5 (AMIPII), NH 1979-1999 NH for DJF Storm tracks and Climate change Lennart Bengtsson

  20. The same for all seasons (NH) MAM DJF JJA SON Storm tracks and Climate change Lennart Bengtsson

  21. Summary of results for ECHAM5 AMIP runs, NH extra-tropics • Minor differences in areas of cyclogenesis from ERA40, some reduction over Kuroshio- and the Gulfstream area. • Storm track density and intensity agree well • Statistical distribution of storms for the whole region is practically identical for all three realizations and with ERA40 Storm tracks and Climate change Lennart Bengtsson

  22. Storm tracks ERA40 (left)ECHAM5 ( right) SH (JJA) Storm tracks and Climate change Lennart Bengtsson

  23. Number of vortices ( max. intensity)ERA 40 and ECHAM5 (AMIPII), SH 1979-1999 SH for DJF Storm tracks and Climate change Lennart Bengtsson

  24. The same for all seasons (SH) Storm tracks and Climate change Lennart Bengtsson

  25. Result of FGGE:ERA40 storm tracks at the SH before and after 1979 Storm tracks and Climate change Lennart Bengtsson

  26. Summary of results for ECHAM5 AMIP runs, SH extra-tropics • There are some differences in areas of cyclogenesis with a reduced number in northern Patagonia compared to ERA40 and more cyclogenesis over the Indian ocean • Some reduced activity ( track density) along the Antarctic front ( Pacific sector) compared to ERA40 but increased activity in the Indian ocean • Systematic underestimation of cyclone intensity prior to 1979 in ERA40 ( due to lack of data) • Overall good agreement in cyclone statistics but slightly more intense storms in ECHAM5 than in ERA40 Storm tracks and Climate change Lennart Bengtsson

  27. Tropical track density (MJJASO)ECHAM5 (top), ERA40 (bottom) Storm tracks and Climate change Lennart Bengtsson

  28. Storm track intensity and densityECHAM5 and ERA 40 (MJJASO) Storm tracks and Climate change Lennart Bengtsson

  29. Number of vortices ( max. intensity)ERA 40 and ECHAM5 (AMIPII), Tropics Extreme storms Storm tracks and Climate change Lennart Bengtsson

  30. Summary of results for ECHAM5 AMIP runs, NH tropics • ECHAM5 has more eddy activity over the African continent with a slightly more northerly position • In the Pacific ocean the eddy activity is less than in ERA40 except in the eastern Pacific. • Some differences in the statistical distributing with more stronger storms in ECHAM5 except for a very few intense vortices ( less than one /year) where there some more in ERA40. Storm tracks and Climate change Lennart Bengtsson

  31. Effect of ENSO (ERA 40)Warm-Cold events Storm tracks and Climate change Lennart Bengtsson

  32. Effect of ENSO (ERA 40)ERA 40 left/top and ECHAM5 right/bottom Storm tracks and Climate change Lennart Bengtsson

  33. Effect of ENSO (ERA 40)ERA40 (top) ECHAM5 (bottom) Storm tracks and Climate change Lennart Bengtsson

  34. Storm track and ENSO • There is a good agreement between ECHAM5 and ERA40 in the response to ENSO (using SST in NINO3 as a measure) • Most marked is the storm track enhancement over southern US stretching into the Atlantic and the storm track enhancement in the northeast Pacific • There is a weakening of the tropical Atlantic storm track and a southward transition of the Pacific storm track Storm tracks and Climate change Lennart Bengtsson

  35. Ocean Model (MPI-OM) • Marsland et al., 2003: Ocean Modelling, 5(2), 91-127 • 40 levels, bottom topography, partial grid cells • 1.5° resolution, grid poles over land areas • Parameterization include isopycnal diffusion, horizontal tracer mixing, vertical eddy mixing, convective overturning, slope convection Storm tracks and Climate change Lennart Bengtsson

  36. MPI Coupled model • Jungclaus et al., (2004) J. Climate submitted • SST, sea ice concentration and thickness, snow on ice, ocean surface velocity are passed on to atmosphere. • Accumulated fluxes ( one day) are transferred to the ocean • River runoff and glacier calving are treated interactively in the atmospheric model with fresh water fluxes passed on to the ocean • Surface wind stress over ocean is calculated relative to the ocean current • There is no flux adjustment Storm tracks and Climate change Lennart Bengtsson

  37. Climate change experiment • Coupled model was run with pre-industrial forcing for 500 years ( negligible drift 0.026K/century) • 20th century runs 1860-2000 with observed anthropogenic forcing including CFCs, ozone and sulphate aerosols ( direct and indirect) • 3 runs from different ocean and atmospheric states • The runs were continued until 2100 using IPCC SRES scenario A1B Storm tracks and Climate change Lennart Bengtsson

  38. What is A1B? • Middle of the line scenario • Carbon emission peaking in the 2050s (16 Gt/year) • CO2 reaching 450 ppm. in 2030 • CO2 reaching 700 ppm. in 2100 • SO2 peaking in 2020 then coming done to 20% thereof in 2100 Storm tracks and Climate change Lennart Bengtsson

  39. How will climate change affects the storm tracks? • We compare three 30 year periods of 1961-1990 (20C) and 2071-2100 (21C) • The 20C run agrees closely with the AMIP run • Two different kinds of changes stand out: • (a) A broad conservation of the total number of storms tracks except a minor reduction of the weaker storms • (b) Geographical changes in the storm tracks Storm tracks and Climate change Lennart Bengtsson

  40. Changes in storm track density and intensity (21C-20C) DJF (left), JJA (right) NH Storm tracks and Climate change Lennart Bengtsson

  41. Changes in storm track density (21C-20C) DJF NH Storm tracks and Climate change Lennart Bengtsson

  42. Change in storm track density Storm tracks and Climate change Lennart Bengtsson

  43. Change in storm track intensity Storm tracks and Climate change Lennart Bengtsson

  44. Change in storm tracks DJF (21C-20C)number( max intensity) NH Storm tracks and Climate change Lennart Bengtsson

  45. Change in storm tracks JJA (21C-20C)number( max intensity) NH Storm tracks and Climate change Lennart Bengtsson

  46. Changes in storm tracks (21C-20C)north British isles (left), Mediterranean area (right) Storm tracks and Climate change Lennart Bengtsson

  47. Changes in storm track density (21C-20C) DJF, SH Storm tracks and Climate change Lennart Bengtsson

  48. Changes in storm track density and intensity (21C-20C) DJF (left), JJA (right) SH Storm tracks and Climate change Lennart Bengtsson

  49. Change in storm tracks DJF (21C-20C)number( max intensity) SH Storm tracks and Climate change Lennart Bengtsson

  50. Change in storm tracks JJA (21C-20C)number( max intensity) SH Storm tracks and Climate change Lennart Bengtsson

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