Footprinting Global Tropical Cyclones James Done, Greg Holland and Ming Ge: NCAR, Willis Research Network Ioana Dima-West, Geoffrey Saville and Sam Phibbs: Willis Towers Watson Yuqing Wang: U. Hawaii WRN Autumn Seminar Nov 1 st 2017
The 2017 Hurricane Season Named storms: 16 (12.1) Hurricanes: 10 (6.4) Major hurricanes: 6 (2.7) Harvey Irma Maria Easterly Wave Developments WRN Autumn Seminar Nov 1 st 2017
Records Smashed September: Named-Storm Days 53.25 52.25 (2004) Hurricane Days 40.25 34.50 (2006) (Phil Klotzbach, CSU) Major Hurricane Days 18 17.25 (1961) ACE 175 155 (1928) Harvey: Irma: 1.54m of rain 185mph for 37 hours. Phil Klotzbach (CSU) Three cat 4+ U.S. landfalls. WRN Autumn Seminar Nov 1 st 2017
A Hurricane Drought? Harvey was the first major hurricane U.S. landfall since Wilma (2005). Why the drought? - physical? - luck? - definitional? 2006-2016 storms Emphasis on count of storms above wind speed threshold is misplaced. WRN Autumn Seminar Nov 1 st 2017
Warm Oceans Phil Klotzbach (CSU) WRN Autumn Seminar Nov 1 st 2017
Warm Oceans Promotes Rapid Intensification: Harvey and Jose: Cat 1 to Cat 4 in 24 hours Maria: Cat 1 to Cat 5 in 15 hours WRN Autumn Seminar Nov 1 st 2017 Phil Klotzbach (CSU)
Light Winds Phil Klotzbach (CSU) WRN Autumn Seminar Nov 1 st 2017
Slow-Moving Harvey Rapid coastal strengthening to category 4. Track guidance fell away. Perfect set-up for record rains over Houston. WRN Autumn Seminar Nov 1 st 2017
Intense Irma 10-day warning of a strong hurricane in the U.S. Southeast. Repeated eye-wall cycles kept winds below 200mph. Uncertain right turn. Best possible route to minimize damage. WRN Autumn Seminar Nov 1 st 2017
Pinhole Maria Pinhole eye, 10 miles across. Eye-wall cycle prevented a category 5 landfall on PR. Second strongest behind San Felipe II (1928). WRN Autumn Seminar Nov 1 st 2017
Fast-Moving Nate Crossed Gulf of Mexico in 24 hours. Warm waters, loop current. Landfalling depression or Category 3? WRN Autumn Seminar Nov 1 st 2017
200 Historical Global Footprints WRN Autumn Seminar Nov 1 st 2017 12
Current Footprinting Approaches Parametric radial wind profiles: - fast, simple terrain, landuse, inland decay factors. WRN Autumn Seminar Nov 1 st 2017 13
Current Footprinting Approaches Parametric radial wind profiles: - fast, simple terrain, landuse, inland decay factors. Spatial analysis of observations: - asymmetries, but few storms, globally inconsistent. WRN Autumn Seminar Nov 1 st 2017 14
Current Footprinting Approaches Parametric radial wind profiles: - fast, simple terrain, landuse, inland decay factors. Spatial analysis of observations: - asymmetries, but few storms, globally inconsistent. Geostatistical spatial modeling: - fast, only applied to European windstorm so far. WRN Autumn Seminar Nov 1 st 2017 15
Current Footprinting Approaches Parametric radial wind profiles: - fast, simple terrain, landuse, inland decay factors. Spatial analysis of observations: - asymmetries, but few storms, globally inconsistent. Geostatistical spatial modeling: - fast, only applied to European windstorm so far. Numerical modeling: - many physical processes, but slow, track error. WRN Autumn Seminar Nov 1 st 2017 16
Topographic Speed-Up A factor proportional to terrain height and shape. Can reach 2. (Miller et al. 2012) WRN Autumn Seminar Nov 1 st 2017 17
Channel Effects Winds parallel to mountains. Winds between mountains. WRN Autumn Seminar Nov 1 st 2017 18
Terrain drives damage Damaged roof locations in hurricane Fabian (2003). Miller et al. (2012) WRN Autumn Seminar Nov 1 st 2017 20
Footprinting Approach Historical track data (EBTrACS and JTWC) Holland et al. (2010) parametric pressure profile Kepert and Wang (2001) numerical boundary layer model. Fast, topographic and roughness effects, no track error, but some missing processes (e.g., strong thermal effects). WRN Autumn Seminar Nov 1 st 2017 21
The KW01 Model Diagnoses boundary-layer flow using dry equations of motion for a given pressure field. High-order turbulence scheme - prognostic TKE, turbulence dissipation. - diagnostic length scale (<80m). Ignores strong thermal effects. Rapidly achieves steady state. 22 WRN Autumn Seminar Nov 1 st 2017
Mods to KW01 1. Allow storms to move: - add environment pressure gradient to TC forcing, - add storm translation velocity to horizontal advection. 23 WRN Autumn Seminar Nov 1 st 2017
Mods to KW01 1. Allow storms to move: - add environment pressure gradient to TC forcing, - add storm translation velocity to horizontal advection. 2. Allow storms to change intensity and size: - update pressure gradient and allow winds to respond, - force gradient winds at model top. 24 WRN Autumn Seminar Nov 1 st 2017
Mods to KW01 1. Allow storms to move: - add environment pressure gradient to TC forcing, - add storm translation velocity to horizontal advection. 2. Allow storms to change intensity and size: - update pressure gradient and allow winds to respond, - force gradient winds at model top. 3. Include some topographic effects: - included in model equations. 4. Include variable surface roughness effects: - drag coefficient = f(terrain height and landuse). 25 WRN Autumn Seminar Nov 1 st 2017
Effects of Complex Topography Hurricane Maria (2017) ms -1 WRN Autumn Seminar Nov 1 st 2017 26
Variable Surface Roughness Hurricane Wilma (2005) ms -1 WRN Autumn Seminar Nov 1 st 2017 27
Eye-Wall Asymmetries? Hurricane Patricia (2015) WRN Autumn Seminar Nov 1 st 2017 28
Good comparison with HWIND Hurricane Wilma (2005) WRN HWIND ms -1 Similar asymmetry. Similar wind speed reduction at the coast. WRN Autumn Seminar Nov 1 st 2017 29
Surface Station Comparisons Hurricane Maria (2017) ms -1 WRN Autumn Seminar Nov 1 st 2017 30
Hurricane Harvey ms -1 ms -1 ms -1 WRN Autumn Seminar Nov 1 st 2017 31
Hurricane Harvey WRN Autumn Seminar Nov 1 st 2017 32
Hurricane Irma ms -1 ms -1 WRN Autumn Seminar Nov 1 st 2017 33
Reconstructing older events Typhoon Ellen (1983): Data: V max, lat, lon: IBTrACS. R max : Hong Kong radar. Constant 35km. R 34 : Hong Kong barogram. Set to 150km at landfall, then decrease following wind decay WRN Autumn Seminar Nov 1 st 2017 34
Ellen s Footprint at 78m Unique view of risk to high rise structures. ms -1 WRN Autumn Seminar Nov 1 st 2017 35
Application to Hazard Risk Combining with TC risk modeling to produce new views of global wind risk. Particularly valuable in regions of complex terrain. 10% annual wind speed (ms -1 ) WRN Autumn Seminar Nov 1 st 2017 36
Summary A globally-consistent topography-aware historical footprint dataset. New views of historical events. Dataset version 1.0. WRN Autumn Seminar Nov 1 st 2017 37