HWRF v3.7a Tutorial Nanjing, China, December 2, 2015 HWRF Ocean: MPIPOM-TC Ligia Bernardet NOAA SRL Global Systems Division, Boulder CO University of Colorado CIRS, Boulder CO Acknowledgement Richard Yablonsky (formerly of University Rhode Island) 1
Importance of using a coupled model Accurate SST representation is important for TC forecast Having a good SST initialization is critical For most storms, SSTs does not change much in 5-day period For some cases, SST can change in a shorter time scale Intense/large/slow moving storms Can cause upwelling (transport of colder water to the surface) SST reduces and affects TCs Uncoupled TC models with static SST neglect SST cooling during model integration à high intensity bias Can also affect TC track, structure
Katrina Courtesy Rich Yablonsky
What is the Princeton Ocean Model? Three-dimensional, primitive equation, numerical ocean model (commonly known as POM; Mellor 2004) Originally developed by A. Blumberg and G. Mellor in the late 1970 s Transferred to and developed by University of Rhode Island (URI) since mid-1990 s POM code changes made at URI specifically to address ocean response to hurricane wind forcing ( POM-TC ) Included in the GFDL operational hurricane model since 2001 and in HWRF since 2007 Most recent updates are ability to run in any basin and MPI capability (MPIPOM-TC) Implemented in HWRF with ~ 9-km grid spacing and 9-min timestep
HWRF ocean domains In operations, HWRF uses an ocean model only in the AL and P basins. Other basins are run uncoupled by default. Comprehensive tests of coupled HWRF performance on worldwide basins not performed yet. Options for initialization need to be evaluated. In this tutorial, we will teach the experimental ocean coupling capability for WP
POM-TC Sigma Vertical Coordinate 23 vertical sigma levels; free surface (η) Level placement scaled based on ocean bathymetry Largest vertical spacing occurs where ocean depth is 5500 m Location of 23 half-sigma levels when ocean depth is 5500 m: 5, 15, 25, 35, 45, 55, 65, 77.5, 92.5, 110, 135, 175, 250, 375, 550, 775, 1100, 1550, 2100, 2800, 3700, 4850, and 5500 m
Physics of Storm-Core SST Change Vertical mixing/entrainment (Slide 8) Upwelling (Slide 9) Horizontal advection (Slide 10) Heat flux to the atmosphere (small by comparison)
1) Vertical mixing/entrainment Wind stress surface layer currents Current shear turbulence Turbulent mixing entrainment of cooler water POM-TC uses the Mellor-Yamada 2.5 turbulence closure submodel to parameterize vertical mixing Sea Warm surface sea temperature surface temperature decreases A T M O S P H R O C A N Subsurface Cool subsurface temperature temperature increases This is a 1-D (vertical) process
2) Upwelling Cyclonic wind stress divergent surface currents Divergent currents upwelling Cyclonic hurricane Upwelling cooler water brought to surface vortex A T M O S P H R Warm sea surface temperature O C A N Cool subsurface temperature This is a 3-D process
3) Horizontal advection Preexisting cold pool is located outside storm core Preexisting current direction is towards storm core Cyclonic hurricane Ocean currents advect cold pool under storm core vortex A T M O S P H R Warm sea surface temperature O C A N Cool subsurface temperature This is a horizontal process
< < Prescribed propagation speed Cyclonic hurricane vortex < < A T M O S P H R < < Homogeneous initial SST < < O C A N < < < Horizontally-homogeneous subsurface temperature < What is the impact of varying storm translation speed?
2.4 m s -1 4.8 m s -1 Hurricanes have historically propagated in the Gulf of Mexico: < 5 m s - 1 73% and < 2 m s - 1 16% of the time And in the western tropical North Atlantic: < 5 m s - 1 62% and < 2 m s - 1 12% of the time So 3- D effects (e.g. upwelling) are important Yablonsky and Ginis (2009, Mon. Wea. Rev.)
Initialization Prior to coupled model integration of HWRF/MPIPOM-TC, MPIPOM-TC must be initialized with a realistic 3-D temperature (T) and salinity (S) field GDM is used operationally for Atlantic GDMv3 is used operationally for ast Pacific and is supported for basins In AL, this is enhanced by adding features: cold/warm rings and loop current This T & S field must then be used to generate realistic ocean currents via geostrophic adjustment The spun-up ocean must then incorporate the pre-existing hurricane generated cold-wake by applying TC s wind stress using the TC Vitals
Importance of realistic initialization of 3D fields Typical of Gulf of Mexico in Summer & Fall Typical of Caribbean in Summer & Fall
Gustav 2008082800 xample: Ocean Initialization & Response (Next 5 Slides)
August GDM T/S Climatology SST (C) ~75-m Temperature (C) Starting point is August GDM Temperature/Salinity climatology August GDM is then interpolated in time to start date by blending with September GDM
Features & Sharpening (AL only) SST (C) ~75-m Temperature (C) GDM T/S climatology is modified using the feature-based model This includes cross-frontal sharpening
00-h Phase 1: GFS SST Assimilated SST (C) ~75-m Temperature (C) Land/sea mask is applied At 00-h Phase 1, daily NCP SST is assimilated into the upper ocean mixed layer T/S fields vertically-interpolated to POM σ-levels
48-h Phase 1 / 00-h Phase 2 SST and Surface Current Vectors ~75-m Temperature and Current Vectors During 48-h of phase 1 integration, SST is held constant while currents geostrophically adjust 48-h phase 1 = 00-hour phase 2
72-h Phase 2 / 00-h Coupled SST and Surface Current Vectors ~75-m Temperature and Current Vectors (Land/sea mask applied) During 72-h of phase 2 integration, cold wake is generated by applying NHC message file wind 72-h phase 2 = 00-hour coupled HWRF/MPIPOM-TC
WRF-NMM/POM-TC Coupling Wind speed (U a ) Temperature (T a ) Humidity (q a ) Atmospheric Model Air-Sea Interface Momentum flux (τ) Sensible heat flux (Q H ) Latent heat flux (Q ) Momentum flux (τ) Temperature flux Shortwave radiation Ocean Model SST (T s ) τ = ρ C U U Q C U ( T T ) a D a a H V = Q = CU ( qa qs ) a H a a s L C P
Thank you for your interest! You can Ask questions during the tutorial Visit our website: http://www.dtcenter.org/hurrwrf/users Contact me later: ligia.bernardet@noaa.gov Reach our user helpdesk: hwrf-help@ucar.edu Consult references Biswas, M. K., L. Carson, C. Holt, and L. Bernardet, 2015: Community HWRF Users Guide V3.7a. Developmental Testbed Center, 145 pp. [Available at http://www.dtcenter.org/hurrwrf/users/docs/users_guide/hwrf_v3.7a_ug.pdf]. Mellor, G. L., 2004: User s guide for a three-dimensional, primitive equation, numerical ocean model (June 2004 version). Prog. in Atmos. and Ocean. Sci., Princeton University, 56 pp. Tallapragada, V. and coauthors, 2015: Hurricane Weather Research and Forecasting (HWRF) Model: 2015 scientific documentation. Developmental Testbed Center, 113 pp. [Available at http://www.dtcenter.org/hurrwrf/users/docs/scientific_documents/hwrf_v3.7a_sd.pdf]. Yablonsky, R. M., and I. Ginis, 2008: Improving the ocean initialization of coupled hurricane-ocean models using feature-based data assimilation. Mon. Wea. Rev., 136, 2592-2607. Yablonsky, R. M., and I. Ginis, 2009: Limitation of one-dimensional ocean models for coupled hurricane-ocean model forecasts. Mon. Wea. Rev., 137, 4410-4419. Yablonsky, R. M., and I. Ginis, 2013: Impact of a warm ocean eddy s circulation on hurricane-induced sea surface cooling with implications for hurricane intensity. Mon. Wea. Rev., 141, 997-1021. Yablonsky, R. M., I. Ginis, B. Thomas, V. Tallapragada, D. Sheinin, and L. Bernardet, 2014: Description and Analysis of the Ocean Component of NOAA s Operational Hurricane Weather Research and Forecasting Model (HWRF). J. Atmos. Oceanic Technol, 32, 144-163.