Matthew J. Hoffman CEAFM/Burgers Symposium May 8, 2009 Johns Hopkins University Courtesy NOAA/AVHRR Courtesy NASA Earth Observatory

 Overview of ocean instabilities  Overview of the breeding method  Application to global ocean model  Development of bred vector energy equations to diagnose instability dynamics  Study of Pacific tropical instabilities

 Flow Instabilities are prevalent in the upper ocean  Most occur in strong currents—western boundary currents, Southern Ocean  Instabilities take place on different timescales  Tropical Pacific instabilities are some of the strongest Ducet et al., 2000

 Pacific Tropical Instability Waves are seen in the Pacific equatorial cold tongue  Periods of days, Wavelength of ~1000km  Tropical waves are coupled to the atmospheric boundary layer and are important for heat and momentum balances  Masina et al. (1999) argued for baroclinic energy conversion dominating  Qiao and Weisberg (1995)argued for barotropic energy conversion dominating Jesse Allen, NASA Earth Observatory – SST from Advanced Microwave Scattering Radiometer on Aqua

 Developed by Toth and Kalnay (1993, 1997) to estimate the shape of growing errors in a non- linear atmospheric model  Also provides initial conditions for ensemble forecasting  2 parameters in the method—rescaling size and time between rescaling  Parameters can be tuned to isolate instabilities of different time scales  Yang et al. (2005) used breeding on a coupled GCM to identify slow growing ENSO modes

 A small, random perturbation is added to the initial state of the system  Both the perturbed and unperturbed (control) conditions are integrated forward in time  The control forecast is subtracted from the perturbed forecast, yielding the bred vector  The bred vector is rescaled to its initial size and added to the control forecast as a new perturbation

 GFDL Modular Ocean Model (MOM) 2b code  Driven by monthly averaged NCEP reanalysis winds from  SST and surface salinity from World Ocean Atlas 1994  Same setup used by Carton et al. (2000) for SODA  1 ° resolution in longitude, stretched latitude grid ranging from 1 ° in midlatitudes to ½ ° in tropics  20 vertical levels – 15 meters level thickness near surface

 10 day bred vectors identify many instabilities in the ocean  Instabilities are seen in the Southern Ocean, in boundary currents, and in the Tropical Pacific, among other locations

 Seasonal cycle is clear  Speed is 0.46m/s  Wavelength is 1000km  25 day period

 Seasonal cycle is clear  Speed is 0.46m/s  Wavelength is 1000m  25 day period  Interannual cycle tied to El Niño-La Niña cycle (ENSO) El Niño

 Seasonal cycle is clear  Speed is 0.46m/s  Wavelength is 1000m  25 day period  Interannual cycle tied to El Niño-La Niña cycle (ENSO) La Niña

 Momentum Equations:  Kinetic energy defined as  Bred kinetic energy is:

 Terms have physical interpretation

 Horizontal and vertical divergence of energy transport

 Terms have physical interpretation  Horizontal and vertical divergence of energy transport  Work of pressure force

 Terms have physical interpretation  Horizontal and vertical divergence of energy transport  Work of pressure force  Baroclinic conversion term

 Terms have physical interpretation  Horizontal and vertical divergence of energy transport  Work of pressure force  Baroclinic conversion term  Barotropic conversion term

 Tropical Pacific shows positive conversion (bred potential to bred kinetic)  Shows Instability Growth  South Atlantic shows negative conversion (bred kinetic to bred potential)  Stabilizing region

 Tropical Pacific shows positive conversion (bred potential to bred kinetic)  Shows Instability Growth  South Atlantic shows negative conversion (bred kinetic to bred potential)  Stabilizing region

 Tropical Pacific shows positive conversion (bred potential to bred kinetic)  Shows Instability Growth  South Atlantic shows negative conversion (bred kinetic to bred potential)  Stabilizing region

 Monthly averages over a 30 year period are shown for January  Depth averaged over upper 150m  Baroclinic conversion is strongest from 3°N-5 ° N  Barotropic conversion is strongest at the equator  Baroclinic conversion is stronger in this model  Energy conversion is strongest when bred vectors are strongest (La Niña)

 Baroclinic conversion is strongest at coldest temperatures (cold tongue)  Barotropic conversion is strongest at shear points (between South Equatorial Current and Equatorial Undercurrent)  Different locations for the different mechanisms At 3.5 ° NAt 0.25 ° N

 Breeding is an easy way to identify instabilities in a dynamical system  Breeding energy equations allow bred vectors to be used to diagnose the dynamical causes of instabilities  Tropical Pacific instabilities have a baroclinic and barotropic component  Baroclinic component is stronger in this model and occurs along the north edge of the cold tongue between 3 ° N and 5 ° N  Barotropic component occurs at the equator between the South Equatorial Current and the Equatorial Undercurrent

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