Introduction to Ocean Numerical Modeling #0 General Introduction. Global model SSH regional model SST

Transcription

1 Introduction to Ocean Numerical Modeling #0 General Introduction Global model SSH regional model SST Gildas Cambon, IRD/LOPS, France

2 Global model SSH WEEK 1 regional model SST Day 1: 09:30 11:00: Introduction + Equations of geophysical fluid dynamics 11:30 13:30: Discretization + First steps in numerical modeling 15h00 18h00: Statistical tools for model validation (A. Montecinos) Day 3: 09:30 12:00: Presentation of 3D models + CROCO 13:45 15:45: Practical using the shallow water model 16:00 18:00: Practical for Statistical tools for model validation (A. Montecinos) Day 4: 09:30 12:00: Evaluation 15:00 18:00: Finish practical and open discussion Day 2: 09:30 12:00: First steps in numerical modeling 14:00 15:45: Practical using simplified 1D equations 16:00 17:45: Practical for Statistical tools for model validation (A. Montecinos)

3 Goals: To understand the concepts of numerical modelling of the Ocean. To be aware of the methods and limitations in numerical modelling. PDF available at hap://stockage.univ-brest.fr/~cambon/asi18/sess1/lectures_sess1/

4 1 Why study the Physics of the Oceans? 2 Ocean general properties 3 Ocean observations 4 Ocean models

5 Why study the Physics of the oceans? 1. We get food from the ocean. Fish: about 15.4% of animal protein consumption and 5.5% total protein consumption by humans in the 1990s. (source FAO) Example: fisheries in upwelling ecosystems (source Benguela Current Commission) Surface chlorophyll concentration ( Center (source SeaWiFS & CZCS, NASA/Goddard Space Flight Benguela fisheries: tons, US$19 billion per year.

6 Why study the Physics of the oceans? 2. We use the ocean. Example: transport Example: exploitation Example: leisure

7 Why study the Physics of the oceans? 3. Influence on weather and climate image source Ocean heat content for m (Levitus et al. 2009)

8 Why study the Physics of the oceans? 3. Influence on weather and climate Ocean northward heat transport for 1988 Source Stewart et al., 2005, ocng_textbook/contents.html

9 Oceanic geometry Source oceansjsu.com/105d/ exped_commotion/8.html Width: ~ km Depth: ~ 5 km

10 Oceans and Currents Surface circulation Image source Surface temperature Surface salinity

11 A wide range of scales for ocean processes Figure adapted from Cushman-Roisin and Beckers, 2009.

12 Ocean observation Research cruises

13 Source Ocean observation Moorings Source Source

14 Ocean observation Satellite Oceanography Jason 2 satellite, operated by EUMETSAT Source

15 Ocean observation Coastal Radar Stations Source Source

16 Ocean observation ARGO profilers Source

17 Ocean observation Gliders

18 Ocean Observation Paleo-oceanography

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20 Ocean dynamics are complex Surface circulation Iso-surface of vorticity for the Agulhas rings... and highly non-linear

21 It is difficult to observe the Ocean In-situ observations (boat): - VERY expensive - 1 station at a time (no global coverage). - difficult to get all the variables at the same time. - limited time period. Moorings: - Long time series (a few months to a few years). - Very localized (1 point). - Subject to fooling and vandalism. Satellites: - Global coverage. - Quasi-synoptic view (i.e. Possible to get almost a snapshot of the global ocean) - Only surface measurements. - Few variables: SST, SSH, Ocean color (phytoplankton). - Problem of clouds (SST, color) or reference level (SSH). Lagrangian floats (surface drifters, profilers, etc..): - Quasi-synoptic observations (if enough floats). - Limited coverage. - Difficult to control. New technologies (gliders, sea-soar, etc..): - Prototypes. + It is very difficult to understand these observations...

22 ... Use of models: Pros: - Can be relatively cost effective. - Gives you a synoptic view for all the variables at all times. - Possibility to diagnose the equilibriums (ex: role of bottom friction). - Possibility to use simplified models to understand the processes. - Possibility to track processes in time (ex: fate of upwelled water). - Possibility to test hypothesis (ex: Remove Madagascar). - Possibility to run events from the past (ex: Paleo-climatology). - Possibility to test what if scenarios (ex: global warming). - Possibility to couple different models (ex: atmosphere, water quality, biogeochemistry, land, rivers, fish, economy). - Possibility to do forecasts. Downloaded from Miami Isopycnic Coordinate Ocean Model web site Cons: - A model solution is not reality. - Sometimes it doesn t work. - Staying all day in front of a computer J

23 Good point : we know the equations to solve Bad point : we don't know how to solve them => Use of numerical modelling

24 Principle: Boundary conditions Ocean at time t Primitive Equations Ocean at time t + dt