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GungHo! A new dynamical core for the Unified Model Nigel Wood, Dynamics Research, UK Met Office © Crown copyright Met Office.

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Presentation on theme: "GungHo! A new dynamical core for the Unified Model Nigel Wood, Dynamics Research, UK Met Office © Crown copyright Met Office."— Presentation transcript:

1 GungHo! A new dynamical core for the Unified Model Nigel Wood, Dynamics Research, UK Met Office
© Crown copyright Met Office

2 Outline Unified Model – where we are now & the need for change GungHo!
Some results from each workpackage Summary © Crown copyright Met Office © Crown copyright Met Office 2

3 Current Unified Model “New Dynamics” Davies et al. (2005)
Regular lat/lon grid. Non-hydrostatic dynamics with a deep atmosphere. Semi-implicit time integration with 3D semi-Lagrangian advection. Atmospheric tracer advection Physics: Spectral band radiation Diagnostic or prognostic cloud Mixed-phase ppn Mass flux convection Boundary layer Gravity wave schemes Coupling possible to non-atmospheric components: Land surface model Ocean model Sea ice model Chemistry/aerosol model © Crown copyright Met Office

4 Relative performance 3 day Northern Hemisphere surface pressure errors
3 day Northern Hemisphere surface pressure errors © Crown copyright Met Office

5 T24/TN Scalability (17km) Nodes Perfect scaling 24 nodes
Same plot but as a scaling plot. 24 nodes Nodes (1 node=32 processors) © Crown copyright Met Office

6 The finger of blame… At 25km resolution, grid spacing near poles = 75m
At 10km reduces to 12m! © Crown copyright Met Office © Crown copyright Met Office 6 6

7 Challenges! Scalability – remove the poles!
© Crown copyright Met Office © Crown copyright Met Office

8 Challenges! Scalability – remove the poles!
Speed – cannot sacrifice this for low resolution moderate core counts Accuracy – need to maintain standing of model Space weather  600km deep model… Danger: Everything to everyone…or Nothing to anyone? © Crown copyright Met Office © Crown copyright Met Office

9 GungHo! Globally Uniform Next Generation Highly Optimized
“Working together harmoniously” © Crown copyright Met Office

10 5 Year Project Split into two phases: 2 years “research” (2011-13)
“To research, design and develop a new dynamical core suitable for operational, global and regional, weather and climate simulation on massively parallel computers of the size envisaged over the coming 20 years.” Split into two phases: 2 years “research” ( ) 3 years “development” ( )

11 UK Collaboration of GFD, numerical and computational scientists
5 FTEs from Met Office (Dynamics Research; HPC Optimisation; UM infrastructure) 5 FTEs from NERC (Bath, Exeter, Imperial, Leeds, Manchester, Reading, Warwick) 2 FTEs from STFC (Hartree Centre)

12 GungHo Issues How to maintain accuracy of current model on a GungHo grid? Principal points about current grid are: Orthogonality C-grid These provide a number of good numerical properties (Staniforth & Thuburn QJ 2012) Challenge is to retain those on a non-orthogonal grid © Crown copyright Met Office

13 Some workpackage results
© Crown copyright Met Office 13

14 Grids Good dispersion Minimal grid imprinting No computational modes
C-grid dispersion relations Grids Exact Low order FEM Frequency FD Good dispersion Minimal grid imprinting No computational modes Finite element approach Focus on: Cubed-sphere; possibly triangles Higher order FEM Partially mass lumped FEM Group velocity Cotter (Imperial), Melvin & Staniforth (MetO) © Crown copyright Met Office Nondimensional wavenumber

15 Grids Higher order FEM Good dispersion Minimal grid imprinting
No computational modes Finite element approach Focus on: Cubed-sphere; possibly triangles U V Φ Partially mass lumped FEM Cotter (Imperial), Melvin & Staniforth (MetO) © Crown copyright Met Office

16 Recent results Williamson Test Case 5 with 160K d.o.f.s (320x160) 9 m
Thuburn (Exeter) Williamson Test Case 5 with 160K d.o.f.s (320x160) 9 m 6 m FEM Hexagonal FEM Cubed-sphere 10 m 11 m h background = 5000 m. Reference solution = 1024x512. Rotated = by 45 degrees. Reference solution cubically interpolated to each grid. SISL not SLICE. ENDGame lat-lon ENDGame rotated lat-lon © Crown copyright Met Office

17 Are implicit schemes viable?
Weak horizontal scaling for a 3D Helmholtz problem Baseline resolution = 64x64 Nz=128 Grid cells per processor = 520K Cs*Dt/Dx=const=8.4 One side of cubed-sphere Algebraic Multi-grid Conjugate Gradient Geometric Multi-grid Mueller & Scheichl (Bath) Hector © Crown copyright Met Office

18 What to do if not… Horizontally Explicit – Vertically Implicit (HEVI)
Computational modes arise from multistep schemes  Examine range of Runge-Kutta Implicit-Explicit (IMEX) schemes Weller (Reading) & Lock (Leeds) © Crown copyright Met Office HEVI Implicit

19 Test cases Finite difference scheme applied on a variety of grids
Simple solid body rotation (Williamson test case 2) Height and velocity errors after 5 days Weller, Thuburn and Cotter, MWR, 2012 Weller (Reading), Thuburn (Exeter) & Cotter (Imperial) © Crown copyright Met Office

20 Computational Science
Ham (Imperial), Ford & Pickles (STFC), Riley (Manchester) Vertical loop inner most Indirect addressing for horizontal F2003 © Crown copyright Met Office

21 Transport Mass conservation = #1 user requirement!
Inherent part of mimetic approach But want to maintain non-split approach of current SL scheme OK in horizontal (CFL<1 on uniform mesh) – see previous simulations Challenge is in vertical… © Crown copyright Met Office

22 Timetable… Further development and testing of horizontal [2013]
Testing of proposals for code architecture [2013] Vertical discretization [2013] 3D prototype development [ ] Operational…by 2020  Long term step change in scalability © Crown copyright Met Office

23 Thank you! Questions? © Crown copyright Met Office

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