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Status report of WG 2 – Numerical aspects COSMO General meeting, Israel, Jerusalem

Status report of WG 2 – Numerical aspects COSMO General meeting, Israel, Jerusalem 11-14 Sept. 2017 Michael Baldauf, Uli Blahak (DWD) , Guy de Morsier, Pascal Spörri (MeteoCH), Andreas Will, Jack Ogaja (Univ. Cottbus), Werner Schneider (Univ. Bonn). Outlook

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Status report of WG 2 – Numerical aspects COSMO General meeting, Israel, Jerusalem

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  1. Status report of WG 2 – Numerical aspects COSMO General meeting, Israel, Jerusalem 11-14 Sept. 2017 Michael Baldauf, Uli Blahak (DWD), Guy de Morsier, Pascal Spörri (MeteoCH), Andreas Will, Jack Ogaja (Univ. Cottbus), Werner Schneider (Univ. Bonn)

  2. Outlook • Investigationsforthenew COSMO-D2 setup • The new Bott (2010) advectionscheme • Higher orderscheme (horizontal) • Extended targeteddiffusionagainstcoldpools • PP CDIC • PP CELO  Bogdan Rosa • new PP EX-CELO  Zbigniew Piotrowski M. Baldauf (DWD)

  3. At DWD, COSMO-D2 will replacethecurrentCOSMO-DE withthefollowingchanges: • increase horizontal resolutionfrom 2.8 km to 2.2 km • increasenumberofverticallevelsfrom 50 to 65 • increaseareafrom 10.5° * 11.5° to 13° * 14.3° COSMO-D2: 651 * 716 * 65 GPe 1440 * 1590 * 22 km³ COSMO-DE: 421 * 461 * 50 GPe 1160 * 1280 * 22 km³ Time schedule: since June 2017: pre-operational phase Q2/2018: operational introduction M. Baldauf (DWD)

  4. New choiceofverticallevels in COSMO-D2: • increaseresolutionmainlyoftheboundarylayer goal: improveinitiationofconvection • changefrom Gal-Chen to SLEVE-coordinate COSMO-D2 (SLEVE) COSMO-DE B. Ritter, B. Fay, U. Schättler, A. Seifert, C. Schraff, H. Reich, C. Gebhardt, M. Buchhold, F. Fundel, T. Hanisch, H. Frank, … M. Baldauf M. Baldauf (DWD)

  5. Frequency spectra for <PS> (horizontal average) COSMO-D2 2.2 km/L65 24h 12h 6h 2h 1h Hindcast-runs i.e. BCs by ICON-EU (6.5km) analysis from the ENS-VAR-DA COSMO-DE 2.8 km/L50 Observations: • dailycycle: 24h • solar tides at period12h(inducedfrom global ICON) • BC update: Nyquist-fr. = 1/2h! • ICON-analysis every 3h  N.-fr.=1/6h • obviouslynofurtherartifacts, instabilities, … M. Baldauf (DWD)

  6. Power spectra of kinetic energy KE spectra COSMO-D2 COSMO-DE SW-inflow, some heavy showers M. Baldauf, B. Ritter (DWD)

  7. KE spectra COSMO-D2 COSMO-DE M. Baldauf, B. Ritter (DWD)

  8. KE spectra COSMO-D2 COSMO-DE M. Baldauf, B. Ritter (DWD)

  9. Power spectra of vertical velocity w² spectra COSMO-D2 COSMO-DE SW-inflow, some heavy showers M. Baldauf (DWD)

  10. Conclusionsfrompowerspectra • nothinggoesobviouslywrongwiththe 2.2km resolution: spectrafor C-D2 arerelativelysimilartothoseof C-DE(C-DE KE spectrum at 12.08.17 + 12h has a strangeincrease at smallscales) • effectiveor 'practical' resolution: • oftenfor t=0 (analysis time) similarfor C-D2 and C-DE • forlaterforecasttimesmostly (but not always!) higherforC-D2 thanfor C-DE (asitshouldbe) • only in a fewcases a k -3-behaviour isvisible on the large scale(probablytheareaistoosmall) • sometimes a (weak) maximum in w² spectrum around 4 dx is visible.Skamarock et al. (2014) JAS: "We believe that the filter-scale peak is likely associated with grid-scale convection, waves generated by convection, and other marginally or underresolved small-scale processes." M. Baldauf (DWD)

  11. The new Bott advectionscheme … as an optionalcandidatefortraceradvection Bott (2010) MWR: • triestosolvethe 'mass-consistency'-problemwithout parallel computationof a continuityequation,but with an add./subtr. ofthedivergence in thedirection-splitting scheme • withoutfull Strang-splitting  efficiencygain;however still x-y-z / z-y-x forodd/even time steps • 4th orderscheme Followingslides: Verificationresultsforthecomparisonof operational COSMO-DE and COSMO-DE withnew Bott scheme Werner Schneider (Univ Bonn)Uli Blahak (DWD) M. Baldauf (DWD)

  12. Synop verification Bott (2010) current M. Baldauf (DWD)

  13. Synop verification Bott (2010) current M. Baldauf (DWD)

  14. Upper air verification M. Baldauf (DWD)

  15. Summary fortheverificationresultsofthenew Bott-scheme • Synop-Verif. of T2mand v10misslightly positive, neutral for TD2m, RH2m • Synop-Verif. ofcategoricalmeasuresforrain andgustsis negative,cloudinessis neutral • Temp-Verif. isvery positive forthenew Bott-scheme • Proposal: • theresultsare not entirelysatisfying, howevergoodenough • to bring thenew Bott-schemeas an option (!) intotheofficialcode (v5.6) • (fulfil COSMO science plan , sec. 5.2.4) M. Baldauf (DWD)

  16. Higher order discretization A. Will, J. Ogaja (BTU Cottbus) • Status • Large improvement in efficiencydone! In thecomparison advS4-P4 / advUP5-P2:advection ~10%, fast waves ~3% more expensive.withoutartificialdiffusion, thecostsareroughlythe same! • Dissertation J. Ogajaisavailable. • Model crash COSMO-DE at ‚20.06.2013‘ hasbeensolved • Summerlyprecipitation dry biasismuchreduced in theconvection-permittingsetup! • Next steps: • Transfer the code from version 5.0 to 5.6 ( A. Will, M. Baldauf) • Run this new version on NUMEX ( M. Baldauf) • Deliver documentation (COSMO Sci. Doc. part I, possibly alsoa COSMO-TR (?)) ( A. Will) • expected availability for the official code version: ~June 2017 ~Dec. 2017 M. Baldauf (DWD)

  17. Extended targeted diffusion against cold pools G. de Morsier, P. Spörri (MeteoCH) Motivation: 5th order advection can produce artificially cold pools in narrow valleys  targeted diffusion necessary. However, the current implementation (diffusion with 5-point stencil, only applied for T) did not cure every cold pool ocuring in COSMO-1 (1.1km) or COSMO-E (2.2 km, 21 members, with SPPT); (both setups don't use any artificial horizontal diffusion in inner domain!) Proposal: extend targeted diffusion to a 9-point stencil and apply to T, u, v where needed. This cured every T anomaly in a 6 month experiment! Status: Code ready for COSMO v5.6 (only a switch still necessary) for both Fortran and STELLA code version. M. Baldauf (DWD)

  18. Temperature Anomaly Problem (2)

  19. Temperature Anomaly

  20. Status reportofthePriority Project‚Comparisonbetweenthedynamicalcoresof COSMO and ICON‘ (CDIC) COSMO General meeting, Jerusalem 11-14 September 2017 Project team (current): Michael Baldauf, Florian Prill (DWD), Rodica Dumitrache, Amalia Iriza (NMA), Damian Wojcik (IMGW), Guy de Morsier (MeteoCH), Marina Shatunova, Denis Blinov, Alexandr Kirsanov (Roshydromet) with strong supportfrom Günther Zängl, Daniel Reinert, Uli Schättler (DWD) M. Baldauf (DWD)

  21. Aimofthe COSMO priorityproject ‚Comparisonofthedynamicalcoresof COSMO and ICON‘ (CDIC): deliver an asobjectiveaspossiblecomparisonofthedynamicalcores of COSMO and ICON withtheemphasis on limited areamodelling. • Task 1: idealisedtests (mainfocus) • Task 2: semi-realistictests • Task 3: scalability/performance • Task 4: Principalpropertiesofthenumericalformulation • Task 5: Suitabilityforotherapplications (climate/chemistry) M. Baldauf (DWD)

  22. Task 1. Good performance on a standard set of idealized test cases Definedtestcases 1. Advectiontestwithnonlineardynamics(Schär et al., 2002) ? 2. Atmosphere at rest(Zängl et. al (2004) MetZ) 3. Coldbubbleunstationarydensityflow(Straka et al., 1993) 4. Mountain flowtests (stationary, orographicflows) 4.1 Schär et al. (2002), section 5b 4.2 Bonaventura (2000) JCP (selection) 4.3 3D-case (dry)  5. Linear Gravity waves(Baldauf, Brdar, 2013) 6. Warm bubble(Robert (1993), Giraldo (2008)) 7. Moist, warm bubble(Weisman, Klemp, 1982) 8. Advectiontestsfortracerschemes (solid bodyrotation, …) ! M. Baldauf (DWD)

  23. Test case 4.1: 2D linear flow over mountains x=500m z=300m COSMO ICON colorsandblackdottedlines: COSMO or ICON greylines:analyticsolution(Baldauf, 2008, COSMO-NL) vertically equidistant grid M. Baldauf (DWD)

  24. Test case 4.3a: 3D linear flow over mountains COSMO ICON colorsandgreylines: COSMO or ICON simulation blacklines:analyticsolution(Baldauf, 2008, COSMO-NL) M. Baldauf (DWD)

  25. Test case 4.3a: 3D linear flow over mountains COSMO ICON colorsandgreylines: COSMO or ICON simulation blacklines:analyticsolution M. Baldauf (DWD)

  26. Test case 4.3b: 3D nonlinear flow over mountains COSMO ICON h0=1000m  max h = 234.9m  max  = 13.2° M. Baldauf (DWD)

  27. Test case 4.3b: 3D nonlinear flow over mountains COSMO ICON h0=3000m  max h = 704.7m  max  = 35.2° M. Baldauf (DWD)

  28. Test case 4.3b: 3D nonlinear flow over mountains COSMO ICON stable only with Mahrer-discretization h0=4000m  max h = 939.6m  max  = 43.2° M. Baldauf (DWD)

  29. Test case 4.3b: 3D nonlinear flow over mountains COSMO ICON COSMO: unstable stable until h0=4600mmax h = 1080m  max  = 47.2° h0=5000m  max h = 1174m  max  = 49.6° M. Baldauf (DWD)

  30. Test case 4.3b: 3D nonlinear flow over mountains COSMO ICON COSMO: unstable h0=8000m  max h = 1879m  max  = 62.0° M. Baldauf (DWD)

  31. Summary fortestcases 4.x: flowovermountainstests • In the Schär et al. 2D linear mountainflowtestbothmodels COSMO and ICON behavequitesimilar; withslightadvantagesfor ICON. • Also in the 3D linear testtheanalyticsolutionisvery well simulated metrictermsarecorrectlyimplemented in bothmodels(noclearwinner) • ICON toleratesmuchsteeperslopesthan COSMO(Zängl (2012) MWR) • The highmountaintestsshouldberepeatedwith ‚non-periodic BCs‘ topreventfromincreasingblockingeffects M. Baldauf (DWD)

  32. Test case 5: linear gravity + sound waves setup similar to Skamarock, Klemp (1994) MWR • Test properties: • test dry Euler equations • unstationary inspect time integr. • noorography • smallamplitude linear  comparisonwithanalyticsolution An analytic solution for the compressible non-hydrostatic Euler equations is given in Baldauf, Brdar (2013) QJRMS M. Baldauf (DWD)

  33. Test case 5: linear gravity + sound waves Convergence behaviour COSMO ICON T‘ 2nd order 1st order w due to a bug fix in the test setup (proper use of periodic BCs) the COSMO result is now better than that described in BB2013 M. Baldauf (DWD)

  34. Summary fortestcase 5: linear gravity + soundwaves • Test 1 (only fast waves): ICON showsnearly 2nd order convergenceCOSMO showsnearly 2nd order only in T, but less in w w errorissmaller in ICON forfineresolutions • Test 2 (FW + advection): ICON behaviourissimilartotest 1. COSMO convergence order isslightlyreducedforcoarseresolutions ICON errorsare a bit larger than in COSMO,forfineresolutions a bitsmaller • Test 3 (FW + Coriolis): bothmodelsshow 2nd order convergence; but theerrorsaresmaller in ICON Remark: to get 2nd order, one needs to switch off any vertical off-centering M. Baldauf (DWD)

  35. Test case 3: cold bubble R. Dumitrache, A. Iriza (NMA) Testsetup by Straka et al (1993) • Test properties: • testof dry Euler equations (without Coriolis force) • unstationary • stronglynonlinear • comparisonwithreferencesolutionfrompaper M. Baldauf (DWD)

  36. COSMO Test case 3: cold bubble  at t=15 min. for x= 200, 100, 50, 25m ICON  somethinggoeswrong… diffusion? still tobedone… Reference solution from Straka et al.: M. Baldauf (DWD)

  37. Test case 2: atmosphere at rest Test setupsimilartoZängl et al. (2004) same settings in COSMO and ICON for • grid (COSMO quadrilat., ICON trianglewith dx=2km, dz=19.8m…780m, htop=20km, vcflat=15km, rdheight=16km) • referenceatmosphere (irefatm=2) • initial profile: piecewisepolytropic M. Baldauf (DWD) M. Baldauf (DWD)

  38. Test case 2: atmosphere at rest ICON COSMO y_vert_adv_dyn='impl3' COSMO y_vert_adv_dyn='impl2' M. Baldauf (DWD)

  39. Test case 2: atmosphere at rest ICON COSMO y_vert_adv_dyn='impl3' COSMO y_vert_adv_dyn='impl2' M. Baldauf (DWD)

  40. Test case 2: atmosphere at rest ICON COSMO y_vert_adv_dyn='impl3' COSMO y_vert_adv_dyn='impl2' M. Baldauf (DWD)

  41. Test case 2: atmosphere at rest time series of wmax COSMO, impl2 ICON COSMO, expl COSMO, impl3 M. Baldauf (DWD)

  42. Summary fortestcase 2: atmosphere at rest • disturbancessets in faster in COSMO than in ICON • themaximumverticalvelocity at saturationissmaller in COSMO(at least forfirst 24h) • In COSMO the operational (!) settingy_vert_adv_dyn='impl2'isunstable, only'expl'and'impl3'remainstable.However, thelattertwooptionsbothneed additional investigations. M. Baldauf (DWD)

  43. Test case 7: Weisman, Klemp (1982) test setup • Idealized moist convection experiment designed to reproduce the development and subsequent evolution of a convective cloud • Test basic consistency of the coupling between dry model equations and moist microphysics and turbulence parameterization • horizontal resolution: 2km • COSMO, ICON: microphysics with 3-cat. ice  WK82: Kessler D. Wojcik (IMGW) • Following plots show: • Vertical wind: on 4150 m height (contours, negative values dashed) • Horizontal wind: on 87 m height (arrows) • Gust front: on 10 m height (thick blue line, - 0.5 K temperature perturbation) • Precipitation: on 10 m height (dashed, for QR values exceeding 1 and 4 g / kg) M. Baldauf (DWD)

  44. Results for Us = 25 m/s ICON model COSMO model W-K 1982 40 min 80 min WG2 COSMO General Meeting 2017

  45. Results for Us = 25 m/s ICON model COSMO model W-K 1982 120 min WG2 COSMO General Meeting 2017

  46. Summary • In this experiment ICON model demonstrates capability to reproduce realistic convective nonhydrostatic flows • There is no indication of basic errors in the coupling between dry ICON dynamical core and moist microphysics and turbulence parameterizations • When rather little horizontal environmental vorticity in present (Us = 15 m/s) the ICON model reproduces basic convective structures (gust front, convective updraft, precipitation region and surface outflow). The convective updraft tends to get more ‘blurred’, but that probably results from different effective diffusivity of the two models • In the middle case (Us = 25 m/s) the convective updraft for the ICON model is more compact (comparing to Us = 15 m/s) bus still less compact in comparison with COSMO R-K • In the case with high env. vorticity (Us = 35 m/s) the ICON model updraft is more compact comparing with COSMO R-K and more similar to the benchmark solution. Also the lateral drift of the convective cell is more similar to the benchmark solution WG2 COSMO General Meeting 2017

  47. Overall conclusions for task 1 • Most of the planned idealised tests have been inspected, almost all of these have been finished • In general, no detrimental effects of ICON visible (in the contrary!) • However, the question remains„what is a fair comparison“?E.g. quadrilateral vs. triangle grid, …: what is the ‚right‘ resolution?Probably the best is to compare „error as fct. of model run time“ (on the same computer)(but this needs some extra considerations for 2D slice tests) M. Baldauf (DWD)

  48. Task 2: Ability to handle semi-realistic cases reasonably well Test casesaredefined: • strong advectivecase: storm ‚Elon‘, 9-10 Jan. 2015 (MeteoCH) • strong advectivecase: storm 'Carmen', 12 Nov. 2010 (MeteoCH) • Bora event: 6-8 Feb. 2012 (possibly also 19 Feb. 2016) (RHM) However, the ICON developersdidn‘twanttodistributethe ‚limited areamode‘ versionbeforethe ICON trainingscourse 28.02.-03.03.17 becausedocumentation will not bereadybeforethisevent.  heavy delay in thistask  projectprolongationrequired M. Baldauf (DWD)

  49. Task 3. Scalability/Performance suitable for operations as well as for future supercomputing platforms strong scaling tests on Cray XC40 (Broadwell): COSMO-D2 and ICON-D2 setups, 27h forecast runs Code improvements in ICON for reading of boundary data have been necessary before starting the strong scalability tests (F. Prill) Further optimisation planned by reducing latency by collecting all levelsbefore communication. Comparison: Efficiency of ICON is higher than in COSMO. However, the apparently reduced scalability in ICON for #procs>1000 still stems from the distribution of boundary data (even influences time measurement of dynamics) M. Baldauf (DWD)

  50. Task 3 COSMO-D2 this bad scaling (caused by RTTOV) has been improved by U. Schättler in COSMO 5.4f probably needed for COSMO-D2 M. Baldauf (DWD)

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