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AMPS: A real-time application of WRF over Antarctica

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  1. AMPS: A real-time application of WRF over Antarctica Michael G. Duda, Kevin W. Manning, and Jordan G. Powers NCAR / MMM Division NCAR-NCAS WRF Workshop

  2. What is AMPS? • AMPS: Antarctic Mesoscale Prediction System • Real-time system using WRF with polar modifications • Twice-daily model runs (launched at 00 and 12 UTC) • Each run extends out to 120h • About 1 GB of plot products produced from each run and made available through web interface • Most products customized for forecasters • Goals of AMPS project • Support USAP weather forecasting • Improve Antarctic NWP NCAR-NCAS WRF Workshop 1

  3. Overview • Model setup • Experiences • Increasing horizontal resolution and raising model top • Surface warm bias • Future improvements • Model sensitivity to radiation scheme NCAR-NCAS WRF Workshop 2

  4. Model domain configuration 1 2 3 5 4 6 All nests are two-way interactive. 43 half-eta levels 10 hPa model top NCAR-NCAS WRF Workshop 3

  5. Model domain configuration McMurdo Station 1.7-km Ross Island nest 15-km Antarctic nest NCAR-NCAS WRF Workshop 4

  6. Model options • WRF v3.0.1 with polar modifications (tuned for use in high latitudes; http://polarmet.mps.ohio-state.edu/PolarMet/pwrf.html) • Fractional sea ice • Improved treatment of heat transfer for ice sheets Physics options Dynamics options NCAR-NCAS WRF Workshop 5

  7. Data assimilation • WRF-Var for data assimilation on 45-km and 15-km grids • Assimilated observations include • “Conventional” observations (radiosonde, AWS, ship/buoy/aircraft) • Satellite obs (Meteosat 7,9; GOES-11,12; MODIS winds; QuikSCAT winds) • GPS RO soundings (refractivity) NCAR-NCAS WRF Workshop 6

  8. Cycled soil temperatures • GFS soil temperatures have generally been too warm in Antarctica • Solution: cycle the soil temperature field from one forecast to the next • Cycled soil temperatures have the effect of lowering soil temperature in model • However, observations of 2-m air temperature still showed a warm bias NCAR-NCAS WRF Workshop 8

  9. Cycled soil temperatures Soil temperature cycled over ~1 yr (?) using the Noah LSM Soil temperature from GFS 0 - 10 cm layer 100 - 200 cm layer NCAR-NCAS WRF Workshop 9

  10. Moving from a 60-km to a 45-km coarse grid • In Nov 2008, increased horizontal resolution from 60-km in coarse grid to 45-km; all other nests increased proportionately • Raise model top from 50 hPa to 10 hPa, increase number of vertical levels from 31 to 44 • Increase in model top originally motivated by satellite data assimilation • New configuration requires about 3.4 times as much computation (current wallclock time for one AMPS run ~4.5 h) NCAR-NCAS WRF Workshop 11

  11. AMPS vertical coordinate configuration Fouradditional layersbelow 1km New vertical level structure Significantly thinner layers (higher resolution)‏ near surface Lowest 2 km Older 31-level configuration New 44-level configuration NCAR-NCAS WRF Workshop 12

  12. AMPS vertical coordinate configuration New vertical level structure New configuration: Model lid at 10 mb Above 2 km Damping layer in top 7 km Vertically propagating waves damped, little spurious reflection Extending model top to 10 mb improves the assimilation of satellite data Old configuration: Model lid at 50 mb NCAR-NCAS WRF Workshop 13

  13. New vertical level structure • To remove strong reflections from model top, w-Rayleigh damping activated in top 7 km of the model Vertical velocity cross section, no damping Vertical velocity cross section, with w-Rayleigh damping NCAR-NCAS WRF Workshop 14

  14. Performance of new setup The 45-km / 10 hPa Ptop grid setup replaced the 60-km / 50 hPa Ptop setup on 3 Nov 2008 Oct 18 Nov 18 Nov 3 60-km, 50 hPa Ptop 45-km, 10 hPa Ptop What impact did this change in grid structure have on the performance of forecasts? NCAR-NCAS WRF Workshop 15

  15. Performance of new setup: ACC In terms of 500 hPa height anomaly correlation, the new setup (10 hPa Ptop, 45-km coarse grid) is definitely an improvement • Differences in ACC (except for 00h) are statistically significant at the 5% level • “Climatology” computed from 31 days of 6-hourly FNL data between Oct 15 and Nov 15 • NB: No data archived past 72h for 60-km setup NCAR-NCAS WRF Workshop 15

  16. Performance of new setup • What about in terms of error profiles? 24h 48h 72h Zonal wind MAE (measured against radiosonde) for 20-km grid (blue) and 15-km grid (red) NCAR-NCAS WRF Workshop 16

  17. Performance of new setup • Zonal wind MAE (measured against MODIS winds) NCAR-NCAS WRF Workshop 17

  18. Model issues: surface warm bias • Increase land ice albedo from 70% to 80% NCAR-NCAS WRF Workshop 18

  19. Model issues: surface warm bias • Increase land ice albedo from 70% to 80% 2-m temperature bias in 36-h forecasts (12-21 Jan 2009) Courtesy: Julien Nicolas, OSU NCAR-NCAS WRF Workshop 19

  20. Model issues: surface warm bias • Time series of model 2-m temperatures at Nico AWS from Jan 10 to Feb 6 NCAR-NCAS WRF Workshop 20

  21. Future work: CAM radiation scheme • KEVIN’S WORK WITH CAM RADIATION? NCAR-NCAS WRF Workshop 22

  22. Questions? NCAR-NCAS WRF Workshop 23