1. Real-time forecasting for the Antarctic: An evaluation of the Antarctic Mesoscale Prediction System (AMPS) David H. Bromwich 1, Andrew J. Monaghan 1, Kevin Manning 2 and Jordan G. Powers 2 1- Polar Meteorology Group, Byrd Polar Research Center, The Ohio State University, Columbus, Ohio 2- Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, Colorado

2. 1. Evaluating AMPS: Overview Statistical analysis of AMPS performed for 2-year period (Sep 2001-Aug2003) Surface: 2-m temperature Surface pressure 3-m winds 500 hPa Temperature Geopotential Height Winds Dewpoint temperature Diurnal cycle at Relay Station Soundings at McMurdo Comparison of model skill at 3.3-km vs. 10-km Effects of implementing a new nudging upper boundary condition

3. 1. Evaluating AMPS: Surface Performance (12-36 hr forecasts) 2-m Temperature 3-m Wind Speed Surface Pressure Surface pressure and near- surface temperature at most sites have correlations of r>0.95 and r>0.75, respectively, and small biases. Surface wind speeds reflect the complex topography and generally have correlations between 0.5-0.6, and positive biases of 1-2 m s-1.

4. 1. Evaluating AMPS: Surface Performance (12-36 hr forecasts below 500 m) 2-m Temp Cloud % Wnd Spd Sfc Pres Correlation coefficients generally consistent throughout annual cycle Temperature bias goes from negative in summer to positive in winter – likely because wind speed, which is slightly too fast, is eroding surface inversion in winter

5. 1. Evaluating AMPS: Diurnal Cycle at Relay Station, January 2003 (12-36 hr forecasts) 2-m Temp Wnd Spd Sfc Pres Wnd Dir Daily Cycle Diurnal cycle is reproduced with good skill Surface pressure bias likely due to uncertainties of reducing pressure at model elevation to station elevation the near-simultaneous timing of the peak wind speed with the maximum daily temperature suggests that the behavior of the near-surface winds is due to momentum transfer as the stable boundary layer heats up and higher momentum air aloft mixes downward. Opposite behavior found at coastal stations. PMM5=solid AWS=dashed

6. 1. Evaluating AMPS: 500-hPa Performance (12-36 hr forecasts) Temperature Wind Speed Geopotential Hgt Dewpoint Temp High correlations for temperature, geopotential height, and wind speed. Biases are typically small, and either +/- (not systematic) Lower skill in dewpoint forecasts – may be due to low absolute humidity at 500 hPa, which makes small errors look big.

7. 1. Evaluating AMPS: McMurdo Soundings (12-36 hr forecasts) Temperature Wind Speed Dewpoint Temp Geopotential Hgt Correlations generally high throughout atmosphere. Temperature biases are small and become generally warmer and slightly positive near the tropopause (~300 hPa). Winds are captured with the best skill in the free atmosphere – decreases near surface due to topography

8. 1. Evaluating AMPS: 10-km vs 3.3-km domain (24-36 hr forecasts) Ratio of 3.3-km standard deviation to 10-km standard deviation (normalized) Spectral Density vs frequency for wind speed at 2 AWS sites near McMurdo Conclusion – The 3.3-km domain is more sensitive and more accurate than the 10-km domain Observed=thick gray 3.3-km = solid black 10-km = dashed black

9. 2. Implementing the Nudging UBC in AMPS: Overview AMPS switched from its old UBC (rigid lid at 100 hPa) to its new UBC (nudging UBC at 50 hPa) in May 2003 Here we compare three months of statistics from two winter periods: 1.JJA 2002 (“Before” new UBC) 2.JJA 2003 (“After” new UBC) The Correlations, RMSEs, and biases of the following fields are examined: Column Temperature Column Wind Speed 150-hPa Temperature 150-hPa Wind Speed Surface Pressure The statistics are calculated for the AMPS 30-km grid versus radiosonde and surface observations, and unless otherwise noted, are valid for the 36-60 hr forecasts.

10. 2. Implementing the Nudging UBC in AMPS: Temperature and Wind Speed Soundings (36-60 hr, averaged over all stations) In general, correlations and RMS errors are improved throughout model column Temperature biases reduced (become cooler) in top layers of model Winds become stronger throughout column

11. 2. Implementing the Nudging UBC in AMPS: Surface Pressure (36-60 hr) Not much change in correlations – performance very high before/after new UBC RMS errors are improved at all stations Biases reduced at 15 of 16 stations BeforeAfter

12. 2. Implementing the Nudging UBC in AMPS: Performance vs. Forecast Hour Surface Pressure (averaged over all stations) RMS errors improved by about 1 hPa throughout forecast Improvement to bias in later forecast hours

13. Summary: Surface pressure and near-surface temperature at most sites have correlations of r>0.95 and r>0.75, respectively, and small biases. Surface wind speeds reflect the complex topography and generally have correlations between 0.5-0.6, and positive biases of 1-2 m s-1. In the free atmosphere, r>0.95 (geopotential height), r>0.9 (temperature), and r>0.8 (wind speed) at most sites. The 3.3-km domain is more sensitive to spatial and temporal changes in the winds than the 10-km domain, which represents an overall improvement in forecast skill especially on the windward side of the island where the Williams Field and Pegasus runways are situated, and in the lee of Ross Island, an important area of mesoscale cyclogenesis. New Nudging UBC increases in the skill of temperature and wind speed forecasts throughout the atmospheric column. Surface pressure bias and RMSE are reduced as well The new UBC reduces unrealistically high vertical motions throughout the column

14. 3. AMPS Case Study: Experimental Design Ran 2 AMPS forecasts for 12Z October 02, 2003 1.Old-100 (Rigid Lid, Top = 100 hPa) 2.New-50 (Nudging UBC, Top = 50 hPa) Look at differences in cross sections of vertical motion on AMPS 30-km domain

15. 3. AMPS Case Study: Synoptic Situation Hour 60Hour 66Hour 72 An upper level ridge approaches West Antarctica. Upward(red)/Downward(blue) motion becomes enhanced

16. 3. AMPS Case Study: Vertical Motion Hour 60Hour 66Hour 72

17. Rothera Possession Island Mt Siple Byrd Theresa Elizabeth Uranus Glacier Ski-Hi Halley Novolazarevskaja Relay Station Mawson Mirnyj Casey Dumont D’Urville Terra Nova Bay Dome C Elaine Gill Marilyn McMurdo Whitlock Manuela Ferrell South Pole Weddell Sea Ross Sea Bellingshausen Sea Amundsen Sea Ross Ice Shelf Ronne- Filchner Ice Shelf Amery Ice Shelf South Pacific Ocean South Indian Ocean South Atlantic Ocean

18. Unused slides to follow: