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David H. Bromwich 1 , Andrew J. Monaghan 1 , Kevin Manning 2 and Jordan G. Powers 2

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

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David H. Bromwich 1 , Andrew J. Monaghan 1 , Kevin Manning 2 and Jordan G. Powers 2

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  1. Real-time forecasting for the Antarctic: An evaluation of the Antarctic Mesoscale Prediction System (AMPS) David H. Bromwich1, Andrew J. Monaghan1, Kevin Manning2 and Jordan G. Powers2 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) • 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. Surface Pressure 2-m Temperature 3-m Wind Speed

  4. 1. Evaluating AMPS: Surface Performance (12-36 hr forecasts below 500 m) • 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 2-m Temp Sfc Pres Wnd Spd Cloud %

  5. 1. Evaluating AMPS: Diurnal Cycle at Relay Station, January 2003 (12-36 hr forecasts) 2-m Temp PMM5=solid AWS=dashed Sfc Pres • 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. Wnd Spd Wnd Dir Daily Cycle

  6. 1. Evaluating AMPS: 500-hPa Performance (12-36 hr forecasts) • 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. Geopotential Hgt Temperature Dewpoint Temp Wind Speed

  7. 1. Evaluating AMPS: McMurdo Soundings (12-36 hr forecasts) • 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 Temperature Geopotential Hgt Wind Speed Dewpoint Temp

  8. 1. Evaluating AMPS: 10-km vs 3.3-km domain (24-36 hr forecasts) Observed=thick gray 3.3-km = solid black 10-km = dashed black 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

  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: • JJA 2002 (“Before” new UBC) • 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 Before After

  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 • Old-100 (Rigid Lid, Top = 100 hPa) • 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 • An upper level ridge approaches West Antarctica. • Upward(red)/Downward(blue) motion becomes enhanced Hour 60 Hour 66 Hour 72

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

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

  18. Unused slides to follow:

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