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Soil moisture biases and their correction in CanSIPS operational forecasts

This study examines the soil moisture biases in CanSIPS operational forecasts and proposes a bias correction method to improve forecast accuracy. The effectiveness of the correction method is validated through hindcast verification, showing restored soil moisture to hindcast climatology in operational forecasts.

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Soil moisture biases and their correction in CanSIPS operational forecasts

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  1. Soil moisture biases and their correction in CanSIPS operational forecasts Bertrand Denis, Juan-Sebastian Fontecilla Canadian Meteorological Centre (CMC), Dorval, Québec Bill Merryfield, Slava Kharin, John Scinocca, Woo-Sung Lee Canadian Centre for Climate Modelling and Analysis (CCCma), Victoria, BC 38th CDPW - 22 Oct 2013

  2. The Canadian Seasonal to Interannual Prediction System (CanSIPS) • Developed at CCCma • Operational at CMC since Dec 2011 • 2 models CanCM3/4, 10 ensemble members each • Forecasts initialized at the start of every month • Hindcast verification period = 1981-2010 • Forecasts contribute to NMME and WMO/APCC/IRI ensembles • Forecast range = 12 months Reference: Merryfield et al., MWR, 2013

  3. CanSIPS contribution to NMME CanCM3 CanCM4

  4. CanSIPS Land initialization Direct atmospheric initialization through assimilation of 6-hourly T, q, u, v • Atmospheric model = CanAM4 (von Salzen et al., Atm.-Ocn 2013) Indirect land initialization through response to model atmosphere www.eoearth.org/view/article/152990 • Land model = CLASS2.7 (Versegny, Atm.-Ocn 2000)

  5. Data Sources: Hindcasts vs Operational * *pending availability of CMC NEMOVAR analysis

  6. Data Sources: Hindcasts vs Operational * *pending availability of CMC NEMOVAR analysis

  7. CMC assimilation began 1 Jan 2010 Change in atmospheric data source:Effect on soil moisture • Plots below compare soil moisture in first forecast month for ERA vs CMC-based initialization • VFSM = volume fraction of soil moisture (%) • Anomalies are relative to 1981-2010 hindcast climatology CanCM3 CanCM4 Global mean VFSM anomaly Canada mean VFSM anomaly ERA assimilation CMC assimilation

  8. Forecast month Canada mean soil moisture anomalies in July initialized forecasts Grand ensemble mean + ERA interim verification CanCM3 CanCM4 2012 (CMC) 2011 (CMC) 2010 (ERA) Soil moisture July lead 0 soil moisture anomalies 2012 (CMC) 2011 (CMC) 2010 (ERA) WET DRY

  9. Solution: Modify CMC-based assimilation runs using bias correction method of Kharin & Scinocca (GRL 2012) assimilated ERA-based soil moisture model soil moisture • First, “assimilate” soil moisture from ERA-based runs starting 1 Jan 2010 • Calculate empirical corrective forcing G for mid-2010 to mid 2012 • Apply G to soil moisture in adjusted CMC-based assimilation runs • Anticipated result: soil moisture drift corrected usual model equations assimilation terms mean annual cycle ?

  10. Result: Soil moisture restored to hindcast climatology in operational forecasts Canada mean soil moisture anomalies in July initialized forecasts Grand ensemble mean + ERA interim verification CanCM3 CanCM4 2012 (CMC) 2012 (ERA) 2012 (corrected CMC) Correction implemented operationally beginning with June 2013-initialized forecast

  11. Effects of soil moisture biases on forecasts Mean differences in JJA forecasts for 2010-12 (lead 0) Dots indicate statistical significance according to t test CMC – ERA initialization corrected CMC – ERA initialization 2m temperature C precipitation mm day-1

  12. July 2012 forecast ERA Interim verification CMC initialization corrected CMC initialization ERA initialization Forecast anomalies represent centroid of Gaussian fits to raw lead 0 anomalies

  13. Summary • Change from ERA reanalysis for atmospheric assimilation in hindcasts to CMC analysis in operational forecasts led to accumulating soil moisture deficit • This has been fixed using the bias correction procedure of Kharin & Scinocca (GRL 2012) • Soil moisture in hindcasts is OK • Soil moisture in operational forecasts produced after June 2013 inclusive is OK • Soil moisture in operational forecasts produced from Nov 2011 to May 2013 inclusive suffers from this bias

  14. CanSIPS initialization * *

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