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Rongqian Yang, Kenneth Mitchell, Jesse Meng NCEP Environmental Modeling Center (EMC)

Rongqian Yang, Kenneth Mitchell, Jesse Meng NCEP Environmental Modeling Center (EMC). Summer and Winter Season Reforecast Experiments with the NCEP Coupled Forecast System (CFS) using Different Land Models and Different Initial Land States.

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Rongqian Yang, Kenneth Mitchell, Jesse Meng NCEP Environmental Modeling Center (EMC)

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  1. Rongqian Yang, Kenneth Mitchell, Jesse Meng NCEP Environmental Modeling Center (EMC) Summer and Winter Season Reforecast Experiments with the NCEP Coupled Forecast System (CFS) using Different Land Models and Different Initial Land States This development is sponsored by CPPA Program of the NOAA Climate Program Office Acknowledgment to : S. Saha, S. Moorthi, W. Wang, C. Thiaw 33rd Annual Climate Diagnostics and Prediction Workshop 21 October 2008

  2. Objective of this project: Upgrade the land physics and initial land states of the NCEP Climate Forecast System (CFS) and assess the impact on CFS summer and winter season reforecasts. Motivation: While SST anomalies are believed to be the foremost source of seasonal predictability in coupled global models, land surface anomalies are generally believed to be the second most important source of seasonal predictability (e.g. anomalies of soil moisture, snowpack, vegetation cover).

  3. Noah LSM 4 soil layers (10, 30, 60, 100 cm) Frozen soil physics included Surface fluxes weighted by snow cover fraction Improved seasonal cycle of vegetation cover Spatially varying root depth Runoff and infiltration account for sub-grid variability in precipitation & soil moisture Improved soil & snow thermal conductivity Higher canopy resistance More OSU LSM 2 soil layers (10, 190 cm) No frozen soil physics Surface fluxes not weighted by snow fraction Vegetation fraction never less than 50 percent Spatially constant root depth Runoff & infiltration do not account for subgrid variability of precipitation & soil moisture Poor soil and snow thermal conductivity, especially for thin snowpack and moist soils Land Model Upgrade in CFS experiments:Noah LSM (new) versus OSU LSM (old): Noah LSM replaced OSU LSM in operational NCEP medium-range Global Forecast System (GFS) in late May 2005 Many Noah LSM upgrades & assessments were result of collaborations with CPPA PIs

  4. Initial Land States: Two SourcesGLDAS/Noah & Global Reanalysis 2 (GR2/OSU): • GLDAS: an uncoupled land data assimilation system driven by observed precipitation analyses (CPC CMAP analyses) • Executed using same grid, land mask, terrain field and four-layer Noah LSM as in experimental CFS forecasts • Non-precipitation land forcing is from GR2 • Executed retrospectively from 1979-2006 (after spin-up) • GR2: a coupled atmosphere/land assimilation system wherein land component is driven by model predicted precipitation • applies the OSU LSM with two soil layers • nudges soil moisture based on differences between model and CPC CMAP precipitation

  5. Monthly Time Series (1985-2004) Area-average Illinois 2-meter Soil Moisture [mm]: Observations (black), GLDAS/Noah (purple),GR2/OSU (green) Climatology The climatology of GLDAS/Noah soil moisture is higher and closer to the observed climatology than that of GR2/OSU.

  6. GLDAS/Noah (top ) versus GR2/OSU (bottom)2-meter soil moisture (% volumetric) May 1stClimatology 01 May 1999Anomaly Observed 90-day Precipitation Anomaly (mm) valid 30 April 99 GLDAS/Noah GLDAS/Noah GR2/OSU GR2/OSU Left column: GLDAS/Noah soil moisture climo is generally higher then GR2/OSU Middle column: GLDAS/Noah soil moisture anomaly pattern agrees better than that of GR2/OSU with observed precipitation anomaly (right column: top)

  7. CFS Experiment Design: four configurations Choice ofLand Model CFS/Noah CFS/OSU Choice of LandInitial Conditions GLDAS/Noah GR2/OSU (CONTROL) GLDAS/Noah--CLIMO GR2/OSU • Four configurations of T126 CFS: • A)CFS/OSU/GR2: - OSU LSM, initial land states from GR2 (CONTROL)‏ • B) CFS/Noah/GR2: - Noah LSM, initial land states from GR2 • C) CFS/Noah/GLDAS: - Noah LSM, initial land states from T126 GLDAS/Noah • D) CFS/Noah/GLDAS-Climo: - Noah LSM, initial land states from GLDAS/Noah climo Summer CFS Experiments: all 4 configurations above (A, B, C, D) 25-year (1980-2004) summer reforecasts (10 member ensembles) from mid April and early May initial conditions Winter Land Related Experiments: top 2 configurations in table (A & C) 24-year (1981-2004) winter reforecasts (10 member ensembles) from late Nov and Dec initial conditions

  8. Summer Results 25-year (1980-2004) CFS summer reforecasts (10 members) from mid April and early May initial conditions

  9. Partition 25 summers (80-04) intoENSO Neutral & Non-neutral samplesusing MJJ Nino3.4 SST anomaly0.7C as a threshold magnitude 15 neutral summers:80,81,84,85,86,89,90,94,95,96,98,00,01,03,04 10 non-neutral summers: 82,83,87,88,91,92,93,97,99,02 (red: warm, blue: cold)

  10. 10 non-neutral ENSO years: JJA precipitation AC score Worst Case

  11. 15 neutral ENSO years: JJA precipitation AC score Next Worst Case Worst Case

  12. CONUS-average JJA precipitation AC score 0.18 0 Non-Neutral Years Significance test (T-statistic) shows differences wrt third bar are not significant at 90% confidence. Neutral Years 0.04 Significance test (T-statistic) shows differences wrt third bar are significant at 90% confidence. -0.06

  13. Winter Results 24-year (1981-2004) winter reforecasts (10 members) from late Nov and Dec initial conditions Only two of four configurations were executed:-- OSU/GR2 (Control)-- Noah/GLDAS

  14. Partition 24 winters (1981-2004) intoENSO Neutral & Non-neutral samplesusing JFM Nino3.4 SST anomaly0.5C as a threshold magnitude 10 neutral winters: 81, 82, 84, 90, 91, 93, 94, 97, 02, 04 14 non-neutral winters: 83, 85, 86, 87, 88, 89, 92, 95, 96, 98, 99, 00, 01, 03

  15. 14 Non-neutral Years: JFM Precipitation AC Score: 10 Neutral Years: JFM Precipitation AC Score:

  16. CONUS-average JFM precipitation AC score Non-neutral Years 0.2 Significance test (T-statistic) shows differences are not significant at 90% confidence 0 Neutral Years 0.2 Significance test (T-statistic) shows differences are not significant at 90% confidence I 0

  17. Conclusions • When upgrading the land surface model of the CFS, it is imperative to upgrade to the same land surface model in the supporting data assimilation system • Positive impact of land surface upgrade on CFS seasonal forecast skill for precipitation is modest • Significant only for summer season and only in neutral ENSO years (and then only small positive impact) • Essentially neutral impact for winter season and non-neutral ENSO summers • Differences in CFS precipitation skill over CONUS between neutral and non-neutral ENSO years is larger than the skill differences between two different land configurations for same sample of years • Indicates that impact of SST anomaly is greater than impact of land surface configuration

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