# Presentation: 438712

** **
**Summer and Winter Season Reforecast Experiments with the NCEP Coupled Forecast System (CFS) using **
**Different Land Models and Different Initial Land States**

- Acknowledgment to : S. Saha, S. Moorthi, W. Wang, C. Thiaw

**This development is sponsored by CPPA Program of the NOAA Climate Program Office**

*33**rd** Annual Climate Diagnostics and Prediction Workshop*
*21 October 2008*

## 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).

## Land Model Upgrade in CFS experiments:Noah LSM (new) versus OSU LSM (old):

**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

**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**

## Initial Land States: Two Sources GLDAS/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

## Monthly Time Series (1985-2004) Area-average Illinois 2-meter Soil Moisture [mm]:

**Observations (black), ****GLDAS/Noah (purple),****  ****GR2/OSU (green)**

**The climatology of GLDAS/Noah soil moisture is higher and closer to the observed climatology than that of GR2/OSU**.

## GLDAS/Noah (top ) versus GR2/OSU (bottom) 2-meter soil moisture (% volumetric)

**Observed 90-day**
**Precipitation Anomaly**
**(mm) valid 30 April 99**

**GLDAS/Noah (**_**top **_**)**** versus ****GR2/OSU (**_**bottom**_**)** **2-meter soil moisture** (% volumetric)
**May 1****st**** **_**Climatology**_**             01 May **_**1999**__** **__**Anomaly**_

**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)

**GLDAS/Noah**

**GLDAS/Noah**

**GR2/OSU**

**GR2/OSU**

## CFS Experiment Design: four configurations

**  ****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

**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

**CFS Experiment Design: four configurations**

## Summer Results

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

## Partition 25 summers (80-04) intoENSO Neutral & Non-neutral samplesusing MJJ Nino3.4 SST anomaly0.7C as a threshold magnitude

_**10 non-neutral**__ summers_:
- 82,83,87,88,91,92,93,97,99,02   (red: warm, blue: cold)

_**15 neutral**__ summers_:80,81,84,85,86,89,90,94,95,96,98,00,01,03,04

## 10 non-neutral ENSO years: JJA precipitation AC score

**Worst**
**Case**

## 15 neutral ENSO years: JJA precipitation AC score 

**Worst**
**Case**

**Next**
**Worst**
**Case**

## CONUS-average JJA precipitation AC score

- differences wrt third bar are
- _not significant_ at 90% confidence.

- Significance test (T-statistic) shows
- differences wrt third bar are
- _significant_ at 90% confidence.

_**Non-Neutral**_** Years**

_**Neutral**_** Years**

**CONUS-average JJA precipitation AC score**

- 0.04

- -0.06

## Winter Results

- Only two of four configurations were executed:-- OSU/GR2 (Control)-- Noah/GLDAS

-  **24-year** (1981-2004) winter reforecasts (10 members)
- 		from late Nov and Dec initial conditions

## Partition 24 winters (1981-2004) intoENSO Neutral & Non-neutral samplesusing JFM Nino3.4 SST anomaly0.5C as a threshold magnitude

_**14 non-neutral**__ winters_:
**83, 85, 86, 87, 88, 89, 92, 95, 96, 98, 99, 00, 01, 03**

_**10 neutral**__ winters_:
**81, 82, 84, 90, 91, 93, 94, 97, 02, 04**

## 14 Non-neutral Years:  JFM  Precipitation AC Score:

**14 **_**Non-neutral Years**_**:  JFM  Precipitation AC Score:**

**10 **_**Neutral Years**_**:  JFM Precipitation AC Score:**

## CONUS-average JFM precipitation AC score

**CONUS-average JFM precipitation AC score**

_**Non-neutral**_** Years**

- I

- Significance test (T-statistic) shows
- differences are _not significant_
- at 90% confidence

_**Neutral**_** Years**

- Significance test (T-statistic) shows
- differences are _not significant_
- at 90% confidence

- 0.2

- 0.2

- 0

- 0

## 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