# Presentation: 185703

## Temperature and Altimetry Assimilation into a High Resolution OGCM with a Localized Ensemble Kalman Filter Christian Keppenne1, Michele Rienecker2, Jossy Jacob3, Robin Kovach4 & Nicole Kurkowski51,3,4Science Applications International Corporation San Diego, CA 921212Global Modeling and Assimilation OfficeNASA Goddard Space Flight CenterGreenbelt, MD 20771AGU Ocean Sciences Meting, Honolulu, Hawaii, February 20, 2006 1clk@gmao.gsfc.nasa.gov, 2michele.rienecker@nasa.gov, 3jjacob@gmao.gsfc.nasa.gov , 4kovach@gmao.gsfc.nasa.gov, 5kurkowsk@gmao.gsfc.nasa.gov 

## Outline

**Poseidon OGCM and GMAO coupled forecasting system**
**EnKF implementation for Poseidon**
**Assimilation experiments**
**Impact of T+SSH assimilation on CGCM seasonal hindcast skill **

## CGCM and OGCM

**Poseidon (Schopf and Loughe, 1995)**
**Quasi-isopycnal vertical coordinate**
**Prognostic variables are *****h*****, *****t*****, *****s*****,***** u***** and *****v***
**Sea surface height (SSH) is diagnostic: ******** = ********i****buoyancy(t****i****, s****i****) h****i**
**About 30 million prognostic variables  at ****1/3 x 5/8 x L27**** resolution**** **

**GMAO CGCM coupled forecasting system**
**- GMAO AGCM, 2 x 2.5 x L34**
**- LSM:  Mosaic (SVAT)**
** ****OGCM: Poseidon v4, 1/3 x 5/8 x L27**
** ****Production ODAS:  OI of in situ temperature profiles with  salinity adjustment**
**- Experimental ODAS: EnKF**
**Note: ODAS is run on OGCM prior to coupling to AGCM & LSM**

**CGCM and OGCM**

## EnKF implementation

**Model errors: use model EOFs to generate state perturbations**
**Forcing errors: add random perturbations to wind stress forcing**

**Multivariate update**
**Multivariate compactly supported covariances**
**Update T, S, u & v**
**Layer thicknesses (h)  adjust between analyses **
**Incremental update**
**Process SSH and T observations separately**

**Parallel implementation (message passing: MPI, SHMEM)**
**Runs on SGI Altix or HP SC45**
**Time/month on 240 Altix CPUs:**
**8+1 ensemble members: 2.1 hours**
**16+1 ensemble members: 3.8 hours**
**32+1 ensemble members: 7 hours **
**Online bias estimation**
**Used in SSH assimilation**
**Hybrid (3DVAR + ensemble) covariances**
**Used in T assimilation**

**EnKF implementation**

## Online bias estimation

**Online bias estimation**

## Assimilation experiment
Assimilate T/P anomalies + TAO & XBT temperature profiles 1/1/2001-12/31/2001
Online bias estimation in SSH assimilation
Random forcing from 32 OGCM leading EOFs + wind-stress perturbations
Compare 9, 17 & 33 member EnKF
Compare with 
no-assimilation control
Production ODAS (temperature OI + salinity correction)

**Assimilate T/P anomalies + TAO & XBT temperature profiles 1/1/2001-12/31/2001**
**Online bias estimation in SSH assimilation**
**Random forcing from 32 OGCM leading EOFs + wind-stress perturbations**
**Compare 9, 17 & 33 member EnKF**
**Compare with **
**no-assimilation control**
**Production ODAS (temperature OI + salinity correction)**
** **

**Experiments**

## Slide 7

## Slide 8

## Marginal T Kalman gains for a 1C innovation at two different locations

## Marginal S Kalman gains for a 1t T innovation at two different locations (units of s)

## Marginal T Kalman gain for a unit T innovation at (125W, 0N, 100m)

## Marginal S Kalman gain for a 1 t T innovation at (125W, 0N, 100m)

** ****EnKF9 produces spurious covariance  structures**
** ****Apparent consistency between EnKF17 & EnKF33**

## Impact of assimilation on CGCM hindcast skill
Old code with assimilation in model layers: 17-member EnKF
Assimilate T + SSH for February-April of each year of 1993-2002
Couple OGCM to AGCM & LSM after running ODAS
12-month CGCM hindcasts initialized using ocean states from EnKF runs
	(to save CPU time, CGCM hindcasts have only 5 ensemble member) 

Assess impact of assimilation on SST hindcast skill
Compare to history of CGCMv1 May-start hindcasts (problematic month)

**Old code with assimilation in model layers: 17-member EnKF**
**Assimilate T + SSH for February-April of each year of 1993-2002**
**Couple OGCM to AGCM & LSM after running ODAS**
**12-month CGCM hindcasts initialized using ocean states from EnKF runs**
**	****(to save CPU time, CGCM hindcasts have only 5 ensemble member) **
**Assess impact of assimilation on SST hindcast skill**
**Compare to history of CGCMv1 May-start hindcasts (problematic month)**
**	**

## Niño-3.4 SST

## Conclusions

Online bias correction important when T data & SSH anomalies are assimilated.
16+1 and 32+1 EnKF runs have comparable performance
EnKF-initialized hindcasts can miss or underestimate El Niño events but result in less false El Niño or La Niña alerts than production forecasts

**Online bias correction important when T data & SSH anomalies are assimilated.**
**16+1 and 32+1 EnKF runs have comparable performance**
**EnKF-initialized hindcasts can miss or underestimate El Niño events but result in less false El Niño or La Niña alerts than production forecasts**