# Presentation: 657124

## Upper Tropical Pacific Variation during recent ENSO: An Evaluation of Global Ocean Data Assimilation System (GODAS)

***Upper Tropical Pacific Variation during recent ENSO: ******An Evaluation of Global Ocean Data Assimilation System (GODAS)***

**Dongxiao Zhang                          **_**Yan Xue**_
**   **
**    ****Michael J. McPhaden                David Behringer          **

## 2005-08 NINO3.4 Predictions

***2005-08 NINO3.4 Predictions***

**Notes:**
The recent enson cycle I referred to is the 2005 cooling and the 2006-7 El nino. This forecast plume from IRI display all the dynamical model performance, jun 05 – mar 07. the last set of prediction start from march 2007, shown in this figure. Observation is the black line.
Allmost all the models missed the prediction of 2005 cooling. Many models predicted to the opposite direction. The NCEP CFS, indicated by the blue diamonds, though not successful gettign the magnitude right, it has some limited success in the cooling dirction. But it has relatively poor performance in predicting thhe 2006-7 el noni, evevn the forecst starts from july and august.   

## Objective

**Evaluate the extent to which systematic errors in GODAS may limit skill in NOAA Climate Forecast System (CFS) forecasts**

**Notes:**
With Yan and Dave as part of Climate Test Bed

## Data Products

**GODAS**
**Model: GFDL MOM v3, 75°S-65°N**
**Horizontal resolution: 1° x 1° resolution (enhanced to 1/3° in latitude within 10 °of  the equator)**
**Vertical resolution: 40 levels with 10-m resolution in upper 200m**
**Forcing: NCEP atmospheric reanalysis-2 wind stress; SST relaxed to weekly Reynolds analysis; SSS relaxed to annual mean climatology**
**Data assimilation: Temperature profiles from TAO, TRITON, ARGO, and XBT; ****“synthetic” subsurface salinity based on mean T/S**
**Available: 1980-present**
**Near real-time PMEL temperature/salinity analysis**
**Data: Argo, TAO/TRITON (Temp & Salinity)**
**Resolution: 10 days, 0.5° lat x 0.5° long**
**Available: 2005-present**
**Analysis on density surfaces**

## PMEL analysis

**Notes:**
To examine the ongoing enso cycle, we developed a real time ... for every 10 days starting from jan 2005. this product uses all the argo profiles that passed our own data quality controll, and all the tao/triton measurements that include salinity. Manuplating data on density surfaces has the advantage not to create artifitial water masses when averaging cross fronts such as those in the equatorial region. Fine meridional and long zonal decorrelation scales are used in the equatorial region. The three panels show the sss, salinity at 125m and geostrophic velocities reference to 1000m, for August 5th, 2007. 

## 20°C isotherm standard deviation (2005-2008)

**Notes:**
Enso theories rely on either zonal advection feedback or thermocline feedback, the two dominant terms in controlling the mixed layer temperature tendency, as I will show later. The 2 figures show the relationship between the 20 isotherm, a measure of thermocline variability, averaged over equatorial pacific, and the nino3.4, generallyconsistent with recharge oscillator or delayed oscillator theory. The left axis is the z20 anomalies. Negative vaues means the shoaling of the thermocline , the discharge of warm water above 20c out of the equatorial box. The upper panel is based on BMRC subsurface temperature analysis and renold smith oi sst. The lower one is based on the godas data assimulation. The maximum cross-correlation is maximumam at 0.7 when z20 lead by 6-9month. While the max. cross correlation in godas is 0.6 with z20 leading by 7-9 months.   Statistically speaking, z20 is a good predictor of nino3.4 up to 6-9 month in advance. 
There are however plenty of exceptions, the  2005 cooling and recent el nino is one of them. The green line is from our product based soly on profiles that have both temp and salinity measurements which is almost identical with the BMRC analysis. Looking more closely, you can tell that the 2005 discharge is inphase with the nino3.4 cooling, while the recharge process lead the el nino by 6 month. If thermocline feedback is the dominant process, this would suggest the cooling is hardly opredictable and the warming. For the godas assmulation however, z20 anomaly led the cooling in 2005 but was in phase with the warming in late 2006. 

Simplified enso theories have relied on zonal advection feed back and thermocline feedback. The zonal advection and entrainment, which is directly related to thermocline feed back, are two most dominant terms controling the mixed layer temperature tendency, as I will show in GODAS analysis.  In recharge/discharge theory, the recharge of the warm water in the upper tropical pacific leads to the El nino, while the discharge leads to la ninaThermocline feed back is the heart of the discharge/recharge oscillatorof jin 97, which proposes the phase transion mechanism of enso is the rechagr and discharge of warm water of the upper tropical pacific.  In  simplified enso theories, thermocline feedback is the heart of delayed oscillator and the discharge /recharge oscillator theories. one invloves the Two competing mechanisms have been proposed to expalin the phase transition between 

## 20oC isotherm anomalies 5°S-5°N Average (2005-08)

***20******o******C isotherm anomalies 5******°******S-5******°******N Average (2005-08)***

**Notes:**
To see the details of the z20 evolution in two analyses, we plot the hov diagram of the z20 average over 5s-5n. Time goes up. The eastward propagation of z20 anomalies are well defined in early 2005 and late 2006, in our product. In godas, the abrupt cold anomalies in the easrern pacific endded the eastward propagation of warm anomaly in late march. And the observed cross basin eastward propagation in jja is missing in godas too.  The variability of the thermocline, especially the zonal contrast is more vigorous in gods than in our analysis.

## SSS standard deviation (2005-2008)

***SSS standard deviation (2005-2008)***

**Notes:**
Enso theories rely on either zonal advection feedback or thermocline feedback, the two dominant terms in controlling the mixed layer temperature tendency, as I will show later. The 2 figures show the relationship between the 20 isotherm, a measure of thermocline variability, averaged over equatorial pacific, and the nino3.4, generallyconsistent with recharge oscillator or delayed oscillator theory. The left axis is the z20 anomalies. Negative vaues means the shoaling of the thermocline , the discharge of warm water above 20c out of the equatorial box. The upper panel is based on BMRC subsurface temperature analysis and renold smith oi sst. The lower one is based on the godas data assimulation. The maximum cross-correlation is maximumam at 0.7 when z20 lead by 6-9month. While the max. cross correlation in godas is 0.6 with z20 leading by 7-9 months.   Statistically speaking, z20 is a good predictor of nino3.4 up to 6-9 month in advance. 
There are however plenty of exceptions, the  2005 cooling and recent el nino is one of them. The green line is from our product based soly on profiles that have both temp and salinity measurements which is almost identical with the BMRC analysis. Looking more closely, you can tell that the 2005 discharge is inphase with the nino3.4 cooling, while the recharge process lead the el nino by 6 month. If thermocline feedback is the dominant process, this would suggest the cooling is hardly opredictable and the warming. For the godas assmulation however, z20 anomaly led the cooling in 2005 but was in phase with the warming in late 2006. 

Simplified enso theories have relied on zonal advection feed back and thermocline feedback. The zonal advection and entrainment, which is directly related to thermocline feed back, are two most dominant terms controling the mixed layer temperature tendency, as I will show in GODAS analysis.  In recharge/discharge theory, the recharge of the warm water in the upper tropical pacific leads to the El nino, while the discharge leads to la ninaThermocline feed back is the heart of the discharge/recharge oscillatorof jin 97, which proposes the phase transion mechanism of enso is the rechagr and discharge of warm water of the upper tropical pacific.  In  simplified enso theories, thermocline feedback is the heart of delayed oscillator and the discharge /recharge oscillator theories. one invloves the Two competing mechanisms have been proposed to expalin the phase transition between 

## Surface Salinity and Mixed Layer Depth, 5oS-5oN Average 

**Notes:**
So far we just talked about the thermocline feedback. The godas has some serious bias in the surface layer too. The upper pannels show the sss in GODAS and argo analysis. The lower panels show the mld the their difference in the right. The variability of sss in godas is sinnigficantly supressed, due to its synthetic salinity update based on climatological t-s relationship.  These result in an overestimate of the mld in godas, especially near the eastern edge of warm pool across the Nino4 area. This is the region where zonal advection feedback has been proposed to be important for the enso’s full development.

## 5oS-5oN Averaged Anomalies 

**Notes:**
This hov muller diagram shows why. While the cfs starts from correct initial condition, warm or deeper thermocline in the east, and cooler and shallower in the west, the slower eastward propagation of thermocline anomalies compared to obseration might be responsible to the missed sudden ending of el nino in the forecast. This slow propagaion in cfs is consistent with the reported prolonged 5-year regular ENSO in the free coupled runs of CFS by Wang et al. cfs paper.

## SSS at 165°E, 0°N vs. Nino3.4

***SSS at 165°E, 0°N vs. Nino3.4***

**Notes:**
Enso theories rely on either zonal advection feedback or thermocline feedback, the two dominant terms in controlling the mixed layer temperature tendency, as I will show later. The 2 figures show the relationship between the 20 isotherm, a measure of thermocline variability, averaged over equatorial pacific, and the nino3.4, generallyconsistent with recharge oscillator or delayed oscillator theory. The left axis is the z20 anomalies. Negative vaues means the shoaling of the thermocline , the discharge of warm water above 20c out of the equatorial box. The upper panel is based on BMRC subsurface temperature analysis and renold smith oi sst. The lower one is based on the godas data assimulation. The maximum cross-correlation is maximumam at 0.7 when z20 lead by 6-9month. While the max. cross correlation in godas is 0.6 with z20 leading by 7-9 months.   Statistically speaking, z20 is a good predictor of nino3.4 up to 6-9 month in advance. 
There are however plenty of exceptions, the  2005 cooling and recent el nino is one of them. The green line is from our product based soly on profiles that have both temp and salinity measurements which is almost identical with the BMRC analysis. Looking more closely, you can tell that the 2005 discharge is inphase with the nino3.4 cooling, while the recharge process lead the el nino by 6 month. If thermocline feedback is the dominant process, this would suggest the cooling is hardly opredictable and the warming. For the godas assmulation however, z20 anomaly led the cooling in 2005 but was in phase with the warming in late 2006. 

Simplified enso theories have relied on zonal advection feed back and thermocline feedback. The zonal advection and entrainment, which is directly related to thermocline feed back, are two most dominant terms controling the mixed layer temperature tendency, as I will show in GODAS analysis.  In recharge/discharge theory, the recharge of the warm water in the upper tropical pacific leads to the El nino, while the discharge leads to la ninaThermocline feed back is the heart of the discharge/recharge oscillatorof jin 97, which proposes the phase transion mechanism of enso is the rechagr and discharge of warm water of the upper tropical pacific.  In  simplified enso theories, thermocline feedback is the heart of delayed oscillator and the discharge /recharge oscillator theories. one invloves the Two competing mechanisms have been proposed to expalin the phase transition between 

## Heat Budget in Nino3.4 Area

***Heat Budget in Nino3.4 Area***

**Notes:**
Enso theories rely on either zonal advection feedback or thermocline feedback, the two dominant terms in controlling the mixed layer temperature tendency, as I will show later. The 2 figures show the relationship between the 20 isotherm, a measure of thermocline variability, averaged over equatorial pacific, and the nino3.4, generallyconsistent with recharge oscillator or delayed oscillator theory. The left axis is the z20 anomalies. Negative vaues means the shoaling of the thermocline , the discharge of warm water above 20c out of the equatorial box. The upper panel is based on BMRC subsurface temperature analysis and renold smith oi sst. The lower one is based on the godas data assimulation. The maximum cross-correlation is maximumam at 0.7 when z20 lead by 6-9month. While the max. cross correlation in godas is 0.6 with z20 leading by 7-9 months.   Statistically speaking, z20 is a good predictor of nino3.4 up to 6-9 month in advance. 
There are however plenty of exceptions, the  2005 cooling and recent el nino is one of them. The green line is from our product based soly on profiles that have both temp and salinity measurements which is almost identical with the BMRC analysis. Looking more closely, you can tell that the 2005 discharge is inphase with the nino3.4 cooling, while the recharge process lead the el nino by 6 month. If thermocline feedback is the dominant process, this would suggest the cooling is hardly opredictable and the warming. For the godas assmulation however, z20 anomaly led the cooling in 2005 but was in phase with the warming in late 2006. 

Simplified enso theories have relied on zonal advection feed back and thermocline feedback. The zonal advection and entrainment, which is directly related to thermocline feed back, are two most dominant terms controling the mixed layer temperature tendency, as I will show in GODAS analysis.  In recharge/discharge theory, the recharge of the warm water in the upper tropical pacific leads to the El nino, while the discharge leads to la ninaThermocline feed back is the heart of the discharge/recharge oscillatorof jin 97, which proposes the phase transion mechanism of enso is the rechagr and discharge of warm water of the upper tropical pacific.  In  simplified enso theories, thermocline feedback is the heart of delayed oscillator and the discharge /recharge oscillator theories. one invloves the Two competing mechanisms have been proposed to expalin the phase transition between 

## Meridional Structure Along 140°W

***1950-1999***

**Temperature**

**Salinity**

***Density surface************************kg m*********

***Shallow Overturning in the Subtropical Cells***

**Notes:**
T and S structures along 140w, from 20s to 40n. Arrows along the high salinity tongue show the equatorward convergence of the subducted subtropical waters. The loop formed by the subduction, eqautorward convergence in the pycnocline, equatorial upwelling, and poleward Ekman flows is the so called shallow meridional overturning, or subtropical cells (STC) named by McCreary et al.. Early demonstration of this loop can also be found in Liu et al. numerical simulations. The white contours show packed density surfaces in the upper pycnocline , centered at 25 sigma_theta.The base of the upper pycnocline is about at 26.2 sigma-theta.
Two mechanisms relying on shallow overturning have been proposed to explain the decadal variability of tropical SST: one is the T’Vbar by Gu and Philander, in which midlatitude SST’ can be subducted, advected, and upwelled to change the tropical sst. Observational work by schmeider et al. suggest that the subducted temperature anomalies were largely dissipated with little appreciable amplitude could enter the equatorial region, though some modeling works including Jingjia’s indicate this mechanism may be viable in the south Pacific.    

the other one is the v’Tbar mechanism, bi Kleeman et al. who suggest that the the decadal variability of tropical Pacific temperature is determined by the rate at which stcs 
Transport thermocline water to the equator.

To reduce aliases due to the steep slope and energetic high frequency vertical motion of tropical pycnocline, all our calculations and interpolation are done along density surfaces.   Variables including dynamic height in each individual profiles are first interpolated onto a series a density surfaces of every 0.2 sigma_theta, objective analysis was then used to map the variable onto a grid of  every 0.5 deg lon. X 0.5 deg lat.  

## Interior STC transport convergence is estimated from equatorward thermocline transports, marked by arrows,  at 9°S and 9°N.

***Interior STC transport convergence is estimated from equatorward thermocline transports, marked by arrows,  at 9°S and 9°N.***

**Notes:**
Enso theories rely on either zonal advection feedback or thermocline feedback, the two dominant terms in controlling the mixed layer temperature tendency, as I will show later. The 2 figures show the relationship between the 20 isotherm, a measure of thermocline variability, averaged over equatorial pacific, and the nino3.4, generallyconsistent with recharge oscillator or delayed oscillator theory. The left axis is the z20 anomalies. Negative vaues means the shoaling of the thermocline , the discharge of warm water above 20c out of the equatorial box. The upper panel is based on BMRC subsurface temperature analysis and renold smith oi sst. The lower one is based on the godas data assimulation. The maximum cross-correlation is maximumam at 0.7 when z20 lead by 6-9month. While the max. cross correlation in godas is 0.6 with z20 leading by 7-9 months.   Statistically speaking, z20 is a good predictor of nino3.4 up to 6-9 month in advance. 
There are however plenty of exceptions, the  2005 cooling and recent el nino is one of them. The green line is from our product based soly on profiles that have both temp and salinity measurements which is almost identical with the BMRC analysis. Looking more closely, you can tell that the 2005 discharge is inphase with the nino3.4 cooling, while the recharge process lead the el nino by 6 month. If thermocline feedback is the dominant process, this would suggest the cooling is hardly opredictable and the warming. For the godas assmulation however, z20 anomaly led the cooling in 2005 but was in phase with the warming in late 2006. 

Simplified enso theories have relied on zonal advection feed back and thermocline feedback. The zonal advection and entrainment, which is directly related to thermocline feed back, are two most dominant terms controling the mixed layer temperature tendency, as I will show in GODAS analysis.  In recharge/discharge theory, the recharge of the warm water in the upper tropical pacific leads to the El nino, while the discharge leads to la ninaThermocline feed back is the heart of the discharge/recharge oscillatorof jin 97, which proposes the phase transion mechanism of enso is the rechagr and discharge of warm water of the upper tropical pacific.  In  simplified enso theories, thermocline feedback is the heart of delayed oscillator and the discharge /recharge oscillator theories. one invloves the Two competing mechanisms have been proposed to expalin the phase transition between 

## Summary

**PMEL has developed a near real-time gridded T, S, and geostrophic current product to validate GODAS over 2005-08.**
**All terms in mixed layer heat budget equation, except *****v*****dT/dy, are important in controlling SST tendency term.**
**The observed STC variability is well reproduced in GODAS, and contributes to the persistent entrainment cooling during 2007-08 La Nina.**
**The equatorial Pacific heat content, or Z20, associated with the development of ENSO cycle agree reasonably well in GODAS and PMEL analyses, though GODAS variability tends to be larger.**
**GODAS surface salinity variability is too weak and mixed layers are too deep in the western Pacific warm pool, with  potential adverse affects on zonal currents, advection and ENSO SST development when used to initialize CFS.**

**Notes:**
Entrainment only became important in late 2006. this is in  . ...., where  was the dominant term through the entire period.
This suggest that very en nino has it own characteristics. The recent el nino would be more difficult to predict than large enninos since the zonal advection process invloves more mixed layer dynamics, which is neither well handled in godas nor in coupled gcms. We would like to extend our analysis to cfs forecast runs and focusing on individual members. We hope through our diagnostics we could come up a strategy to form different weightings for indivitual members, that can hopefully improve the forecast.

## Questions

**Why does the annual cycle variability in GODAS upper ocean temperatures tend to be higher than observed? Does it contribute to the overshoot of CFS prediction during either warm or cold events?**
**What accounts for the systematic error in warm pool mixed layer currents and how do those errors affect temperature advection and ENSO SST evolution?**
**GODAS will benefit from assimilation of ocean salinity measurements.  What is the optimal method for reducing systematic errors in analyzed fields?**

**Notes:**
Entrainment only became important in late 2006. this is in  . ...., where  was the dominant term through the entire period.
This suggest that very en nino has it own characteristics. The recent el nino would be more difficult to predict than large enninos since the zonal advection process invloves more mixed layer dynamics, which is neither well handled in godas nor in coupled gcms. We would like to extend our analysis to cfs forecast runs and focusing on individual members. We hope through our diagnostics we could come up a strategy to form different weightings for indivitual members, that can hopefully improve the forecast.

##  Zonal velocity (cm/s) at 10m in TAO and GODAS 

**Notes:**
To determine the relative importance of zonal advection and thermocline feed back. We conducted heat budget analysis of the mixed layer in godas. The right panels show the period of 96-99 enso cycle and the left show the 2005-2007 cycle. The upper and lower panels show analysis in the regions of nino3.4 and nino4 longitudinal band, but on the equator, since this is where vertical entrainment is largest. It is my intention to make meridional advection and surface flux less visible and drwa you attention to the temperature tendency black, zonal advection red, and entrainment blue. The surface flux is always a dampng term, largely offsite the vertical entrainment. And meridional advection is small on average. The  time series ranges from -1.4 to 1.4 c/month  in the three panels, but -3 to 4 c/month in the upper right panel. For the 97-99  enso, the entrainments are large in both regions, and are most important in controlling the dtdt. Even though the zonal advection is very large in the nino4 region, it can not explain the sharp traisition from warming to cooling in early 98.  To the contrary, the dtdt is more correlated with zonal advection during 2005-2007. In nino34 region, the entrainment is opposite to the dtdt cooling in 2005, and only became important in 2006, warming. in the nino4 region, the dt dt is dominated by zonal advection through the entire period. The entrainment term is quite small.