# Presentation: 406678

## Internal Variability in the Oceansand Air-Sea interactions

- Raghu Murtugudde
- Earth System Science Interdisciplinary Center/METO
- University of Maryland, College Park, MD
- Markus Jochum
- MIT
- Cambridge, MA

## Internal Variability in the Oceans: Western Boundery Currents

_**Internal Variability in the Oceans**_: Western Boundery Currents

## Kessler 2003

## Mesoscale Variability in the tropical Atlantic: Tropical Instability Waves

_**Mesoscale Variability in the tropical Atlantic: Tropical Instability Waves**_

## Slide 5

## Tropical Atlantic

- ITCZ tends to be sensitive to the weak meridional SST gradient during boreal spring months.

**And the gradient can be reversed due to internal variability in the ocean!**

**Jochum et al. 2004**

## Meridional heat flux at 20oW.

## Correlation of SST anomalies at 20oW/0oN with surrounding SSTAs and with anomalies at 0oN.

**It’s not advection.....**

## Mean SSTs and the Eddy Kinetic Energy for the high resolution model

_**Mean SSTs and the Eddy Kinetic Energy for the high resolution model**_

**Jochum et al. 2004**

## Enhanced resolution and resolving mesoscale variability clearly impacts

- Model SST simulations. But how is it accomplished?

## .

_**Heat Budgets? Better have an  INTERACTIVE heat flux formulation!**__** **__**Advective Atmospheric Mixed Layer**_

- P_u_

- θ**v**

- = (1+β**v**)C0 ω0(θ**V**0 – θ**V**) + PR** ́,**

- (1)

- P_u_

**.**

- q = C0 ω0q 0 - C0 ω0(1+μ)q ,

- (2)

- θ = θ**V**/(1+0.61q)

- (3)

**Advection**

**Radiative cooling**

- we

- qb=γq

- q0

- q

- θ

- θ0

- w0 – surface
-            wind

- FBq

- F0q

- FBθ

-  Inversion

- Cloud layer

- Mixed layer

- F0θ

**Turbulence Closure**

- FBθ  = wB*( θB - θ )
- FBq = wB*(qB – q)

- wE(θBV – θV) = βVF0θv

- wE = δC0w0

## Slide 12

## What do the heat budgets say?

- Coarse resolution leads to excessive diffusion of heat from the ITCZ to the
- Cold-tongue.

**Jochum et al. 2004**

## High resolution tells a different story!

**Entrainment is enhanced slightly and yet diffusion is reduced greatly.**

**Jochum et al. 2004**

## Entrainment increases with a higher resolution but there is  a seasonality to it.

## Warmer SSTs even though entrainment increases....because the latent and sensible heat losses are reduced.

- Warmer SSTs even though entrainment increases....because the latent and sensible heat losses are reduced.

## With a non-local heat flux formulation, the heat transports in the ocean

**With a non-local heat flux formulation, the heat transports in the ocean**
**and the atmosphere can adjust realistically  to SST variability**.

## The TIWs are well-known in the equatorial Pacific. Are they a source of stochasticity just like MJOs? Do they have a strong-enough decadal variability to impact mean conditions?

**The TIWs are well-known in the equatorial Pacific****. ****Are they a source of stochasticity just like MJOs?**** ****Do they have a strong-enough decadal variability to impact mean conditions?**

**Jochum and Murtugudde 2004**

## The energy, seasonality, and spectrum of TIW in the model are in very good

- agreement with all available observations.

## The variance of SST  due to internal variability is comparable to any other source

- of stochastic forcing or changes due to STCs.

_**MORE IMPORTANTLY, the decorrelation length scales are ~1000Km!!!**_

## Both SST changes in the eastern equatorial Pacific

- and the SSTgradient changes across  the equator
- are comparable to most interannual signals.

## The zonal gradient also shows significant internal variability. Potential for

- SST-wind feedbacks?

## Slide 23

## The story form the heat budget in the deep tropical Pacific is the same as in the

**The story form the heat budget in the deep tropical Pacific is the same as in the**
**Atlantic!  TIWs are not mixing heat horizontally! It’s not the diffusion of heat.**

##  A NEW PARADIGM FOR THE ROLE 

_**OF TIWs on SSTs.**__** **_

## Slide 26

## Slide 27

## Slide 28

## Slide 29

## Slide 30

## Circulation schematic for Southwest Monsoon

**Circulation schematic for Southwest Monsoon**

**„****Great Whirl“ and „Southern Gyre“**
**Upwelling concentrated in****  wedges and filaments **
**cyclonic domes both sides****  of Sri Lanka: upwelling? **
**Indonesian Throughflow****  max.**
**Ekman transport **_***southward***_**  in both hemispheres, but****  northward winds on equ.**
**Subduction in southern****  subtropics**** **

## Circulation schematic for Northeast Monsoon

**Somali Current and****  East African Coast Current****  merge into SECC**
** ****Doming NE of Madagascar****   open-ocean uwelling?**
**Indonesian Throughflow****  min.**
**some subduction in****  northern Arabian Sea**
**Ekman transport **_***northward***_** in both hemispheres**

**In between monsoon seasons: eastward wind stress causes****„Wyrtki Jets“ along equator, that send out coastal Kelvin waves****   **

## Mesoscale features in Indian Ocean SSTs are often associated with high mean SSTs.

## The other tropical ocean.... High mean SSTs and high convective energy.

**The other tropical ocean****.... High mean SSTs and ****high convective energy**.

**Jochum and Murtugudde 2004b**

## Is it good news that the SST anomaly variance associated with the internal

**Is it good news that the SST anomaly variance associated with the internal**
**variability is restricted coastal  regions and the southern subtropics?**
**What about Java?  But the decorrelation scales are only ~400km.**

## Variance of anomalies due to internal variability can be as large as most

**Variance of anomalies due to**** ****internal variability**** ****can be as large as most**
**Interannual anomalies****. ****A challenge for coupled climate models...**

## Heat flux convergence over 2oS-2oN,45oE-50oE: horizontal (black), vertical (red),

- _Heat flux convergence over 2__o__S-2__o__N,45__o__E-50__o__E__:_ horizontal (black), vertical (red),
-  net armospheric (green)  and total (blue) heat flux convergences.

## Consequences for Interannual variability: Quantifying the impact of TIWs

**Jochum and Murtugudde 2004c**

## Coastal upwelling in the east is improved because TIWs enhance zonal SST

- Gradient: Zonal advection into the cold-tongue clearly impacts the coastal region.

## The warm pool gets  warmer SSTs through zonal advection from the cold-tongue.

## Slide 41

## Slide 42

## Slide 43

## Slide 44

## Slide 45

## Slide 46

## Biogeochemical Consequences of TIWs: The 1998 El Niño-La Niña Transition   

_**Biogeochemical Consequences of TIWs: The 1998 El Niño-La Niña Transition**_**   **

## TIWs reduce the cold-bias in SST, restratify the thermocline better in the east,

**And improve the thermocline gradient over much of the equatorial ocean.**

## Is it all STCs or do we have a TIW driven tropical mechanism for Decadal 

**Is it all STCs or do we have a TIW driven tropical mechanism for Decadal **
**ENSO Variability??**

**Rothstein et al. 2000**

## The thermocline differences are restricted to the TIW scales.

## Even in the central-western Pacific, TIWs determine the differences

- _Even in the central-western Pacific, TIWs determine the differences_

## Wind-response to TIWs in a OGCM-Lindzen/Nigam model: Seasonality

**Ballabrera et al. 2004**

## When does the ocean mesoscale variability affect coupled climate variability?