Upper Ocean Processes in the Indian Ocean associated with the Madden-Julian

Oscillation Toshiaki Shinoda (Texas A&M Univ., Corpus Christi), Weiqing Han (Univ. of

Colorado), Yuanlong Li (Univ. of Colorado), Chunzai Wang (NOAA/AOML)

1. Large-scale ocean variability: Satellite observations and OGCM experiments2. Impact on Indonesian Throughflow3. Diurnal cycle4. Variability of the Seychelles-Chagos thermocline ridge

Large-scale Ocean Variability

CINDY/DYNAMO field campaign September 2011 – March 2012

Describe large-scale upper ocean variations surrounding the intensive array based on the analysis of the satellite-derived data and OGCM experiments.

MJO events during DYNAMO

Strong convection in the Indian Ocean associated with the MJO

Strong westerly anomalies

Satellite-derived Data

Surface winds: Windsat Daily 3-day average 0.25x0.25 deg. Precipitation: TRMM 3B52 3-hourly 0.25x0.25 deg. Sea Surface Height (SSH): AVISO Daily 1x1 deg. Sea Surface Temperature (SST): Blended Analysis (Reynolds et al. 2007) Daily 0.25x0.25 deg. Surface current: OSCAR 5-day average 1x1 deg. Sea Surface Salinity (SSS): Aquarius weekly 1x1 deg.

Horizontal resolution: 1/25º, 1/12º Period: 2003-2012 Surface forcing fields: NOGAPS

Global Hybrid Coordinate Ocean Model (HYCOM)

RAMA

Windsat

NCEP

Surface winds

Shinoda et al. (2013)

Large–scale SST variation

Large-scale surface salinityAquarius

RAMA

Zonal Current SSH

Reflected Rossby wavesSSH (Satellite) SSH (HYCOM) D20 (HYCOM)

Yoneyama et al. (2013)

Webber et al. (2010)

Impact on Indonesian Throughflow

Seasonal variation of the Indonesian ThroughflowObservation (Gordon et al. 2008) Modeling (Shinoda et al. 2012)

PAC Rossby waves

Wyrtki Jet

Velocity component (50 m depth: shading )and SSH(contour) along the line

Wyrtki Jet

Yoshida Jet

Wyrtki Jet

Global HYCOM

How do strong MJO events during DYNAMO impact the Indonesian Throughflow?

Large changes in upper ocean currents

Southward current is very weak in Jan.-Feb. in contrast to the seasonal cycle (rapid recovery of southward currents in Jan.-Feb.)

Meridional velocity at Makassar Strait

Yoshida jet

Indonesian Throughflow

Anomalous northward currents in the Indonesian Sea in January can be traced back to the Yoshida Jet generated by the MJO

Diurnal Cycle

High vertical resolution (1m) in the upper 10m HYCOM is able to reproduce observed diurnal warming

Impact of diurnal cycle on intraseasonal variability

TOGA COARE Nov. 1992-Mar. 1993

Shinoda (2005), Shinoda and Hendon (1988)

SCTR 55°–70°E, 12°–4°S CEIO (65°–95°E, 3°S–3°N)

Li et al. (2013)

Thermocline Ridge Variability

Impact of SCTR interannual variation

Interannual variations of SCTR (e.g., deeper thermocline during IOD)How does ocean interannual variabiliti (OIV) impacts intraseasonal SST in SCTR?Additional HYCOM experiments (NoOIV): No interannual variation of surface forcing fields.

---------- 95% significance ----------- 85% significance based on F-test

The OIV effect enhances the intraseasonal SSTs in the eastern TR region by about 0.1 C (20% of the total SST variability) (significant at 95% level) and slightly reduces them in the western TR (not significant).

Li et al. (2014)

Amplitude of the 20-90-day SST

Enhancing effect, strong-TR years,

Shallow Z20

Reducing effect, weak-TR years,

Deep Z20

Yearly Z20 from MR and NoOIV

MR NoOIV

• A Strong TR (shallow thermocline) enhances intraseasonal SSTs, while a weak TR (deep thermocline) reduces intraseasonal SSTs.

The OIV effect varies from year to year !

SSTt

HF

ENT

Composite analysis for strong and weak TR years

Weak-year composite Strong-year composite

SST variability, HF and ENT are greatly enlarged by a strong TR year, but only slightly reduced by a weak TR.

An asymmetry between strong and weak years

MLD is an important cause

Weak-year composite Strong-year composite

> 10 m< 5 m

An important source of the asymmetry: the MLD changes, which is shallower than normal by at least 10m in strong TR years, but is deeper than normal by only less than 5m in weak TR years. This difference leads to the strong/weak asymmetry of ENT and HF and thus the overall enhancing effect of the OIV.

12S-4S Mean Winter Temperature

Strong TR

Weak TR

SummaryA variety of upper ocean processes associated with the MJO that influence SST are identified by the analysis of OGCM experiments and satellite observations. These include:

Equatorial jetDiurnal cycleVariation of theromocline ridgeRemote ocean variability

Further analyses are needed to understand how SST changes caused by these upper ocean processes feedback on the atmosphere.

References:Li, Y., W. Han, T. Shinoda, C. Wang, R.-C. Lien, J.N. Moum, and J.W. Wang, 2013: Effects of Solar Radiation Diurnal Cycle on the Tropical Indian Ocean Mixed Layer Variability during Wintertime Madden-Julian Oscillation Events. J. Geophys. Res., DOI:10.1002/jgrc.20395.

Li Y., W. Han, T. Shinoda, C. Wang, M. Ravichandran, J.-W. Wang, 2014: Revisiting the Wintertime Intraseasonal SST Variability in the Tropical South Indian Ocean: Impact of the Ocean Interannual Variation. J. Phys. Oceanogr., doi: http://dx.doi.org/10.1175/JPO-D-13-0238.1.

Shinoda, T,. Jensen, M. Flatau, S. Chen, W. Han, C. Wang 2013: Large-scale oceanic variability during the CINDY/DYNAMO field campaign from satellite observations. Remote Sensing –Special issue on Observing the Ocean’s Interior from Satellite Remote Sensing, 5, 2072-2092.

Shinoda, T., W. Han, E. J. Metzger, H. E. Hurlburt , 2012: Seasonal Variation of the Indonesian Throughflow in Makassar Strait. J. Phys. Oceanogr., 42, doi:10.1175/JPOD-11-0120.1.