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JAMSTEC/DCOP
Qoosaku MOTEKIQoosaku MOTEKI
Masaki KATSUMATA
Kunio YONEYAMA
Kentaro ANDO
Takuya HASEGAWA
Drastic thickening
...
depth(m) Salinity(psu)
temperature ( )℃
MLD:10m
ILD:30m
barrier layer thickness
BLT=ILD-MLD:20m
ILD( T=0.2 )⊿ ℃
MLD( [ T=0...
Sato, K., T. Suga, and K. Hanawa, 2004: Barrier layer in the North Pacific
subtropical gyre. Geophysical Research Letters....
R/V MiraiR/V Mirai
2015/12/13 00Z
MJO observed during cruise
Global-IR
strong sfc. westerlies
Drastic thickening of BL
BLT (barrier layer thickness)
increased
from 5m to 60m within 1-day,
up to 85m during 5-days.
How...
IL deepeningby
vertical mixingwith MJO forcing
MLDMLD
ILDILD
BLTBLT
MJO
depth(m)
shallow ML/IL/BLshallow ML/IL/BL
before M...
depth(m)
IL deepeningby
vertical mixingwith MJO forcing
(increasing turbulence under strong winds)
vertical mixingvertical...
BL thickeningby
vertical mixingwith MJO forcingand
stretchingwith downwelling thermocline
stretched haloclinestretched hal...
Argo fortunately trapped in the
marginal sea from Nov. 2015
track of
MJO
Pre-YMC
Argo
Argo captured thinning process of BL
after the MJO
10 days after MJO,10 days after MJO,
high SST can behi...
MJO
Pre-YMC
high SST > 30℃ can be recovered
in the next 10 days
air-sea couplingair-sea coupling
simulation should usesimu...
Drastic thickening of BL
was due to the vertical mixing
under the MJO forcing.
High SST can be recovered
in the next 10 da...
downwelling Kelvin wave arrives
Sumatra
R/V MiraiR/V Mirai
ECCO2(sea surface hight anomaly) JRA55(surface westerly wind)
low SSS(< 33psu)low SSS(< 33psu)
2015/12/13 00Z
surface salinity
ECCO2
BLT representation by ECCO2
(vertical resolution of 10 m is NOT enough)
MLDMLD
ILDILD
BLTBLT
MJO
depth(m)
V. mixing simulation
1D diffusion simulation
by Gasper et al. (1990) model
Integration: 6 days
Initial: CTD 2015/12/12 14Z...
S0(P-E)=100
〜 10-2
m/day
Mixing term: +10-2
∼10-4
/m/day
CTD observation
水深(m)
水深(m)
1D TKE simulation
水深(m)
ECCO2ECCO2
IL: T=0.2⊿ ℃IL: T=0.2⊿ ℃
ref. lev. 15mref. lev. 15m
CTD Obs.CTD Obs.
IL: T=0.2⊿ ℃IL: T=0.2⊿ ℃
ref. lev. 20mref....
BL formation: Salinity stratification tendency
H. adv. V. adv. tilting
stretchin
g vertical mixing
Cronin, M. F., and M. J...
Factors for drastic thickening
BLT increased by
vertical mixing by MJO forcing and
downwelling thermocline
by oceanic Kelv...
BL thickeningby
vertical mixingwith MJO forcingand
stretchingwith downwelling Kelvin wave
mitigating haloclinemitigating h...
Estimation of BL formation
tendency : +10-1
〜 10-2
/m/day
||
H. advection : +10-3
〜 10-4
/m/day
V. advection : +10-2
〜 10-...
Pair (+Szt:−Szt) means
BL thickening
Sal. strat. tendency: ±1×10-1
/m/day
U: +103
m/day
∇Sz: -10-6
〜 10-7
/m2
Advection term: +10-3
∼10-4
/m/day
∇S: -10-5
〜 10-6
/m
Uz: -103
/day
Tilting term: −10-2
∼10-3
/m/day
wz: -10-1
〜 10-2
/day
Sz: +10-1
/m
Stretching term: +10-2
∼10-3
/m/day
MJO passagedisturbance passage
25m
25m
10m
60m
85m
MJO passagedisturbance passage
35m 35m
20m
25m
25m
10m
60m
70m
85m
100m
review on previous studies
Cronin and McPhaden 2002, JC
“Barrier layer formation during westerly wind bursts”
Tilting is c...
review on previous studies
Vialard, J., and P. Delecluse, 1998, JPO
“An OGCM study for the TOGA decade.
Part II: Barrier-l...
review on previous studies
Girishkumar, et al. 1998, JGR-O
“Intraseasonal variability in barrier layer thickness
in the so...
80km80km100km
80km80km100km
depth(m) Salinity(psu)
temperature ( )℃
fresh lens
fresh lens index:
(σ10m−σ6m)/4 (kg/m4
) > 0
(fresh lens)
depth(m) Salinity(psu)
temperature ( )℃
reference depth: 10m
fresh lens index:
(σ10m−σ6m)/4 (kg/m4
) < 0
(mixed above 10 m)
80km80km100km
MJO
MLDMLD
ILDILD
BLTBLT
depth(m)
ILD( T=0.2 )⊿ ℃
MLD
( [ T=0.2 ])⊿σ ⊿ ℃
ARGO
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passag...
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15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passage during the Pre-Years of the Maritime Continent Campaign

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Qoosaku Moteki, Japan Agency for Marine Earth Science and Technology, Yokosuka city, Japan; and K. Yoneyama, M. Katsumata, K. Ando, and T. Hasegawa
The drastic thickening of the barrier layer in the marginal sea off the western coast of Sumatra during the passage of the Madden Julian Oscillation (MJO) observed during December 2015 is investigated. Before the MJO arrival, the halocline above 20 m depth was very strong and the barrier layer thickness was 5-10 m from based on R/V Mirai observations. During the MJO forcing of 13-16 December, the isothermal layer was drastically deepened from 20 m to 100 m. Meanwhile, the mixed layer deepening was lagged behind the isothermal layer deepening by 1 day, and the barrier layer underwent dramatic thickening to 60 m within 24 hours. An evaluation of the vertical salinity gradient tendency showed that the dramatic thickening of the barrier layer was due to the vertical oceanic mixing by the atmospheric MJO forcing and the vertical stretching by the oceanic downwelling coastal Kelvin wave intruding from the open ocean. One of the important factors in the drastic barrier layer thickening was concluded to be the atmospheric external forcing and the oceanic internal wave being in-phase. The downwelling oceanic Kelvin wave continuously lowered the thermocline from the middle of November to the end of December, and the salinity stratification in the vicinity of the thermocline was continuously mitigated by the vertical stretching. Under such conditions, the MJO forcing caused vertical mixing of the freshwater with the strong salinity stratification and temperature stratification near the surface. The combination of the two distinct processes caused the drastic thickening of the barrier layer, and the barrier layer thickness reached a maximum of 85 m 5 days after the MJO arrival.

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15A.5 Drastic Thickening of the Barrier Layer Off the Western Coast of Sumatra Due to the Madden Julian Oscillation Passage during the Pre-Years of the Maritime Continent Campaign

  1. 1. JAMSTEC/DCOP Qoosaku MOTEKIQoosaku MOTEKI Masaki KATSUMATA Kunio YONEYAMA Kentaro ANDO Takuya HASEGAWA Drastic thickening of the barrier layerbarrier layer off the western coast of Sumatra due to the MJO passage during the Pre-YMC Moteki et al. 2018,. under revision, Progress in Earth and Planetary Sciences
  2. 2. depth(m) Salinity(psu) temperature ( )℃ MLD:10m ILD:30m barrier layer thickness BLT=ILD-MLD:20m ILD( T=0.2 )⊿ ℃ MLD( [ T=0.2 ] 0.07kg/m⊿σ ⊿ ℃ ≒ 3 ) reference depth:10m BL prevents upwellingBL prevents upwelling colder watercolder water
  3. 3. Sato, K., T. Suga, and K. Hanawa, 2004: Barrier layer in the North Pacific subtropical gyre. Geophysical Research Letters. Seasonal distribution of BLT Boreal summer Boreal winter large seasonality of BLlarge seasonality of BLlarge seasonality of BLT variationlarge seasonality of BLT variation
  4. 4. R/V MiraiR/V Mirai 2015/12/13 00Z MJO observed during cruise Global-IR strong sfc. westerlies
  5. 5. Drastic thickening of BL BLT (barrier layer thickness) increased from 5m to 60m within 1-day, up to 85m during 5-days. How did the BL drastically thicken during the MJO passage?
  6. 6. IL deepeningby vertical mixingwith MJO forcing MLDMLD ILDILD BLTBLT MJO depth(m) shallow ML/IL/BLshallow ML/IL/BL before MJObefore MJO IL deepeningIL deepening after MJOafter MJO ML remainsML remains shallowshallow
  7. 7. depth(m) IL deepeningby vertical mixingwith MJO forcing (increasing turbulence under strong winds) vertical mixingvertical mixing by windsby winds vertical mixingvertical mixing by windsby winds
  8. 8. BL thickeningby vertical mixingwith MJO forcingand stretchingwith downwelling thermocline stretched haloclinestretched halocline makes difference btw.makes difference btw. MLD/ILDMLD/ILD salinity stratification is stretched bysalinity stratification is stretched by downwelling thermoclinedownwelling thermocline MJO depth(m) strong salinitystrong salinity stratification bystratification by continuous rainfallcontinuous rainfall
  9. 9. Argo fortunately trapped in the marginal sea from Nov. 2015 track of
  10. 10. MJO Pre-YMC Argo Argo captured thinning process of BL after the MJO 10 days after MJO,10 days after MJO, high SST can behigh SST can be recovered throughrecovered through thinning process of BLthinning process of BL thickening BL wasthickening BL was captured wellcaptured well
  11. 11. MJO Pre-YMC high SST > 30℃ can be recovered in the next 10 days air-sea couplingair-sea coupling simulation should usesimulation should use higher V. reso. to exactlyhigher V. reso. to exactly represent BLrepresent BL If thereIf there’’s not BL, colder waters not BL, colder water upwelling could decreaseupwelling could decrease SSTSST cooled ocean sfc. withcooled ocean sfc. with thick BL can be easilythick BL can be easily recovered as beforerecovered as before Argo
  12. 12. Drastic thickening of BL was due to the vertical mixing under the MJO forcing. High SST can be recovered in the next 10 days because the colder water upwelling is prevented. Higher vertical resolution could improve the SST variability.
  13. 13. downwelling Kelvin wave arrives Sumatra R/V MiraiR/V Mirai ECCO2(sea surface hight anomaly) JRA55(surface westerly wind)
  14. 14. low SSS(< 33psu)low SSS(< 33psu) 2015/12/13 00Z surface salinity ECCO2
  15. 15. BLT representation by ECCO2 (vertical resolution of 10 m is NOT enough) MLDMLD ILDILD BLTBLT MJO depth(m)
  16. 16. V. mixing simulation 1D diffusion simulation by Gasper et al. (1990) model Integration: 6 days Initial: CTD 2015/12/12 14Z Forcing: Surface Met. Obs. SR ・ LR ・ Wind Stress
  17. 17. S0(P-E)=100 〜 10-2 m/day Mixing term: +10-2 ∼10-4 /m/day
  18. 18. CTD observation 水深(m) 水深(m)
  19. 19. 1D TKE simulation 水深(m)
  20. 20. ECCO2ECCO2 IL: T=0.2⊿ ℃IL: T=0.2⊿ ℃ ref. lev. 15mref. lev. 15m CTD Obs.CTD Obs. IL: T=0.2⊿ ℃IL: T=0.2⊿ ℃ ref. lev. 20mref. lev. 20m
  21. 21. BL formation: Salinity stratification tendency H. adv. V. adv. tilting stretchin g vertical mixing Cronin, M. F., and M. J. McPhaden, 2002: Barrier layer formation during westerly wind bursts. J Geophys Res-Oceans, 107. tendency H. adv. tilting stretching vertical mixing
  22. 22. Factors for drastic thickening BLT increased by vertical mixing by MJO forcing and downwelling thermocline by oceanic Kelvin wave. in-phase of MJO and oceanic Kelvin wave
  23. 23. BL thickeningby vertical mixingwith MJO forcingand stretchingwith downwelling Kelvin wave mitigating haloclinemitigating halocline by vertical mixing afterby vertical mixing after MJO forcingMJO forcing salinity stratification is stretching bysalinity stratification is stretching by downwelling Kelvin wavedownwelling Kelvin wave MJO depth(m) strong salinitystrong salinity stratification bystratification by continuous rainfallcontinuous rainfall
  24. 24. Estimation of BL formation tendency : +10-1 〜 10-2 /m/day || H. advection : +10-3 〜 10-4 /m/day V. advection : +10-2 〜 10-3 /m/day tilting : -10-2 〜 10-3 /m/day stretching : +10-2 〜 10-3 /m/day V. mixing : +10-2 〜 10-4 /m/day
  25. 25. Pair (+Szt:−Szt) means BL thickening Sal. strat. tendency: ±1×10-1 /m/day
  26. 26. U: +103 m/day ∇Sz: -10-6 〜 10-7 /m2 Advection term: +10-3 ∼10-4 /m/day
  27. 27. ∇S: -10-5 〜 10-6 /m Uz: -103 /day Tilting term: −10-2 ∼10-3 /m/day
  28. 28. wz: -10-1 〜 10-2 /day Sz: +10-1 /m Stretching term: +10-2 ∼10-3 /m/day
  29. 29. MJO passagedisturbance passage 25m 25m 10m 60m 85m
  30. 30. MJO passagedisturbance passage 35m 35m 20m 25m 25m 10m 60m 70m 85m 100m
  31. 31. review on previous studies Cronin and McPhaden 2002, JC “Barrier layer formation during westerly wind bursts” Tilting is critical for the BL formation.
  32. 32. review on previous studies Vialard, J., and P. Delecluse, 1998, JPO “An OGCM study for the TOGA decade. Part II: Barrier-layer formation and variability“ Stretching by subduction from convergence is critical.
  33. 33. review on previous studies Girishkumar, et al. 1998, JGR-O “Intraseasonal variability in barrier layer thickness in the south central Bay of Bengal“ Stretching by Rossby wave is critical. intraseasonal time scale
  34. 34. 80km80km100km
  35. 35. 80km80km100km
  36. 36. depth(m) Salinity(psu) temperature ( )℃ fresh lens fresh lens index: (σ10m−σ6m)/4 (kg/m4 ) > 0 (fresh lens)
  37. 37. depth(m) Salinity(psu) temperature ( )℃ reference depth: 10m fresh lens index: (σ10m−σ6m)/4 (kg/m4 ) < 0 (mixed above 10 m)
  38. 38. 80km80km100km
  39. 39. MJO MLDMLD ILDILD BLTBLT depth(m) ILD( T=0.2 )⊿ ℃ MLD ( [ T=0.2 ])⊿σ ⊿ ℃
  40. 40. ARGO

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