Graduate Course: Advanced Remote Sensing Data Analysis and Application

SURFACE HEAT BUDGETS IN THE PACIFIC WARM POOL DURING

TOGA COARE

Shu-Hsien ChouDept. of Atmospheric Sciences

National Taiwan Universityshchou@atmos1.as.ntu.edu.tw

886-2-2362-5896, ext 262

Objectives:

• Study temporal and spatial variability of surface heat budgets over Pacific warm pool during TOGA COARE

• Examine relation of SST variations to surface heat and momentum fluxes, and solar radiation penetration through ocean mixed layer

Chou, S-H., W. Zhao, and M.-D. Chou, 2000: Surface heat budgets and sea surface temperature in the Pacific warm pool during TOGA COARE. J. Climate, 13, 634-649.

Outlines:• TOGA COARE Activities• Motivations• GSSTF1 data• Surface Radiation Budgets Derivation• Validation of Surface Heat Budgets and

wind stress• Spatial Distributions of IOP-mean Surface

Heat Budgets and Related Parameters over Pacific Warm Pool

• Spatial Distributions of Monthly Variations of Solar Heating, Evaporative Cooling, and Net Surface Heating over Pacific Warm Pool during COARE IOP (Nov 92-Feb 93)

• 1-D Ocean Mixed Layer Heat Budget• Spatial Distributions of IOP-mean Net

Surface Heating, SST Tendency, Solar Radiation Penetration, Mixed Layer Depth and Wind Stress over Pacific Warm Pool

• Time Series of 5-day Running Mean SST, Surface Heat Budgets, Solar Radiation Penetration, Ocean Mixed Layer Depth, and Wind Stress for Northern and Southern Warm Pools during IOP

TOGA COARE

• TOGA COARE: Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE)

• Domain: 10oS – 10oN, 140-180oE

• Intensive observing period (IOP): Nov 92-Feb 93

• Intensive flux array (IFA): 1oN-5oS, 150o-160oE

• Surface flux measurements in IFA during IOP:

1. Improved meteorological Instrument (IMET) buoy (1.75oS, 156oE)

2. Research vessel (Rv) Moana Wave (1.7oS, 156oE)

3. Rv Wecoma cruised butterfly pattern around IMET buoy

• High temporal resolution measurements of surface radiative, turbulent, and freshwater fluxes are very useful for studying air-sea interactions, validating satellite retrievals and general circulation models (GCM).

Motivations:

• Equatorial western Pacific warm pool is a climatically important region; characterized by warmest SST with small gradient, frequent heavy rainfall, strong atmospheric heating, weak mean winds with highly intermittent westerly wind bursts (WWBs), weak currents, and shallow ocean mixed layer

• Heating drives global climate and plays a key role in EN

SO & Asian-Australian monsoon (Webster et al. 1998) • Small changes in SST of Pacific warm pool associated

with eastward shift of warm pool during ENSO events affect the global climate (Palmer and Mansfield 1984)

• TOGA COARE aims to better understand various physical processes responsible for SST variation in western Pacific warm pool

• For timescale < a season, warm pool SST is mainly determined by surface fluxes, solar radiation penetration, and ocean mixed layer depth, which are affected by variations in surface winds and clouds

• Two super cloud clusters and two WWBs associated with two Madden-Julian oscillations (MJOs) propagated from Indian Ocean to central Pacific during COARE IOP; these have important impact on warm pool SST variations

Version 1 Goddard Satellite-Based Surface Turbulent Fluxes (GSSTF1; Chou et al. 1997) (1) Latent heat flux (2) Zonal wind stress(3) Meridional wind stress (4) Sensible heat flux (5) 10-m specific humidity(6) 500-m bottom layer water vapor(7) 10-m wind speed(8) Sea-air humidity difference

Duration: July 1987–Dec 1994

Spatial resolution: 2o x 2.5o lat-lon

Temporal resolutions: one day, and one month (Combine DMSP F8, F10, F11 satellites)

Archive at NASA/GSFC DAAC:http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/hydrology/hd_gsstf1.0.html

Chou, S.-H., C.-L. Shie, R. M. Atlas, and J. Ardizzone, 1997: Air-sea fluxes retrieved from Special Sensor Microwave Imager. J. Geophys. Res., 102, 12705-12726.

RETRIEVAL OF GSSTF1: (Chou et al. 1997)

wind stress =CD (U–Us)2

sensible heat flux FSH = Cp CH (U–Us) (s–)

latent heat flux FLH = Lv CE (U–Us) (Qs–Q)

• U -- daily SSM/I-v2 10-m wind (Wentz 1994)

• (S - ) --- daily ECMWF (SST - 2m)

• QS --- sat. specific humidity at daily NCEP SST (Reynolds and Smith 1994)

• Q -- daily SSM/I-v2 10-m specific humidity

(Chou et al. 1995, 1997) • stress direction -- SSM/I-v2 10-m wind direction (Atlas, et al. 1996)

• CD, CH, CE depend on U, (s–) & (Qs–Q) (surface layer similarity theory)

Chou, S.-H., C.-L. Shie, R. M. Atlas, and J. Ardizzone, 1997: Air-sea fluxes retrieved from Special Sensor Microwave Imager. J. Geophys. Res., 102, 12705-12726.

Retrieval of Radiation Budgets: (Chou et al. 1998)

• Surface net solar (shortwave) radiative flux FSW = (1- sfc ) Ssfc

So: Solar constant o : Cosine of solar zenith angle: Atmospheric transmittancevis :GMS-4 albedosfc :Sea surface albedo (0.05)

• Surface IR (longwave) radiative flux FLW = Ts

4 - Fsfc Fsfc = Fo (Ts / To)4

Fo = 502 - 0.47 TB - 6.75 W + 0.0565 WTB

Ts : Sea surface temperature (SST) To : Mean SST (302K)

W : SSM/I-total column water vaporTB : GMS-4 IR brightness temp (11-m) : Stefan-Boltzmann constant

Chou, M.-D.,W. Zhao, and S.-H. Chou, 1998: Radiation budgets and cloud radiative forcing in the Pacific warm pool during TOGA COARE. J. Geophy. Res., 103, 16 967-16 977.

= So o(vis , o)Ssfc

Cor=0.86Bias=1.8

Cor=0.75Bias=-7.1

Cor=0.4Bias=-2.6

Cor=0.71Bias=-2.4

Cor=0.78Bias=0.0018

Cor=0.82Bias=13.8

HEAT BUDGET OF OCEAN MIXED LAYER*:

h CP (∂TS/∂t) = FNET - f(h) FSW

f(h) = e-h + (1- ) e-h

(Paulson and Simpson 1977)

(∂TS/∂t): SST tendency (K s-1)h: Ocean mixed-layer depth (m): Density of sea water (103 kg m-3)CP: Heat capacity of sea water (3.94 x103 J kg-1 K-1)

FNET: Net surface heating (W m-2)FSW: Net surface solar heating (W m-2)f (h): Fraction of FSW penetrating h: Weight for visible region (0.38)(1- ): Weight for near infrared region : Absorption coefficient of sea water for visible

region (0.05 m-1): Absorption coefficient of sea water for near

infrared region (1.67 m-1)

*Neglect horizontal advection of heat and entrainment of cold water from thermocline (due to small SST gradient, weak current, and barrier layer between mixed layer bottom and thermocline top)

26.1

44.8

-18.6

29.6

-0.14

0.7

35.5

55.6 m

28.4 m

42 m

Table 7. Surface heat budgets and relevant parameters in the Pac

ific warm pool (135oE-175oE, 10oS-10oN) during COARE IOP (N

ovember 1992-February 1993).________________________________________________________Parameter Units 0-10oS 0-10oN 10oS-10oN _

____________________________________________________

FSW W m-2 195.7 191.0 192.9

FLW W m-2 51.5 54.8 53.4

FSH W m-2 6.5 7.3 6.9

FLH W m-2 108.2 147.5 131.9

FNET W m-2 29.6 -18.6 0.7

SST oC 29.1 28.7 28.8

SST-T2m K 1.0 0.9 0.9

Qs-Q10m g kg-1 5.1 5.5 5.4

U10m m s-1 5.3 6.6 6.1

TB K 268.3 271.4 270.1

W g cm-2 5.3 4.9 5.0

h m 28.4 55.6 42.0

f(h) FSW W m-2 44.8 26.1 35.5_______________________________________________________

Conclusion:• Retrieved surface fluxes compare reasonably well wi

th those from IMET buoy, RVs Moana Wave and Wecoma

• Surface net heating is negligible when averaged over warm pool and IOP (ocean gains heat in summer hemisphere but loses heat in winter hemisphere)

Southern warm pool:• Variation of surface net heat flux is dominated by sol

ar radiation (modulated by two MJOs)• Significant solar radiation penetrates through bottom

of shallow ocean mixed layer (due to weak surface wind)

• SST variation (modulated by two MJOs) does not follow surface net heat flux

Northern warm pool:• Variation of surface net heat flux is dominated by ev

aporation (modulated by strong seasonal variation of trade wind)

• Small solar radiation penetrates through bottom of deep ocean mixed layer (due to strong surface wind)

• SST undergoes seasonal variation and follows surface net heat flux