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Graduate Course: Advanced Remote Sensing Data Analysis and Application

Graduate Course: Advanced Remote Sensing Data Analysis and Application SURFACE HEAT BUDGETS IN THE PACIFIC WARM POOL DURING TOGA COARE Shu-Hsien Chou Dept. of Atmospheric Sciences National Taiwan University shchou@atmos1.as.ntu.edu.tw 886-2-2362-5896, ext 262 Objectives:

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Graduate Course: Advanced Remote Sensing Data Analysis and Application

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  1. Graduate Course: Advanced Remote Sensing Data Analysis and Application SURFACE HEAT BUDGETS IN THE PACIFIC WARM POOL DURING TOGA COARE Shu-Hsien Chou Dept. of Atmospheric Sciences National Taiwan University shchou@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.

  2. 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

  3. 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: • Improved meteorological Instrument (IMET) buoy (1.75oS, 156oE) • Research vessel (Rv) Moana Wave (1.7oS, 156oE) • 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).

  4. Motivations: • Equatorial western Pacific warm pool is a climatically important region; characterized by warmest SST with small gradient, frequentheavy rainfall, strong atmospheric heating, weak mean winds with highly intermittent westerly wind bursts (WWBs), weak currents, and shallowocean mixed layer • Heating drives global climate and plays a key role in ENSO & 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

  5. 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: 2ox 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.

  6. RETRIEVAL OF GSSTF1: (Chou et al. 1997) wind stress t = r CD (U–Us)2 sensible heat flux FSH = r CpCH (U–Us) (qs–q) latent heat flux FLH= r LvCE (U–Us) (Qs–Q) • U -- daily SSM/I-v2 10-m wind (Wentz 1994) • (qS - q) --- daily ECMWF (SST - q2m) • 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, (qs–q) & (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.

  7. Retrieval of Radiation Budgets: (Chou et al. 1998) • Surface net solar (shortwave) radiative flux • FSW= (1- asfc) Ssfc Ssfc =Somot(avis , mo) • So:Solar constant • mo:Cosine of solar zenith angle • t: Atmospheric transmittance • avis: GMS-4 albedo • asfc: Sea surface albedo (0.05) • Surface IR (longwave) radiative flux • FLW= s Ts4- 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 vapor TB: GMS-4 IR brightness temp (11-mm) s: 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.

  8. Cor=0.86 Bias=1.8 Cor=0.75 Bias=-7.1 Cor=0.4 Bias=-2.6 Cor=0.71 Bias=-2.4 Cor=0.78 Bias=0.0018 Cor=0.82 Bias=13.8

  9. HEAT BUDGET OF OCEAN MIXED LAYER*: h r CP (∂TS/∂t)=FNET-f(h) FSW f(h)=g e-ah + (1- g) e-bh (Paulson and Simpson 1977) (∂TS/∂t): SST tendency (K s-1) h: Ocean mixed-layer depth (m) r: Density of sea water (103 kg m-3) CP: Heat capacity of sea water (3.94 x103 J kg-1 K-1) FNET: Net surfaceheating (W m-2) FSW: Net surface solar heating (W m-2) f (h): Fraction of FSWpenetrating h g: Weight for visible region (0.38) (1- g): Weight for near infrared region a: Absorption coefficient of sea water for visible region (0.05 m-1) b: 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)

  10. -18.6 0.7 29.6 -0.14 26.1 35.5 44.8

  11. 55.6 m 42 m 28.4 m

  12. Table 7. Surface heat budgets and relevant parameters in the Pacific warm pool (135oE-175oE, 10oS-10oN) during COARE IOP (November 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 _______________________________________________________

  13. Conclusion: • Retrieved surface fluxes compare reasonably well with 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 solar 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 evaporation (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

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