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: 10 o S – 10 o N, 140-180 o E Intensive observing period (IOP): Nov 92-Feb 93 Intensive flux array (IFA): 1 o N-5 o S, 150 o -160 o E Surface flux measurements in IFA during IOP: 1.Improved meteorological Instrument (IMET) buoy (1.75 o S, 156 o E) 2.Research vessel (Rv) Moana Wave (1.7 o S, 156 o E) 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).

4. 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 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: 2 o x 2.5 o 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/h d_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  =  C D (U–U s ) 2 sensible heat flux F SH =  C p C H (U–U s ) (  s –  ) latent heat flux F LH =  L v C E (U–U s ) (Q s –Q) U -- daily SSM/I-v2 10-m wind (Wentz 1994) (  S -  ) --- daily ECMWF (SST -  2m ) Q S --- 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) C D, C H, C E depend on U, (  s –  ) & (Q s –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 F SW = (1-  sfc ) S sfc S o : Solar constant  o : Cosine of solar zenith angle   : Atmospheric transmittance  vis : GMS-4 albedo  sfc : Sea surface albedo (0.05) Surface IR (longwave) radiative flux F LW =  T s 4 - F sfc F sfc = F o ( T s / T o ) 4 F o = 502 - 0.47 T B - 6.75 W + 0.0565 WT B T s : Sea surface temperature (SST) T o : Mean SST (302K) W : SSM/I-total column water vapor T B : 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. = S o  o  (  vis,  o ) S sfc

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

14. HEAT BUDGET OF OCEAN MIXED LAYER*: h  C P (∂T S /∂t) = F NET - f(h) F SW f(h) =  e -  h + (1-  ) e -  h (Paulson and Simpson 1977) (∂T S /∂t): SST tendency (K s -1 ) h:Ocean mixed-layer depth (m)  :Density of sea water (10 3 kg m -3 ) C P : Heat capacity of sea water (3.94 x10 3 J kg -1 K -1 ) F NET :Net surface heating (W m -2 ) F SW :Net surface solar heating (W m -2 ) f (h):Fraction of F SW 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)

15. 26.1 44.8 -18.6 29.6 -0.14 0.7 35.5

16. 55.6 m 28.4 m 42 m

20. Table 7. Surface heat budgets and relevant parameters in the Pacific warm pool (135 o E-175 o E, 10 o S-10 o N) during COARE IOP (November 1992-February 1993). ________________________________________________________ Parameter Units 0-10 o S 0-10 o N 10 o S-10 o N _____________________________________________________ F SW W m -2 195.7 191.0 192.9 F LW W m -2 51.5 54.8 53.4 F SH W m -2 6.5 7.3 6.9 F LH W m -2 108.2147.5 131.9 F NET W m -2 29.6-18.6 0.7 SST o C 29.128.7 28.8 SST-T 2m K 1.0 0.9 0.9 Qs-Q 10m g kg -1 5.1 5.5 5.4 U 10m m s -1 5.3 6.6 6.1 T B K 268.3271.4 270.1 W g cm -2 5.3 4.9 5.0 h m 28.4 55.6 42.0 f(h) F SW W m -2 44.8 26.1 35.5 _______________________________________________________

21. 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