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Abstract
Pacific Warm Pool Temperature Regulation during TOGA COARE: Upper Ocean Feedback Gary S.E. Lagerloef, Roger Lukas, Robert A. Weller and Steven P. Anderson The Hasselmann feedback model was applied to hindcast western Pacific warm pool sea surface temperatures (SST) with heat flux observations obtained near 2oS 156oE from October1992 - February 1993 during TOGA COARE . The model versus observed SST correlations were greater than 0.85. Two important feedback (or damping) time scales emerged, with efolding times of lambda^1=0.2 days and 8 days, fitting to the diurnal and sub-diurnal variationsrespectively. Distinct mixed layer depth scales were also found for the respective time scales. A time varying depth parameter with a median of ~5 m was derived for the shorter time scale, and varied with the observed daily minimum mixed layer depth. A constant ~16 m was optimal for the longer time scale, which is similar to the time-averaged observed mixed layer depth of 14.8 m and the Monin-Obukhov scale of ~17 m. This bears on the choice of mixed layer parameters for climate model simulations of warm pool conditions observed in TOGA COARE. The low frequency time and depth scale parameters give a negative feedback of about 95 Wm2 oC1, which is significantly greater than previous studies haveindicated. This restoring influence was treated separately from fluxes across the air-sea interface such as latent, radiative and sensible heat loss or cloud shading, and is thus attributed to oceanic mixed layer processes. The frequency band where the damping or feedback becomes important is defined by [omega~lambda], which we find coincides with the diurnalcycle and the ~50 d Madden-Julian oscillations (MJO) for the respective lambda^1 time scales. This indicates a possible dynamic connection between the surface heat forcing and mixed layer dissipation time scales, which we suggest might be accounted for if the dissipation is parameterized as being proportional to the amplitude of SST variations. |
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