AN EVALUATION OF EXPENDABLE BATHYTHERMOGRAPH AND TROPICAL ATMOSPHERE-OCEAN ARRAY DATA FOR MONITORING TROPICAL OCEAN VARIABILITY

Two important sources of information for monitoring and predicting the Fl Nino-Southern Oscillation are the Tropical Atmosphere Ocean (TAO) buoy array and the volunteer observing ship expendable bathythermograp h (VOS XBT) network. The subsurface ocean temperature measurements of these two networks are evaluated in the context of analysis and monito ring of medium- to low-frequency variability in the tropical Pacific O cean. It is shown that both systems capture the principal features tha t characterize variability in the equatorial central and eastern Pacif ic Ocean but only TAO can capture the higher temporal fluctuations in detail. In the western Pacific, the VOS XBT network is able to capture the slowly moving, westward propagating Rossby waves and their reflec tion and interaction with the western boundary. TAO is limited in this respect because of its equatorial focus. The accuracy of temperature maps is estimated using the rms analysis error variance. The accuracy of the VOS XBT network fluctuates in space and time but is relatively steady averaged over the tropical region, while that of TAO has gradua lly improved as the basin wide array has been implemented. Case studie s using VOS XBT data only, TAO data only, and the combined full data s et indicate the networks are complementary and supportive, evaluated b asin wide and over the tropical region. The high temporal resolution a nd regularity of the equatorially focused TAO network are complemented by the broad-scale,irregular tropical VOS XBT sampling in the equator ial region and by VOS coverage outside the domain of TAO. A proxy for net information content is derived from the estimated rms error varian ce of the analysis. For the equatorial region, TAO now provides in exc ess of 70% of the information, its dominance beginning in 1992. For th e tropical region (20 degrees S-20 degrees N) the net information cont ent of the respective systems is of comparable magnitude, each equival ent to in excess of 100 independent samples per 10-day period in 1994, reinforcing the notion that both systems are valuable sources of subs urface ocean information for monitoring medium- to low-frequency tropi cal variability.