ACCURACY OF CURRENT PROFILE MEASUREMENTS - EFFECT OF TROPICAL AND MIDLATITUDE INTERNAL WAVES

The effect of midlatitude and tropical internal wave variability on cu rrent profile measurements is investigated and quantified to yield pra ctical error estimates. First, a data set of Pegasus current profiles from the tropical Atlantic (6-degrees-S to 6-degrees-N) is analyzed fo r their rms down/up differences, which are compared with predictions f rom Garrett-Munk type internal wave theory and with statistics derived from current meter moorings in the same region. The agreement in term s of amplitudes and vertical distribution proves that most of those di fferences are due to internal waves and not instrumental errors. Nonet heless, this is the noise of the measurements, if low-frequency motion s are sought, and the errors can thus be quantified using the same int ernal wave theories. At midlatitudes the error variance is the usual 4 4(N/3 cph) cm2/s2 with some latitude dependence, and the effect of ave raging in the vertical or summing several profiles (e.g., up and down) is estimated. The same is done for equatorial situations, where const ruction of a crude equatorial frequency spectrum for internal waves yi elds 77(N/3 cph)cm2/s2 for the error variance. Again, error reduction due to averaging is estimated.