The estimation of the upper ocean mixed layer depth at ocean weather station Papa using the varlational approach



The variations of the thermal characteristics of the near-surface ocean layers exert a significant impact on the heat influx to the atmosphere, and through this on the atmosphere circulation. To examine the ocean heat sources, the estimates of the current state of the oceanic thermal field drawn from operational temperature measurements are needed. The distribution of these measurements over the depth is highly irregular. Relatively detailed information is available only on the sea surface temperature (SST) measured both in situ from opportunity ships and drifting buoyes and by means of remote sensing from satellites. To obtain immediately the upper ocean mixed layer depth h, which in conjunction with the SST represents one of the main parameters characterizing oceanic near-surface heat storage, the measurements of vertical temperature profiles are needed. The number of XBT measurements commonly contained in operational data bases is highly restricted (~ 150 daily XBT measurements in the Northern Hemisphere) and is not enough for immediate obtaining of the mixed layer depths over the spacious ocean domains. In this connection indirect methods of estimating h are needed. One of the methods based on variational approach has been proposed by Resnyansky (1985). The estimates of h were obtained from the temporal sequences of SST at an ocean location. The values of h corresponding to minimal differences between modelled and observed SSTs within a given time interval are taken as a resultant estimate. The method has been tested using simulated data. The present paper is devoted to the further testing of the method using the actual observations at ocean weather station Papa in the North Eastern Pacific over the period from 1972 to 1974. The dependence of the estimation uncertainties on the model parameters as well as on the type of the basic state set to stabilize the estimates is considered.

Full Text: