CALCULATION ACCURACY OF EVAPORATION AT DIFFERENT AVERAGING PERIODS BY OBSERVATION DATA IN THE SOUTHERNBALTIC

Abstract

The evaporation or moisture flow in the boundary layer is one of important components in the ocean-atmosphere interaction system. The most commonly used formulas for calculating evaporation include standard hydrometeorological parameters — atmospheric pressure, wind speed, drop of humidity, and height, at which measurements are made, and the exchange rate of moisture, which also depends on these parameters. The correct method is to calculate moisture flow based on current or hourly parameter values and then average the flow values for the required period: day, month or year. In the absence of current data of observation parameters, flow values should be calculated based on averaged parameter values. In this case, the calculated values of evaporation strongly depend on the method and the averaging period. Using the example of rather long observation series (2002—2016) at stations in the Southern Baltic, a quantitative assessment of the effect of averaging on the calculated values of the moisture flow both for direct calculation from the current observation data and for averaged data is made. The probable explanations are given for a significant variation in the calculated values of evaporation in the Baltic Sea by different authors. The coefficients for the correction of evaporation values obtained from the averaged values of hydrometeorological parameters are calculated. It is shown that averaging the parameters per day is acceptable with almost no loss of accuracy (error no more than 2-4 %). Averaging the values of hydrometeorological parameters over the period of a month leads to an underestimation of the calculated evaporation values by 20-30 %. When averaging over a period of about a year, the error increases to 30-35 %. The conclusions and correction coefficients are valid for calculations of evaporation in the Baltic Sea and can be used in other areas of middle and high latitudes, where the evaporation values do not differ by orders of magnitude (tropics, equator, zones of significant variability of environmental parameters).