Differences between true mean daily, monthly and annual air temperatures and air temperatures calculated with three equations: a case study from three Croatian stations

Differences between true mean daily, monthly and annual air temperatures T0 Eq. (1)] and temperatures calculated with three different equations (2), (3) and (4)] (commonly used in climatological practice) were investigated at three main meteorological Croatian stations from 1 January 1999 to 31 December 2011. The stations are situated in the following three climatically distinct areas: (1) Zagreb-Gri? (mild continental climate), (2) Zavi?an (cold mountain climate), and (3) Dubrovnik (hot Mediterranean climate). T1 Eq. (2)] and T3 Eq. (4)] mean temperatures are defined by the algorithms based on the weighted means of temperatures measured at irregularly spaced, yet fixed hours. T2 Eq. (3)] is the mean temperature defined as the average of daily maximum and minimum temperature. The equation as well as the time of observations used introduces a bias into mean temperatures. The largest differences occur for mean daily temperatures. The calculated daily difference value from all three equations and all analysed stations varies from ?3.73 °C to +3.56 °C, from ?1.39 °C to +0.79 °C for monthly differences and from ?0.76 °C to +0.30 °C for annual differences.