Accuracy of ACARS Wind and Temperature Observations Determined by Collocation

A collocation study of meteorological reports from commercial aircraft relayed through the Aircraft Communications, Addressing, and Reporting System (ACARS) has been performed to estimate standard deviations of observation errors for wind and temperature. ACARS observations were collected over an area in the western and central United States for a 13-month period, and this dataset was examined for pairs of reports within small spatial (⩽10 km) and temporal (⩽10 min) windows. The results showed an observation error of a single horizontal component of wind of 1.1 m s−1 and 0.5 K for temperature above the boundary layer. Within the boundary layer, the rms difference of wind and temperature between aircraft was larger, presumably due to larger small-scale variations in the atmosphere and, in the case of wind, from aircraft maneuvers. These observation error estimates are valuable for use in data assimilation and for determination of forecast error from ACARS observation-minus-forecast differences. By comparing standard deviations at different levels, estimates of mesoscale variability at a 10-km scale in the lower troposphere were also calculated. These values (rms vector error of 1.8 m s−1 for wind, rms error of 0.5 K for temperature) can be interpreted as estimates of the 10-km lower-tropospheric error of representativeness, also useful for data assimilation.