Accuracies of marine meteorological observations made on merchant ships

Accuracies of wind speed and air temperature observations were assessed. Wind speed observation reported to the Japan Meteorological Agency in 1996 and 1997 were examined by comparing them with the NSCAT surface wind observations. Systematic errors in wind direction measurements are negligibly small, but the random error is as large as 44 degrees. In overall evaluation, wind speed observed aboard is overestimated by 1.30 m s^-1 and the random error is 2.83 m s ^-1, respectively. It is confirmed that anemometer height correction can successfully reduce the systematic error for instrumental observation. In contrast, the systematic errors in visually observations were not reduced by applying a newly developed correction method. The numerical experiments were also conducted for several types of merchant ships to examine the distributions of wind speed around the ships. The results of the experiments give some idea where an anemometer should be installed on and how much the systematic error can be expected. Basic field experiments were performed to quantitatively evaluate the bias error on the air temperature measurement aboard. It is confirmed that the relationship between the bias error and insolation that was shown by previous studies; i.e., the bias is almost linearly proportional to the magnitude of insolation in the same time. The bias also seems to weakly depend on fetch of the wind on the ship