ON COMPUTING SCREEN TEMPERATURES, HUMIDITIES AND ANEMOMETER-HEIGHT WINDS IN LARGE-SCALE MODELS

Many large-scale models use the Louis approximate equations to paramet rise boundary-layer transfer processes, In this paper a simple, effici ent technique is described to derive screen temperatures and humiditie s and anemometer-height winds from model variables at the surface and the lowest model level, The method uses Dyer-Businger profile relation ships to predict the wind, potential temperature and specific humidity at screen or anemometer height, The bulk Richardson number is then ca lculated and corrected values of the wind, potential temperature and s pecific humidity are calculated using the Louis profile equations, Thi s ensures consistency in the estimates, since the fluxes were obtained from the Louis scheme, The same methodology could be used directly fo r other boundary-layer schemes based on Richardson number, For very st able conditions the Dyer-Businger scheme may give poor estimates, but the method still works, provided an upper bound is placed on the Richa rdson number used in the Louis correction, Convergence to less than fi ve per cent for wind, 0.25 per cent for temperature and five per cent for humidity occurs within two corrections.