REALIZABILITY CONSTRAINTS FOR LAND-SURFACE SCHEMES

It is well known that turbulent transfer models can sometimes produce results that cannot be realised in nature. In this paper we develop si mple rules to check the physical robustness of parameterisations of la nd-surface turbulent transfer for heterogeneous surfaces. The methodol ogy draws upon areal-averaging by parameter aggregation and by flux ag gregation. Both techniques have been demonstrated to be valid. Combini ng the two techniques enables one to determine the surface potential t emperature and specific humidity, averaged over the grid-box. When thi s is done the implied turbulent transfer is sometimes counter-gradient . The implications of this result are discussed. The methodology prese nted is general and provides a complementary way of evaluating the rol e of coupling land-surface schemes to atmospheric host models to that presented by Polcher et al. [Polcher, J., McAvaney, B., Gaertner, M.-A ., Hahmann, A., Noilhan, J., Phillips, T., Pitman, A., Schlosser, A., Schulz, J.-P., Timbal, B., Verseghy, D., Viterbo, P., Xue, Y., 1998. A proposal for a general interface between land-surface schemes and gen eral circulation models. Global Planet. Change, this issue.]. (C) 1998 Elsevier Science B.V. All rights reserved.