A NUMERICAL STUDY OF THE PBL CONDITIONS OVER RECLAIMED GRASSLAND

PBL conditions over reclaimed grassland in North China(49°19'N, 119°55'E) are examined using the improved version of the model developed by Nickerson et al. (1986). Basic results are presented as follows: i) the reclaimed section, or the "heat island", has noon intensity of 4-6°C, the surface disturbance can be felt at 700 m AGL and convective perturbance at the PBL top, with a convective speed of 1-2 cm/s; ii) once grassland is reclaimed on a large scale, the PBL climate will develop into further aridity; iii) irrigation can alleviate the intensity and dryness of the "island" but fails to prevent the climate from aridization; iv) the local circulation in the PBL keeps its direction unchanged in 24 hours, i.e.,wind blows toward the "island" at the height below 150-200 m at roughly 2 m/s and returns at higher levels with a slightly smaller speed. Further, moist flow can extend 30-50 km horizontally inside the reclamation.