184.108.40.206 Improved Global and Regional Data
Specification of land surface properties has improved through new, more accurate global satellite observations. In particular, satellite observations have provided albedos of soils in non-vegetated regions (e.g., Tsvetsinskaya et al., 2002; Ogawa and Schmugge, 2004; Z. Wang, et al., 2004; Zhou et al., 2005) and their emissivities (Zhou et al., 2003a,b). They also constrain model-calculated albedos in the presence of vegetation (Oleson et al., 2003) and vegetation underlain by snow (Jin et al., 2002), and help to define the influence of leaf area on albedo (Tian et al., 2004). Precipitation data sets combining rain gauge and satellite observations (Chen et al., 2002; Adler et al., 2003) are providing diagnostic constraints for climate modelling, as are observations of runoff (Dai and Trenberth, 2002; Fekete et al., 2002).
220.127.116.11 Field Observational Programs
New and improved local site observational constraints collectively describe the land processes that need to be modelled. The largest recent such activity has been the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) project (Malhi et al., 2002; Silva Dias et al., 2002). Studies within LBA have included physical climate at all scales, carbon and nutrient dynamics and trace gas fluxes. The physical climate aspects are reviewed here. Goncalves et al. (2004) discuss the importance of incorporating land cover heterogeneity. Da Rocha et al. (2004) and Quesada et al. (2004) quantify water and energy budgets for a forested and a savannah site, respectively. Dry season evapotranspiration for the savannah averaged 1.6 mm day–1 compared with 4.9 mm day–1 for the forest. Both ecosystems depend on deep rooting to sustain evapotranspiration during the dry season, which may help control the length of the dry season (see, e.g., Section 18.104.22.168). Da Rocha et al. (2004) also observed that hydraulic lift recharged the forest upper soil profiles each night. At Tapajós, the forest showed no signs of drought stress allowing uniformly high carbon uptake throughout the dry season (July through December 2000; Da Rocha et al., 2004; Goulden et al., 2004). Tibet, another key region, continues to be better characterised from observational studies (e.g., Gao et al., 2004; Hong et al., 2004). With its high elevation, hence low air densities, heating of the atmosphere by land mixes air to a much higher altitude than elsewhere, with implications for vertical exchange of energy. However, the daytime water vapour mixing ratio in this region decreases rapidly with increasing altitude (Yang et al., 2004), indicating a strong insertion of dry air from above or by lateral transport.