Surface characteristics and meteorological variables

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To calculate the resistances, several surface characteristics are needed.

Local roughness length for momentum is determined by eddy correlation measurements at lower height in IMGRASS site. The reference height is taken as 2 meters. The regional effective values of z0m are estimated by fitting wind-speed measurements at different levels to the logarithmic velocity profiles using least-square method and taking for higher and denser canopy and d=0 for the lower and sparse covered canopy. Blending height is considered as a suitable reference level (Brutsaert and Sugita, 1992) to estimate regional heat flux. In the HEIFE area, the available lower-level sounding was measured two hour earlier (09:00h in the morning) than the satellite overpass time in another site of HEIFE which is about 30km away from Zhang-Ye site. This lower-level sounding was used to determine blending height and wind speed and potential temperature at this height. Unfortunately, we do not have the same measurements during the day of ATSR-2 acquisition in the IMGRASS campaign. Reference height and meteorological variables at the reference height are simply taken as those at the lowest level of standard meteorological radiosounding in the early morning (at

The reference source height in the canopy, Zo, is considered as the order of magnitude of roughness length for momentum, z0m or the proportion of canopy height. In our study we have taken Zo = 2/3hc for both areas. For partial canopies, uo can be obtained by extrapolating the logarithmic profiles of wind speed to with the assumption that the logarithmic form of wind speed is valid down to the canopy space. The surface and meteorological variables used in the study are listed in Table 4.

Table 4. Surface and meteorological data used in the study_

Table 4. Surface and meteorological data used in the study_

height(m)

IMGRASS

field

0.1

0.02

2

*

*

0.5

regional

0.2

0.02

445

10

20.2

*

HEIFE

regional

1.2

0.5

500

1.8

25.4

*

Note: * values are from measurements (for uref and Tref) or modeling (for LAI). For regional scale, Tref is the potential temperature.

Note: * values are from measurements (for uref and Tref) or modeling (for LAI). For regional scale, Tref is the potential temperature.

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