Comparison of Meteorological Elements in Dry and Wet Seasons and Parameterization of Momentum and Sensible Heat Exchange Coefficients near the Underlying Surface of the Zhuhai Phoenix Mountain Forest

The variation characteristics of the energy flux and meteorological elements of the underlying surface of the forest during the wet and dry seasons were compared and analyzed by using observation data obtained from November 2014 to May 2016 from the Zhuhai Phoenix Mountain Land–Atmosphere Interaction Observation Tower Station. The variation characteristics of the momentum and sensible heat exchange coefficients in three wind direction ranges (315°–45°, 45°–135°, and 135°–225°) along with the canopy−surface wind speed under different stability conditions, as well as the parameterizations of these coefficients were analyzed. The sensible heat and latent heat fluxes in the dry season were equivalent, whereas in the wet season latent heat is much higher than the sensible heat. Negative sensible heat occurs during the night in both the dry and wet seasons, with the sensible heat being transported from the atmosphere to the forest. The variation range of the relative humidity is large and is closely related to the meteorological conditions in the area. The vertical gradient of the relative humidity is larger at night and smaller during the day. The vertical gradient of the air temperature in the dry season is more significant than that in the wet season. The wind speed changes gently in winter but violently in summer. There is an obvious gradient in the low-level wind speed with height, whereas the high-level wind is chaotic. The wind direction at different heights does not differ significantly. In neutral and near-neutral states, the momentum exchange coefficients C_dn are 0.05, 0.0055, and 0.022, respectively, when the wind directions are 315°–45°, 45°–135°, and 135°–225°, and the sensible heat exchange coefficients C_hn are 0.0055, 0.003, and 0.004, respectively. Under stable and unstable conditions, the momentum exchange coefficient C_d and the sensible heat exchange coefficient C_h obviously change with the wind velocity v on the canopy surface. Under stable conditions, C_d and C_h increase with increases in v, and under unstable conditions, C_d, and C_h decrease with increases in v. We fitted the relationships between C_d, C_h in the forest canopy and v under stable and unstable conditions in different wind directions, and obtained the parameterized formula.