Assessment and Improvement of Noah-MP over the Tibetan grasslands in growing season

<p>The Tibetan grasslands has very strong land-air interactions and plays an important role in the regional climate system of the Tibetan Plateau and understanding of land-air interactions in the Tibetan grasslands is significantly important for the sustainable development of it under the climate change. In this paper, we assessed the Noah-MP by conducting ensemble experiments for analyzing the sensitive physical processes, and selected the optimal combinations of parameterization options at four alpine meadow sites in the Tibetan grassland ecosystems. Measurements collected from four study sites over the Tibetan grassland ecosystems in the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) are used. The results showed that the dynamic vegetation (Dveg), the canopy stomatal resistance (Crs), the runoff and the groundwater (Run) and the surface exchange coefficient (Sfc) physical processes are the most sensitive control physical processes for energy and water fluxes in the Tibetan grassland ecosystems. Importantly, the optimal combination of parameterization options in Noah-MP overestimates the sensible heat flux (<em>H</em>) and underestimates soil moisture (<em>θ</em>) obviously. After finding the problems in the simulations outputed by the optimal combination of parameterization options, two groups of improved experiments were conducted to find out the reason. We found that the improved calculation of the surface exchange coefficient can alleviate the overestimation <em>H</em>, and the improved method of soil parameters considering the soil organic carbon (SOC) and an exponential form of root vertical distribution for each soil layers can effectively solve the underestimation of <em>θ</em> at all four sites.</p>

Evaluation of a Time-Dependent Model for the Intensification of Tropical Cyclones

Axisymmetric and three-dimensional simulations are used to evaluate the theory of tropical cyclone (TC) intensification proposed by K. A. Emanuel, which is based on gradient wind balance and moist-neutral ascent along angular momentum (M) surfaces. According to the numerical model results, the intensification of the TC can be divided into two periods, phase I and phase II. During phase I, the TC intensifies while the M and saturation entropy (s*) surfaces evolve from nearly orthogonal to almost congruent. During phase II, the M and s* surfaces in the eyewall and outflow are congruent as the TC intensifies, which is consistent with Emanuel’s study. Therefore, the condition of moist slantwise neutrality in Emanuel’s study is sufficiently satisfied throughout the intensification in phase II. It is also found that the sensitivity of the intensification rates to the surface exchange coefficient for entropy Ck matches Emanuel’s theoretical result, which is that the intensification rate is proportional to Ck. However, the intensification rate varies in proportion to the surface exchange coefficient for momentum Cd, while the Emanuel model growth rate is insensitive to Cd. Furthermore, although the tendency diagnosed by Emanuel is qualitatively similar to the numerical model result during phase II, it is not quantitatively similar. The present analysis finds the inclusion of non–gradient wind effects in the theoretical framework of Emanuel’s study produces an intensification rate that is quantitatively similar to the numerical model results. The neglect of non–gradient wind effects in Emanuel’s study may be the reason for the different dependence of its intensification rate on Cd compared to that of the numerical model. Other aspects of Emanuel’s study in the context of recent research on TC intensification are discussed.

Back-exchange: a novel approach to quantifying oxygen diffusion and surface exchange in ambient atmospheres

A novel two-step Isotopic Exchange (IE) technique has been developed to investigate the influence of oxygen containing components of ambient air (such as H2O and CO2) on the effective surface exchange coefficient (k*) of a common mixed ionic electronic conductor material.

Oxygen diffusion and surface exchange in the mixed conducting oxides SrTi1−yFeyO3−δ

Variation of the surface exchange coefficient with Fe concentration suggests single mechanism of oxygen exchange for e−-poor and e−-rich SrTi1−yFeyO3−δ oxides.

Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime

The model explains the range of apparent activation energies measured in different kinetic regimes of oxygen exchange at oxide surfaces.