[1] The roles of deep convection and generated waves in the Tropical Tropopause Layer (TTL) are investigated using a global nonhydrostatic model, the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), which runs on the Earth Simulator with a horizontal spacing of 7 km. The model data, which successfully simulated a Madden-Julian Oscillation (MJO) event for the period between 15 December 2006 and 15 January 2007, are analyzed. The frequency of deep convective clouds that reach the TTL is one of the key diagnostics for dehydration and transport. The present results revealed that the proportion of cumulus clouds that penetrate the lapse-rate tropopause and the bottom boundary of the TTL (defined as the lapse rate minimum) is $0.5% and $20%, respectively, in the region between 5 S and 5 N. This result is reasonably consistent with atmospheric observations. Deep convective activity that reaches the TTL was observed over southern Africa, the Indian Ocean, the Indonesian maritime continent, the western Pacific, and southern America. Deep convection over the continents was most active during the local evening period. Over the oceans, high clouds reaching the tropopause were seen over the Indian Ocean and the seas around Java, where two tropical cyclones were generated. Prominent diurnal variations in tropopause temperature associated with deep convection occurred over the Indonesian maritime continent. These diurnal variations were superimposed on large, low-frequency temperature variations associated with equatorial Kelvin waves generated by the MJO convection. Probably because of coarse vertical resolution, temperature variations simulated by the NICAM are larger than those in the real atmosphere. The two tropical cyclones caused relatively large tropopause temperature variations with a cyclone scale ($500 km horizontally). The gravity waves generated by tropical cyclones cause small tropopause temperature variations that extend for 1000 km from the cyclone. We conclude that the Kelvin waves associated with the MJO convection cause the largest amplitude of temperature variations in the TTL and that tropical cyclones and diurnal variations of convective activity have large local impacts on temperature variations in the TTL.
Abstract. A previously proposed vegetation isoline equation suffers from errors if the soil background of a canopy layer is bright. These errors arise from the truncation of the second-and higher-order terms that represent photon interactions between the canopy and the soil. An isoline equation that includes a second-order interaction term is introduced. The equation was initially derived by explicitly including a second-order interaction term in both the red and near-infrared (NIR) reflectance spectra (symmetric approximation). We also examined an alternative model in which the interaction term was included only in the NIR band (asymmetric approximation). In this model, the derived isolines tend to shift upward (overcorrection effects). Numerical experiments revealed that the errors in the isoline obtained by the asymmetric approximation were reduced in magnitude to nearly one-fifth of the errors in the previously proposed method. Its accuracy was higher than that of the symmetric approximation, despite the fact that the asymmetric approximation included fewer terms than the symmetric approximation. The improved model accuracy resulted from the overcorrection effects, which compensated for the truncation error. With the simplicity and improved accuracy, the current isoline equations provide a good alternative to the previous approach.
This study introduces a series of vegetation isoline equations derived by accounting higher-order interaction terms between canopy layer and soil surface. Our focus is to investigate accuracies of the derived isoline equations in the context of applications for hyperspectral data analysis. The objective is to derive vegetation isoline equations that relate reflectances between two wavelengths with higher order interaction terms under an assumption of partial vegetation cover (fraction of vegetation cover is less than unity). Accuracies of the derived isoline equations were evaluated numerically based on a radiative transfer model. The results show that the accuracy in the isoline equations are improved from the original form (the first-order approximation case) by including the higher-order interaction terms. However, a special caution is needed for the choice of the wavelengths and the form of the equations (which depends on the order of interaction terms considered during the derivation), since the accuracies of the isoline equations depends largely on those choices.
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