Accelerated photosynthesis routine in LPJmL4

The increasing impacts of climate change require strategies for climate adaptation. Dynamic global vegetation models (DGVMs) are one type of multi-sectorial impact model with which the effects of multiple interacting processes in the terrestrial biosphere under climate change can be studied. The complexity of DGVMs is increasing as more and more processes, especially for plant physiology, are implemented. Therefore, there is a growing demand for increasing the computational performance of the underlying algorithms as well as ensuring their numerical accuracy. One way to approach this issue is to analyse the routines which have the potential for improved computational efficiency and/or increased accuracy when applying sophisticated mathematical methods. In this paper, the Farquhar–Collatz photosynthesis model under water stress as implemented in the Lund–Potsdam–Jena managed Land DGVM (4.0.002) was examined. We additionally tested the uncertainty of most important parameter of photosynthesis as an additional approach to improve model quality. We found that the numerical solution of a nonlinear equation, so far solved with the bisection method, could be significantly improved by using Newton's method instead. The latter requires the computation of the derivative of the underlying function which is presented. Model simulations show a significantly lower number of iterations to solve the equation numerically and an overall run time reduction of the model of about 16 % depending on the chosen accuracy. Increasing the parameters θ and αC3 by 10 %, respectively, while keeping all other parameters at their original value, increased global gross primary production (GPP) by 2.384 and 9.542 GtC yr−1, respectively. The Farquhar–Collatz photosynthesis model forms the core component in many DGVMs and land surface models. An update in the numerical solution of the nonlinear equation in connection with adjusting globally important parameters to best known values can therefore be applied to similar photosynthesis models. Furthermore, this exercise can serve as an example for improving computationally costly routines while improving their mathematical accuracy.</p

Retrieval of Multimodal Aerosol Size Distribution by Inversion of Multiwavelength Data

The ill-posed problem of aerosol size distribution determination from a small number of backscatter and extinction measurements was solved successfully with a mollifier method which is advantageous since the ill-posed part is performed on exactly given quantities, the points r where n(r) is evaluated may be freely selected. A new twodimensional model for the troposphere is proposed. Keywords: Multiwavelength LIDAR, aerosol size distribution, ill-posed problem, inversion, mollifier method, coated and absorbing aerosols 1. INTRODUCTION Atmospheric aerosols play an important role in many atmospheric processes, e.g. in the complex processes of tropospheric ozone production and of stratospheric ozone destruction. Aerosols provide surfaces for example for chemical reactions which activate Cl from CFCs. One of the key aspects in a further understanding of the importance of aerosols is the investigation of the spatial and temporal variability of their microphysical properties, e.g. parameter..

Nonlinear Inverse Unbalance Reconstruction in Rotor Dynamics

This paper is devoted to the identification and reconstruction of unbalance distributions in an aircraft engine rotor with a nonlinear damping element. We have developed a rotor model that takes into account the nonlinear behavior of a squeeze film damper between the engine’s shaft and casing for large oscillation amplitudes. Based on the Tikhonov regularization for nonlinear ill–posed problems, we provided a three–step algorithm that enables us to identify and reconstruct single and distributed unbalances from data measured at the casing of the engine. In view of practical capability, the algorithms were accelerated to meet the requirement of tolerable computation time for larger models, too.

The MICADO first light imager for the ELT: overview, operation, simulation

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