Rothamsted Research, Herfordshire, UK.
Phytopathology. 2011 Dec;101(12):1465-70. doi: 10.1094/PHYTO-01-11-0001.
It is well known that the dynamics of plant disease epidemics are very sensitive to the functional form of the contact distribution?the probability distribution function for the distance of viable fungal spore movement until deposition. Epidemics can take the form of a constant-velocity travelling wave when the contact distribution is exponentially bounded. Fat-tailed contact distributions, on the other hand, lead to epidemic spreads that accelerate over time. Some empirical data for contact distributions can be well represented by negative exponentials while other data are better represented by fat-tailed inverse power laws. Here we present data from numerical simulations that suggest that negative exponentials and inverse power laws are not competing candidate forms of the contact distribution but are instead representative of different atmospheric conditions. Contact distributions for atmospheric boundary-layers with stabilities ranging from strongly convective (a hot windless day time scenario) to stable stratification (a cold windy night time scenario) but without precipitation events are calculated using well-established state-of-the-art Lagrangian stochastic (particle tracking) dispersal models. Contact distributions are found to be well represented by exponentials for strongly convective conditions; a -3/2 inverse power law for convective boundary-layers with wind shear; and by a -2/3 inverse power law for stably stratified conditions.
众所周知，植物病害流行的动力学对接触分布的函数形式非常敏感——即真菌孢子存活运动距离的概率分布函数，直到沉积。当接触分布呈指数有界时，流行病可能呈恒定速度传播波的形式。另一方面，长尾接触分布会导致流行病随时间加速传播。一些接触分布的经验数据可以很好地用负指数表示，而其他数据则可以更好地用长尾逆幂律表示。在这里，我们提供了数值模拟的数据，这些数据表明负指数和逆幂律并不是接触分布的竞争候选形式，而是代表不同的大气条件。使用成熟的先进拉格朗日随机（粒子跟踪）扩散模型，计算了从强对流（炎热无风的白天场景）到稳定分层（寒冷有风的夜间场景）但没有降水事件的大气边界层的接触分布。对于强对流条件，接触分布可以很好地用指数表示；对于具有风切变的对流边界层，接触分布可以用-3/2 次幂律表示；对于稳定分层条件，接触分布可以用-2/3 次幂律表示。
