Dynamic meteorology: data assimilation methods by L. Bengtsson, M. Ghil, E. Källen

By L. Bengtsson, M. Ghil, E. Källen

One of many major purposes we can't inform what the elements should be the next day is that we don't be aware of properly sufficient what the elements is at the present time. Mathematically talking, numerical climate prediction (NWP) is an initial-value challenge for a procedure of nonlinear partial differential equations within which the required preliminary values are identified basically incompletely and inaccurately. facts on the preliminary time of a numerical forecast should be supplemented, notwithstanding, by way of observations of the atmos­ phere over a time period previous it. New gazing platforms, specifically polar-orbiting and geostationary satellites, that are offering observations regularly in time, make is actually necess­ ary to discover new and extra passable equipment of assimilating meteorological observations - for the twin function of defining atmospheric states and of issuing forecasts from the states hence outlined. basic development during this region has been made in recent times and this publication makes an attempt to provide a assessment and a few feedback for extra advancements within the box of meteorological facts assimila­ tion tools. the ecu Centre for Medium diversity climate Forecasts (ECMWF) each year organises seminars for the advantage of meteorologists and geophysicists of the ECMWF Member states. The 1980 Seminar was once dedicated to info assimilation equipment, and this publication comprises chosen lectures from that seminar. the aim of the seminar used to be twofold: it was once meant to provide a uncomplicated advent to the topic, in addition to an outline of the most recent advancements within the box.

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Fig. 8. 5 Basic Equations of the Atmospheric Boundary Layer 45 According to the HLR theory, the inner layer depth linner which can be calculated from linner = 2k 2L / ln(linner / z0), is usually much higher than the saltation layer. The velocity profile in this layer follows logarithmic law, while the friction velocity u* is not equal to the inflow friction velocity u*0, but substituted by another value with taking into account of the local disturbance instead.

34) At the upper boundary of the saltation layer, the turbulence shear stress is determined by the outer flow field, and is generally taken as τ 0. It can be inferred from Eqs. 34 that τ a + τ s = τ 0, so u ∂u 1 τ0 −τ s = A *a = . 35) According to the contribution of the Sauermann et al. 36) where Hs is the thickness of mean saltation. If the value of z0 is properly attained, the continuity of the flow field’s velocity outside the saltation layer can be assured. In addition, the analytic expression of the velocity in the wind-blown sand flux was also given by Raupach (1991).

11), to form the so-called Reynolds-Averaged Navier-Stokes (RANS) model. Though practical, the closed RANS model is not universal since Reynolds stress mainly originates from the large-scale fluctuation and its properties are closely related to the boundary condition of the flow. In other words, there does not exist a uniform model which can be applied to all complex flows. As far as computational complexity is concerned, the Large Eddy Simulation (LES) model lies between the DNS and the RANS model.

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