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The Chinese loess/palaeosol succession is one of the most comprehensive and intensively studied archives of Neogene and Quaternary global palaeoclimate events. Its stratigraphic details are widely recognised to indicate close links to the history and function of the East Asian Winter Monsoon (EAWM) - one of the most active components of the Earth's climate system. But the formal meteorological links between the EAWM and dust emission, both in the present day and in the past, have not been established and with it, the veracity of the loess record as an indicator of the EAWM questioned. Here we show that present day major dust events over northern China, while largely occurring during spring, are nevertheless 'conditioned' by the strength of the preceding EAWM. We also demonstrate, for the first time, a close link between the occurrence of dust events and the strength of the EAWM. From these findings, linked to global-scale climate model simulations, we conclude that the Chinese loess succession provides a convincing proxy record of the strength of the East Asian Winter Monsoon. (C) 2016 Published by Elsevier Ltd.

Polar motion is an important Earth orientation parameter, but our understanding of its relation to global climate change is highly uncertain. In this study, we examine the links between polar motion excitation and annual mean air temperature during the period of 1962-2013 and discuss the possible responsible mechanisms. The regions of positive correlation correspond well with the warming centers. Spectral analysis shows that they have strong signals at similar frequencies. Strong correlations are also found between the polar motion and surface air pressure and vertical integrated zonal wind. This implies that polar motion serves as an important indicator of global climate change, and thus, the feedbacks between the solid Earth and the climate system deserve careful considerations.

Wind tunnel experiments of dust emissions from different soil surfaces are carried out to better understand dust emission mechanisms. The effects of surface renewal on aerodynamic entrainment and saltation bombardment are analyzed in detail. It is found that flow conditions, surface particle motions (saltation and creep), soil dust content and ground obstacles all strongly affect dust emission, causing its rate to vary over orders of magnitude. Aerodynamic entrainment is highly effective, if dust supply is unlimited, as in the first 2-3 min of our wind tunnel runs. While aerodynamic entrainment is suppressed by dust supply limits, surface renewal through the motion of surface particles appears to be an effective pathway to remove the supply limit. Surface renewal is also found to be important to the efficiency of saltation bombardment. We demonstrate that surface renewal is a significant mechanism affecting dust emission and recommend that this mechanism be included in future dust models.

The land-atmosphere system is characterized by pronounced land surface heterogeneity and vigorous atmospheric turbulence both covering a wide range of scales. The multiscale surface heterogeneities and multiscale turbulent eddies interact nonlinearly with each other. Understanding these multiscale processes quantitatively is essential to the subgrid parameterizations for weather and climate models. In this paper, we propose a method for surface heterogeneity quantification and turbulence structure identification. The first part of the method is an orthogonal transform in the probability density function (PDF) domain, in contrast to the orthogonal wavelet transforms which are performed in the physical space. As the basis of the whole method, the orthogonal PDF transform (OPT) is used to asymptotically reconstruct the original signals by representing the signal values with multilevel approximations. The patch idea is then applied to these reconstructed fields in order to recognize areas at the land surface or in turbulent flows that are of the same characteristics. A patch here is a connected area with the same approximation. For each recognized patch, a length scale is then defined to build the energy spectrum. The OPT and related energy spectrum analysis, as a whole referred to as the orthogonal PDF decomposition (OPD), is applied to two-dimensional heterogeneous land surfaces and atmospheric turbulence fields for test. The results show that compared to the wavelet transforms, the OPD can reconstruct the original signal more effectively, and accordingly, its energy spectrum represents the signal's multiscale variation more accurately. The method we propose in this paper is of general nature and therefore can be of interest for problems of multiscale process description in other geophysical disciplines.

Since the pioneering work of Bagnold in the 1940s, aeolian research has grown to become an integral part of earth-system science. Many individuals have contributed to this development, and Dr. Michael R. Raupach (1950-2015) has played a pivotal role. Raupach worked intensively on wind erosion problems for about a decade (1985-1995), during which time he applied his deep knowledge of turbulence to aeolian research problems and made profound contributions with far-reaching impact. The beauty of Raupach's work lies in his clear conceptual thinking and his ability to reduce complex problems to their bare essentials. The results of his work are fundamentally important and have many practical applications. In this review we reflect on Raupach's contribution to a number of important aspects of aeolian research, summarise developments since his inspirational work and place Raupach's efforts in the context of aeolian science. We also demonstrate how Raupach's work provided a foundation for new developments in aeolian research. In this tribute, we concentrate on five areas of research: (1) drag partition theory; (2) saltation roughness length; (3) saltation bombardment; (4) threshold friction velocity and (5) the carbon cycle. (C) 2015 Elsevier B.V. All rights reserved.

Size-resolved dust flux measurements are important for estimation of concentration and physical properties of dust particles in the atmosphere and their impacts on cloud and radiation transfer. In this study, we evaluate the power law relationship between size-resolved dust flux, F-air,F-d, and friction velocity, u(*). During the Japan-Australia Dust Experiment, size-resolved dust fluxes were estimated with the gradient method by using data from optical particle counters and profile measurements of wind speed and air temperature in a dry, non-crusted fallow wheat field in Australia. When a power law is fitted to the U-*-F-air,F-d relation, i.e., F-air,F-d-u(*)(n), the coefficient of determination R-2 is largest for n = 4. However, when a power law is fitted separately to data of each particle size range, n is found to depend on the particle size with values of 2.54 (0.7 mu m), 3.40 (1.1 mu m), 3.80 (1.7 mu m), 4.32 (2.6 mu m), 4.67 (4.6 mu m), and 4.53 (7.0 mu m), respectively, and maximum n was 4.67 for the 4.6 mu m diameter. This suggests that the F-air,F-d-u(*)(n) relationship is not universal, and embedded in n is the nature of soil aggregation. For practical purposes, n should be determined separately for each particle size range when estimating size-resolved dust fluxes. (C) 2013 Elsevier B.V. All rights reserved.

In this paper, the severe dust event of 3-8 July 2009 in the Middle East is simulated using the WRF-DuMo model. To improve the model capacity in dust emission estimates, the effect of soil salt on threshold friction velocity for wind erosion is taken into consideration. A soil-salt propagation map and the other input parameters are compiled based on remote sensing and a Geographic Information System. The satellite images and synoptic data are used for the validation of the model results. Synoptic analysis is done for the Middle East and the synoptic systems for the severe dust event are identified. Comparison of the model results with the observed data shows that in the Aral-Caspian Sea area, central Iran and the Dead Sea Basin, dust emission is suppressed due to the high soil-salt content. The model shows better performances when the soil-salt effect is considered. (C) 2014 Elsevier B.V. All rights reserved.

Surface heterogeneity is present on every scale of the land surface. However, its role in the exchange processes between the land surface and the atmosphere is still an open question. In this paper, we present a method, which combines the decomposition of land-surface heterogeneity into fine and coarse structures with the quantification of the structures using information entropy. The resulting entropy spectrum allows the assessment of the amount of information on different scales. The wavelet transformation and the most frequent-value method are used as filters for the decomposition. We also derive an analytical formula for estimation of the probability density function (PDF) of filtered random surface parameters using the most frequent-value method. By analyzing the entropy spectrum of synthetic data, we derive rules for the interpretation of the entropy spectrum. We then apply them to real data and appraise, which scale of the heterogeneity is important for land surface and atmosphere interactions.

Further developments of a parameterization scheme for convective turbulent dust emission (CTDE) are presented. The scheme is advanced by including (1) a new statistical description of instantaneous momentum flux, (2) a correction function for cohesive force to account for the effect of soil moisture, and (3) a correction function for lifting force to consider the effect of vegetation roughness elements. The probability density function describing instantaneous momentum flux is now derived from large-eddy simulations for different atmospheric stabilities. The vegetation correction function is based on a drag partition theory. Additional improvements on the representations of interparticle cohesive force and particle size distribution are introduced. The new CTDE scheme is tested against the field data obtained at a sand storm monitoring station in the Horqin Sandy Land in China in 2011 and during the Japan-Australia Dust Experiment in Australia in 2006.

The simulation of size-dependent sand transport and dust emission requires particle size distributions (PSDs) of parent soil as input data. However, soil PSDs are difficult to measure and different sample pre-treatment and measurement techniques can give different results which may significantly affect the model estimates of sand/dust fluxes. In large-scale (regional to global) dust models (e.g. GCMs), soils are usually classified according to their hydraulic properties and this classification is not necessarily consistent with soil classifications based on PSD. Over the Australian continent, 29 soil samples have been collected and their PSDs analyzed at high resolution (256 size classes) by Coulter Multisizer.It is found that samples for a given USDA soil texture class (e.g. loam), can have profoundly different PSDs. This suggests that a new soil type classification dedicated for wind-erosion modeling is needed; which reflects the natural particle and aggregate size condition of soils. In this study, we use a wind erosion model to test how uncertainties in PSDs affect the model performance. The range of uncertainties in sand and dust fluxes arising from particle-size uncertainties is quantified.

This document examines the application of the CEMSYS wind erosion and dust transport model as a means of monitoring the impact of wind erosion at national and regional scale. In its current form CEMSYS takes into consideration the atmospheric conditions (wind speed, rainfall etc.) and land surface (soil type, vegetation cover etc.) and estimates wind erosion quantities such as sand flux and dust flux. Other wind erosion related quantities, such as deposition rates, net erosion (sand + dust flux – deposition) threshold friction velocity, and friction velocity are calculated. These quantities can be averaged on an hourly, daily, monthly, or yearly basis. This trial of the CEMSYS model looks at its application to the Australian mainland and area of NSW bounded by 139 to 146E and 31 to 37S. The following topics are covered: •description of CEMSYS •application of CEMSYS on an event, monthly and yearly basis •description of the modelling products that can be used by end user products for reporting proposes •limitations of the CEMSYS model •linkages of the CEMSYS output to other approaches outlined above.