Changes In Surface Wind Speed Research Articles

Seasonal Variations in Anthropogenic and Natural Particles Induced by Rising CO2 Levels

Using an aerosol–climate coupled model, this paper has investigated the changes in distributions of anthropogenic and natural particles due to 4 × CO2-induced global warming, under the low emission scenario of Representative Concentration Pathway 4.5 (RCP4.5). Special attention is paid to the seasonal variations of aerosol size modes. With rising CO2 levels, surface warming, and changes in atmospheric circulations and hydrologic cycles are found during both summer (JJA) and winter (DJF). For anthropogenic particles, changes in fine anthropogenic particulate matter (PM2.5, particles with diameters smaller than 2.5 μm) decrease over high-latitude regions and increase over the tropics in both DJF and JJA. Global mean column concentrations of PM2.5 decrease by approximately 0.19 mg m−2, and concentrations of coarse anthropogenic particles (CPM, particles with diameters larger than 2.5 μm) increase by 0.005 mg m−2 in JJA. Changes in anthropogenic particles in DJF are similar to those in JJA, but the magnitudes of maximum regional changes are much smaller than those in JJA. The coarse anthropogenic particles (CPM, particles with diameters larger than 2.5 μm) increase over northern Africa and the Arabian Peninsula during JJA, whereas changes in anthropogenic CPM during DJF are minimal. During both JJA and DJF, changes in anthropogenic CPM are about two orders of magnitude smaller than those of anthropogenic PM2.5. Enhanced wet deposition by large-scale precipitation under rising CO2-induced surface warming is the critical factor affecting changes in anthropogenic particles. For natural particles, the distribution of change in the natural PM2.5 burden is similar to that of natural CPM, but much larger than natural CPM during each season. Both natural PM2.5 and CPM burdens increase over northern Africa and the Arabian Peninsula during JJA, but decrease over most of the continental regions during DJF. Changes in surface wind speed, divergence/convergence of surface wind, and precipitation are primary reasons for the variation of natural particles.

Surface Wind Speed Changes and Their Potential Impact on Wind Energy Resources Across China During 1961-2021.

Enabling the rational use of energy and the realization of the "dual carbon goals" across China will require systematic analysis of temporal and spatial changes in surface wind speed (SWS), determination of key factors influencing SWS, and quantification of wind energy resources. We investigated changes of SWS and their potential impact on wind energy resources using daily SWS data from meteorological observations and based on wind power density (WPD) across China during 1961-2021. The SWS changes were related to atmospheric circulation, surface friction (urbanization and vegetation changes), aerosol emissions and the replacement of observation instruments. The increase of SWS after 2015 was closely related to changes of atmospheric circulation that were reflected by changes of Asian Meridional Circulation Index, North Atlantic Oscillation, and Arctic Oscillation. Compared with the mean SWS, the extreme SWS exhibited a more obvious downward trend and earlier abrupt change. The annual mean SWS decreased by 16.80% in the last six decades, resulting in a decrease of 47.78% in wind energy potential. Regions with annual WPD more than 100W·m-2 were mainly in western China, northeastern China, northwestern China and some coastal areas. The WPD decreased mainly in northeastern China, northern China, and some coastal areas during the last six decades; it increased mainly in western China. Regions with annual WPD more than 100W·m-2 and robust coefficient of variation less than 0.5 are high-quality wind energy resource areas and were found mainly in western China, northern China, northeast China, and coastal areas.

Examining the influence of mid-tropospheric conditions and surface wind changes on extremely large fires and fire growth days

Background Previous work by the author and others has examined weather associated with growth of exceptionally large fires (‘Fires of Unusual Size’, or FOUS), looking at three of four factors associated with critical fire weather patterns: antecedent drying, high wind and low humidity. However, the authors did not examine atmospheric stability, the fourth factor. Aims This study examined the relationships of mid-tropospheric stability and dryness used in the Haines Index, and changes in surface wind speed or direction, to growth of FOUS. Methods Weather measures were paired with daily growth measures for FOUS, and for merely ‘large’ fires paired with each FOUS. Distributions of weather and growth were compared between the two fire sets graphically and statistically to determine which, if any, weather properties correspond to greater growth on FOUS than on large fires. Key results None of the factors showed a robust difference in fire growth response between FOUS and large fires. Conclusions The examined measures, chosen for their anecdotal or assumed association with increased fire growth, showed no indication of that association. Implications Focus on wind changes and mid-tropospheric properties may be counterproductive or distracting when one is concerned about major growth events on very large fires.

Changes in surface wind speed and its different grades over China during 1961–2020 based on a high‐resolution dataset

AbstractChanges in surface wind speed are important for wind energy planning, especially in China, which has the highest new and total wind power capacities globally. In this article, based on a daily high‐resolution observation dataset for the period of 1961–2020, changes in the surface wind speed and its different grades over China were analysed. The results showed that following significant declines from 1961 to 2002, the annual and seasonal mean surface wind speeds began to increase over China and most of its subregions (all subregions except for East China) after 2002. Opposite trends were found in the probabilities for most different grades of surface wind speed from 1961 to 2002 and from 2002 to 2020. In addition, we compared the results with those from NCEP‐1, JRA‐55, and ERA5, which showed that all of the reanalysis data could reasonably reproduce the observed spatial distributions of the surface wind speed and its different grades, although with bias in values and smaller interannual variabilities. The wind reversal over China was closely related to changes in the trends of the sea level pressure gradient. Moreover, the variation in the Pacific Decadal Oscillation (PDO) has a significantly negative correlation coefficient with the surface wind speed over East, Central, and South China.

The imprint of the ENSO activities on the South China Sea wave climate

Global warming is changing the global wave climate, making waves stronger. In this study, we find that the wave climate in the South China Sea (SCS) undergoes an intensifying trend under global warming background, by examining the ERA-5 wave reanalysis data over 1979–2018. Results show a significant increase in most of the SCS, of 0.2% per year in significant wave height (SWH) and 0.15% per year in wave period (WP), but there is no significant change in surface wind speed (WS), which may correspond to the weakening of the Asian monsoon. The increase of the swell is the main characteristic of wave climate change in the SCS. We further examined the possible factors to cause the increasing of SWH, and found that the frequency of gale events occurring in the SCS and its adjacent regions increased over study period. The more frequent gale events can explain the significant increasing tendency of the SWH in the SCS by causing the occurrence of swell. The increasing appearance of gale events is closely related to the intensification of El Nino/Southern Oscillation (ENSO). ENSO activities also can regulate the interannual variability of wave climate in the SCS through the surface wind. Therefore, ENSO activities play an important role in the change of wave climate in the SCS.

Intra-seasonal differences in the atmospheric systems contributing to interannual variations of autumn haze pollution in the North China Plain

Our understanding of the factors influencing the interannual variation of autumn haze pollution in the North China Plain (NCP) remains quite limited. Here, we investigate interannual variations of atmospheric haze pollution and associated atmospheric anomalies in the NCP during autumn (September, October, and November). Pronounced anticyclonic anomalies tend to be observed around northeastern Asia when more severe haze pollution occurs over the NCP during this season. However, the processes underlying the impact of the atmospheric anomalies on the NCP haze show considerable intra-seasonal differences. In September, anticyclonic anomalies impact the NCP haze via modulating the surface relative humidity (SRH) and boundary layer height (BLH), while changes in surface wind speed (SWS) are not found to be related to the NCP haze. In contrast, the interannual variation of the NCP haze has a close relationship with the changes of SWS, SRH, and BLH in both October and November. The factors responsible for formation of the anticyclonic anomalies around northeastern Asia are found to differ greatly over the 3 months. In September, the formation of anticyclonic anomalies is related to the East Atlantic (EA) pattern, which triggers an eastward propagating atmospheric wave train extending from Europe to northeastern Asia. In October, the Scandinavia teleconnection is crucial for generating anticyclonic anomalies. While in November, the formation of the anticyclonic anomalies is largely due to the joint effect of the Scandinavia and East Atlantic/Western Russian teleconnections, as well as the non-negligible influence caused by sea surface temperature anomalies in the tropical central-eastern Pacific.

Seasonal Variations of Aerosol Optical Depth over East China and India in Relationship to the Asian Monsoon Circulation

Seasonal variation features of aerosol optical depth (AOD) over East China and India in association with the Asian monsoon system are investigated, based on the latest AOD data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, the NCEP Final (FNL) Operational Global Analysis data, the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) data, and the NCEP/NCAR reanalysis data from March 2000 to February 2017. The results indicate that AOD in East China is significantly larger than that in India, especially in spring. The seasonal mean AOD in East China is high in both spring and summer but low in fall and winter. However, the AOD averaged over India is highest in summer and lower in spring, fall, and winter. Analysis reveals that AOD is more closely related to changes in surface wind speed in East China, while no obvious relation is found between precipitation and the AOD distribution on the seasonal timescale. As aerosols are mainly distributed in the atmospheric boundary layer (ABL), the stability of the ABL represented by Richardson number (Ri) is closely correlated with spatial distribution of AOD. The upper and lower tropospheric circulation patterns significantly differ between East China and India, resulting in different effects on the AOD. The effect of advection associated with lower tropospheric circulation on the AOD and the influence of convergence and divergence on the AOD distribution play different roles in maintaining the AOD in East China and India. These results improve our understanding of the mechanism responsible for and differences among the aerosol changes in East China and India.

Recent recovery of surface wind speed in northwest China

Previous studies have reported that much of the surface wind speed (SWS) over the mid‐latitudes of the northern hemisphere has declined. However, very few studies have investigated the relatively recent phenomenon of wind recovery. Based on 68 wind data series, this paper examines changes in wind speed in northwest China between 1969 and 2015. In 1992, following a decade of sharply decreasing at a rate of 0.036 m s−1 a−1 (p < .05), the SWS began to significant increase at a rate of 0.004 m s−1 a−1. The specific reasons for this increase are as follows: (a) The decrease in SWS during the pre‐1992 slowdown period is the result of declining wind speeds in spring and summer, whereas increases in wind speed during the post‐1992 recovery period are caused by increased wind in winter. (b) The number of days featuring strongly varying wind speeds has changed. Specifically, the number of days above 2 m s−1 all show a significant decreasing trend from 1969 to 1992, whereas the number of days of 1–3 m s−1 shows a significant upward trend from 1993 to 2015. (c) Stations located between 1,000 and 1,500 m.a.s.l. (meter above sea level) are more sensitive to climate change than those at other altitudes, which shows the biggest decline (increase) trend during wind speed slowdown (recovery) period. These stations could potentially act as climatic indicators to predict future wind speed changes. SWS in northwest China have been affected by changes both in large‐scale atmospheric circulation and in regional warming. Surface pressure gradient variations between high‐ and low‐latitude regions may be important contributors to wind speed changes under asymmetric warming. However, urbanization is only moderately responsible for trend changes in SWS.

Elevation-dependent sensible heat flux trend over the Tibetan Plateau and its possible causes

The present study documents the elevation-dependent sensible heat (SH) flux trend over the Tibetan Plateau (TP). The SH displays a decreasing trend over the TP above 2000 m with the magnitude of trend increasing with the elevation, but an increasing trend at low elevation stations. The above feature is more obvious in spring and summer. Surface wind speed is consistently the major contributor to the variation in SH trend from lower to higher altitude areas. Meanwhile, the role of the difference of ground-air temperature (Ts–Ta) in SH trend is enhanced above 2500 m regions. The SH variation associated with the change in Ts–Ta may be influenced primarily by the diminution in sunshine duration and snow depth at higher-altitude regions, and the latter is particularly important. The portion of the SH variation related to the change in surface wind speed is mainly attributed to the dynamic process related to the Pacific Decadal Oscillation (PDO). The warming in the northwestern Pacific in relation to the switch of the PDO from a warm phase to a cold phase in the recent decades causes divergence anomalies in the upper troposphere, which induces propagation of a wave pattern extending eastward until reaching the southwest TP. That leads to an enhancement in divergence of the upper troposphere and subsequently a boost in surface convergence and rising motion over southwest TP. Consequently, due to the easterly anomaly to the east of the convergence, surface wind speed is reduced over the central and eastern TP, especially in the higher altitude areas.

Will surface winds weaken in response to global warming?

The surface Walker and tropical tropospheric circulations have been inferred to slow down from historical observations and model projections, yet analysis of large-scale surface wind predictions is lacking. Satellite measurements of surface wind speed indicate strengthening trends averaged over the global and tropical oceans that are supported by precipitation and evaporation changes. Here we use corrected anemometer-based observations to show that the surface wind speed has not decreased in the averaged tropical oceans, despite its reduction in the region of the Walker circulation. Historical simulations and future projections for climate change also suggest a near-zero wind speed trend averaged in space, regardless of the Walker cell change. In the tropics, the sea surface temperature pattern effect acts against the large-scale circulation slow-down. For higher latitudes, the surface winds shift poleward along with the eddy-driven mid-latitude westerlies, resulting in a very small contribution to the global change in surface wind speed. Despite its importance for surface wind speed change, the influence of the SST pattern change on global-mean rainfall is insignificant since it cannot substantially alter the global energy balance. As a result, the precipitation response to global warming remains ‘muted’ relative to atmospheric moisture increase. Our results therefore show consistency between projections and observations of surface winds and precipitation.

Historical Changes in the Beaufort–Chukchi–Bering Seas Surface Winds and Waves, 1971–2013

Abstract This study characterizes historical changes in surface wind speed and ocean surface waves in the Beaufort–Chukchi–Bering Seas using Environment Canada’s Beaufort Wind and Wave Reanalysis for the period 1970–2013. The results show that both the significant wave height () and mean wave period () have increased significantly over the Bering Sea in July and August and over the Canadian Beaufort Sea westward to the northern Bering Sea in September, and that the 1992–2013 trends in September mean agree well with satellite-based trend estimates for 1993–2010. Most outstandingly, the regional mean has increased at a rate of 3%–4% yr−1 of the corresponding 1970–99 climatology; it has more than tripled since 1970. Also, the regional mean has increased at a rate of 0.3% to 0.8% yr−1. The trends of lengthening wave period and increasing wave height imply a trend of increasing wave energy flux, providing a mechanism to break up sea ice and accelerate ice retreat. The results also show that changes in the local wind speeds alone cannot explain the significant changes in waves. The wind speeds show significant increases over the Bering Sea to the north of Alaska in July and over the central part of the domain in August and September, with decreases in the region off the Canadian coasts in August. In the region west of the Canadian coast, the climatological mean wind direction has rotated clockwise in July and August, with the climatological anticyclonic center being displaced northeastward in August.

Can Current AGCMs Reproduce Historical Changes in the Atmospheric Diabatic Heating over the Tibetan Plateau

AbstractRecent studies have demonstrated a persistent decreasing trend in the spring sensible heat (SH) source over the Tibetan Plateau (TP) during the past three decades. By comparing simulations from nine state-of-the-art atmospheric general circulation models (AGCMs) driven by historical forcing fields with both observational data and five reanalysis datasets, the authors found that the AGCMs are unable to reproduce the change in the SH flux over the TP. This deficiency arises because the observed decreasing trend in SH flux depends primarily on the change in surface wind speed according to the bulk formula, whereas in the models it is also influenced largely by changes in the land-air temperature difference related to the systematic cold bias. In addition, an obvious discrepancy exists in other aspects of the diabatic heating simulated by the models, suggesting that a significant improvement is required in the physical schemes associated with land surface processes and diabatic heating over the compli...

Estimating the impact of the changes in land use and cover on the surface wind speed over the East China Plain during the period 1980–2011

Long-term changes in surface wind speed (SWS) are influenced by both large-scale circulation and relative resistance. The effects of large-scale circulation are embodied by the pressure-gradient force (PGF), which is mostly a natural factor, whereas the resistance is due to the drag between the air and the surface as well as in the different boundary layers, which is mainly caused by the anthropogenic land use and cover change (LUCC). We performed experiments using a simple dynamical method in which a balance among the PGF, Coriolis force, and drag is reached to separate the effects of the PGF and LUCC on the SWS, and then, to quantitatively estimate the influence of the LUCC on the SWS over the East China Plain (ECP) during the period 1980–2011. The results show a distinct decrease in the SWS in the station observation data with a rate of −0.13 m s−1 (10 year)−1, but there is no statistically significant long-term trend in the reanalysis data. At the same time, the drag coefficient induced by the LUCC shows an increasing trend, which is consistent with the 30 % increase in the rate of urbanization during the study period. In addition, the PGF fluctuates with distinct seasonal and interannual changes, and it has an insignificant long-term increasing trend during the period 1980–2011. At the same time, the spatial distribution of the linear trend coefficient of the normalized PGF is inconsistent with that of the SWS, but the linear trend coefficient of the normalized drag coefficient shows a similar spatial distribution as the SWS. Therefore, the increase in the drag coefficient induced by the LUCC should account for the long-term decrease in the SWS. The difference between the model wind speed, in which the drag coefficient is constrained to its value in the year 1980, and the observed wind speed at each station (SWSD) can reflect the influence of the LUCC on the SWS. Furthermore, the long-term changes in East Asian monsoons may not completely account for the observed wind speed decrease near the surface in the ECP region, but it is an important factor in the SWS.

Effect of Offshore Wind farm Design on the Vertical Motion of the Ocean

In this study the vertical motion of the ocean is studied numerically. A wake model that includes details of the wind farm design, such as the location of the turbines, diameter of rotors and hub height, is used to calculate the change in surface wind speed resulting from potential wind farms in the Havsul area. Using the calculated wind velocities to force a three dimensional ocean model (Regional Ocean Modeling System), the ocean response to two different wind farm designs is estimated. It is found that the wind farm design has a significant effect on the upwelling and downwelling near the wind farm, as the difference in maximum upwelling velocity after 1 day of simulation exceeds 30 m/day. The pronounced changes in vertical velocities are attributed to changes in the horizontal flow over varying topography due to wind stress modifications by the wind farms.

Change in surface latent heat flux and its association with tropical cyclone genesis in the western North Pacific

The present study investigates the influence of June through November (JJASON) thermal state of the western North Pacific warm pool on surface latent heat flux and their association with tropical cyclone (TC) genesis by using 25 level water temperature data with European Centre for Medium-Range Weather Forecasts (ECWMF) operational ocean analysis (ORA-S3), the monthly mean fluxes from Objectively Analyzed Air-sea Fluxes (OAFlux) Project, and the tropical cyclone data from the International Best Track Archive for Climate Stewardship (IBTrACS). It is found that positive (negative) latent heat flux anomalies over the western North Pacific are associated with warm (cold) state of the warm pool. The analysis suggests that the change in sea-air humidity difference has a direct contribution to surface latent heat flux anomalies over the western Pacific in warm state years of the warm pool. However, the change in surface wind speed is the main cause of surface latent heat flux anomalies over central tropical Pacific. In cold state years, change in the sea-air humidity difference has a direct contribution to surface latent heat flux anomalies over the western Pacific and central and eastern tropical Pacific, and the change in surface wind speed appears not to be a cause of identified surface latent heat flux anomalies. Moreover, the results show that the sea-air humidity difference contributes to tropical cyclone genesis in warm state years, but in cold state years, tropical cyclone genesis occurs mainly in regions of sea-air humidity difference decrease and surface wind speed increase.

Changes in Surface Wind Speed over North America from CMIP5 Model Projections and Implications for Wind Energy

The centennial trends in the surface wind speed over North America are deduced from global climate model simulations in the Climate Model Intercomparison Project—Phase 5 (CMIP5) archive. Using the 21st century simulations under the RCP 8.5 scenario of greenhouse gas emissions, 5–10 percent increases per century in the 10 m wind speed are found over Central and East-Central United States, the Californian Coast, and the South and East Coasts of the USA in winter. In summer, climate models projected decreases in the wind speed ranging from 5 to 10 percent per century over the same coastal regions. These projected changes in the surface wind speed are moderate and imply that the current estimate of wind power potential for North America based on present-day climatology will not be significantly changed by the greenhouse gas forcing in the coming decades.

Can Current AGCMs Reproduce Historical Changes in the Atmospheric Diabatic Heating over the Tibetan Plateau?

Recent studies have demonstrated a persistent decreasing trend in the spring sensible heat(SH) source over the Tibetan Plateau(TP) during the past three decades. By comparing simulations from nine state-of-the-art atmospheric general circulation models(AGCMs) driven by historical forcing fields with both observational data and five reanalysis datasets, the authors found that the AGCMs are unable to reproduce the change in the SH flux over the TP. This deficiency arises because the observed decreasing trend in SH flux depends primarily on the change in surface wind speed according to the bulk formula, whereas in the models it is also influenced largely by changes in the land-air temperature difference related to the systematic cold bias. In addition, an obvious discrepancy exists in other aspects of the diabatic heating simulated by the models, suggesting that a significant improvement is required in the physical schemes associated with land surface processes and diabatic heating over the complicated topography.

Future change of the global monsoon revealed from 19 CMIP5 models

The variability of global monsoon area (GMA), global monsoon precipitation (GMP), and global monsoon intensity (GMI) in the present climate (1979–2003) and the future warmer climate (2075–2099) under Representative Concentration Pathways 4.5 (RCP4.5) scenario was examined based on 19 Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. In the present‐day simulations, the ensemble mean precipitation reproduces the observed GMA, GMP, and GMI, although the spread of individual models is large. In the RCP4.5 simulations, most (17 of 19) of the CMIP5 models project enhanced global monsoon activity, with the increases of GMA, GMP, and GMI by 1.9%, 3.2%, and 1.3%, respectively, per 1 K of surface warming. The diagnosis of a column‐integrated moisture budget indicates that the increase in GMP is primarily attributed to the increases of moisture convergence and surface evaporation, whereas horizontal moisture advection has little effect. A further separation of dynamic and thermodynamic factors shows that increase of the moisture convergence comes mainly from the increase of water vapor, but is partly offset by the convergence effect. The increase of the surface evaporation is caused by the increase of sea‐air specific humidity difference, while the change in surface wind speed plays a minor role. The GMP experiences a great year‐to‐year variation, and it is significantly negatively correlated with the Niño3.4 index averaged over a typical monsoon year (defined from May to the following April) in the pre‐industrial control and present‐day simulations, similar to observations. Under the RCP4.5 warming, such rainfall variability is intensified, and the relationship between monsoon and El Niño strengthens. A large proportion of intensification in the year‐to‐year monsoon rainfall variability arises from the land monsoon region.

A high time resolution study of boundary layer ozone chemistry and dynamics over the Arctic Ocean near Alert, Nunavut

During the field campaign “Out On The Ice” (OOTI) in the spring of 2004 at Alert, Nunavut (N82°30′, W62°19′) an event occurred where surface ozone (O3) and reactive bromine species in the boundary layer showed dramatic changes on a timescale of minutes and a spatial scale of a few kilometers. In apparent direct response to changes in surface wind speed and direction, surface O3 mole fractions of >30 nmol.mol−1 replaced stable, O3 depleted boundary layer conditions for about 5 hours. High time resolved (seconds to minutes) chemical and meteorological observations on the ice and on land, as well as synoptic weather maps and routine radiosonde data are used to constrain the unfolding of the event. It is hypothesized that the bromine oxide (BrO) distribution in the troposphere over the frozen ocean features a maximum in a narrow transition layer that separates the boundary layer from free tropospheric air above.

The structure and genesis of Weichselian to early hologene aeolian sand sheets in western Europe

Weischselian to Early Holocene aeolian sands are widespread in the lowlands of western Europe. To a large extent these deposits occur in the form of sheet-like coversands with slipfaced dunes being much rarer. Whereas the latter type of landform corresponds to a single facies with dune-foreset cross-bedding (= aeolian facies 1), two structurally different facies are distinguishable in the sand sheets. This paper concentrates on the two sand-sheet facies which are referred to as aeolian facies 2 and aeolian facies 3. Data on these two types are based on (1) a survey of existing literature, and (2) a detailed analysis of lacquer peels and larger-scale exposures in England, The Netherlands and the Federal Republic of Germany. Aeolian facies 2 is defined by the spatial position of its beds, which may be either horizontal, inclined or oppositely dipping in the case of structures formed by fluctuating winds. Horizontal bedding is by far the most common type. Inclined bedding is related either to small, isolated dome dunes or to scoop-shaped deflation surfaces. The structures resulting from fluctuating winds are rare and do not represent an inherently large measure of directional variability of the wind regime. The internal structure of the beds is dominated by aeolian planebed lamination with or without concordantly infilled wind-scours. Degradation of this stratification type because of interference by coarse particles is discussed. Aeolian facies 3 is uniquely typified by the alternation of coarser- and finer-grained horizontal thin beds that are either wavy or even in shape. Depositional models of facies 3 are given at both the local and regional scales. In both cases the coarser-grained layers result from tractional deposition of saltating and creeping grains whilst the finer-grained strata were laid down by settling from suspension. Periodic changes in surface wind speed, the presence of a damp depositional surface and the availability of both sand and silt in the source area are necessary conditions for the working of the models. The large-scale model is associated with specific environmental conditions of the Weichselian Upper Pleniglacial. The local-scale model accounts for the fact that facies 3 is also found in units of Weichselian Late Glacial or Early Holocene age. The regional-scale model involves stepwise tractional transport over long distances so that grains of distant provenance were mixed with material from sources nearer to the receiving site. This process was an important control on the mineralogical composition of the resultant deposits. The prevalence of aeolian planebed lamination in both facies 2 and the coarser-grained layers of facies 3 is attributed to the interaction of three factors, viz. the rarity of topographic barriers, the sparseness of vegetation cover and a high ratio between wind energy and sand availability during the processes of transport and deposition. In the lowlands of Europe, sand sheets are gradually replaced in an easterly direction by coeval wind dunes. The possible causes of this phenomenon are considered.