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Accurate assessment of extreme wind gusts is important for many infrastructure requirements, particularly in building design standards and for insurance purposes. In a previous paper (Aylott et al. 2020) Northern Ireland’s record wind gust – 108 kn (56 m s-1) recorded at Kilkeel on 12 January 1974 — was critically re-examined, and found to be almost certainly incorrect due to instrumental error or a power surge. A recommendation was made that other longstanding United Kingdom record wind gusts should also be independently re-examined to assess their veracity. In this paper the arguments for and against the authenticity of the current record low-level wind gust for Scotland, and the UK national record, namely 123 kn (63 m s 1) recorded at the Kinnaird Head Lighthouse at Fraserburgh on 13 February 1989, are reviewed. Two ‘gusts’ > 100 kn were probably record artefacts owing to brief power supply interruptions to the recording anemograph, and accordingly neither should remain included in the list of national wind speed records.

Accurate assessment of record extreme wind gusts is important for building design standards and for industries such as insurance and forestry. Re‐inspection of archived anemograph records, together with indirect supporting evidence, shows that the current record wind gust for Northern Ireland – a gust of 108 kn (56 m/s) recorded at Kilkeel on 12 January 1974 – is almost certainly incorrect. We recommend that other longstanding UK record wind gusts should also be independently reassessed for veracity by an independent Climate Extremes Committee, following WMO and US best practice examples.

Downslope windstorms are responsible for wildfires, wind gusts, and turbulence in the lee side of the Taebaek Mountains, called Yeongdong region (YD) in Korea. We classified the synoptic conditions...

Seed dispersal is one of the most important steps in the plant life cycle. However, there is, generally, a lack of fieldworks focused on wind dispersal and especially on semachorous dispersal (seeds spread when the fruits are shaken by wind and other vectors, such as animals), including boleochorous dispersal. Therefore, we aimed to determine how different types of wind and animals affected seed dispersal under natural conditions in the widespread species Scrophularia canina. We evaluated the effects of wind gusts (simulating them using a leaf blower) and wild animals (using differently sized dogs) on seed dispersal in a population located in south‐western Europe. We found that S. canina is a semachorous species, and its spatial seed dispersal was affected by wind gust speed and direction, plant structure and vector type. The results also revealed the presence of xerochasy, individual anisotropy with strong winds, and primary short‐distance dispersal associated with successional processes independent of the vector. Additionally, there was a masking effect of plant structure on the seed shadow outline. It is essential to conduct fieldworks to reveal what actually happens in nature, taking into account the characteristics determining seed dispersal. In addition, in these works it is important to find out what factors affect seed distributions of anemochorous and semachorous species.

Over the past 15 years, adjoint-based, ensemble-based and hybrid methods have been developed for estimating observation impact based on the forecast sensitivity to observation impact (FSOI). These methods are now commonly used in global modelling systems. However, little attention has been given to assessing observation impact in regional convection-permitting modelling systems. This study presents the first evaluation of ensemble-based estimates of observation impact over an extended period of six weeks in such a convection-permitting modelling system, namely the regional ensemble system of Deutscher Wetterdienst. Another aspect that has received little attention is the choice of the forecast-error verification metric. Nearly all previous studies used the difference between the forecast and a subsequent analysis of the same modelling system expressed in terms of energy (total energy norm). While such a self-verification generally needs to be treated with caution, it appears unsuitable for convection-permitting regional forecasts. Firstly, total energy does not really reflect parameters that forecast users are interested in, and important forecast quantities such as surface wind gusts and precipitation are not even part of the analysis. Secondly, systematic analysis and forecast errors are non-negligible in the presence of convection, especially for important variables that are related to convection. To overcome this issue, we introduce the use of independent radar observations for the verification of observation impact and compare results for a variety of different observation-based metrics for a six-week high-impact weather period in summer 2016. This revealed a particular sensitivity of the estimated impact to model as well as observation biases and sensitivity studies indicated that even small biases can have an influence on the estimated impact. Additionally, we demonstrate that FSOI can be used to identify biases through comparison of results for different metrics.

On 18 May 2015 there were reports of localized wind damage just north of Swansea in south Wales. Observations indicated the development of a mesoscale cyclonic circulation at the tip of a frontal wave which first formed just west of south Wales. This mesoscale circulation subsequently ran eastwards across south Wales around the time of the reported damage, accompanied by gale force gusts on its southern flank. The resulting system then evolved into a pronounced shallow cold frontal zone that propagated eastwards into southern England over the next few hours, bringing further gale force gusts. Observational data, including Doppler radar and 1 min surface observations, are combined to investigate the causes of this mesoscale circulation and synthesize the results into a conceptual model. The mesoscale development was found to share some of the characteristics of larger scale cyclonic systems that sometimes produce more widespread and sometimes severe wind-related impacts. Recognition of the precursor synoptic environment may enable identification of similar features which, combined with Doppler radar data, may assist nowcasting of small areas of damaging winds.

This contribution employs instrumental records to analyse the temporal and spatial variability of monthly, seasonal and annual maximum wind gusts (MWGs) in the Czech Republic. The development of an observation network capable of measuring wind gusts, the possible technical weaknesses of wind measurements and problems with establishing homogeneity in wind-gust data are described. For the 1961–2014 period, quality-checked data from 19 synoptic stations of the Czech Hydrometeorological Institute throughout the territory of the Czech Republic are examined, divided into three altitudinal groups. In terms of the spatial variability of MWGs, correlation coefficients between stations decreasemore strongly in relation to station distance rather than altitude. Spatial correlations are better expressed (by higher correlation coefficients) in the winter half-year than in the summer half-year. Linear trends in monthly, seasonal and annual MWGs for the 19 synoptic stations, for their three altitudinal groups, and for the entire Czech Republic show statistically significant decreases (deepest in November and autumn), with the exception of spring (for stations above 300 m) and summer. The 10 highest MWG events of all are selected. The spatial distribution of wind gusts for two prominent windstorms, Kyrill (18–19 January 2007) and Emma (1–2 March 2008), are presented. Changes in MWGs series are compared with fluctuations in atmospheric circulation responding to the North Atlantic Oscillation. Decreasing MWG trends are discussed with respect to diminishing storminess and surface wind speeds (wind stilling) recorded during recent decades in Europe, as well as over other continents.

An extreme Koshava episode (EKE) from 30 January to 4 February 2014 has been studied. Koshava is a local windstorm in Southeast Europe. EKE was characterized by wind gusts above 45 m s−1 and deep snowdrifts. Strong Eurasian anticyclone in combination with large temperature gradient between the anticyclone region and the Mediterranean caused the EKE. The anticyclone had the probability of occurrence of 0.1%. Koshava layer was either statically stable or adiabatic. The event was numerically modelled using two mesoscale models: WRF-NMM and NMMB. Wind directions were forecasted more accurately than the mean speed and gusts.

One composite index of the Meteo-France AROME high-resolution forecast model results from the quantitative comparison of forecast rainfall and wind gusts with observations from surface stations. It is based on the regional Brier probability score in order to take into account some tolerance about the positions of storm structures. This approach is necessary to validate the added benefit of the AROME model compared with lower-resolution models. This index is used to monitor the continuous model improvements and the history of the last 4 years allows the impact of the successive upgrades of this operational model to be followed. The use of the normalization of models scores by persistence forecast scores enables most of the inter-annual variability to be removed.

A wind gust can cause severe dynamic conditions that affect the operational behavior of the whole doubly fed induction generator (DFIG) wind energy conversion system and, as a result, the quality of power exchanged with the grid. In addition, it can cause great disturbances to critical system's variables with possible damages to the system's construction—to mechanical or electrical part. The knowledge of DFIG reaction in such conditions is useful for both protection issues and the risk assessment concerning system's tolerance, maintenance costs and revenue losses, because of the disconnection from the grid. In this paper, a quantitative and qualitative behavior analysis of a 2 MW DFIG wind energy conversion system under a wind gust and converter faults, which has been carried out via simulation, is presented. The pitch controller parameters impact to its behavior, when a gust appears, has been investigated. Copyright © 2015 John Wiley & Sons, Ltd.

The increasing size of wind turbines, their height and the area swept by their blades have revised the need for understanding the vertical structure of wind gusts. Information is needed for the whole profile. In this study, we analyzed turbulence measurements from a 100 m high meteorological mast at the Danish National Test Station for Large Wind Turbines at Hovsore in Denmark. The site represents flat, homogeneous grassland with an average gust factor of 1.4 at 10 m and 1.2 at 100 m level. In a typical surface-layer gust parametrization, the gust factor is composed of two components, the peak factor and the turbulence intensity, of which the turbulence intensity was found to dominate over the peak factor in determining the effects of stability and height above the surface on the gust factor. The peak factor only explained 15% or less of the vertical decrease of the gust factor, but determined the effect of gust duration on the gust factor. The statistical method to estimate the peak factor did not reproduce the observed vertical decrease in near-neutral and stable conditions and near-constant situation in unstable conditions. Despite this inconsistency, the theoretical method provides estimates for the peak factor when comparing gust durations of 1 and 3 s with averaging period lengths of 10 min and 1 h. A new technique to study the timing of maxima at different levels relative to the maximum gust at some level was developed. Results showed that a 10 m level maximum gust was typically preceded by maxima at higher levels and vice versa: a 100 m gust was usually followed by a maximum at lower levels.

Bauwerke konnen infolge Wind- und Boenbeanspruchungen enormen Belastungen ausgesetzt werden. Schadensfalle aus der Vergangenheit zeigten, dass selbst schwere Fassadenaufbauten beschadigt oder zum Herabsturzen gebracht werden konnen. Um von planerischer Seite die notige Sicherheit zu schaffen, ist es daher sinnvoll, Fassaden- und Ausenwandaufbauten vor ihrem Praxiseinsatz umfangreich auf ihre Windsogwiderstandsfahigkeit zu prufen. Bisher dominieren hierzu Prufverfahren, die Windlasten eher statisch simulieren konnen. Zur Prufung von Konstruktionen auf realistische Boenbelastungen wurde am Institut fur Bauphysik der Leibniz Universitat Hannover ein dynamischer Windsogversuchsstand entwickelt und im Praxisverhalten getestet. Mit den zu erreichenden Unterdrucken von maximal 20 kPa ist der Versuchstand in der Lage, Windlasten an Prufkorpern auch mit dynamischem Verhalten zu simulieren. Der Versuchsstand zeichnet sich hierbei durch eine hohe Wiederholgenauigkeit aus, die Messwerte werden luckenlos und mit einer hohen Abtastrate dokumentiert. Dynamic wind uplift test station at the “Institut fur Bauphysik”, Leibniz University Hanover. From everyday experience it is known that structures induced by suction and gust loads may be exposed to enormous stress. Damages occurred in the past prove that heavy facade systems can be partly destroyed or even be forced to crashing down. To create the necessary safety it is appropriate to test the wind suction resistance of facade systems and external wall constructions before using them in practice. However, current test methods dominate which simulate wind loads rather static than dynamic. Therefore, the “Institut fur Bauphysik” of the Leibniz University Hanover has developed a dynamical wind suction test station which is able to examine constructions regarding their dynamical wind suction resistance. Thereby testing the dynamic wind suction resistance means the abrupt and rapid applying of vacuum pressure on the tested construction, holding the vacuum pressure for a specific time and relieving the pressure on the specimen.

Abscission of seeds in some plant species occurs as a result of strong wind gusts that exert sufficient drag forces to liberate the seed from its parent. This may be an adaptive feature, as release into stronger wind gusts has been shown to lead to greater dispersal distances, which is likely to have evolutionary advantages. We test the hypotheses that (i) seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations and (ii) that the preferential abscission of seeds into upward wind gusts will result in the dispersal of seeds over greater distances. As a case study, we studied the abscission dynamics of Conyza bonariensis (L.) Cronquist (fleabane), which is an important weed with global distribution. Using abscission data obtained through a series of seed release experiments, we confirm that abscission of seeds in C. bonariensis is most likely to occur during strong and upward wind gusts. We demonstrate that, for a given wind speed, seeds released into upward wind gusts will, on average, travel further than those seeds released into wind gusts with horizontal or downward orientations. We also show that preferential release into upward wind gusts has some influence on the distance travelled, but the strength of this influence is dependent on the correlation between wind orientation and wind speed. For this particular study, the sensitivity of release to the horizontal wind speed seems to have a larger effect on the distance travelled than sensitivity to wind orientation.

This paper describes an ensemble-based first guess support tool for severe weather, which has evolved over time to support changing requirements from the UK National Severe Weather Warning Service (NSWWS). This warning tool post-processes data from the regional component of the Met Office Global and Regional Ensemble Prediction System (MOGREPS), and is known as MOGREPS-W (‘W’ standing for ‘warnings’). The original system produced area-based probabilistic first guess warnings for severe and extreme weather, providing forecasters with an objective basis for assessing risk and making probability statements. The NSWWS underwent significant changes in spring 2011, removing area boundaries for warnings and focusing more on a risk-based approach. Warnings now include details of both likelihood and impact, whereby the higher the likelihood and impact, the greater the risk of disruption. This paper describes these changes to the NSWWS along with the corresponding changes to MOGREPS-W, using case studies from both the original and new systems. Calibration of the original MOGREPS-W system improves forecast accuracy of severe wind gust and rainfall warnings by reducing under-forecasting. In addition, verification of forecasts from different groups of areas of different sizes shows that larger areas have better forecast accuracy than smaller areas. © 2013 British Crown copyright, the Met Office. Published by John Wiley & Sons Ltd.

Sting jets are transient coherent mesoscale strong wind features that can cause damaging surface wind gusts in extratropical cyclones. Currently, we have only limited knowledge of their climatological characteristics. Numerical weather prediction models require enough resolution to represent slantwise motions with horizontal scales of tens of kilometres and vertical scales of just a few hundred metres to represent sting jets. Hence, the climatological characteristics of sting jets and the associated extratropical cyclones cannot be determined by searching for sting jets in low-resolution datasets such as reanalyses. A diagnostic is presented and evaluated for the detection in low-resolution datasets of atmospheric regions from which sting jets may originate. Previous studies have shown that conditional symmetric instability (CSI) is present in all storms studied with sting jets, while other rapidly developing storms of a similar character but no CSI do not develop sting jets. Therefore, it is assumed that the release of CSI is needed for sting jets to develop. While this instability will not be released in a physically realistic way in low-resolution models (and hence sting jets are unlikely to occur), it is hypothesized that the signature of this instability (combined with other criteria that restrict analysis to moist mid-tropospheric regions in the neighbourhood of a secondary cold front) can be used to identify cyclones in which sting jets occurred in reality. The diagnostic is evaluated, and appropriate parameter thresholds defined, by applying it to three case studies simulated using two resolutions (with CSI-release resolved in only the higher-resolution simulation).

Especially in summer time, Romania is affected by deep convections associated with severe weather phenomena (hail, wind gusts, flash floods, frequent thunder). The interannual variability of the Cb (cumulonimbus) cloud frequency recorded at 20 weather stations from the southern part of Romania in the 1961–2007 interval was investigated in connection with the atmospheric circulation variability. Using the Canonical Correlation Analysis (CCA) three types of atmospheric circulations have been identified that control about 60% of the interannual variability of the Cb cloud frequency. The three types of identified circulations facilitate warm and moist air advection from the Mediterranean, and cold air advection from northern Europe towards the south of Romania, creating conditions for Cb clouds to occur. Copyright © 2011 Royal Meteorological Society

The synoptic evolution and impacts of storm ‘Klaus’ that affected Europe on 23–24 January 2009 are assessed. Klaus was the costliest weather hazard event worldwide during 2009. Peak wind gusts reached 55ms-1 (107kn), accompanied by heavy rain, snow and flooding across Northern Iberia and southern France. Klaus underwent explosive development between the Azores and the Iberian Peninsula at an unusually low latitude. This development was supported by an extended and intense polar jet across the North Atlantic Basin, strong upper-air divergence associated with a second jet streak and an extraordinary export of tropical moisture into the genesis region. Copyright © 2011 Royal Meteorological Society

A reliable forecast of the wind vector at a given site is an important problem with a broad scope of application. Many uses are in the field of wind power in which prediction of strong winds is important; other uses are in the field of civil engineering, where wind gusts are important to structural integrity. For predicting air pollution events or the hazard zone in case of toxic gas accidents the low wind scenarios are of the highest importance, especially under stable conditions. These low wind scenarios are the situations which meso-scale numerical models encounter difficulties or are often neglected when dealing with wind power tasks. Additional drawbacks of meso-scale numerical models in this context are their lack of site-specific detail and the fact that they are very demanding numerically. The ‘similar days’ method presented here is a method for the prediction of winds at a given location which works well also for low and variable wind conditions. The method is very efficient numerically: typically, runtime is less than a minute on a single PC. This method is based on using the last few hours' measurements at the given site and comparing it to an historical database. A set of criteria is defined to determine the time series similarity. Those similar days are used to construct the forecast. The similar days method was applied to a total of 5 years of measurements collected in two different locations. Very good agreement was achieved between prediction and measurements. Copyright © 2009 Royal Meteorological Society

The behavioural finance literature posits a link between the weather and equity markets via investor moods. This paper examines the impact of weather on the Australian stock market over the period 1958–2005. A regression-based approach is employed where daily market returns on the Australian Securities Exchange’s All Ordinaries Price Index are regressed against eight daily weather observations (precipitation, evaporation, relative humidity, maximum and minimum temperatures, hours of bright sunshine, and the speed and direction of the maximum wind gust) at Sydney’s Observatory Hill and Airport meteorological stations. Consistent with studies elsewhere including the Australian market, the results indicate that the weather has absolutely no influence on market returns. Some directions for future research that may help address some of the deficiencies found in this intriguing body of work are provided.

Weather warnings are of great importance for the protection of life and property. The Storm Warning Observatory at Lake Balaton was founded with the aim of providing holidaymakers with warnings 1-2 hours ahead of expected wind gusts exceeding 12 or 17 ms−1. As a result of successive investigations an objective decision procedure has been developed which combines methods based on conventional data with the use of radar data. This procedure can be executed interactively on a computer. The permanence of wind hazards was investigated during frontal and convective weather situations using radar data and synoptic observations. The resulting distribution functions of empirical probability for the permanence of wind hazards associated with cumulonimbus can be used for the further optimisation of the decision method.

Wind gust factors are determined from data obtained on the south shore of the Rio-Antirio Strait, at the western entrance of the Gulf of Corinth, during the passage of frontal depressions. It was found that in this region the wind gusts decrease as the wind speed increases. The measured gust factors fall in-between those used for structural design in the United Kingdom and those used in the United States.

Trends in extremes in station daily sea-level pressure differences at 0900 NZST are examined, and extreme daily wind gusts, across New Zealand, since the 1960s. Annual time series were examined (with indices of magnitude and frequency over threshold percentiles) from the daily indices selected. These follow from earlier indices of normalized monthly mean sea-level pressure differences between station pairs, except the daily indices are not normalized. The frequency statistics quantify the number of extreme zonal (westerly and easterly), or extreme meridional (southerly or northerly), pressure gradient events. The frequency and magnitude of extreme westerly episodes has increased slightly over New Zealand, with a significant increase in the westerly extremes to the south of New Zealand. In contrast, the magnitude and frequency of easterly extremes has decreased over New Zealand, but increased to the south, with some trends weakly significant. The frequency and magnitude of daily southerly extremes has decreased significantly in the region. Extreme daily wind gust events at key climate stations in New Zealand and at Hobart, Australia, are highly likely to be associated with an extreme daily pressure difference. The converse was less likely to hold: extreme wind gusts were not always observed on days with extreme daily pressure difference, probably due to the strong influence that topography has on localized station winds. Significant correlations exist between the frequency indices and both annual-average mean sea-level pressures around the Australasian region and annual-average sea surface temperature (SST) anomalies in the Southern Hemisphere. These correlations are generally stronger for indices of extreme westerly or extreme southerly airflows. Annual-average pressures in the Tasman Sea or Southern Ocean are highly correlated to zonal indices (frequency of extreme westerlies). SST anomalies in the NINO3 region or on either side of the South Island are significantly correlated with the frequency of extreme westerly airflows. Copyright © 2005 Royal Meteorological Society

Geomorphological evidence and historical wind records indicate that eolian processes have heavily influenced San Miguel Island environments for much of the Late Quaternary. The island is almost constantly bombarded by prevailing northwesterly winds, with peak velocities exceeding 75 km/h and wind gusts reaching over 100 km/h. These strong winds played an important role in the location, formation, and preservation of the island's more than 600 archaeological sites. Excavation and surface collection at a stratified Middle and Late Holocene archaeological site on the island's north coast suggest that wind related disturbances result in significant displacement of light fish bones, produce concentrations of shellfish and heavy mammal bones, and cause significant abrasion, etching, and polishing of bones, shells, and artifacts. These data illustrate that wind not only alters surface materials but can significantly disturb subsurface deposits to a depth of at least 20 cm. Working in concert with a variety of taphonomic processes, wind can play a fundamental role in the preservation of archaeological sites and careful scrutiny during excavation and laboratory analysis is required to delineate its effects. © 2002 Wiley Periodicals, Inc.

Recently, it has been demonstrated that control techniques based on sliding mode control (SMC) are robust and their performances are quite remarkable for applications to active/hybrid control of seismic-excited linear, non-linear or hysteretic civil engineering structures. In this paper, sliding mode control methods are further extended by introducing a compensator. The incorporation of a compensator provides (i) a convenient way of making trade-offs between control efforts and specific response quantities of the structure through the use of linear quadratic optimal control theory, and (ii) a convenient design procedure for static output feedback controllers to facilitate practical implementations of control systems. Since civil engineering structures generally involve excessive degrees of freedom, a controller design based on a full-order system may be difficult, in particular for wind-excited tall buildings. In this paper, three reduced-order control methods have been used and their performances have been investigated. Applications of sliding mode control with compensators to active control of buildings subject to either earthquakes or strong wind gusts have been demonstrated through numerical simulations. Simulation results show that the performance of the sliding mode controller with compensators for the reduced-order system is quite close to that of the controller based on the full-order system as long as enough vibrational modes are taken into account in the reduced-order system. © 1997 John Wiley & Sons, Ltd.

Summary The effect of speed and humidity of the airflow and the mist sprayed with airflow on the liberation of conidia of Heterobasidion annosum from pure cultures was studied in a small windtunnel. The conidia were liberated more easily in humid than in dry airflow. Liberation was most abundant when mist was added to the airflow. Threshold speed for the liberation of conidia was calculated to vary between 1.8 m/s and 3.9 m/s. According to the results, conidia of H. annosum may be liberated into the air by wind gusts associated with high humidity or mist and thus the conidia may have a role in aerial dispersal, although this is probably small compared with basidiospores.

Quantitative feedback theory is developed for the design of an automatic station-keeping flight control system to regulate the position of an aircraft receiving fuel relative to the tanker aircraft during air-to-air refueling. A robust flight control system is designed for automating the station-keeping task. A simple outer loop feedback control system is developed that achieves stable position regulation in the presence of wind gusts and fuel transfer related disturbances. The modelling and analysis clearly show the usefulness of QFT in the design of flight control systems for aircraft with large structured parametric uncertainty. Linear and nonlinear simulations are performed to validate the design. © 1997 by John Wiley & Sons, Ltd. This paper was produced under the auspices of the US government and it is therefore not subject to copyright in the US.

In this paper an attempt is made to study the climatological characteristics of very low relative humidity (below or equal to 10 per cent) in northern Crete, especially at Heraklio, by utilizing data from a 34-year period (1956–1989). Specifically, after selecting the very low humidity days based on a previously determined definition and the synoptic situation with which they are associated, the following aspects were examined: (i) the interannual and monthly variation, (ii) the mean duration of very low humidity occurrence on each day at Heraklio and its monthly frequency, (iii) the mean values of the meteorological elements (temperature, wind, wind gusts, pressure, total and low-cloud amounts, and visibility) for the time of synoptic observations reporting very low humidity at Heraklio and for the corresponding times of the day gust before it for both Heraklio and Tibaki, that is, on the northern and southern coasts of Crete. Also by comparing Heraklio's and Tibaki's mean values of the meteorological elements it was possible to determine the contribution of the Cretan relief characteristics to the very low humidity occurrence at Heraklio.

We introduce a model that interprets atmospheric increment statistics as a large scale mixture of subsets of isotropic statistics. When mixing is weak the same statistics as for isotropic turbulence is recovered while for strong mixing robust intermittency is obtained. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Blowouts are the main feature of wind erosion in the dunes along the Dutch coast. A number of characteristics, such as their growth against the prevailing wind and the spontaneous stabilization when certain dimensions are reached, are believed to be caused by a prominent quality of the southwest wind, viz. its gustiness. This hypothesis is tested in a two-dimensional computer model which simulates the effect of wind gusts on a sandy surface along the main axis of the blowout. A number of constraints based on field observations are built into the model. The results closely resemble the longitudinal section of the blowout.

New measurements show that in a barley crop wind gusts of more than five times the mean speed occur frequently. Moreover, for the impaction of fungal spores to crop foliage, the known dependence of impaction efficiency on wind speed shows that at low speeds the efficiency increases rapidly as wind speed rises. If it is wind gusts that cause spores to be lifted from plant surfaces and to enter the airstream, then calculations show that in a gusting wind the efficiency of impaction to surfaces will be higher than would be predicted from the mean wind speed. These findings are supported by results from field experiments that investigated the lift-off from plant surfaces and from metal plates, respectively, of spores of Erysiphe graminis (barley mildew) and of lycopodium (club moss). This influence of gusts may thus explain in part why, within crops, spore concentration and deposition change rapidly with distance from spore source.