Frequency Of Strong Winds Research Articles

Effects of Soil and Land Surface Conditions in Summer on Dust Outbreaks in the Following Spring in a Mongolian Grassland

We propose an index of soil and land surface conditions for wind erosion to investigate their effects on dust outbreaks. The index is the normalized dust outbreak frequency (NfDO), which is the ratio of dust outbreak frequency to strong wind frequency. NfDO for April was always low in Mandalgobi, Mongolia, when the accumulated precipitation amount for June to August (PrecJun-Aug), soil moisture averaged for June to August (SMJun-Aug), and above-ground biomass for August (AGBAug) of the previous year exceeded their thresholds (100 mm, 13 mm, and 2.2*10-2 kg m-2, respectively). This suggests that dead leaves of grasses in spring, which are the residues of vegetation from the preceding summer, suppress dust outbreaks. However, when PrecJun-Aug, SMJun-Aug, and AGBAug are lower than the thresholds, NfDO varies over a wide range. This implies that when there are few dead leaves in spring, other possible factors after summer such as liquid precipitation leading to soil freezing, snow cover, melted water, and grazing, affect erodibility in spring. These results suggest that changes in soil and land surface conditions, rather than in wind conditions, chiefly affect the increased frequency of dust outbreaks. This dead-leaf hypothesis can be used as an early warning of dust-storm hazards.

Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO

Abstract. The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: until 1975, 1976–1992 and 1993–2008. Frequencies have been computed also for the "winter" (October to March) period, per quadrants, and for occurrences exceeding the speed of 15 m s−1. At Reykjavick a recent increase in the frequency of strong winds has occurred from various directions. Between 62° N (Thorshavn) and 59° N (Kirkwall) strong wind has been increasing since 1975. Minor changes can be observed at Stornoway, whereas at Malin Head the greatest increase for southerlies and westerlies is observed during the 1976–1992 period. At Belmullet, the frequency of strong southerlies has almost doubled since 1992, while at Shannon and Valentia it remains quite low. Finally at Brest and Belle-Ile, westerlies are predominant among winds >15 m s−1. Important changes in time and latitude appear in the correlation with the NAO (North Atlantic Oscillation) index. The highest correlation coefficients, calculated with monthly or seasonal means between the early 1950s and 1975, are observed from between 58° N (Stornoway) and Iceland, whereas low positive coefficients are reported more south. During the period 1976–1992, when increasing NAO index is predominant, positive correlation improves southwards as far as 54° (Belmullet) with some improvement also at Shannon and Valentia, while it remains low or even negative near the French Atlantic coast. Finally in the 1993–2008 period, correlation improves for all the stations south of 54° N (Belmullet), while it weakens more north.

Understanding the impact of climate change on Northern Hemisphere extra-tropical cyclones

Extra-tropical cyclones strongly influence weather and climate in mid-latitudes and any future changes may have large impacts on the local scale. In this study Northern Hemisphere storms are analysed in ensembles of time-slice experiments carried out with an atmosphere only model with present day and future anthropogenic emissions. The present day experiment is forced by observed sea-surface temperature and sea-ice. The sea-surface temperatures and sea-ice for the future experiment are derived by adding anomalies, from parallel but lower resolution coupled model experiments, to the observed data. The storms in the present day simulation compare fairly well with observations in all seasons but some errors remain. In the future simulations there is some evidence of a poleward shift in the storm tracks in some seasons and regions. There are fewer cyclones in the Northern Hemisphere in winter and spring. The northeast end of the North Atlantic storm track is shifted south in winter giving more storms and increased frequency of strong winds over the British Isles. This shift is related to an increase in baroclinicity and a southward shift of the jet that occurs as a response to a minimum in ocean warming in the central North Atlantic. An increase in the frequency of storms over the UK is likely to cause enhanced levels of wind and flood damage. These results concur with those from some other models, however, large uncertainties remain.

Increased activity on Ebeko Volcano, Paramushir I., North Kurils in 2005–2006

In recent years the gas hydrothermal activity of Ebeko Volcano has been characterized by a constant heat flow and a constant chemical composition of water and fumarole gases. The volcano’s activity suddenly increased on January 27, 2005. Two high-output steam-gas jets 5 m across formed in the Active Funnel of the North Crater. A new high-output, high-temperature, fumarole field originated in the funnel in July 2005. Changes have been recorded in the chemical composition of fumarole gases. Ratios between individual components of the gas were calculated, with the ratios being geochemical precursors of eruptions for the volcano under study. Based on these results and on the very fact of increased fumarole activity on Ebeko, an intermediate-term forecast of explosive eruptions has been developed. Atmospheric contamination by a toxic gas (hydrogen sulfide) is described. It was previously thought that toxic gases pose a short-lived threat only to the population of the town of Severo-Kuril’sk because of frequent strong winds prevailing there. It is shown that the presence of a snow cover during increased activity on Ebeko sharply enhances the hazard of contamination by toxic gases, the hazard being constant both on the volcano itself and in the Severo-Kuril’sk area.

Long-term variation of Asian dust and related climate factors

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dust-transport model. Simulation results were examined using visibility-based observations by Chinese and Japanese Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Niño/Southern Oscillation (ENSO) affects the dust transport path. Analyses of average dust transport flux at 130°E clarified variation of the transport path between La Niña years and El Niño years.

Population dynamics of epiphytic bromeliads: Life strategies and the role of host branches

Summary Epiphytes need to balance the trade-off between long-term survival and colonizing new branches in their resource-limited and high-risk canopy habitats. We censused populations of five bromeliad species over two years and calculated matrix population models to determine the key factors influencing population growth rates. Additionally, logistic regression models were applied to study how demographic features change with microsite characteristics and disturbance. The bromeliads studied are slow-growing, with species preferring thinner branches maturing faster. Population growth rates were below unity in all species except for the drought-resistant Tillandsia juncea. Population growth rates depended almost exclusively on survival, above all of adult plants. Fecundity had only little impact, even in species of the outer canopy where branchfall-related disturbance and mortality are frequent. Survival rates and the probability to become reproductive increased with light availability in most species. Microsite characteristics had the greatest impact on seedling survival, although this contributed very little to population growth rates. We conclude that branchfall-related mortality is a key factor for population persistence of epiphytes dwelling in the outer canopy, and that resource availability constrains the possibility to counteract disturbance with higher fecundity. For species of the outer canopy an increased disturbance by more frequent strong winds could further constrain population growth. Because population persistence strongly relies on the survival of adult plants, harvesting bromeliads for ornamental or other purposes should be restricted to immature individuals. In the future, better models of epiphyte populations in a habitat with highly patchily dynamics should be based on a metapopulation approach.

Regional Difference in the Characteristic of Dust Event in East Asia: Relationship among Dust Outbreak, Surface Wind, and Land Surface Condition

The regional differences in the characteristics of dust events (i.e., all phenomena related with dust; dust in the production and suspension phases) in East Asia were investigated by use of surface meteorological data from March 1988 to May 2004. Referring to the topography and land cover type (e.g., Bare Desert, Semi Desert Shrubs, Grassland, Cultivated Land), East Asia was divided into 11 regions. Dust outbreaks (i.e., dust in the production phase) frequently occur in the Gobi Desert, the western part of the Loess Plateau, and the Taklimakan Desert, whose land cover types are Bare Desert and Semi Desert Shrubs (i.e., Desert). Although the result of frequent dust outbreaks is common among these regions, the frequency of floating dusts (i.e., dust in the suspension phase) differs greatly. Floating dusts are frequently observed in the Taklimakan Desert because most of the dust particles are blocked by the steep topographical surroundings such as the Tibetan Plateau, Pamirs, and Tian Shan Mountains. On the other hand, floating dusts are seldom observed in the Gobi Desert and Loess Plateau. In these regions, although dusts are produced by synoptic disturbances, they are immediately swept away by these same synoptic disturbances.We clarified the regional differences in the relationships among dust outbreak, surface wind, and land surface condition by analyzing the correlation between dust outbreak frequency and strong wind frequency at a threshold wind speed ofa constant, 6.5 m sec−1. Our analysis showed that the surface wind is primarily responsible for dust outbreaks in Desert regions in March and April. On the other hand, land surface conditions are the determining factor for dust outbreaks in Grassland regions. Land surface conditions affect dust outbreaks in May even in Desert regions, but almost no impact ofwind is seen. An examination of the effect of snow cover on the threshold wind speed, using the parameterization of Kurosaki and Mikami (2004), shows snow cover to have marked effects on dust outbreaks in Inner Mongolia and the Hexi Corridor in March, and in Northern Mongolia in April. The seasonal and year-to-year variations in dust outbreaks, and the mean threshold wind speed of dust outbreak are also compared among regions.

Effect of snow cover on threshold wind velocity of dust outbreak

This study proposes parameters to measure the effect of snow cover on the threshold wind velocity of dust outbreak for dust models. We used statistics of snow cover, wind velocity and dust outbreaks in East Asia for the months of March and April for the years from 1988 to 2003. Dust events frequently occur in that region in those months, although snow and melting snow cover a broad area, making it difficult to know the distribution of dust from East Asia. Our equation, presented in this paper, shows the degree to which snow cover affects dust outbreaks. To validate this equation, we checked the correlation between frequency of strong winds and dust outbreaks. Our results showed that this correlation is improved when the effect of snow cover is considered. We discuss the effects of soil wetness, vegetation, and errors due to the subgrid heterogeneity of snow coverage as well.

Recent frequent dust events and their relation to surface wind in East Asia

A remarkable increase in dust outbreaks has occurred in the eastern part of the Asian Continent over the last three years (2000–2002) compared with the previous seven years (1993–1999). This finding corresponds well with the annual change of Kosa (i.e., yellow sand) events for the same period in Japan. Dust outbreaks occurred in limited regions around southern Mongolia, the Badain Jaran Desert, and the western Loess Plateau from 1993–1999. However, the area of frequent dust outbreaks expanded extensively to the east, and dust outbreaks also frequently occurred in regions around the North China Plain, northeastern China, and the Korean Peninsula in 2000–2002. Good correspondence was found between the surface wind and dust outbreaks in year‐to‐year variations and in spatial distributions. This indicates that frequent strong winds are the primary cause of the recurrent dust outbreaks in the last three years.

The FETCH experiment: An overview

The “flux, etat de la mer, et télédétection en conditions de fetch variable” (FETCH) was aimed at studying the physical processes associated with air–sea exchanges and mesoscale oceanic circulation in a coastal region dominated by frequent strong offshore winds. The experiment took place in March–April 1998 in the northwestern Mediterranean Sea (Gulf of Lion). Observations were collected with the R/V L'Atalante, with an air–sea interaction spar (ASIS) buoy, with waverider buoys, and with research aircraft equipped for in situ and remote sensing measurements. The present paper is an introduction to the following special section, which groups 12 papers (including this one) presenting results on turbulent flux measurements at the ocean surface, on the behavior of the marine atmospheric boundary layer, on the ocean waves characteristics, on the ocean circulation, and on remote sensing of surface parameters. This overview presents the background and objectives of FETCH, the experimental setup and operations, and the dominant atmospheric and oceanic conditions and introduces the different papers of the special section.

Sediment-Trap Measurements of Suspended Mine Tailings in Shallow Water Cover

Disposal of pyrites mine tailings under shallow water covers is an effective and commonly used method for reducing tailings oxidation, thus minimizing the formation of acid rock drainage. However, wind-wave-induced resuspension of tailings under the water cover could compromise suspended solids discharge criteria and increase the overall sulfide oxidation, since dissolved oxygen concentration are higher in the water cover than in the pore water. This article reports field measurements of suspended tailings collected approximately 2-10 cm above the tailings surface by means of 16 sediment traps partly buried in the tailings bed. The traps were distributed over ab area of about 600x300 m, where the water cover depth varied from 0 to 2 m. The traps were sampled on three occasions during a total study period of 93 days distributed over two field seasons. Wind speed and direction were monitored at the site during the study. Hourly average wind speeds ranged from 0 to 10 m/s. Suspended tailings were recovered in every sediment trap on each sampling event. Comparison of particle size distributions for suspended solids and bed tailings suggests that at this site and for the duration of this study, tailings erosion and resuspension occurred primarily in areas where the water cover depth was 1.0 m or less, and that suspended tailings were transported by currents to other parts of the water cover. The amount of tailings resuspension was related to the frequency of strong winds blowing in the direction of maximum fetch. Comparison of suspended solids and bed tailings compositions indicates that suspended tailings oxidized at a larger rate than bed tailings.

Koeleria macrantha (Ledeb.) Schultes (K. alpigena Domin, K. cristata (L.) Pers. pro parte, K. gracilis Pers., K. albescens auct. non DC.)

<i>Koeleria macrantha</i> (Ledeb.) Schultes (<i>K. alpigena</i> Domin, <i>K. cristata</i> (L.) Pers. pro parte, <i>K. gracilis</i> Pers., <i>K. albescens</i> auct. non DC.)

Nonlocal wind‐driven fjord–coast advection and its potential effect on plankton and fish recruitment

The Bergen Ocean Model (BOM), a three‐dimensional physical coastal ocean model, was used for a numerical simulation experiment to investigate short‐term effects of wind‐generated coastal upwelling and downwelling on the dynamics of adjacent large outer and smaller inner fjords. The effect of the real alongshore wind regime on advection for an idealized fjord topography, resembling Masfjorden, western Norway, is used as an example. This modelling exercise is a supplement to, and its predictions support, the various hypotheses investigated in ecosystem simulation studies of the Masfjorden. The model predicts that coastal winds from the north cause upwelling and transport the upper water layer out from the fjords. Winds from the south cause downwelling and transport the upper water layer into the fjords. The transport is rapid and ≈50% of the upper water layer may be replaced within 1–2 days. Implications of these physical processes for the dispersal and retention of planktonic organisms and the early life stages of fish are discussed. If strong southerly winds occur frequently, this will transport planktonic organisms into the fjord and may increase the carrying capacity for planktivorous fish. In contrast, frequent strong northerly winds may reduce the abundance of planktonic organisms, including the early life stages of marine fish, and thus possibly reduce recruitment to fjord fish populations. Frequent shifts between southerly and northerly winds would cause an exchange of early life stages between neighbouring fjords and thus enhance genetic exchange.

Wind-induced long term increase and short term fluctuations of shallow water suspended matter and nutrient concentrations, Ringkøbing Fjord, Denmark

Abstract The terrestrial supply of nutrients to the shallow lagoon Ringkøbing Fjord has shown a significant downward tendency for phosphorus during the past 10 years. In spite of a decreasing supply, there is at the same time an increase in nutrient concentrations, especially for P, but also for the suspended matter content in the fjord- Analyses af wind data from nearby lighthouses show that the frequency of strong winds from the SW (equal to the longest fetch) has gone up in the same period of time and that both the nutrients and suspended matter concentrations in the water column are well correlated with available wind energy and hence, with the possibilities for wave-induced resuspension of material from the fjord bottom. During a 6 month period, daily fluctuations of concentrations in the water column were measured in samples taken by automatic samplers at four stations with different exposures. Due to wave induced resuspension, the day to day variations were between 2-895 mg DW l-1 of suspended matter, 0.2.-24.5 mg l-1 of organic matter, 0.1-1.1 mg l-1 of Total-N, and 0.01-0.18 mg l-1 of Total-P. Fortnightly measurements of erosion rates at station bottoms showed that as much as 3 cm of the sediment surface were resuspended during periods of hard wind conditions. The resuspended particles had mode sizes of 30-40µ, i.e. high sinking rates are assumed. The concentrations af suspended matter observed in the water column, however, were not below 40 mg DW l-1 in 50% og the time, leading to a marked effect on light penetration in water. The Secchi-depth is on average reduced to 0.6 m in summer and 0.7 m in winter.

Wind erosion on sugar beet fields in Scania, southern Sweden

Wind data and wind erosion records are analysed for the period 1948–1988 during spring, on sugar beet fields when they are vulnerable to wind erosion, in Scania, southern Sweden. From about 1970 and onwards, reported wind erosion has increased dramatically. Reasons for this are found in changes in the wind climate at different scales. At the regional scale, the frequency of strong winds (greater than or equal to 9 ms −1 20 m above ground) in spring has increased significantly after about 1970. N E-E winds are found to be the most erosive. A tendency to a higher ratio of strong easterly winds in spring is seen over the two latest decades. Furthermore, during the second half of the study period, a larger proportion of weeks containing strong winds (23.2%) were associated with wind erosion compared with the first half (5.8%). This increased wind action could be explained by a changed local wind climate owing to field enlargements and removal of windbreaking vegetation in the agrarian landscape during the study period. Additional contributors to wind erosion may be changes in wind climate at the micro level by the introduction of new methods in beet cultivation.

Practical application of nutation damper for suppressing wind-induced vibrations of airport towers

Air-traffic controllers discomfort caused by vibrations of structures due to relatively frequent strong winds is an important problem in designing tall airport towers. Authors have had an oppurtunity to participate in providing suppression measure for wind induced vibrations of the new airport towers at the Haneda and Narita International Airports. The nutation damper is adopted to suppress wind-induced vibrations. The experiments on the characteristics of the nutation damper are carried out in the range of small amplitudes. Effectiveness of the floating particles to improve damping efficiency of the nutation damper is also studied. Response analyses of the airport towers suggest that the damper of 1% mass ratio with floating particles can reduce acceleration by around 55% thus improving their serviceability significantly.

Practical application of nutation damper for suppressing wind-induced vibrations of airport towers

Air-traffic controllers discomfort caused by vibrations of structures due to relatively frequent strong winds is an important problem in designing tall airport towers. Authors have had an oppurtunity to participate in providing suppression measure for wind induced vibrations of the new airport towers at the Haneda and Narita International Airports. The nutation damper is adopted to suppress wind-induced vibrations. The experiments on the characteristics of the nutation damper are carried out in the range of small amplitudes. Effectiveness of the floating particles to improve damping efficiency of the nutation damper is also studied. Response analyses of the airport towers suggest that the damper of 1% mass ratio with floating particles can reduce acceleration by around 55% thus improving their serviceability significantly.

Behavioural responses of the planktonic stages of the American lobster Homarus americanus to thermal gradients, and ecological implications

The behavioural responses of each planktonic stage (I to IV) of American lobster Homarus americanus to a thermal gradient were studied during complete day/night cycles using an experimental approach. The thermocline markedly influenced the vertical position of larvae of all stages, limiting their distribution to the upper part of the water column. In both absence or presence of a thermocline, older individuals (stages 111 & IV) were observed deeper in the water column than younger individuals (stages I & 11). The vertical distribution of larvae was unaffected by the day/night regime. The ecological significance of this temperature-driven behaviour of the larvae relative to the recruitment dynamics of the adult stocks is discussed. We hypothesize that factors causing a breakdown in the thermocline should decrease recruitment to the adult population. The validity of this hypothesis was explored for the lobster stock of Iles-de-la-Madeleine (Gulf of St. Lawrence, Quebec). Significant negative correlations obtained between the frequency of strong winds (> 30 km h' ) during dispersal and settlement periods. and subsequent lobster landings (with an 8 yr lag) in this region over a 15 yr interval support the hypothesis.

Meridional and seasonal variations of the sea surface chlorophyll concentration in the southwestern tropical Pacific (14 to 32°S, 160 to 175°E)

Sea surface chlorophyll concentrations (SSCC) (3369) have been measured from January 1978 to December 1982 in the area 14 to 32°S. 160 to 175°E, on samples taken by voluntary observing ships. A log-transformation is first applied to the data to stabilize the variance; a function of time and latitude is obtained which accounts for 16% of the variance of the logs. It is then subtracted from the logs, resulting in a field with a zero mean and a constant and uncorrelated error, in which the longitude effect is small and will be neglected. The data are distributed into a one-month, two-degree latitude grid; the subgrid noise variance is 0.472 and corresponds to a variation coefficient of 78% after return to the antilog. Objective analysis is applied to obtain optimal estimates of the SSCC in the limits of the study. The most striking feature is an enrichment in austral winter, developing northward to about 20 to 22°S, with SSCC in the range 0.15 to 0.40 mg m −3. A positive correlation between SSCC and integrated (0 to 150 m) chlorophyll (log transformation, r = 0.714, n = 150) is found in the same region using existing data from oceanographic cruises; the results from SSCC data can thus cautiously be applied to the whole euphotic layer. The data from oceanographic cruises support the hypothesis that the winter enrichment results from an enhanced vertical mixing after the cooling of the sea surface. This is confirmed by the direct relationship between the frequency of strong winds and the importance of the winter enrichment. There is some indication that the combination of available light and mixed-layer depth is limiting south of 28°S in June and July, resulting in two maxima in May and August. The wind effect is inverse in the northern part where Trichodesmium spp. patches form during the calms; these patches are only surface features and are not indicative of a biomass increase at deeper levels. The interannual variability is reflected by the ratio of the range of the standard year to that of the monthly anomalies which varies from 0.5 at 15°S to 1.11 at 29°S.

Insect habitats in Antarctica

About fifty species of terrestrial arthropods have been collected in Antarctica; these include mites, ticks, springtails, sucking lice, biting lice and flies. The mites include both free-living and parasitic forms, the springtails and flies are free-living, and the ticks and lice are parasitic. The ticks, parasitic mites, and biting lice are associated with birds, and the sucking lice with seals. The number of species are about equally divided between free-living and parasitic forms. The ability of insects and mites to survive the very low winter temperatures and frequent strong winds of Antarctica is of considerable interest; judged in relation to commonly accepted ideas of tolerance, the environment is extremely forbidding.