Tail Wind Research Articles

The residence times of aircraft emissions in the stratosphere using a mean emission inventory and emissions along actual flight tracks

Flight routes of commercial aircraft are adjusted to the actual meteorological situation in order to benefit from tail winds and avoid head winds and dangerous flight conditions. This study investigates whether these adjustments have an impact on the partitioning and the residence times of aircraft emissions in the stratosphere and troposphere. A Lagrangian dispersion model is used in combination with a mean emission inventory and emissions along actual flight tracks. Both inventories are established from Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) aircraft position data in the North Atlantic Flight Corridor (NAFC) over a 1‐year period. The results show that stratospheric emissions released in the NAFC are transported in a northeasterly direction towards polar regions on a timescale of a few days. The mean residence time of these emissions is about 23 days, which is shorter than documented in previous studies. The greatest fluxes from the stratosphere into the troposphere occur during the first 10 days and have their maxima over Europe and North Africa. About 62% and 67% of the emissions are directly deposited in the stratosphere in the mean emission inventory and in the inventory of the actual flight tracks, respectively. The deposition in the stratosphere was found to be sensitive to the definition of the tropopause height. However, the transport and partitioning of the emissions in the stratosphere and troposphere are only moderately affected if an inventory of the actual flight tracks is used instead of a mean emission inventory. Therefore, the systematic errors made in chemistry climate models, which use mean inventories, are small and can be tolerated for most applications.

The Effects of Wind and Altitude in the 200-m Sprint

A mathematical model is used to determine the effect of wind resistance and altitude on 200-m race times. The model is used to simulate the effect of different wind speeds, wind directions, and lane allocation in the 200-m sprint. For the 200-m event there is a single wind gauge recording only the wind’s component velocity in the straight, and not the wind direction. For record purposes the wind reading should not exceed 2 m/s. It is evident that for the same official wind reading, an athlete may face vastly different conditions. The model estimates that for the same wind reading, the prevailing conditions can produce a time difference of as much as 0.5 s. Results indicate that many legal performances in the 200-m are currently ruled out for record purposes. Some performances which are officially wind-assisted have in fact been hindered by an overall head wind when it is averaged throughout the race. Conversely, some performances which are run into a head wind in the straight have benefited from an overall tail wind. We estimate that, on average, for a 2-m/s wind blowing down the straight, the 200-m runner benefits from an overall tail wind of only 0.95 m/s. The lower air density at an altitude of 1,500 meters produces an advantage of 0.11 s in the 200-m, which equates to a 2-m/s tail wind at sea level blowing directly down the straight. Correction estimates are provided for the combined effect of both wind and altitude in 200-m races. A new all-time world top five ranking list for men and women is produced for the 200-m event, corrected for wind and altitude effects.

超音波風向風速計とＧＰＳを用いた風の移動観測法

A mobile observation method of wind using a sonic anemometer and GPS was developed. Wind direction and speed are estimated every second by subtracting the wind vector due to the movement of the automobile, measured by GPS, from the wind vector on the automobile, measured by sonic anemometer. The sonic anemometer should be firmly attached at 40cm behind the front of the automobile at 1.9m height from the ground and the mounting arm should not shake vertically. The survey error of the GPS on the mobile observation of wind can be neglected. The measurement accuracy of the wind speed and wind direction in this observation method were 1.5m/s and 11°, respectively. It is possible to measure wind direction and speed in a tail wind, head wind, or crosswind for the car, moving at any speed. To clarify the characteristics of “Aso Oroshi”, mobile observation of wind was carried out in the valley of Aso somma. It was shown that mobile observation method of wind was effective for observation of the local wind.

Budgeting the Flight of a Long-Distance Migrant: Changes in Nutrient Reserve Levels of Bar-Tailed Godwits at Successive Spring Staging Sites

A single population of Bar-tailed Godwits limosa lapponica was studied before departure from their wintering grounds on the Banc d'Arguin in Mauritania, and at a spring staging site in the Dutch Wadden Sea. On the Banc d'Arguin the godwits started gaining body mass in the course of March at rates of about 2.8 g d-1 in ♂ ♂ and 3.2 g d-1 in ♀ ♀, before leaving north between 25 and 27 April. In the Wadden Sea, body mass increased linearly over the entire staging period (29 April–31 May) at 5.6 g d-1 in ♂ ♂ and 7.5 g d-1 in ♀ ♀. Half of the mass increase was due to the deposition of fat, the other half to increases in fat-free tissue (mainly muscle protein). If the godwits flew at the heights with most tail wind assistance by varying their flight altitude up to 5.5 km, they gained an average wind assistance of 18 km h-1, which would add considerably to their estimated air speed of 57 km h-1. At an average ground speed of 57 18 = 75 km h-1 the godwits would cover the required 4300 km in 57.3 h. During this flight, ♂ ♂ and ♀ ♀ were estimated to lose 136 g and 178 g respectively. Since half of these mass losses consisted of fat, they represent energetic equivalents of 3163 kJ and 3857 kJ respectively, leading to estimated flight costs of 55 kJ h-1 for ♂ ♂ and 67 kJ h-1 for ♀ ♀. The energy reserves stored on the Banc d'Arguin would not enable the Bar-tailed Godwits to cover the distance between W. Africa and the Wadden Sea in one flight without making good use of favourable high-altitude winds.

Magnetic field of Mars: Summary of results from the aerobraking and mapping orbits

The Mars Global Surveyor (MGS) Magnetic Field Investigation was designed to provide fast vector measurements of the ambient magnetic field in the near‐Mars environment and over a wide dynamic range. The fundamental objectives of this investigation were to (1) establish the nature of the magnetic field of Mars; (2) develop appropriate models for its representation; and (3) map the Martian crustal remanent field (if one existed) to a resolution consistent with the spacecraft orbit altitude and ground track separation. Important and complementary objectives were the study of the interaction of Mars with the solar wind and of its ionosphere. The instrumentation is a synergistic combination of a twin‐triaxial, fluxgate magnetometer system and an electron reflectometer. The twin‐magnetometer system allows the real‐time detection of spacecraft‐generated fields, while the electron reflectometer adds remote magnetic field sensing capabilities as well as information about the local electron population. After Mars orbit injection in September 1997 and through the aerobraking (AB) and science‐phasing orbits (SPO) that followed, observations were acquired from more than 1000 elliptical orbits with periapses ranging from 85 to 170 km above Mars' surface. Following injection into the final ∼400 km altitude circular‐mapping orbit, data have been acquired from more than 6000 orbits in the fixed 0200–1400 local time plane. Major results obtained so far by the Magnetometer/Electron Reflectometer (MAG/ER) investigation in the course of the mission include (1) the determination that Mars does not currently possess a magnetic field of internal origin (dynamo), (2) the discovery of linear, strongly magnetized regions in its crust, closely associated with the ancient, cratered terrain of the highlands in the southern hemisphere, and (3) multiple magnetic “cusps” that connect the crustal magnetic sources to the Martian tail and shocked solar wind plasma. The solar wind interaction with Mars is therefore similar in many ways to that at Venus and at an active comet, primarily an ionospheric/atmospheric interaction. A comet‐like “magnetic pileup” region and boundary develop that stand off the solar wind, and mass loading by pickup ions of planetary origin plays an important role in defining interaction regions and overall geometry. This paper focuses primarily on the results obtained by the magnetometer (MAG) portion of the investigation during the MGS aerobraking, science‐phasing, and mapping orbits. A companion paper on this issue summarizes the results obtained from the Electron Reflectometer (ER) sensor.

Optimal departure decisions of songbirds from an experimental stopover site and the significance of weather

Recent models have worked with the assumption that birds try to minimize either time, energy or predation risk during migration, or some combination of these. The few empirical studies available have suggested that time minimization may be the most common strategy. One way of distinguishing between strategies is to study the departure decisions of migrating birds. We supplied migrating European robins, Erithacus rubecula, with food ad libitum in the field and monitored their changes in body mass prior to departure. The overall mass gain rate (ktot, the ratio of daily mass increase to lean mass) of 10 birds using the feeding station was on average 0.05 (range 0.03–0.09). Departure fuel loads (fdep, the ratio of fuel mass to lean mass) were on average 0.53 (range 0.35–0.66). There was no significant correlation between fdepand ktot, which indicates a strategy of minimizing the energy cost of transport, rather than minimizing time but other aspects of the fuel deposition pattern suggest that time minimization may also be important. Whereas the behaviour of the robins was difficult to interpret in the light of optimal migration strategies, the importance of weather was striking. The robins selected the best weather conditions (tail wind, high air pressure and no precipitation) within the likely period of departure.

Photoevaporating Flows from the Cometary Knots in the Helix Nebula (NGC 7293)

We explain the Ha emission of the cometary knots in the Helix Nebula (NGC 7293) with an analytical model that describes the emission of the head of the globules as a photoevaporated flow produced by the incident ionizing radiation of the central star.We compare these models with the Ha emission obtained from the HST archival images of the Helix Nebula. From a comparison of the Ha emission with the predictions of the analytical model we obtain a rate of ionizing photons from the central star of about 5e45 s^-1, which is consistent with estimates based on the total Hb flux of the nebula. We also model the tails of the cometary knots as a photoevaporated wind from a neutral shadow region produced by the diffuse ionizing photon field of the nebula. A comparison with the HST images allows us to obtain a direct determination of the value of the diffuse ionizing flux. We compare the ratio of diffuse to direct stellar flux as a function of radius inside an HII region with those obtained from the observational data through the analytical tail and head wind model. The agreement of this model with the values determined from the observations of the knots is excellent.

Spring weather and the migration of geese from Scotland to Iceland

Records of first arrivals of geese at sites in Iceland between 1950 and 1997 are combined with dates of departures from Scottish roosts and flights seen over northern Scotland to identify when migratory movements occurred. Greylag Geese Anser anser moved earliest, the mean date of first sightings in Iceland being 3 April (s.d.14.3 days) and of northward movements over Scotland 14 April (s.d. 12.9 days), the median first arrival and departure dates being 8 and 15 April. The mean date of first sightings in Iceland of pink‐footed geese Anser brachyrhynchus was 13 April (median 21 April) and of Scottish departures 20 April (median 25 April). The mean dates of Scottish departures and Icelandic sightings of Greenland White‐fronted Anser albifrons flavirostris, Barnacle Branta leucopsis and Brent geese Branta bernicla all lay between 18 and 22 April, with median dates from 19 to 27 April. Arrivals in Iceland were associated with anticyclonic conditions over Scotland on the previous day, while cyclonic conditions were avoided. There were more sightings over Scotland when conditions were unfavourable than would be expected from the frequencies of those conditions in April. There were unexpectedly few movements around dates of full moons (+/‐ 2 days). The three grey geese, but not the black geese, have tended to arrive in Iceland earlier in recent years. Head and westerly winds were far more frequent than tail winds, especially after 1970, and there is some evidence of eastward drifting, yet the energetic demands of the flight from Scotland to Iceland can rarely have been severe.

Fast and fuel efficient? Optimal use of wind by flying albatrosses.

The influence of wind patterns on behaviour and effort of free-ranging male wandering albatrosses (Diomedea exulans) was studied with miniaturized external heart-rate recorders in conjunction with satellite transmitters and activity recorders. Heart rate was used as an instantaneous index of energy expenditure. When cruising with favourable tail or side winds, wandering albatrosses can achieve high flight speeds while expending little more energy than birds resting on land. In contrast, heart rate increases concomitantly with increasing head winds, and flight speeds decrease. Our results show that effort is greatest when albatrosses take off from or land on the water. On a larger scale, we show that in order for birds to have the highest probability of experiencing favourable winds, wandering albatrosses use predictable weather systems to engage in a stereotypical flight pattern of large looping tracks. When heading north, albatrosses fly in anticlockwise loops, and to the south, movements are in a clockwise direction. Thus, the capacity to integrate instantaneous eco-physiological measures with records of large-scale flight and wind patterns allows us to understand better the complex interplay between the evolution of morphological, physiological and behavioural adaptations of albatrosses in the windiest place on earth.

Wind selectivity of migratory flight departures in birds

Optimal migration theory predicts that birds minimizing the overall time of migration should adjust stopover duration with respect to the rate of fuel accumulation. Recent theoretical developments also take into account the wind situation and predict that there is a time window (a set of days) during which birds should depart when assisted by winds but will not do so if there are head winds. There is also a final day when birds will depart irrespective of wind conditions. Hence, the wind model of optimal migration theory predicts that birds should be sensitive to winds and that there should be a correlation between departures and winds blowing towards the intended migration direction. We tested this assumption by tracking the departures of radio-tagged passerines during autumn migration in southern Sweden. Our birds were moderately to very fat when released and therefore energetically ready for departure. There was a significant correlation between direction of departure and wind direction. We also found that during days when birds departed there was a significantly larger tail wind component than during days when birds were present but did not depart. Our results show that passerines do take the current wind situation into account when departing on migratory flights. We also briefly discuss possible clues that birds use when estimating wind direction and strength. The inclusion of wind is an important amendment to optimal migration theory of birds and should be explored further.

Gravity Current in an Oscillatory Flow

The behaviour of the two-dimensional gravity current in an oscillatory flow is investigated by computation when homogeneous fluid and another fluid of slightly different density were released in a sinusoidally oscillating flow. The incompressible Navier-Stokes equation for an inhomogeneous fluid and the transport equation for solute were solved by the finite volume method developed in the previous paper and extended by incorporating the oscillatory ambient flow with the implementation of the unsteady inflow and outflow boundary conditions.The results indicate that since the tail wind pushes the head forward further than the head wind brings it backward, the mean speed of the current front increases in oscillatory ambient flows. The change of the ambient flow direction makes the front distorted remarkably and enforces the instability of the density interface at some KC numbers. This instability causes the roll up of the interface and the vortex shedding from the head, both of which increase the entrainment rate in low Froude numbers. It is found that the unsteady boundary layer along the wall affects the inner structure of the current head according to oscillatory flows.

Spring migration of the Garden Warbler(Sylvia borin) across the Mediterranean Sea

Information concerning the strategy adopted by passerine migrants in crossing ecological barriers is still scant, especially as far as spring migration is concerned. With the aim of investigating the pattern of desert and sea crossing in spring, capture frequency, biometry and physical conditions of Garden Warblers ringed at 18 stations spread over the Western and Central Mediterranean were analysed as a function of the geographical position of the ringing sites. The patterns of increasing capture frequency and wing length with longitude, matching those recorded within the species' wide breeding range, suggest wide-front movements across the Sahara and Mediterranean. The progressively delayed trapping hour with latitude indicates that Garden Warblers migrate actively during the day. Despite the potentially favourable spring ecological conditions, the North African coast seems not to be used substantially to restore the reserves depleted during the desert crossing. According to recent estimates of flight range, fat levels recorded at our Mediterranean stations are compatible with the absence of refuelling in North Africa, assuming a fat load at departure of about 27 g or lower fat load and some tail wind assistance.

The effects of winds over a barotropic retrograde slope current

A barotropic, retrograde slope jet, with its cyclonic flank up-slope, is subjected to persistent head winds or tail winds, or variable winds associated with the passage of swiftly moving cyclones. A head wind pushes the current jet up-slope and increases its speed against the wind. Likewise, a tail wind reduces its speed. Cyclones leave a trail of inertial oscillations over a deep, quiescent ocean, but when they pass over a retrograde slope current, the inertial oscillations are dispersed, and they excite topographic Rossby waves which propagate upstream. Using an example from the Barents Sea, it is shown numerically that a head wind can intensify the slope current more than 30% and a typical Polar low can excite significant topographic Rossby waves with a period of 36 hours.

The autumn migration of sedge warblers in relation to weather conditions

Both scientific results and causal observations support the idea that weather influences animal behaviour. The relationship between the migration of birds and various weather elements or atmospheric conditions has mainly been studied in northern Europe (Alerstam 1978, 1990; Akesson 1993) and North America (Emlen 1975; Kerlinger and Moore 1989; Fitzgerald 1993). According to the majority of the studies, most migrations (defined as a large number of birds departing from, or arriving at, a given rest area) always take place in windless, clear, anticyclonic weather or in tail winds (Alerstam 1990). Similar research has not been done on the relationship between the migration of reed warblers (Acrocephalus species) and weather conditions. In the present study, the autumn migration of sedge warblers (Acrocephalus schoenobaenus) was examined in relation to synoptic weather situations.

Höststräcket av fisktärna Sterna hirundo och silvertärna S. paradisaea över södra Sverige

Simultaneous observations of migrating Common and Arctic Terns were carried out during afternoons and evenings for three years, 1990—1992, at eleven sites at the larger lakes in southern Sweden. The force and direction of wind seemed to be the most important factor determining the number of terns observed and the route they took when they passed mainland Sweden from the Baltic Sea. The principal direction of the migration was southwest, with a more westerly orientation for Arctic than for Common Tern. High numbers were recorded mainly in head winds, whereas the terns probably flew at high altitude in tail winds, when they were not observed from the ground. The orientation of the lakes in relation the migration direction also affected the counts by leading line effects. The terns often concentrated in the southern or southwestern parts of the lakes before they continued migration. Approximately 65,000—70,000 Common and Arctic Terns are estimated to pass the region in the autumn.

B243 タンカーに働く風荷重と流れの可視化

Wind forces and moment acting on a tanker ship model in ballast condition were measured at wind tunnel with a view to investigating effects of differences of wind velocity profile and small structural components such as hand rails or pipelines on weather deck upon wind loads. Wind flow around the tanker ship model was also visualized to clarify wind flow structures by smoke method and oil film method for various attack angles ranging from head wind to tail wind.

Satellite tracking of high-arctic northern fulmars

Three northern fulmars (Fulmarus glacialis) were tracked with satellite transmitters while they dispersed from a colony at the North East Water polynya in high-arctic Greenland after breeding failure. The longest cumulative distance recorded was 2043 km in 14 days, giving an average daily movement of 143 km, and the maximum distance covered in 1 day was 369 km. The highest effective flight (ground) speed recorded was 25.8 kmh−1, and when corrected for non-linear flight path the ground speeds ranged between 27.9 and 38.4 kmh−1, which is very close to the theoretical most energy efficient airspeed (Vmp) of approximately 36 kmh−1. Bird flight tracks generally followed ice edges, and on long flights the birds used tail or cross winds. Within areas believed to be foraging areas birds moved cumulative distances of 86–488 km, or 33–147 kmday−1. While in the high-arctic, the birds appeared to select foraging areas mainly in the marginal ice zones, but all birds left the polynya following breeding failure and moved towards boreal waters. One bird was tracked to the polar front zone near Bear Island where an international fishing fleet operated. The study suggests that when the birds were no longer attached to the North East Water polynya by a breeding attempt, they sought alternative foraging grounds. Satellite transmitters or other devices were tested on a total of eight birds' (including the three tracked individuals), all of which probably failed in their breeding attempt. The birds' reactions to the handling and tagging are presented, and the possible reasons for the breeding failure discussed.

On the dynamics of tail fins and wind vanes

This paper describes some investigations of the dynamic yaw behaviour of tail fins and wind vanes employing delta wing planforms. Both single and twin wings were tested, the later were formed from two single wings joined at their apices. Comparisons were made using simple wind tunnel models with aspect ratios from 0.7 to 3.07, and various arm lengths, wind speeds and planform areas. The twin wing was found more highly damped than an equivalent single wing, with damping increasing as the angle between the wings increased. Stall related problems became evident as this angle approached or exceeded that for static stall. A computational model based on unsteady potential slender wing theory was developed to predict yawing motions of both tail fin types and compared with experiments. The computational model was found remarkably accurate for the single wing case even at high initial angles of yaw, but generally inaccurate for the twin wing. Possible reasons for this inaccuracy and the superior twin wing response are given.

The Thermal Ion Dynamics Experiment and Plasma Source Instrument

The Thermal Ion Dynamics Experiment (TIDE) and the Plasma Source Instrument (PSI) have been developed in response to the requirements of the ISTP Program for three-dimensional (3D) plasma composition measurements capable of tracking the circulation of low-energy (0–500 eV) plasma through the polar magnetosphere. This plasma is composed of penetrating magnetosheath and escaping ionospheric components. It is in part lost to the downstream solar wind and in part recirculated within the magnetosphere, participating in the formation of the diamagnetic hot plasma sheet and ring current plasma populations. Significant obstacles which have previously made this task impossible include the low density and energy of the outflowing ionospheric plasma plume and the positive spacecraft floating potentials which exclude the lowest-energy plasma from detection on ordinary spacecraft. Based on a unique combination of focusing electrostatic ion optics and time of flight detection and mass analysis, TIDE provides the sensitivity (seven apertures of ∼ 1 cm2 effective area each) and angular resolution (6°×18°) required for this purpose. PSI produces a low energy plasma locally at the POLAR spacecraft that provides the ion current required to balance the photoelectron current, along with a low temperature electron population, regulating the spacecraft potential slightly positive relative to the space plasma. TIDE/PSI will: (a) measure the density and flow fields of the solar and terrestrial plasmas within the high polar cap and magnetospheric lobes; (b) quantify the extent to which ionospheric and solar ions are recirculated within the distant magnetotail neutral sheet or lost to the distant tail and solar wind; (c) investigate the mass-dependent degree energization of these plasmas by measuring their thermodynamic properties; (d) investigate the relative roles of ionosphere and solar wind as sources of plasma to the plasma sheet and ring current.

The Effect of Wind on 100-m Sprint Times

The effect of wind on the race times of international standard 100-m sprinters was determined using statistical information from official competitions. A time adjustment curve derived from mathematical models was fitted to performances by the finalists at the U.S. Olympic Trials and TAC Championships over the last 10 years, and to multiple performances by individual athletes at recent Olympic Games and World Championships. Consistent results were obtained from the two studies. The rate of improvement in. race time gradually decreased with increasing wind velocity, and so the disadvantage of a head wind was greater than the benefit of a tail wind of the same magnitude. The advantage of a 2-m/s following wind was 0.10 ± 0.01 s for the male sprinters and 0.12 ± 0.02 s for the female sprinters. These results indicated that the altitude of Mexico City (2,250 m) provides an advantage of about 0.07 s. Time adjustment versus wind velocity curves are presented that allow comparison of the merit of 100-m sprint times achieved under diverse wind conditions. The curves supersede those derived by previous investigators.