Topic
Winds aloft
About: Winds aloft is a research topic. Over the lifetime, 275 publications have been published within this topic receiving 7405 citations.
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TL;DR: In this article, a numerical simulation study of the thermospheric winds produced by auroral heating during magnetic storms, and of their global dynamo effects, establishes the main features of the ionospheric disturbance dynamo.
Abstract: A numerical simulation study of the thermospheric winds produced by auroral heating during magnetic storms, and of their global dynamo effects, establishes the main features of the ionospheric disturbance dynamo. Driven by auroral heating, a Hadley cell is created with equatorward winds blowing above about 120 km at mid-latitudes. The transport of angular momentum by these winds produces a subrotation of the mid-latitude thermosphere or westward motion with respect to the earth. The westward winds in turn drive equatorward Pedersen currents which accumulate charge toward the equator, resulting in the generation of a poleward electric field, a westward E × B drift, and an eastward current. When realistic local time conductivity variations are simulated, the eastward mid-latitude current is found to close partly via lower latitudes, resulting in an ‘anti-Sq’ type of current vortex. Both electric field and current at low latitudes thus vary in opposition to their normal quiet-day behavior. This total pattern of disturbance winds, electric fields, and currents is superimposed upon the background quiet-day pattern. When the neutral winds are artificially confined on the nightside, the basic pattern of predominantly westward E × B plasma drifts still prevails on the nightside but no longer extends into the dayside. Considerable observational evidence exists, suggesting that the ionospheric disturbance dynamo has an appreciable influence on storm-time ionospheric electric fields at middle and low latitudes.
1,049 citations
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TL;DR: In this paper, a review brings together numerous theoretical and empirical studies investigating the flight behaviour of migratory birds in relation to the wind, concluding that birds select for favorable wind conditions both at departure and aloft to save energy and that for some long-distance migrants a tail-wind is an indispensable support to cover large barriers.
Abstract: Migration is a task that implies a route, a goal and a period of time To achieve this task, it requires orientation abilities to find the goal and energy to cover the distance Completing such a journey by flying through a moving airspace makes this relatively simple task rather complex On the one hand birds have to avoid wind drift or have to compensate for displacements to reach the expected goal On the other hand flight costs make up a large proportion of energy expenditure during migration and, consequently, have a decisive impact on the refuelling requirements and the time needed for migration As wind speeds are of the same order of magnitude as birds’ air speeds, flight costs can easily be doubled or, conversely, halved by wind effects Many studies have investigated how birds should or actually do react to winds aloft, how they avoid additional costs or how they profit from the winds for their journeys This review brings together numerous theoretical and empirical studies investigating the flight behaviour of migratory birds in relation to the wind The results of these studies corroborate that birds select for favourable wind conditions both at departure and aloft to save energy and that for some long-distance migrants a tail-wind is an indispensable support to cover large barriers Compensation of lateral wind drift seems to vary between age classes, depending on their orientation capacities, and probably between species or populations, due to the variety of winds they face en route In addition, it is discussed how birds might measure winds aloft, and how flight behaviour with respect to wind shall be tested with field data
373 citations
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TL;DR: The authors measured wind velocities in an urban street canyon with a height-to-width ratio of about 1.4 were made when ambient winds aloft were approximately perpendicular to the street.
234 citations
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TL;DR: In this paper, the retarding potential analyzer onboard the Earth Explorer-E (AE-E) satellite was used to measure ion number density at high and low altitude using the rms deviation ΔN/N over a path length of 18 km as an indicator of overall irregularity intensity.
Abstract: We analyzed measurements of ion number density made by the retarding potential analyzer aboard the Atmosphere Explorer-E (AE-E) satellite, which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km. Large-scale (>60 km) density measurements in the high-altitude regions show large depletions of bubble-like structures which are confined to narrow local time, longitude, and magnetic latitude ranges, while those in the low-altitude regions show relatively small depletions which are broadly distributed in space. For this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation ΔN/N over a path length of 18 km as an indicator of overall irregularity intensity. Seasonal variations of irregularity occurrence probability are significant in the Pacific regions, while the occurrence probability is always high in the Atlantic-African regions and is always low in the Indian regions. We find that the high occurrence probability in the Pacific regions is associated with isolated bubble structures, while that near 0° longitude is produced by large depletions with bubble structures which are superimposed on a large-scale wave-like background. Considerations of longitude variations due to seeding mechanisms and due to F region winds and drifts are necessary to adequately explain the observations at low and high altitudes. Seeding effects are most obvious near 0° longitude, while the most easily observed effect of the F region is the suppression of irregularity growth by interhemispheric neutral winds.
198 citations
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TL;DR: In this article, an objective technique for forecasting clear-air turbulence (CAT) is described, which is calculated based on the product of horizontal deformation and vertical wind shear derived from numerical model forecast winds aloft.
Abstract: An objective technique for forecasting clear-air turbulence (CAT) is described. An index is calculated based on the product of horizontal deformation and vertical wind shear derived from numerical model forecast winds aloft. The forecast technique has been evaluated and is now in operational use at two forecast centers with international aviation responsibilities: the National Meteorological Center (NMC) in Washington, D.C., and the Air Force Global Weather Central (AFGWC) in Omaha, Nebraska. The index is also an operational forecast tool at the Canadian Atmospheric Environment Service (AES), and the National Aviation Weather Advisory Unit (NAWAU) in Kansas City, Missouri, both responsible for domestic aviation forecasts. The AFGWC index also includes horizontal convergence in its calculation. Thresholds were selected empirically by comparing index values with the location and intensity of observed CAT. Verification indicates that the index is quite reliable. The probability of detection (POD) va...
184 citations