The Evaluation and Use of the Dectra Navigation System

Dectra is a long-range radio navigation system designed to give accurate position fixing coverage over specific areas, and in particular over long trans-oceanic crossings. The position of an aircraft or ship equipped with a Dectra receiver is continuously available in the form of dial indications relating to coordinates of a Dectra lattice, and in addition this information can be presented pictorially on a normal Decca flight log. The system is at present functioning over the North Atlantic, and flight trials have been in progress since May 1957. This paper discusses the experience gained and the results obtained in the trials.

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Air and Sea Tests of the Dectra Radio-navigation System

Journal of Navigation ◽

10.1017/s0373463300031106 ◽

1959 ◽

Vol 12 (3-4) ◽

pp. 289-307

Author(s):

Claud Powell

Keyword(s):

Long Range ◽

North Atlantic ◽

Navigation System ◽

Data Link ◽

Flight Tests ◽

The North ◽

Radio Navigation System ◽

The North Atlantic ◽

North Atlantic Area ◽

Atlantic Area

The object of this paper is to summarize the results of air and sea trials that have been obtained in the first two years' operation of the experimental Dectra chain in the North Atlantic area. Reference is also made to observations at fixed monitor stations, and briefly to the Dectra data link for air-to-ground transmission of the Dectra fix.Dectra, which stands for ‘Decca Track and Range’, is a long-range position-fixing system derived from the Decca Navigator. Early in 1957 two of the three transmitting stations forming a Dectra chain designed to cover the North Atlantic air routes were put into operation and flight tests began in March of that year; in the following October, air trials started using all three transmissions. Various tests at sea have also been carried out, although on a much less extensive scale than those in the air.

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Lagrangian formation pathways of moist anomalies in the trade-wind region during the dry season: two case studies from EUREC<sup>4</sup>A

10.5194/wcd-2021-42 ◽

2021 ◽

Author(s):

Leonie Villiger ◽

Heini Wernli ◽

Maxi Boettcher ◽

Martin Hagen ◽

Franziska Aemisegger

Keyword(s):

Long Range ◽

North Atlantic ◽

Large Scale ◽

Cold Front ◽

Trade Wind ◽

Long Range Transport ◽

The North ◽

Range Transport ◽

The North Atlantic ◽

The Tropics

Abstract. Shallow clouds in the trade-wind region over the North Atlantic contribute substantially to the global radiative budget. In the vicinity of the Caribbean island Barbados, they appear in different mesoscale organisation patterns with distinct net cloud radiative effects (CRE). Cloud formation processes in this region are typically controlled by the prevailing large-scale subsidence. However, occasionally weather systems from remote origin cause significant disturbances. This study investigates the complex cloud-circulation interactions during the field campaign EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) from 16 January to 20 February 2020, using a combination of Eulerian and Lagrangian diagnostics. Based on observations and ERA5 reanalyses, we identify the relevant processes and characterise the formation pathways of two moist anomalies above the Barbados Cloud Observatory (BCO), one in the lower (~1000–650 hPa) and one in the middle troposphere (~650–300 hPa). These moist anomalies are associated with strongly negative CRE values and with contrasting long-range transport processes from the extratropics and the tropics, respectively. The low-level moist anomaly is characterised by an unusually thick cloud layer, high precipitation totals and a strongly negative CRE. Its formation is connected to an “extratropical dry intrusion” (EDI) that interacts with a trailing cold front. A quasi-climatological (2010–2020) analysis reveals that EDIs lead to different conditions at the BCO depending on how they interact with the associated cold front. Based on this climatology, we discuss the relevance of the strong large-scale forcing by EDIs for the low-cloud patterns near the BCO and the related CRE. The second case study about the mid-tropospheric moist anomaly is associated with an extended and persistent mixed-phase shelf cloud and the lowest daily CRE value observed during the campaign. Its formation is linked to “tropical mid-level detrainment” (TMD), which refers to detrainment from tropical deep convection near the melting layer. The quasi-climatological analysis shows that TMDs consistently lead to mid-tropospheric moist anomalies over the BCO and that the detrainment height controls the magnitude of the anomaly. However, no systematic relationship was found between the amplitude of this mid-tropospheric moist anomaly and the CRE at the BCO. Overall, this study reveals the important impact of the long-range transport, driven by dynamical processes either in the extratropics or the tropics, on the variability of the vertical structure of moisture and clouds, and on the resulting CRE in the North Atlantic winter trades.

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Navigational Aspects of Turboprop Operation on the North Atlantic

Journal of Navigation ◽

10.1017/s0373463300016325 ◽

1957 ◽

Vol 10 (1) ◽

pp. 31-49

Author(s):

J. E. D. Williams

Keyword(s):

Sixteenth Century ◽

Long Range ◽

North Atlantic ◽

Fuel Load ◽

The North ◽

The Status ◽

The North Atlantic ◽

Aircraft Type

If navigation were confined to the function of keeping a craft on a desired track, and estimating its progress periodically, then a long-range turboprop would present no features of navigational interest. Navigation, however, is supposed to encompass a wider field than this. In a famous sixteenth-century definition, ‘Navigation demonstrateth how, by the shortest good way, by the aptest direction, and in the shortest time, a sufficient ship between any two places may be conducted’. The economic realities of modern airliner operation give a new emphasis to those phrases ‘By the shortest good way, by the aptest direction, and in the shortest time’. A Britannia 310, for example, which will be the first, probably the cheapest, and possibly the smallest, long-range turbineengined airliner, costs about £1 million and is capable of producing a gross revenue of £1000 per hour. The sum of payload and fuel load is limited in most long-range cases by maximum take-off weight, and the fuel for one hour of flight is equivalent in weight to about 2 5 passengers and their baggage. It is not surprising in the circumstances that quite minor refinements of navigational technique are worth tens of thousands of pounds per aircraft per year, while major improvements can alter the status of an aircraft type as an instrument of transport. Such aircraft should be considered as acutely sensitive instruments to be operated precisely according to scientifically designed techniques.

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