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Fifty years ago ....
WMO Bulletin 6 (2), April 1957
Apart from arid zone climatology, as mentioned above, other subjects covered by the April Bulletin 50 years ago were meteorological aspects of atomic energy, a progress report on observations made during the trial period of the International Geophysical Year 1957-58, climatic atlases, the Technical Assistance Programme and automatic weather stations, as well as reports of the International Geographical Congress and the second sessions of Regional Association I (Africa) and the Commission for Climatology.
An abridged selection of some of these articles is given below. Others were included in the April 2007 edition of MeteoWorld.
… The Executive Committee Working Group on Climatic Atlases met in Centerton, New Jersey (USA) from 7 to 12 January 1957 to consider comments made by Members on its first report, which contained draft specifications for climatic atlases. …
Revision of specifications
Considerable diversity of opinion had been expressed by Members about the group’s original proposal that the world climatic atlas should be divided into two main sections, namely a dynamic and a physical atlas. It was decided by the group that a more logical division would be into three sections, dealing respectively with land areas (surface elements), sea areas (surface elements) and the free atmosphere. For the moment attention is being concentrated on the maps of surface elements over land areas, for which the group completed the revised specifications.
The most important change adopted by the group in its second report is the addition of a number of maps to meet the needs expressed by Members. These include maps of the frequency of clear and cloudy days, the mean daily maximum temperature, the mean maximum temperature, the mean maximum depth of snow cover and the number of days with precipitation exceeding 1 and 10 mm. Maps no longer included in the list are those of soil conductivity (considered to be impracticable) and of freezing rain (felt to be a local phenomenon primarily of operational interest). The group adhered to its original view that the world climatic atlas project should deal only with basic climatic elements and not with operational factors.
United States automatic weather stations
Evidence of the interest in automatic stations as a means of improving observational networks was also shown by the discussion on this subject at the recent sessions of Regional Association I (Africa) and the Commission for Climatology. This article gives news of two types of automatic weather stations, both of which have been designed and constructed in the United States.
The US Weather Bureau has given details of its newest automatic weather station. This is known as the automatic teletypewriter weather observer and in addition to measuring meteorological conditions it is also capable of converting them to teletypewriter code and transmitting them over the national circuits without being handled by human observers or communicators. The meteorological elements which this apparatus measures at present are visibility, temperature, dew point, wind speed and direction, pressure and precipitation. It is hoped that further development will enable cloud height measurements and the type of weather to be included in the automatic report. Four of these stations are already in operation and a further fifteen are to be set up in the near future.
The automatic teletypewriter weather observer was developed from a system … to transmit meteorological information by Morse-code letters. In this system, commutator-type segments are fitted around the periphery of standard direct-reading instruments. A pointer serves the dual purpose of contacting arm and visual reading pointer. A solenoid beneath the dial pulls the pointer firmly against the commutator plate for 163 ms for each figure transmitted from the indicator. Each of the segments of the commutator is connected to a code-sending mechanism and different Morse letters are transmitted as the meteorological vales change. To use this system with the teletypewriter, an ingenious network of relays and diodes, called a coder has been designed. This unit converts the electrical circuits establishes the commutator segments to teletypewriter code. When the appropriate combination of characters is transmitted by a central station, the Secondary Sequential Control Apparatus responds and triggers the indicators to send meteorological data directly to the printers of dozens of stations simultaneously.
Most of the instruments used to measure the meteorological factors are standard instruments which have been modified or adapted for this special purpose. Precipitation measurements are obtained from a heated tipping-bucket raingauge which counts precipitation amounts on a stepped relay. Cumulative amounts are recorded for periods of six hours, the relay returning to zero at the end of each period. Temperature is indicated on a precision six-inch dial instrument using a mercury-filled flexible tubing with a sensing bulb housed in a standard screen. A dew-cell in a small metal hood on the screen gives the dew point.
Transmissometer measurements are used to determine visibility whilst a standard contacting anemometer provides wind speed and direction. A one-minute sample is taken just prior to each transmission and new readings are taken subsequently every 12 minutes in case the automatic observer is required to furnish a report between the usual hourly observations.
Another feature of this automatic system is its ability to preserve a record of the information transmitted by making a punched tape of each observation. These tapes can be placed on standard punch cards at the records centre so that the information is then available for research, statistical studies and climatological purposes.
The National Bureau of Standards has announced the development of a marine weather station which can be anchored in remote locations and left unattended for six months. Incorporated in a buoy, the station broadcasts the air temperature, sea temperature, pressure and wind speed and direction code at regular intervals throughout the day. At present this equipment is only in the experimental stage but preliminary trials show that it has a radio range in excess of 80 miles.
The automatic station translates weather information into three-letter code groups and transmits the signals on a pulse-modulated 6 Mc/s carrier frequency. These signals can be received on standard communications receivers and evaluated from a decoding table. A single transmission takes three minutes.
The vessel is constructed of aluminium and other non-magnetic alloys and can be anchored in water up to a depth of 1 100 metres, two masts and four watertight wells hold all the electronic and meteorological equipment in shockproof mountings.
Air and sea temperature are measured by simple thermistors and a precision barometer measures pressure. The barometer is modified so that a slave needle rides above a resistance strip and is clamped to the strip at the time of measurement. An especially robust three-cup anemometer drives a small magnetic generator whose output is applied to the grid of a vacuum tube. The wind vane is connected to a selsyn transmitter and receiver circuit activating a servo which positions a magnetic compass synchronously with the vane. Variations of meteorological conditions are converted into variations of resistance by a motor-driven self-balancing bridge circuit.
The power is supplied by dry cells and a rotary converter which changes the low voltage to 120V at 60c/s for the electronic components. In future models of the station a petrol-driven generator and storage battery will replace the dry battery supply.
A chronometer which is automatically rewound during the operational periods of the station provides reliable master control and a programme timer ensures that the identification signal is followed by the correct sequence of meteorological measurements The sending speed may be controlled so that even inexperienced operators have sufficient time to identify the signal. At the conclusion of the transmission period, the master control breaks the contact supplying power to the equipment until the next operational period.
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