In computing, the process, usually automatic, of capturing and recording a sequence of values for later processing and analysis by computer. For example, the level in a water-storage tank might be automatically logged every hour over a seven-day period, so that a computer could produce an analysis of water use.
Weather logging Observations can be collected not only from land stations, but also from weather ships, aircraft, and self-recording and automatic transmitting stations, such as the radiosonde. Radar may be used to map clouds and storms. Satellites have played an important role in televising pictures of global cloud distribution.
As well as supplying reports for the media, the Meteorological Office in Bracknell, near London, does specialist work for industry, agriculture, and transport. Kew is the main meteorological observatory in the British Isles, but other observatories are at Eskdalemuir in the southern uplands of Scotland, Lerwick in the Shetlands, and Valentia in SW Ireland. Climatic information from British climatological reporting stations is published in the Monthly Weather Report, and periodically in tables of averages and frequencies.
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The British Meteorological Office's Daily Weather Report contains a detailed map of the weather over the British Isles and a less detailed map of the weather over the northern hemisphere, and the Daily Aerological Record contains full reports of radiosonde ascents made over the British Isles and from some of the ocean weather ships, together with maps of the heights of the 700 mb, 500 mb, and 300 mb pressure surfaces, giving a picture of the winds at 3,048 m/10,000 ft, 5,182 m/18,000 ft, and 9,144 m/30,000 ft; there is also a map of the height of the tropopause. Ships' reports are plotted on the same charts using the same symbolic form. Data from radiosondes and aircraft are plotted on upper-air charts and on temperature–height diagrams, the diagram in use in Britain being the tephigram. With the help of this diagram it is possible to predict the formation or otherwise of clouds, showers, or thunderstorms, and sometimes to identify the source region of the air mass.
Observation stations may be classified as follows:
Observatories where reliable standard and absolute measurements are made as far as possible with autographic instruments, which are often duplicated for checking and research purposes. Elements such as atmospheric electricity and solar radiation are measured only at observatories and other research establishments.
Climatological reporting stations report the general daily weather conditions and make observations at standard hours during the day to provide cumulative data, such as average temperature, maximum and minimum temperatures, rainfall, sunshine, mean pressure, days of fog, frost, snowfall, and the extent and persistence of snow cover. After statistical analysis, climatic charts and tables are constructed showing the frequency of the different weather elements, such as gales and frost.
Crop weather stations make observations for use in agricultural meteorology, or micrometeorology, where the elements of the weather need to be studied in detail. It is necessary to have detailed information on temperature, humidity, and wind at heights below the average crop height in order to study and control plant diseases spread by aphids or wind-borne viruses. Details of frost hollows, wind breaks, and the degree of frost which will damage plants must all be studied.
Rainfall stations measure the amount of rain that falls. Most stations measure the daily amount, while those in remote areas measure the monthly rainfall.
Synoptic reporting stations, where observations are made simultaneously throughout the world, report in a mutually agreed form so that data can be directly compared between them. Observations are restricted to the elements required for forecasting. Reports are received at a national centre and a selection is broadcast for use by other countries.
The huge mass of synoptic data collected and disseminated for forecasting purposes is plotted on synoptic weather charts. Modified copies of these charts using standard symbols are published daily by most meteorological services.
Measuring and describing conditions meteorological observations, for whatever purpose, must be clear, precise, and strictly comparable between stations. It is easy to decide whether it is fine or cloudy, or if there is a thunderstorm; the distinctions between rain, snow, and hail are obvious; sleet is wet snow, melting snow, or a mixture of rain and snow; soft hail is halfway between snow and hail; and drizzle, which consists of very small drops, is halfway between rain and cloud, the water drops being just large enough to fall to the ground. It is useful also to describe rain as showery, intermittent, or continuous, as light, moderate, or heavy. The rate of rainfall and the total rainfall during a given period can be measured with a rain gauge. Wind strength and direction can be measured accurately by anemometers and wind vanes. Clouds are observed carefully, since they are closely related to other weather conditions. Fog and other hindrances to visibility indicate approaching weather conditions as well as being of great practical importance.