Satellite Observations

The wide separation of weather stations where clouds are observed, and their relative absence at sea (apart from ship observers), have been major problems, especially in the southern hemisphere where 81 per cent of the area is ocean. Fortunately, total coverage of the world is now provided by satellite observations, developed since the 1960s, notably from satellites described as geostationary (Note 8J). These rotate above the equator at the same rate as the Earth, so they appear fixed. Currently there are five of them for meteorological observations, at longitudes 135°W, 75°W, zero, 60°E and 140°E, respectively. Pictures are taken each half-hour (Figure 8.12), recording differences over distances down to about 2.5 km—that distance is the resolution of the technique. Both visible radiation (0.5 pm) and infra-red (10 pm) pictures are taken. The former show clouds as particularly bright, and the latter detect longwave radiation from the Earth, i.e. the pattern of temperatures of the surfaces seen from space, notably cloud-top temperatures (Note 2.C). As a result, examinaton of the features of cloud pictures (or nephanalysis) yields the following information:

(a) the shape and size of cloudy areas;

(b) the spatial organisation of clouds (e.g. cloud streets or cell structures);

(c) cloud height, indicated partly by the shadows cast by high clouds and partly by the cloud-top temperature;

Parts Campbell Stokes Recorder

Figure 8.10 A Campbell—Stokes recorder of the duration of a day's bright sunshine. The glass sphere has a diameter of about 100 mm and focuses sunlight onto a card. The focused light is intense enough to burn a hole in the card when there is no cloud in front of the Sun. The Sun moves across the sky, so the point of focus moves along the card, and the length of the resulting burnt slot shows the duration of bright sunshine.

Figure 8.10 A Campbell—Stokes recorder of the duration of a day's bright sunshine. The glass sphere has a diameter of about 100 mm and focuses sunlight onto a card. The focused light is intense enough to burn a hole in the card when there is no cloud in front of the Sun. The Sun moves across the sky, so the point of focus moves along the card, and the length of the resulting burnt slot shows the duration of bright sunshine.

(d) the cloud type from albedo and cloud-top temperature information (Figure 8.13);

(e) the movement and evolution of clouds from pictures at 30-minute intervals.

Changes of the position of identifiable clouds show wind speeds at cloud height.

Meteorologists have also used a succession of orbiting satellites, which pass over the Poles and encircle the Earth fourteen times a day at a slightly different longitude each time on account of the Earth's rotation. The first such satellite, TIROS 1 (i.e. Television and Infra-Red Observing Satellite), went into orbit in 1960. Orbiting satellites have a finer resolution than geostationary satellites (typically 1 km, but sometimes 30 m), because they pass only 850 km above the ground. They also measure radiation in several parts of the electromagnetic spectrum (Figure 2.1), e.g. at wavelengths between visible (0.5 pm) and infra-red (10 [pm), and in the microwave or radar region (with wavelengths of about 1 cm). These measurements together reveal more details about clouds, such as cloud density, liquid-water content, whether liquid or frozen, cloud-top texture (i.e. smoothness) and even precipitation.

Cyclonic vortex

Cumuliform

Anticyclonic centre

A

Strato-cumuliform

Comma-shaped cloud mass

»

Stratiform

Wave clouds

Cirriform

Cloud line

Cirrus

Striations

<-

Cirrocumulus

Direction of cirrus streakiness

=>

Altostratus

Estimated jet location

*

Stratocumulus

Bright cloud mass

+

Cumulus

Mist

Cirrostratus

Shallow fog

ZJZ

Altocumulus

Ground fog

==

Stratus

Fog

=

Nimbostratus

Cumulonimbus

Figure 8.11 Symbols representing various kinds of clouds or cloud patterns, as identified from surface and satellite observations.

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Figure 8.11 Symbols representing various kinds of clouds or cloud patterns, as identified from surface and satellite observations.

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Responses

  • maya
    What is a campbell stokes recorder?
    8 years ago
  • guarino
    How to make a campbell stokes recorder?
    8 years ago
  • daniela
    How sunshine recorder works?
    8 years ago
  • amelia
    How to draw a sunshine recorder?
    3 years ago
  • Donald
    How to draw campbell sunshine recorder?
    2 years ago
  • ANDREA
    How to draw a campbell stroke sunshine recorder?
    2 years ago
  • Akseli
    How to draw a campbell strokes?
    2 years ago

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