Ambient Weather WS-091-C Guía de usuario descargar pdf (Pagina 100)

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101

Virtual Weather Station User's Guide

-100- 03/07/06

Term Definition

sun just disappears below the sea level horizon. In Great Britain, the center of the sun's

disk is used instead. Time of sunset is calculated for mean sea level. See sunrise for

comparison.

VAPOR PRESSURE The pressure exerted by water vapor molecules in a given volume of air

VIRTUAL TEMPERATURE Virtual temperature is a fictitious temperature that takes into account moisture in the air.

The formal definition of virtual temperature is the temperature that dry air would have if

its pressure and specific volume were equal to those of a given sample of moist air. Virtual

temperature allows meteorologists to use the equation of state for dry air even though

moisture is present.

WIND CHILL INDEX

The calculation of temperature that takes into consideration the effects of wind and

temperature on the human body. Describes the average loss of body heat and how the

temperature feels. This is not the actual air temperature.

WIND DIRECTION The direction from which the wind is blowing. For example, an easterly wind is blowing

from the east, not toward the east. It is reported with reference to true north, or 360

degrees on the compass, and expressed to the nearest 10 degrees, or to one of the 16 points

of the compass (N, NE, etc.).

WIND RUN The distance or length of flow of the air past a point during a given interval of time.

WIND SPEED The rate of the motion of the air on a unit of time. It can be measured in a number of ways.

In observing, it is measured in knots, or nautical miles per hour. The unit most often used

in the United States is miles per hour.

Table 19 - Glossary of Terms

11.1 Beaufort Scale

The Beaufort scale is a system of recording wind velocity (speed) devised in 1806 by Francis Beaufort (1774–1857). It is a

numerical scale ranging from 0 for calm to 12 for a hurricane.

Air speed

Number and

description

Features

kph mph

0 calm smoke rises vertically; water smooth 0–2 0–1

1 light air smoke shows wind direction; water ruffled 2–5 1–3

2 light breeze leaves rustle; wind felt on face 6–11 4–7

3 gentle breeze loose paper blows around 12–19 8–12

4 moderate

breeze

branches sway 20–29 13–18

5 fresh breeze small trees sway, leaves blown off 30–39 19–24

6 strong

breeze

whistling in telephone wires; sea spray from waves 40–50 25–31

7 near gale large trees sway 51–61 32–38

8 gale twigs break from trees 62–74 39–46

1 2 ... 95 96 97 98 99 100 101

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