Measurement of Rain, Wind, Humidity, Evaporation, Temperature, Atmosphere Pressure
Table of Contents
METEOROLOGY:
Meteorology, the study of the earth’s atmosphere and especially the study of weather. A Meteorologist is a person who studies the atmosphere. Meteorology is divided into a number of specialized sciences. Physical meteorology deals with the physical aspects of the atmosphere, such as the formation of clouds, rain, thunderstorms, and lightning. Physical meteorology also includes the study of visual events such as mirages, rainbows, and halos. The study of the winds and the laws that govern atmospheric motion is called dynamic meteorology. Synoptic meteorology is the study and analysis of large weather systems that exist for more than one day. Weather forecasting is part of synoptic meteorology. Agricultural meteorology deals with weather and its relationship to crops and vegetation. The study of atmospheric conditions over an area smaller than 1 sq km (0.4 sq mi) is called micrometeorology. Climate describes the average weather of a region. Climatology, a division of meteorology, is the study of a region’s average daily and seasonal weather events over a long period.
MEASUREMENT OF RAIN:
Hydrologists use an instrument called an automatic recording rain gauge to measure precipitation. The instrument weighs and charts rainwater as it falls, keeping a record on a paper strip. The record shows the time, duration, and intensity of rainstorms. Hydrologists may also use nonrecording gauges, clear tubes with markings in millimeters or inches on them. Light, intermittent snowfall is measured by the same instruments as rainfall. In areas where snow often accumulates to great depths, gauges in the form of collecting tanks store the snow, sometimes over a whole season. To measure the depth of liquid water to which the snowfall is equal, the snow is mixed with a salt brine to melt it as it enters the gauge. Snowfall is also measured with a snow tube, which is inserted into an accumulation of fallen snow to get a sample that is weighed to determine the depth of water equivalent.
Precipitation is any form of water (either liquid or solid) that falls from the atmosphere and reaches the ground, such as rain, snow, or hail. Rain gauges are instruments that measure rainfall. The standard rain gauge consists of a funnel-shaped collector that is attached to a long measuring tube.
MEASUREMENT OF WIND:
Anemometer (Greek anemos, “wind”; metron, “measure”), an instrument that measures wind speed. The most common kind of anemometer consists of three or four cups attached to short rods that are connected at right angles to a vertical shaft. As the wind blows, it pushes the cups, which turn the shaft. The number of turns per minute is translated into wind speed by a system of gears similar to the speedometer of an automobile. Wind velocity is also measured by the pressure of the air blowing into a Pitot tube (an L-shaped tube, one end open toward the flow of air and the other end connected to a pressure-measuring device), and electrically by the cooling effect of the wind on a heated wire, which causes the electric resistance of the wire to change.
MEASUREMENT OF HUMIDITY:
Humidity refers to the air’s water vapor content. Hygrometers are instruments that measure humidity. The maximum amount of water vapor that the air can hold depends on the air temperature; the warm air is capable of holding more water vapor than cold air. Relative humidity is the ratio of the amount of water vapor in the air compared to the maximum amount of water vapor that the air could hold at that particular temperature. When the air is holding all of the moisture possible at a particular temperature, the air is said to be saturated. Relative humidity and dew-point temperature (the temperature to which air would have to be cooled for saturation to occur) are often obtained with a device called a psychrometer. The most common type of psychrometer is a sling psychrometer. This instrument consists of two thermometers mounted side by side and attached to a handle that allows the thermometers to be whirled. A cloth wick covers one thermometer bulb. The wick-covered thermometer bulb (called the wet bulb) is dipped in water, while the other thermometer bulb (the dry bulb) is kept dry. Whirling both thermometers allows water to evaporate from the wick, which cools the wet bulb. By looking up the dry and wet bulb temperatures in a set of tables, known as humidity tables, it is possible to find the corresponding relative humidity and dew-point temperature.
MEASUREMENT OF EVAPORATION:
Conversion of water from liquid to vapor is an important step in the never-ending hydrologic cycle. This process, called evaporation, occurs almost continuously from all water surfaces and moist soil. It is even done by plants, which absorb water from the soil and, in a process known as transpiration, give off water vapor through their leaves. Hydrologists usually measure evaporation by indirect means. They maintain records of evaporation from special pans of a specified size that are exposed to the elements. The data so obtained must be adjusted for each individual case to estimate the evaporation from a particular surface.
MEASUREMENT OF TEMPERATURE:
A Thermometer is an instrument that is used to measure the temperature. In a thermometer, an expanding fluid such as alcohol or mercury is trapped within a closed glass rod. As the fluid expands or contracts, it is measured by marks calibrated for given temperatures. The scale may be marked for either the Celsius or Fahrenheit temperature scales or both.
MEASUREMENT OF ATMOSPHERIC PRESSURE:
A mercury barometer is an accurate and relatively simple way to measure changes in atmospheric pressure. At sea level, the weight of the atmosphere forces mercury 760 mm (29.9 in) up a calibrated glass tube. Higher elevations yield lower readings because the atmosphere is less dense there, and the thinner air exerts less pressure on the mercury.
Broadcasters use data from meteorological satellites to predict weather and to broadcast storm warnings when necessary. Satellites such as the Geostationary Operational Environmental Satellite (GOES) collect meteorological and infrared information about the atmosphere and the ocean. A camera on the GOES is continuously pointed at Earth, broadcasting satellite images of cloud patterns both day and night. Here, the GOES-C satellite is being encapsulated inside its payload fairing aboard a Delta rocket.
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