Parts of a Rain Gauge

Weather is a part of our daily lives. People are always trying to predict the weather, to measure it and to see patterns in it. Often of great concern is rain, and even more so, how much rain. To get a measurement of how much rain falls in any given event, a rain gauge is used.

Simple Gauges

A simple rain gauge is nothing more than a tube with one open end pointed up toward the sky. Along the side of the tube are estimated measurement marks for just how much rain should have fallen.

Support

The bottom end of a rain gauge cylinder is often supported on a pole driven into the ground.

Professional Gauges

Professional rain gauges attempt to be more accurate than a simple collection cylinder. The cylinder in a professional rain gauge is supported on an arm that will swivel a certain degree, and there are fins along the bottom of the cylinder.

Purpose

The fins on the side of the cylinder are to catch the wind. The support arm then allows the rain gauge to turn to face the wind, collecting a more accurate count in case the rain isn't falling straight down.

Cost

No matter how complicated a rain gauge is, the more parts it possesses, the more expensive it will be. This is why only meteorologists who are truly concerned with exact rain fall details use the more complicated rain gauges.

How to Read Rain Gauges

A rain gauge is used to measure how much precipitation has fallen. Farmers and gardeners whose crops depend on a certain amount of water to thrive use a rain gauge to calculate how much water to add to the soil with their hoses or irrigation systems. Meteorologists keep track of how much rain has fallen as part of the record of weather statistics for a region. This information helps to predict floods and to determine the severity of a drought. Children often start learning about weather instruments with a rain gauge because it is so easy to use.

Instructions :

1. Insert a rain gauge into the ground or install it on a pole. It is like a measuring cup that fills with precipitation whenever it rains, sleets, or snows.

2. Notice that the sides of the rain gauge are marked like a kitchen measuring cup with little horizontal lines. Usually the gauge holds five inches of liquid. Each inch is marked. Between the inches, other horizontal lines mark half inches and smaller fractions of an inch.

3. Read the rain gauge right after it stops raining before the sun has time to cause any of the liquid to evaporate. Compare the point where the liquid in the rain gauge meets the scale on the side of the container. The number of the mark where the top of the liquid touches the scale tells you how much precipitation fell.

4. Write down the measurement along with the date, time, and type of precipitation. Keep a log of the measurements taken by your rain gauge. See if your measurements match those of the weather professionals. See if you notice are any patterns or record rainfall amounts.

How A Rain Gauge Works

The modern rain gauge most commonly used consists of four components: an outer tube, and inner tube, a funnel and a measuring stick. The outer tube, normally 20 cm in diameter and 50 cm in height, holds the inner tube which is 1/10th the size of the outer tube. A funnel at the top of the outer tube directs water into the smaller tube. As rain falls, it is collected by the funnel and fills the smaller tube. Since the collection area is ten times the size of the storage area, measurements in the inner tube are exaggerated by a factor of ten. One inch of water in the tube equals 1/10 of an inch of rainfall. The gauge can read up to two inches of rain. Excess rain is trapped in the outer tube.

Accuracy of Rain Gauges

The accuracy of a rain gauge is limited. The design of most rain gauges allows them to capture only rain which is falling relatively straight down. In storms, high winds will be driving the rain at sharp angles, sometimes almost in a horizontal pattern. This can prevent the rain gauge from capturing the rain accurately. Spotty summer storms also make accurate rainfall totals difficult. A spot shower can easily dump an inch of rain on the rain gauge while a half mile away or less there was no rain received. Snow and ice can also distort data by blocking the collection tube.

Picture of Rain Gauges

A rain gauge consists of an outer 13cm diameter cylinder and an inner cylinder with a jar. Rain is collected in the jar by means of a funnel which has a tapered end so that rain cannot easily evaporate.

The rain gauge is sited in open space to receive rain from all angles. It must be located away from buildings and trees that may shelter the raindrops. It is sunk into the ground for stability and its rim is 30cm from the ground to prevent water from splashing into it from the ground.

Types of Rain Gauges

Types of rain gauges include graduated cylinders, weighing gauges, tipping bucket gauges, and simple buried pit collectors. Each type has its advantages and disadvantages for collecting rain data.

Standard of rain gauge

The standard rain gauge, developed around the start of the 20th century, consists of a funnel attached to a graduated cylinder that fits into a larger container. If the water overflows from the graduated cylinder the outside container will catch it. When measurements are taken, the cylinder will be measured and then the excess will be put in another cylinder and measured. In most cases the cylinder is marked in mm and in the picture above will measure up to 25 mm (0.98 in) of rainfall. Each horizontal line on the cylinder is 0.2 mm (0.007 in). The larger container collects any rainfall amounts over 25 mm that flows from a small hole near the top of the cylinder. A metal pipe is attached to the container and can be adjusted to ensure the rain gauge is level. This pipe then fits over a metal rod that has been placed in the ground.

Weighing precipitation gauge

A weighing-type precipitation gauge consists of a storage bin, which is weighed to record the mass. Certain models measure the mass using a pen on a rotating drum, or by using a vibrating wire attached to a data logger. The advantages of this type of gauge over tipping buckets are that it does not underestimate intense rain, and it can measure other forms of precipitation, including rain, hail and snow. These gauges are, however, more expensive and require more maintenance than tipping bucket gauges.

The weighing-type recording gauge may also contain a device to measure the quantity of chemicals contained in the location's atmosphere. This is extremely helpful for scientists studying the effects of greenhouse gases released into the atmosphere and their effects on the levels of the acid rain.

Tipping bucket rain gauge

The tipping bucket rain gauge consists of a large copper cylinder set into the ground. At the top of the cylinder is a funnel that collects and channels the precipitation. The precipitation falls onto one of two small buckets or levers which are balanced in same manner as a scale. After an amount of precipitation equal to 0.2 mm (0.007 in) falls, the lever tips and an electrical signal is sent to the recorder. The recorder consists of a pen mounted on an arm attached to a geared wheel that moves once with each signal sent from the collector. When the wheel turns the pen arm moves either up or down leaving a trace on the graph and at the same time making a loud click. Each jump of the arm is sometimes referred to as a 'click' in reference to the noise. The chart is measured in 10 minute periods (vertical lines) and 0.4 mm (0.015 in) (horizontal lines) and rotates once every 24 hours and is powered by a clockwork motor that must be manually wound.

The tipping bucket rain gauge is not as accurate as the standard rain gauge because the rainfall may stop before the lever has tipped. When the next period of rain begins it may take no more than one or two drops to tip the lever. This would then indicate that 0.2 mm (0.007 in) has fallen when in fact only a minute amount has. Tipping buckets also tend to underestimate the amount of rainfall, particularly in snowfall and heavy rainfall events. The advantage of the tipping bucket rain gauge is that the character of the rain (light, medium or heavy) may be easily obtained. Rainfall character is decided by the total amount of rain that has fallen in a set period (usually 1 hour) and by counting the number of 'clicks' in a 10 minute period the observer can decide the character of the rain.Correction algorithms can be applied to the data as an accepted method of correcting the data for high level rainfall intensity amounts.

Modern tipping rain gauges consist of a plastic collector balanced over a pivot. When it tips, it actuates a switch (such as a reed switch) which is then electronically recorded or transmitted to a remote collection station.

Tipping gauges can also incorporate weighing gauges. In these gauges, a strain gauge is fixed to the collection bucket so that the exact rainfall can be read at any moment. Each time the collector tips, the strain gauge (weight sensor) is re-zeroed to null out any drift.

To measure the water equivalent of frozen precipitation, a tipping bucket may be heated to melt any ice and snow that is caught in its funnel. Without a heating mechanism, the funnel often becomes clogged during a frozen precipitation event, and thus no precipitation can be measured. The Automated Surface Observing System (ASOS) uses heated tipping buckets to measure precipitation.

Optical rain gauge

These have a row of collection funnels. In an enclosed space below each is a laser diode and a photo transistor detector. When enough water is collected to make a single drop, it drips from the bottom, falling into the laser beam path. The sensor is set at right angles to the laser so that enough light is scattered to be detected as a sudden flash of light. The flashes from these photo detectors are then read and transmitted or recorded.

History of Rain Gauges

One source has is that the son of King Sejong the Great, who reigned the Choson Dynasty from 1418 to 145, invented the first rain gauge. King Sejong sought ways to improve agricultural technology to provide his subjects with adequate food and clothing.

In improving agricultural technology, Sejong contributed to the sciences of astronomy and meteorology (weather). He invented a calendar for the Korean people and ordered the development of accurate clocks. Droughts plagued the kingdom and King Sejong directed every village to measure the amount of rainfall.

His son, the crown prince, later called King Munjong, invented a rain gauge while measuring rainfall at the palace. Munjong decided that instead of digging into the earth to check rain levels, it would be better to use a standardized container. King Sejong sent a rain gauge to every village, and they were used as an official tool to measure the farmer's potential harvest. Sejong also used these measurements to determine what the farmer's land taxes should be. The rain gauge was invented in the fourth month of 1441. The invention of the rain gauge in Korea came two hundred years before inventor Christopher Wren created a rain gauge (tipping bucket rain gauge circa 1662) in Europe.

Rainmakers

Born in Fort Scott, Kansas, in 1875, Hatfield claimed to have been "a student of meteorology" for 7 years, during which time he discovered that by sending a secret combination of chemicals into the air clouds could be produced in large enough quantities that rain was sure to follow.

On March 15, 1950, New York City hired Dr Wallace E Howell as the city's official "rainmaker".

Rain Gauges

A rain gauge (also known as a udometer or a pluviometer [Pluviograph ] or an ombrometer or a cup) is a type of instrument used by meteorologists and hydrologists to gather and measure the amount of liquid precipitation (solid precipitation is measured by a snow gauge) over a set period of time.