What is the unit measurement of wind

Weather elements and their measurement


As Weather elements one describes the natural influences such as precipitation, wind or air pressure, which together make up the weather. In order to understand and predict the weather, the weather elements are viewed and measured individually.

On the basis of all this measurement data, one can describe the weather situation at a specific point in time at a specific location.

Some important weather elements are presented here. It also explains how to measure them.

Make a table like the one below. Make a note of the weather element, the units of measurement used for the measurement and the name (s) of the measuring devices used.

Weather elementUnits)Measuring device
Air temperatureDegree Celsius (° C), Kelvin (K), Degree Fahrenheit (° F)Liquid thermometers, bimetal thermometers

Air temperature

Temperature is what I use adjectives like “warm”, “cold”, “hot” etc. to describe. The temperature of the air is essentially influenced by the radiation from the sun. But the rays of the sun mainly warm indirectly: they permeate the atmosphere and warm up the land and the sea. Land and sea then heat the air of the atmosphere from below.

That is, on the way from the sun to the earth the sun's rays only slightly warm the air. The rays of the warmed earth (they are called infrared rays, they are not visible to our eyes) warm up on the way from the earth to the outside the atmosphere strong.

This interplay of “incoming rays” from the sun and “outgoing rays” from the earth is called the Radiation balance of the earth.

The temperature of the air is highest on the ground and decreases with increasing altitude. On the one hand, this is due to the fact that the atmosphere is heated “from below” (by the surface of the sea and the earth). On the other hand, the air pressure decreases towards the top - and lower air pressure also results in lower temperatures. (In higher atmospheric layers it becomes warmer again in some cases.)

Measurement of temperature

Liquid thermometer commonly used in the household. In the housing there is a glass tube in which a colored liquid can rise.

You measure the temperature with one thermometer in degrees Celsius (° C, e.g. "20 ° C") or Kelvin (spoken without "degrees", e.g. "293 K"); in the USA also in degrees Fahrenheit (° F).

Most of the thermometers used in everyday life are so-called Liquid thermometer. They contain a liquid that expands when heated and then rises up a riser pipe. When the ambient air cools down, the liquid contracts again and falls in the riser pipe. If you attach a scale to the riser pipe, you can store the respective temperature at the level of the liquid.

A typical thermometer fluid is mercury. But since it is a very poisonous metal, alcohol is mostly used today for the thermometers that we use in everyday life.

Measuring principle of a bimetal thermometer. The metal shown in dark green on the left expands more strongly when the temperature changes than the metal shown in light green on the right. As a result, the bimetal strip bends when the temperature changes

Another measuring principle also uses the expansion of substances when the temperature changes. So-called Bimetal thermometer consist of two plates made of different metals ("bimetal" means "made of two metals"). These metals expand to different degrees when heated or cooled. But they are firmly connected to one another in the thermometer. This creates tension in the metal plate when the temperature changes, so that it bends easily. The greater the heating or cooling, the greater the bending. With a pointer or a similar device, the extent of the bend can be made visible and displayed on a scale.

Air pressure

The air pressure is created by the weight of the air, which presses on the earth's surface due to gravity.

The air pressure has a great influence on the weather, e.g. because pressure differences in the atmosphere lead to equalizing currents (we call this "wind") and because large pressure structures with lower or higher pressure than in the surrounding area (low and high pressure areas) cause certain weather phenomena.

Measurement

The air pressure is with a barometer measured. Commonly used types of barometers are the can barometer and the liquid barometer. The common one Unit of measure for air pressure is Hectopascals (hPa) (the unit bar (bar) was also used in the past).

An older unit of measurement is the "millimeter of mercury column" (mmHg) - this unit of measurement is based on the first developed barometer, which was a liquid barometer with mercury as the rising liquid and the height of which was given in millimeters (see below).

The normal pressure at sea level is 1013 hectopascals (hPa). Since the air pressure is the weight of the air that acts on a certain area, the unit of measurement can be derived from the physical definition for "pressure": in physics, pressure = force per area (p = K / f). Due to the mass of the entire atmosphere, a weight of approx. 100,000 Newtons is applied to one square meter of the earth. 100,000 Newtons per square meter corresponds to 1,000 hPa. (These numbers are slightly rounded. If you use the exact values, you get the above pressure of 1013 hPa.)

Can barometer

Functional principle of a can barometer

The functional principle of can barometers is based on the fact that a hollow can (mostly made of metal) is deformed by air pressure. The deformation can be read on a scale using a display mechanism that is attached to the can.

There is negative pressure in the can, but no vacuum. This residual air in the can is used to compensate for the influence of the temperature on the air pressure. The air pressure in a closed container increases as the temperature of the air inside it increases. In principle, this also applies to the atmosphere, even if there are other influences here.

Liquid barometer

Functional principle of a liquid batometer

With a liquid barometer, the air pressure acts on a certain amount of liquid, which rises or falls in a riser pipe and thus indicates the air pressure.

barograph

Barographs are used when you want to record the change in air pressure over a longer period of time. A barograph is often a can barometer with a pen attached to its pointer that writes on a rotating roll of paper (see fig.)

wind

Wind is a movement of air with a certain direction. Wind usually arises from the fact that the air pressure in two areas is different, that is, that there is higher air pressure (high pressure area) in one area than in another area (low pressure area).

Measurement of wind speed

Anemometer, a device for measuring wind speed

The Wind speed, i.e. the speed at which the air particles move, can be different. It depends, among other things, on how great the pressure difference is between the two pressure areas. A large pressure difference leads to strong wind (that is, rapid air movement), a small pressure difference leads to weak wind (slower air movement).

You can specify the wind speed in kilometers per hour (km / h) or meters per second (m / s). Another measuring system is the so-called Beaufort scale for wind strengths. It is based on the observation of everyday objects such as trees and how strongly they are moved by the wind. A measure for the wind speed is then derived from these observations.

The wind speed is measured with an anemometer. A typical anemometer consists of an axle and a rotatably suspended rotor. Hemispheres are usually attached to the rotor, which "catch" the wind, which sets the rotor in motion. The speed of rotation of the rotor is measured; it roughly corresponds to the wind speed.

Measurement of the wind direction

The Wind direction is also an important property of the wind. Here you indicate the direction of the compass, from which the wind comes. So a north wind blows from north to south. A south-east wind blows from south-east to north-west.

The wind direction can be measured with a wind vane, for example.

humidity

The air always contains water vapor (that is, gaseous water). Water vapor is invisible and Not the same as the "steam" over the hot saucepan. What we call “steam” in everyday life are tiny droplets of liquid water that are light enough to be carried upwards in the air flow. When we speak of water vapor in meteorology, we mean gaseous water that we Not can see.

The amount of water vapor in the air varies. Sometimes the air is more humid (that is, it contains more water vapor), sometimes it is drier. At any temperature, the air can contain a certain maximum amount of water vapor.

If this maximum amount is exceeded, part of the water vapor becomes liquid and clouds (high in the atmosphere) or fog (on the ground) form. These consist of tiny droplets of liquid Water.

Measurement

The humidity is not easy to measure because it depends on various influences. There is therefore different descriptions of the humidity and different measurement methods ..

Absolute humidity and specific humidity

In connection with air humidity, we can first ask how much water vapor there is in the air and state the amount in grams of water vapor per cubic meter of air (g / m³). This value is the absolute humidity.

Absolute humidity (g / m³): Water vapor content in the air measured in grams of water vapor per cubic meter of air.

The problem here is that we have to reduce the amount of water vapor to one Air volume specify related. However, the volume of the air changes slightly as the air mass expands or is compressed (both of which often happen).

Example: A quantity of air with a volume of 1 cubic meter contains 30 g of water vapor. Their absolute humidity is therefore 30g / m³. When the air pressure of the Ambient air increases, this amount of air is compressed. In the example, half of its volume - i.e. 0.5 cubic meters - should be squeezed. The amount of water vapor remained the same (30 g).

So now we have 30 g of water vapor per 0.5 cubic meter of air, which corresponds to 60 g per 1 cubic meter. The absolute humidity is twice as large as before, although the amount of water vapor has not changed.

In this context the so-called Specific humidity a better measure. It gives the amount of water vapor in grams of water vapor per kilogram Air. Since the mass of the air (measured in kilograms) does not change when it is expanded or compressed, the specific humidity in the above example would have remained the same.

Specific humidity (g / kg): Water vapor content of the air measured in grams of water vapor per kilogram of air.

Saturation moisture

The air can only absorb a limited amount of water vapor. When this capacity is reached, the air is called "saturated". The amount of water vapor (also measured in grams per cubic meter: g / m³) that the air can absorb is called Saturation moisture.

The saturation humidity depends on the temperature of the air: warm air has a greater saturation humidity than cold air.

Saturation moisture (g / kg): The maximum amount of water vapor that the air can absorb at a certain temperature.

Relative humidity

For everyday life it is Relative humidity an important variable. It is a good measure of whether we consider the air dry or humid feel.

The relative humidity is the amount of water vapor present in relation to to the maximum possible water vapor, that is: the specific moisture divided by the saturation moisture. The result is given in percent and says, for example: "The relative humidity is 70%".

The relative humidity can reach a maximum of 100%, then the air is saturated (that is, the specific humidity is equal to the saturation humidity).

Relative humidity (%): The amount of water vapor contained in the air in relation to the saturation humidity.

Precipitation

Rain gauge - in this model you can see a narrower tube inside. This is used to be able to read the water level more precisely. However, this means that the millimeters can no longer be transferred directly to liters per square meter.

If water is excreted from the atmosphere, one speaks of Precipitation. This can have different forms: it can be liquid or solid, for example. We call liquid precipitation rain. Solid precipitation falls e.g. as snow, sleet or hail. In addition, precipitation can "settle" without falling visibly: this is the case, for example, with dew (liquid) or frost (solid).

Measurement

Precipitation can be measured relatively easily by collecting it in a vessel and then reading the water level. In a vessel with straight walls, where the opening is the same size as the base, the water level in millimeters corresponds to the amount of precipitation in liters per square meter.