Rain

of these articles is concerned with rains as precipitation. For further meanings, see rain (term clarifying).

Rains one names a liquid precipitation with a droplet size from usually 0.6-3 mm. Below 0.5 mm one speaks of drizzle (also drizzle). Rain is outside of the polar areas the quantitatively most meaning form of the precipitation. The rain quantity is measured in “mm Niederschlagshöhe ” in a standardized receptacle. 1 mm precipitation corresponds 1 litre per square meter, sees in addition rain height.

Rainstorm
wet-with-rain windowpane

table of contents

emergence and forms

rains develops from ice crystals in the upper troposphere, those as condensation germs for the accumulation offurther quantities of water serve. If they fall then due to the force of gravity to the earth's surface, they melt and receive a drop form. The droplet size varies. The largest drop photographed so far had a diameter of 9 mm; this is however very rarely, there a dropusually already starting from 6 mm into smaller drops zerplatzt.

Under certain temperature - and humidity conditions can also evaporate to rain drops, before they reach the earth's surface (spirit rains), at low temperatures in low air layers to however also freeze andwhen ice grains at the soil hit (ice rain, hail).

A majority of the water vapour contained in the terrestrial atmosphere evaporates from the oceans. Therefore coastal regions , at which the prevailing wind direction is relatively warm landinward and the sea, are muchprecipitation-rich.

upward gradient rain

such as upward gradient rains develops

for upward gradient rain, also pilot rain mentioned, is a kind of the rain emergence. If the wind lets warm, damp air of the sea or flat country at mountain courses or other orografischen collections ascend, air becomes alsoincreasing height always further cooled down. However also their water vapour capacity and the air temperature sink approach the always far dew point on. First air cools down per 100 elevator meter according to the principle of the drying-adiabatic cooling around a degree Celsius.As soon as a relative air humidity is reached by 100 per cent, air cools down according to the principle of the damp-adiabatic cooling only around approximately 0.6 °C per 100 meter. With this process the gaseous condenses to liquid water, which latent warmth sets free and for Wolkenbildung leads. Depending upon strength of the rising movement and air humidity it comes in the consequence to often violent precipitation. These concentrate at the respective orografischen obstacles and achieve therefore often high precipitation intensities, whatto inundations and slope chutes to lead can (in Central Europe particularly with Vb-weather conditions). Mountains have due to these procedures usually a rain and/or. Weather and a rain shade side. The rain side is called also luffing side and the rain shade side as leeward side. Upthe leeward side warms up after to air the Abregnung drying-adiabatically around a degree Celsius per 100 meter, which causes the usually rain-poor foehn.

convection rain

such as convection rains develops

the convection rain is a kind of the rain emergence, those above allin the tropical areas at the equator to find is. Since it is stifling warm there the whole time, Oberflächenwasser in large quantities evaporates, condensed in the height and Kumulonimbus forms - clouds, which lead frequently to thunderstorms. In these areasit rains therefore in the afternoon very frequently.

front rain

such as front rains develops

for front rain, also place rain mentioned, is a kind of rain, which is designated after their emergence at a front.

Front rain arises if warm, damp air masses out tropical areas on cold polar air masses meet. Now the warm air pushes itself over the cool air. Further above and between the fronts warm air cools down. Clouds form and it begin to rain. This kind ofRain is to be found in Europe frequently. It is also locally very limited temporally only by short duration and. Can quite succeed to evade to such a rain alone by a slight local change.

falling speed

the condensing water vapour forms firstPurifying droplets, which become ever heavier with increasing size. If the Gewichtskraft of the drops became larger than their lift strength, it begins to raining. The rain drops fall with increasing speed to the earth. The air resistance, which the drops experience, carries forwardthe square of the falling speed too. If Gewichtskraft and strength became equally large, the rain drop with constant falling speed continues to fall. This force equilibrium with constant falling speed is starting point for the following approximate computation:

<math> \ begin {matrix} \ mbox {Gewichtskraft} &=& \ mbox {air resistance strength} \ \ F_G &=&F_L \ \ m \ cdot g &=& c_w \ cdot A \ cdot \ frac {\ rho_L} {2} \ cdot {v_E} ^2 \ ends {to matrix}< /math>

This relationship can be dissolved after the falling speed:

<math> v_E = \ sqrt \ frac {8 \ cdot r \ cdot g \ cdot \ rho_W} {3 \ cdot c_W \ \ rho_L} /math< cdot> = 6.73 m/s = 24.23 km/h

thereby have the individual variables the followingMeaning:

  • <math> m< /math>: Mass of the drop
  • < math> g< /math>: Acceleration due to gravity
  • < math> cW< /math>: Coefficient of drag of the drop
  • < math> A< /math>: Circular area of the drop as resistance surface
  • < math> \ rho_L< /math>: Density of air
  • < math> v_ {E}< /math>: max. Falling speed
  • < math> r< /math>: Drop radius
  • < math> \ rho_W< /math>: Density of the water

effect

rain washes air out. Besidethe dust loosens it also oxygen, nitrogen, carbonic acid, sulfuric acid and nitric acid. Thus it promotes the decomposition of rocks and works as fertilizer. These admixtures can be so highly concentrated that it colors itself (yellow sulfur rain, red blood rain).

Strong rain leads to rain erosion of the soil, in addition, at machines (z. B. Airplane wing), long lasting rain can lead to Vernässung.

see also

Web on the left of

Commons: Rain - pictures, videos and/or audio files
Wiktionary: Rain - word origin, synonyms and translations
Wikiquote: Rain - quotations
Wiktionary: rain - word origin, synonyms and translations
 

  > German to English > de.wikipedia.org (Machine translated into English)