Drizzle
Encyclopedia
Drizzle is a light rain precipitation
consisting of liquid water drops smaller than those of rain
, and generally smaller than 0.5 mm (0.02 in.) in diameter. Drizzle is normally produced by low stratiform
cloud
s and stratocumulus
clouds. Precipitation rates due to drizzle are on the order of a millimetre per day or less at the ground. Owing to the small size of drizzle drops, under many circumstances drizzle largely evaporates before reaching the surface, and so may be undetected by observers on the ground. The METAR
code for drizzle is DZ.
can lead to treacherous
conditions. Freezing drizzle
occurs when supercooled drizzle drops land on a surface whose temperature is below freezing.
These drops immediately freeze upon impact leading to the buildup of sheet ice on the surface of roads, and very heavy accumulations of ice on
power lines, both of which have major impacts.
and trade wind cumulus
clouds, which exist entirely within the marine boundary layer
. Despite the low rates of surface accumulation, it is becoming apparent that drizzle actually exerts a major influence over the cloud structure, coverage, and radiative properties in these regions. This has motivated scientists to design more sophisticated, sensitive instruments such as high frequency radar
s that can detect drizzle. These studies have shown that the quantity of drizzle is strongly linked to cloud morphology and tends to be associated with
updrafts within the marine boundary layer
. Increased amounts of drizzle tend to be found in marine clouds that form in clean airmasses that have low concentrations of
cloud droplets. This interconnection between clouds and drizzle can be explored using high resolution
numerical modeling such as large eddy simulation
.
clouds. This would lead to increased cloud albedo
on the regional to global scale, and a cooling of the planet. Estimates using complex global climate models suggest that this effect may be partially masking the effects of greenhouse gas
increases on the global surface temperature. However, it is not clear that the representation of the chemical and physical processes needed to accurately simulate the interaction between aerosols, clouds, and drizzle in our current climate models is sufficient to fully understand the global impacts of changes in particulates.
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
consisting of liquid water drops smaller than those of rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
, and generally smaller than 0.5 mm (0.02 in.) in diameter. Drizzle is normally produced by low stratiform
Stratus cloud
A stratus cloud is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide . More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color...
cloud
Cloud
A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
s and stratocumulus
Stratocumulus cloud
A Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
clouds. Precipitation rates due to drizzle are on the order of a millimetre per day or less at the ground. Owing to the small size of drizzle drops, under many circumstances drizzle largely evaporates before reaching the surface, and so may be undetected by observers on the ground. The METAR
METAR
METAR is a format for reporting weather information. A METAR weather report is predominantly used by pilots in fulfillment of a part of a pre-flight weather briefing, and by meteorologists, who use aggregated METAR information to assist in weather forecasting....
code for drizzle is DZ.
Effects
While most drizzle has only a minor immediate impact upon humans, freezing drizzleFreezing drizzle
Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ. When freezing drizzle accumulates on land it creates an icy layer of glaze...
can lead to treacherous
conditions. Freezing drizzle
Freezing drizzle
Freezing drizzle is drizzle that freezes on contact with the ground or an object at or near the surface. Its METAR code is FZDZ. When freezing drizzle accumulates on land it creates an icy layer of glaze...
occurs when supercooled drizzle drops land on a surface whose temperature is below freezing.
These drops immediately freeze upon impact leading to the buildup of sheet ice on the surface of roads, and very heavy accumulations of ice on
power lines, both of which have major impacts.
Occurrence
Drizzle tends to be the most frequent form of precipitation over large areas of the world's oceans, particularly in the colder regions of the subtropics. These regions are dominated by shallow marine stratocumulusStratocumulus cloud
A Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
and trade wind cumulus
Cumulus cloud
Cumulus clouds are a type of cloud with noticeable vertical development and clearly defined edges. Cumulus means "heap" or "pile" in Latin. They are often described as "puffy" or "cotton-like" in appearance. Cumulus clouds may appear alone, in lines, or in clusters...
clouds, which exist entirely within the marine boundary layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
. Despite the low rates of surface accumulation, it is becoming apparent that drizzle actually exerts a major influence over the cloud structure, coverage, and radiative properties in these regions. This has motivated scientists to design more sophisticated, sensitive instruments such as high frequency radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
s that can detect drizzle. These studies have shown that the quantity of drizzle is strongly linked to cloud morphology and tends to be associated with
updrafts within the marine boundary layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
. Increased amounts of drizzle tend to be found in marine clouds that form in clean airmasses that have low concentrations of
cloud droplets. This interconnection between clouds and drizzle can be explored using high resolution
numerical modeling such as large eddy simulation
Large eddy simulation
Large eddy simulation is a mathematical model for turbulence used in computational fluid dynamics. It was initially proposed in 1963 by Joseph Smagorinsky to simulate atmospheric air currents, and many of the issues unique to LES were first explored by Deardorff...
.
Influence of aerosols
It has been hypothesized that increasing the amounts of particulates in the atmosphere through human activities may lead to a suppression of drizzle. According to this hypothesis, because drizzle can be an effective means of removing moisture from a cloud, its suppression could help to increase the thickness, coverage, and longevity of marine stratocumulusStratocumulus cloud
A Stratocumulus cloud belongs to a class of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumuli, and the whole being at a lower altitude, usually below 2,400 m...
clouds. This would lead to increased cloud albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
on the regional to global scale, and a cooling of the planet. Estimates using complex global climate models suggest that this effect may be partially masking the effects of greenhouse gas
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
increases on the global surface temperature. However, it is not clear that the representation of the chemical and physical processes needed to accurately simulate the interaction between aerosols, clouds, and drizzle in our current climate models is sufficient to fully understand the global impacts of changes in particulates.