Meteorology Chapter 5 and 6 7 and 8

Sealevel pressure

1013.25 milibars

Saturation Vapor Pressure over Water Versus over Ice

Another important property of water is that the saturation vapor pressure above ice crystals is lower than above water droplets. Stated another way, when the air surrounding a water droplet is saturated (100 percent relative humidity), it is supersaturated relative to a nearby ice crystal

Surface

Another requirement for condensation is that there must be a surface on which water vapor can condense

Cirrocumulus

Appear as white patched com-posed of small cells or ripples

Clouds

Are classified as being high, middle, low, or vertically developed

Clouds that form in the middle altitude range (2000- 6000 meters

Are described with the prefix alto- (meaning "middle") and include two types: altocumulus and altostratus

Upslope Fog

As the name implies form when relatively humid air moves up a gradually sloping landform or in some cases, up the steep slopes of a mountain

Cumulus

Clouds are individual masses that develop into vertical domes or towers

Stratus

Clouds form in love, horizontal layers that on occasion may produce light drizzle or mist.

Clouds of vertical development

Clouds having their bases in the low height range and extending upward into the middle or high altitudes

Clouds

Consist of billions of minute water droplets and/or crystals that are suspended above Earth's surface.

Cumulus

Consists of globular cloud masses that look like cotton balls or sheep in the sky.

Virga

Depending on the humidity of the air and the size of the drops, rain may completely evaporate before reaching the ground. This phenomenon produces virga,

Drizzle

Fine, uniform droplets of water with diameters less than 0.5 millimeters are called drizzle

A cloud with its base at or very near the ground.

Fog

Low clouds

Form nearer to Earth's surface—up to an altitude of about 2000 meters (6500 feet)—and are generally composed of water droplets, except in winter.

Freezing rain

Freezing rain, also called glaze, in contrast, falls as supercooled raindrops that freeze on contact with roads, power lines, and other structures.

Frontal (Precipitation) Fog

Frontal boundaries where a warm moist air mass is forced to rise over cooler, dryer air below generates FRONTAL PRECIPITATION FOG

Bergeron process

Generates much of the precipitation in the middle and high latitudes, is named for its discoverer, the highly respected Swedish meteorologist Tor Bergeron

Anticyclones

In general, high-pressure systems, also called anticyclones, are associated with dry conditions

freezing nuclei

In the atmosphere, supercooled droplets freeze on contact with solid particles that have a shape closely resembling that of ice (silver iodide, for example). These materials, called

wet growth and dry growth

It was once believed that hailstones traveled up and down many times through a cloud to form a large hailstone composed of spherical clear and milky layers. Recent research, however, indicates that there are two methods by which large hailstones develop

Cumulonimbus

Large, dense, billowy clouds of considerable vertical extent in the form of huge towers.

Low pressure systems

Low-pressure systems that occur in the middle latitudes are called cyclones, or midlatitude cyclones,

Clouds are continual interest because?

Meteorologists because they provide a visual indication of atmospheric conditions.

Hygroscopic nuclei (water seeking)

Most effective particles for condensation aloft

cloudbursts

Most rain originates in either nimbostratus clouds or in towering cumulonimbus clouds that are capable of producing unusually heavy rainfalls known as cloudbursts

Condensation Nuclei

Objects at or near the ground, such as blades of grass, are such surfaces. When condensation occurs aloft, tiny particles known as cloud condensation nuclei serve this purpose.

Air saturation

Occurs in air aloft in one of two ways. First, cool-ing air to its dew-point temperature causes saturation, which results in condensation and cloud formation.

Saturation

Occurs when the air temperature is the same as the dew-point temperature.

Mist

Precipitation containing the very smallest droplets able to reach the ground is called mist. Mist can be so fine that the tiny droplets appear to float, and their impact is almost imperceptible. Mist closely resembles fog.

A Cold Air Column Versus a Warm Air Column

Recall that temperature is a measure of average molecular motion (kinetic energy). Thus, the cold Canadian air described above is composed of slow-moving molecules that are packed closely together.

Evaporation Fog

Result of evaporation of water that is warmer than the surrounding air, include steam fog and precipitation fog

Ridges

Ridges are elongated high-pressure areas that extend toward the poles and are associated with warm air moving poleward

fallstreaks

Similar to virga, ice crystals may sublimate when they enter the dry air below. These wisps of ice particles are called fallstreaks.

Snow

Snow is winter precipitation in the form of ice crystals, or aggregates of ice crystals. The size, shape, and concentration of snowflakes depend to a great extent on the temperature profile of the atmosphere

lenticular clouds

Stationary lens-shaped clouds, called

Two types of Evaporation

Steam fog and frontal fog

Stratocumulus

Stratus-like clouds that develop a scalloped bottom that appear as long parallel rolls or broken globular patches are called

Supercooled Water

The Bergeron process operates in cold clouds at temperatures below 0°C (32°F), where liquid cloud droplets and ice crystals coexist. Contrary to what you might expect, cloud droplets do not usually freeze at 0°C (32°F). In order for water to freeze, it must first cool to its freezing temperature, which causes the water molecules to slow down.

Lifting condensation level

The ascending parcel will have cooled to its dew-point temperature, and saturation is reached

Hydrostatic balance is the balance between the upward push of air toward space and the downward pull of gravity

The balance between the upward push of air toward space and the downward force of gravity is called hydrostatic balance

How Do Cloud Droplets Coalesce?

The collision-coalescence process is not as simple as it may first seem. First, as the larger droplets descend, they produce an airstream around them similar to that produced by an automobile traveling rapidly down the highway. The airstream sweeps aside objects, especially the smallest cloud droplets.

terminal velocity

The maximum speed at which an object falls, called its terminal velocity, occurs when air resistance equals the gravitational pull on the object. Because large droplets have a smaller ratio of surface area as compared to their weight, they fall faster than small droplets

aneroid barometer

The need for a smaller, more portable instrument for measuring atmospheric pressure led to the development of the aneroid barometer

Advection

The term advection refers to air moving horizontally

Pressure Changes Caused by Airflow

This phenomenon called convergence causes air to be squeezed into a smaller space, which results in an air column exerting more force on the surface, increasing air pressure. By contrast, in regions on the surface increasing air pressure drops.

Cloud forms

Three basic shapes, Cirrus, Cumulus.stratus

Snow pillows

To measure the mountain snowpack, which produces 75 percent of the water supply for the western United States, automated weather stations employ snow pillows that have been installed at more than 600 sites

Cirrostratus

Transparent, whitish cloud veils with a fibrous or sometimes smooth appearance that may cover much or all of the sky

Troughs

Troughs, by contrast, are elongated areas of low pressure that sweep equatorward and are associated with cool air moving toward the equator

Raindrops

Typical raindrop has a volume 1 million times that of a cloud droplet

Graupel

Under certain atmospheric conditions, falling snow crystals grow as they intercept tiny supercooled cloud droplets that freeze on them. The resulting snowflakes are described as being rimed. If riming continues and makes the shape of the original six-sided snow crystal no longer identifiable, the soft ice pellet is called graupel

Adiabatic cooling

When a parcel of air ascends, it passes through regions of successively lower air pressure, causing the parcel to expand and cool adiabatically

Steam Fog

When cool, unsaturated air moves over a warm water body, enough moisture may evaporate to saturate the air directly above generating a layer of fog

Evaporation Fogs

When saturation occurs primarily because of the addition of water vapor to air, the resulting fogs are called ...

Fractus

When stratus or cumulus clouds appear broken or fractured

Trace of precipitation

When the amount of rain is less than 0.025 centimeter (0.01 inch), it is generally reported as being a trace of precipitation

Advection fog

When warm, moist air blows over a cold surface, it becomes chilled by contact with the cold surface below. If cooling is sufficient, the result will be a blanket of fog called advection fog.

barometric pressure.

With some refinements, Torricelli's mercury barometer remains the standard pressuremeasuring instrument. Because air pressure is measured with a barometer, it is also commonly called barometric pressure.

Sleet

a wintertime phenomenon, consists of clear to translucent ice pellets. Depending on intensity and duration, sleet can cover the ground much like a thin blanket of snow

Family of high clouds

above 6000 meters [20,000 feet] include cirrus, cirrostratus, and cirrocumulus

atmospheric pressure, or simply air pressure,

as the force per unit area on a surface exerted by the weight of the air above. Average atmospheric pressure at sea level is about 14.7 pounds per square inch (equivalent to 1 kilogram per square centimeter in the metric system).

Radiation Fog

as the name implies, radiation fog results from radiation cooling of the ground and adjacent air

Nimbostratus

clouds derive their name from the Latin nimbus, "rain cloud," and stratus, "to cover with a layer." Nimbostratus clouds tend to produce constant precipitation and low visibility.

Altocumulus

clouds tend to form in large composed of rounded masses or rolls that may or may not merge

weighing gauge

collects precipitation in a cylinder that rests on a spring balance. As the cylinder fills, the movement is transmitted to a pen that records the data.

Cirrus

composed of delicate, icy filaments. Winds aloft often cause these fibrous ice trails to bend to curl Cirrus clouds with hooked filaments

tipping-bucket gauge

consists of two compartments, each capable of holding 0.025 centimeter (0.01 inch) of rain, situated at the base of a funnel.

Fog

defined as a cloud with its base at or very near the ground

standard rain gauge

has a diameter of about 20 centimeters (8 inches) at the top. Once the water is caught, a funnel conducts the rain through a narrow opening into a cylindrical measuring tube that has a cross-sectional area only one-tenth as large as the receiver. Consequently, rainfall depth is magnified 10 times, which allows for accurate measurements to the nearest 0.025 centimeter

Cirrus

high, thin, white clouds

Hail

is precipitation in the form of hard, rounded pellets or irregular lumps

collision-coalescence process

is the dominant process for generating precipitation in warm clouds—clouds with tops warmer than -15°C (5°F). Simply, the collision-coalescence process involves multiple collisions of tiny cloud droplets that stick together (coalesce) to form raindrops large enough to reach the ground before evaporating

Altostratus

is the name given to a formless layer of grayish clouds that cover all or large portions of the sky. Generally, the Sun is visible through altostratus clouds as a bright spot but with the edge of its disc not discernible. However, unlike cirrostratus clouds, altostratus do not produce halos.

Uncinus

meaning hook shaped, applied tp streaks of cirrus clouds that are shaped like a comma resting on its side

collision-coalescence process

occurs in warm clouds, where large cloud drops grow by collecting smaller droplets

Fogs formed by cooling

radiation fog, or advection fog or upslope fog

Rain

restricted to drops of water that fall from a cloud and have a diameter of at least 0.5 millimeter

Pressure Readings on Surface Maps

station pressures

Three members of the family of low clouds (below 2000 meters [6500 feet])

stratus, stratocumulus, and nimbostratus.

Supercooled water

supercooled water readily freezes if it collides with an object, which explains why airplanes collect ice when they pass through a cold cloud of supercooled droplets. Supercooled water droplets also cause freezing rain, which falls as a liquid but then turns to a sheet of ice when it strikes the pavement, tree branches, and car windshield

Nimbus

used in the name of a cloud that is a major producer of precipitation