Chapter 12 and 13

What do the low level clouds extend from?

0-6500 ft

What are the four cloud forms?

1. Cirriform 2. Nimbus 3. Cumuliform 4. Stratiform

What are the different level of clouds?

1. Low clouds 2. Middle clouds 3. High clouds

Where do the high clouds extend from? Depending on the region this changes but list the temperate region.

16,500 to 40,000ft

Where do the middle clouds extend from? Depending on the region this changes but list the temperate region.

6,500-23,000 ft

Describe how vertical motion affects atmospheric stability.

A column of air in the atmosphere will become more stable when it descends (subsides) (see Figure 12-7). As it subsides, it becomes compressed by the weight of the atmosphere and shrinks vertically. The entire layer warms due to adiabatic compression. However, the upper part of the column sinks farther and, thus, warms more than the bottom part. This process acts to decrease the temperature lapse rate and increase stability. Conversely, a column of air in the atmosphere will become less stable when it ascends (rises). As it rises, the rapid decrease in air density aloft causes the column to stretch out vertically. As long as the layer remains unsaturated, the entire layer cools at the dry adiabatic lapse rate (see Table 11-1). However, due to the stretching effect, air at the top of the column cools more than the air at the bottom of the column. This process acts to increase the temperature lapse rate and decrease stability.

What is convective instability?

A rising column of air will become less stable when air at the bottom has a higher relative humidity than air at the top. As the air moves upward, the bottom becomes saturated first and cools at the lesser moist adiabatic lapse rate (see paragraph 11.2). The net effect is to increase the lapse rate within the column and decrease stability. This is associated with the development of thunderstorms.

What are some examples of mid level clouds?

Altocumulus (Ac), Altostratus (As), and Nimbostratus (Ns) are mid-level clouds.

What are some examples of high clouds?

Cirrus (Ci), Cirrocumulus (Cc), and Cirrostratus (Cs) are high-level clouds. Typically thin and white.

What can clouds indicate?

Clouds are like signposts in the sky that provide information on air motion, stability, and moisture. Clouds help pilots visualize weather conditions and potential weather hazards.

What does a cumuliform cloud form entail?

Clouds that look like white, fluffy cotton balls or heaps and show the vertical motion or thermal uplift of air taking place in the atmosphere. The level at which condensation and cloud formation begins is indicated by a flat cloud base, and its height will depend upon the humidity of the rising air. The more humid the air, the lower the cloud base. The tops of these clouds can reach over 60,000 feet - fluffy cotton balls tops can reach over 60,000 ft. Bases vary

What are some examples of low clouds?

Cumulus (Cu), Towering cumulus (TCu), Stratocumulus (Sc), Stratus (St), and Cumulonimbus (Cb) are low clouds composed of water droplets. However, they can also be composed of supercooled liquid water droplets and/or ice crystals when temperatures are below freezing. Cumulus and Cumulonimbus usually have bases in the low level, but their vertical extent is often so great that their tops may reach into the middle and high levels.

What is the effect diurnal heating and cooling?

Daytime heating of the surface increases temperature lapse rates and decreases stability. Conversely, nighttime cooling of the surface decreases temperature lapse rates and increases stability. Temperature variation is maximized over land, at low latitudes, with a clear sky, dry air, and light wind. Conversely, temperature variation is minimized over large bodies of water, at high latitudes, with a cloudy sky, moist air, and strong wind.

What is the difference between fog and a cloud?

Fog differs from cloud only in that the base of fog is at the Earth's surface while clouds are above the surface.

What does a cirriform cloud form entail?

High-level clouds that form above 20,000 feet and are usually composed of ice crystals. High-level clouds are typically thin and white in appearance, but can create an array of colors when the sun is low on the horizon. Cirrus generally occur in fair weather and point in the direction of air movement at their elevation. - high level cloud, thin and white. 20,000 ft base

What could a pilot expect from a cirrocumulus cloud? (Cumulus unstable) (Stratus stable)

Icing and turbulence.

What can a pilot expect from a Nimbostratus and altostratus?

Icing. Stratus usually no turbulence but still have to worry about icing.

What provides greater stability in the atmosphere in terms of a temperature lapse rate and what causes these changes to occur?

If temperature lapse rates increase, then stability decreases. Conversely, if temperature lapse rates decrease, then stability increases. Most of these changes occur as a result of the movement of air, but diurnal (day/night) temperature variations can play a significant role.

With low clouds what can a pilot expect? "If cumulus is included the second part is true."

If the freezing level is low icing. Also turbulence.

What is an example of unstable parcel?

If the lifted parcel is warmer and, therefore, less dense (lighter) than the surrounding air, it will continue to rise on its own until it reaches the same temperature as its environment. Greater temperature differences result in greater rates of vertical motion.

Altocumulus Lenticularis, commonly known as Altocumulus Standing Lenticular (ACSL) are an orographic type of cloud. (Meaning they form over a mountain due to the orographic nature). What does this cloud indicate?

Indicate turbulence and moisture.

What are the two most common ways to measure atmospheric stability?

Lifted Index (LI) and Convective Available Potential Energy (CAPE).

What does a nimbus cloud form entail? What does nimbus mean?

Nimbus comes from the Latin word meaning "rain." These clouds typically form between 7,000 and 15,000 feet (2,100 to 4,600 meters) and bring steady precipitation. As the clouds thicken and precipitation begins to fall, the bases of the clouds tend to lower toward the ground. - rain cloud, bring some sort of precipitation, bases vary usually begin at 7,000 to 15,000 and lower.

Describe how wind affects atmospheric stability.

Stability increases when wind blows colder air into the bottom of the air column (cold air advection) and/or warmer air at the top (warm air advection). So it blows it in the direction the air wants to move.

What does a Stratiform cloud form entail?

Stratus is Latin for "layer" or "blanket." The clouds consist of a featureless low layer that can cover the entire sky like a blanket, bringing generally gray and dull weather. The cloud bases are usually only a few hundred feet above the ground. Over hills and mountains, they can reach ground level when they may be called fog. Also, as fog lifts off the ground due to daytime heating, the fog forms a layer of low stratus clouds. - low layered clouds stretched out over most the sky.

What factors can affect atmospheric stability?

Wind, diurnal heating/cooling, vertical air of motion, moisture.

What is a cloud?

a visible aggregate of minute water droplets and/or ice particles in the atmosphere above the Earth's surface.

How are clouds formed?

as a result of condensation of water vapor in rising currents of air, or by the evaporation of the lowest layer of fog.

As the parcel is lifted, why does the temperature decrease usually?

due to the expansion and latent heat effects

What is CAPE?

is the maximum amount of energy available to an ascending air parcel for convection. CAPE is represented on a sounding by the area enclosed between the environmental temperature profile and the path of a rising air parcel over the layer within which the latter is warmer than the former. Units are joules per kilogram of air (J/kg). Any value greater than 0 joules per kilogram indicates instability and the possibility of thunderstorms. 1,000 joules per kilogram, and in extreme cases may exceed 5,000 joules per kilogram.

What is Atmospheric stability?

is the property of the ambient air that either enhances or suppresses vertical motion of air parcels and determines which type of clouds and precipitation a pilot will encounter.

What is neutral stability?

is the state of a column of air in the atmosphere in which an ascending (or descending) air parcel always has the same temperature (density) as the surrounding environmental air. If the column of air is unsaturated, then neutral stability exists when its lapse rate of temperature equals the dry adiabatic lapse rate. If the column of air is saturated, then neutral stability exists when its lapse rate of temperature equals the moist adiabatic lapse rate.

What is absolute instability?

is the state of a column of air in the atmosphere when it has a superadiabatic lapse rate of temperature (i.e., greater than the dry adiabatic lapse rate). An air parcel displaced vertically would be accelerated in the direction of the displacement. The kinetic energy of the parcel would consequently increase with increasing distance from its level of origin.

What is absolute stability?

is the state of a column of air in the atmosphere when its lapse rate of temperature is less than the moist adiabatic lapse rate. This includes both isothermal(stays the same) and inversion temperature profiles. This results in stable air. An air parcel lifted upward would be colder (denser) than the surrounding environmental air and would tend to sink back to its level of origin.

What is conditional instability?

is the state of a column of unsaturated air in the atmosphere when its lapse rate of temperature is less than the dry adiabatic lapse rate, but greater than the moist adiabatic lapse rate. An air parcel lifted upward would be initially stable, but at some point above its Lifted Condensation Level (LCL) it would become unstable. The term conditional means the parcel must be lifted to a particular level (altitude) before it becomes unstable and rises because of its own buoyancy.

what is lifted index?

is the temperature difference between an air parcel (usually at the surface) lifted adiabatically and the temperature of the environment at a given pressure (usually 500 millibars) in the atmosphere. A positive value indicates a stable column of air (at the respective pressure), a negative value indicates an unstable column of air, and a value of zero indicates a neutrally stable column of air. The larger the positive (negative) LI value, the more stable (unstable) the column of air. used in thunderstorm forecasting; however, CAPE is generally considered a superior measurement of instability. However, LI is easier to determine without using a computer.

What could a pilot expect from an altocumulus cloud?

turbulence and small amounts of icing.