Exam 2 Chap 7 Flashcards
What is a contrail?
Short for condensation trail, this develops when the hot humid air exhausted from a jet engine mixes with the colder dries air of high altitudes.
How can contrails affect weather and climate?
*effects local radiation budget *may stimulate local precipitation by providing ice crystal nuclei for lower clouds
This type of fog develops on mountainsides or hillsides as ascending humid air reaches saturation.
Upslope fog
This type of fog can be described as the cooling of land at night in which the temperature is at a point where water vapor condenses creating a cloud on the surface level to form. This type of fog only last a couple hours after sunrise and usually is seen in marshy wet areas, where the soil is saturated by snow or rain.
This is radiation fog.
This type of fog is caused by the movement of air masses from one area to another in which advection cooling takes place. Air mass advection cooling is, “when the advecting air passes over a relatively cold surface the air mass may be chilled to saturation in its lowest layers” (Mills, pg. 263). This type of fog occurs in the spring where there is “mild and humid air flows over the cold- snow-covered ground”.
Advection Fog
This type of fog occurs when “fog develops in late fall or winter when extremely cold and dry air flows over a large unfrozen body of water. Evaporation and sensible heating cause the lower portion of the air mass to become more humid and warmer than the air above” (Mills, Pg 264). This type of fog usually happens in the fall or winter.
Steam Fog
How is it possible for cloud droplets to become supercooled?
Cloud droplets are described as “supercooled” if their temperature is below the freezing point
of water (0 °C) and yet remain liquid. Cloud droplets normally supercool and remain liquid at
sub-zero temperatures until foreign particles in the water act as ice-forming nuclei, initiating
freezing.
Identify the various atmospheric conditions that influence the height of the base of a
cumuliform cloud. What controls the altitude to which a cumulonimbus cloud builds in the
atmosphere?
The convective condensation level (CCL) is the altitude in the atmosphere at which a rising air
parcel becomes saturated and condensation begins to occur through convection. This level
coincides with the altitude of a cumuliform cloud’s base. The height that a cumulonimbus cloud
reaches depends on the stability of the troposphere. If the air aloft is stable, vertical growth is
inhibited. Unstable air promotes vertical motion, and clouds will grow upward.
Explain why cumuliform clouds are relatively rare over cold-water surfaces and snow-covered
surfaces.
Cumuliform clouds rarely occur over cold-water and snow-covered surfaces because cold
surface temperatures inhibit convection.
What conditions are required for a cloud to form in the atmosphere?
Clouds are visible products of the condensation or deposition of water vapor within the
atmosphere. Most clouds form as the result of air ascending and cooling by expansion and
becoming saturated with water vapor. With further cooling, water vapor deposits on solid and
liquid particles, called cloud condensation nuclei, to form cloud droplets, or under extremely
cold conditions, to form ice crystals.
Identify some of the natural sources of cloud condensation nuclei. What role is played by these
nuclei in the formation of a cloud?
Natural sources of nuclei include volcanic eruptions, wind erosion of soil, forest fires, organic
compounds, and sea spray. Cloud condensation nuclei promote condensation of water vapor at
temperatures above and below the freezing point of water. These nuclei provide surfaces on
which water vapor can condense or deposit.
What is the significance of hygroscopic nuclei in cloud formation?
Hygroscopic nuclei are small particles that possess a chemical attraction for water vapor
molecules. In the atmosphere, they promote condensation and cloud formation at values of
relative humidity under 100%.
Distinguish between atmospheric conditions responsible for development of radiation fog
versus conditions that favor dew formation.
Both dew and radiation fog form when radiational cooling causes the air near the ground to
reach saturation. If conditions are calm, dew will form. Light winds favor the development of
radiational fog by producing slight mixing of air.
In hilly terrain, radiation fog is most common in low areas such as marshes and river valleys.
Please explain why.
Radiational cooling causes air near the surface to cool. Cooling causes air density to increase.
In hilly terrain, the cooler, denser air flows downslope into low lying areas. This phenomenon is
known as cold air drainage. Fog will form in these low lying areas if cooling lowers the air
temperature to and below the temperature at which saturation is achieved, while the hilltops will
often remain clear.
Describe the process involved in the formation of warm-cloud precipitation.
The collision-coalescence process causes precipitation to form in a warm cloud. This process
takes place in clouds made up of cloud droplets of different sizes. Larger droplets, having a
higher terminal velocity than smaller droplets, collide and coalesce with smaller droplets in their
path. The droplets continue to grow, eventually falling to Earth as precipitation.
