Chp 4-7 Review Questions
Name the type of fog that most often forms when warm rain drops fall into an unsaturated layer of colder air near the surface.
'Frontal Fog' This fog usually develops in the shallow layer of cold air just ahead of an approaching warm front or behind a passing cold front. 'Frontal Fog' falls into the category of 'Evaporation Fog' since the method of formation is due to the partial evaporation of rain drops into unsaturated air below cloud base which causes a combination of lowering the air temperature while adding moisture to the atmosphere.
What is the difference between 'Steam Fog' and 'Advection Fog'?
'Steam Fog' forms when cool/cold air is located over a body of warmer water. Due to the thermal properties (specific heat) of water, water temps will cool down slower during the autumn months, therefore 'Steam Fog' is more common over water during cool/cold Fall mornings. 'Advection Fog' forms when warm, moist air moves over a colder surface. This is more likely to occur in Winter and Spring, therefore 'Advection Fog' is more common during the late Winter and early Spring months.
What are the three primary factors that influence the rate of evaporation?
(1) water temperature, the warmer the water, the greater the rate of evaporation (2) wind speed, stronger winds will enhance evaporation (3) moisture content of air above water surface, drier the air, the higher the potential for evaporation.
Explain two ways the Relative Humidity can be changed.
(1)Changing the air's water vapor content while holding the temperature constant: When water vapor is added to the air, with no change in air temp, the RH increases, and when water vapor is removed from the air, with no change in air temp, the RH decreases. (2)Changing the air temperature with no change in water vapor content: An increase in air temp while holding water vapor contain constant will lower the RH, while a decrease in air temp while holding water vapor contain constant will raise the RH.
Identify the following 'Sky Conditions' by total cloud cover in octals (eights) and percentages. Clear SKC Few Scattered Broken Overcast
0 Clear below 24,000' AGL (ASOS) 0 Clear skies (human observation) 0 to 5% 1/8 - 2/8 Few clouds (FEW) >5 to ≤25% 3/8 - 4/8 Partly cloudy (SCT) >25 to ≤50% 5/8 - 7/8 Mostly cloudy (BKN) >50 to ≤87% 8/8 Cloudy (OVC) >87 to 100%
What are the four methods of Fog formation?
1) Cool the air to saturation - Decrease the air temp to the dew-point temp 2) Add moisture to the air - Increase the dew-point temp to the air temp 3) Add moisture to colder air and mix to saturation - Lower air temp while increasing dew-point temp 4) Mix two unsaturated air parcels to create a saturated air parcel
What processes in the atmosphere can cause the atmosphere to become more stable?
1) Warm air advection above the surface 2) Downward movement of air above (subsidence) that will cause the air temperatures above to warm due to compression 3) Cold air advection on and/or near the surface 4) Overnight radiational cooling on the surface 5) Air moving over a colder surface which will cause the surface air temperature to decrease
What mechanisms can cause the atmosphere to become more unstable?
1)Cooling aloft a)Cold air advection above the surface b)Radiational cooling off the top of clouds 2)Warming at the surface a)Daytime solar heating b)Warm air advection on the surface c)Cool air moving over a warmer surface
List and describe three ways in which ice crystals can form in a cloud.
1)Homogeneous Freezing → The freezing of pure water without the benefit of ice nuclei. At temperatures around -40˚C (-40˚F), enough molecules within the water droplet join together in a rigid pattern to form an ice embryo. 2)Deposition → deposition nuclei will allow water vapor to deposit as ice directly onto their surfaces in cold, saturated air, bypassing the liquid phase. 3)Contact Freezing → Super-cooled liquid water freezes on contact with a contact nuclei. The nuclei can be just about anything. This process is the dominate production of ice crystals in some clouds.
Name the four mechanisms that are responsible for the development of the majority of the clouds we observe.
1)Surface heating and free convection 2)Topography (orographic lift) forced ascent 3)Widespread ascent (convergence of surface air) Example: Low pressure system 4)Uplift along weather fronts, air masses of different density interacting with one another
Which clouds are associated with each of the following characteristics. 1. Thin, wispy clouds, made up of ice crystals that can be blown by upper levels winds into long streamers 2. High, thin, layered, ice crystals, may cover a large portion of the sky, can produce halos and/or sun dogs 3. Small individual elements, Nickname is 'Mackerel Sky' 4. Mid-level, gray to blue gray cloud composed of ice crystals and/or water droplets, sun or moon maybe dimly visible as a round disk 5. Mid-level, ice crystals and/or water droplets, rounded individual puffy elements
1. Cirrus 2. Cirrostratus 3. Cirrocumulus 4. Altostratus 5. Altocumulus
Which clouds are associated with each of the following characteristics. 1. Grayish, low, layered, cloud that often covers the entire sky with uniform bases, could produce drizzle 2. Low cloud, puffy elements but shallow, may produce a brief snow shower during the winter season 3. Light to moderate steady rain or snow, no lightning is present 4. Puffy, cotton ball looking, water droplets, often seen on a warm summer afternoon 5. Good vertical growth, may have showery activity but lightning not yet present 6. Scientific name for a thunderstorm, moderate to heavy rain, possible hail, and lightning
1. Stratus 2. Stratocumulus 3. Nimbostratus 4. Cumulus 5. Cumulus Congestus 6. Cumulonimbus
Use your new found knowledge on the topic of stability to answer these two questions. 1.On a typical summer day, how does atmospheric stability change from the daytime to nighttime? 2.What kind of stability is needed for the development of a thunderstorm. In other words, what kind of atmospheric stability will allow the thunderstorm to grow in the vertical?
1.During the daytime, incoming solar radiation will cause the earth's surface and the lowest region of the troposphere to warm causing the atmosphere to become more unstable. During the overnight hours, radiational cooling will cause the earth's surface and lowest region of the troposphere to cool causing the atmosphere to become more stable. 2.In order for a thunderstorm to grow vertically, the temperature within the thunderstorm must be warmer than the surrounding environmental air. Under this condition the thunderstorm is able to build in the vertical because the atmosphere in the region of thunderstorm development is unstable.
Air Dew Point Actual Saturated City Temp Temp Vapor Press Vapor Press Miami 85°F 75°F 29.6mb 41.0mb Fargo 45°F 45°F 10.2mb 10.2mb Chicago 65°F 50°F 12.3mb 21.0mb Dallas 95°F 65°F 21.0mb 56.2mb 1.Which city has the highest relative humidity? 2.Which city has the least amount of water vapor content? 3.Which city has the greatest amount of water vapor content? 4.Which city has the capacity to hold the greatest amount of water vapor?
1.Fargo (Temp and Dew Pt Temp are the same value therefore 100% RH) 2.Fargo (Has the lowest Dew Pt Temp and/or Actual Vapor Pressure of all 4 cities) 3.Miami (Has the highest Dew Pt Temp and/or Actual Vapor Pressure of all 4 cities) 4.Dallas (Has the highest Temp and Saturated Vapor Pressure of all 4 cities, therefore the highest capacity to hold the most water vapor if all 4 locations were saturated at there current temperatures)
What are the five types of fog?
1.Radiation 2.Advection 3.Upslope 4.Evaporation •Steam •Frontal 5.Ice
What are the necessary conditions needed to determine the correct use of the various lapse rates for a parcel of air?
1.The dry lapse rate is used for a parcel's temperature when the parcel of air is unsaturated (RH < 100%). -10°C/km in a rising parcel and +10°C/km in a sinking parcel. 2.The dew-point lapse rate is used for a parcel's dew-point temperature when the parcel of air is unsaturated (RH < 100%). -2°C/km in a rising parcel and +2°C/km in a sinking parcel. 3.The moist lapse rate is used for the parcel's temperature and dew-point temperature when the parcel of air reaches saturation (RH = 100%) -6°C/km for a rising parcel. Note: The moist lapse rate is not used in sinking air because the parcel will warm and RH values will fall to values below 100%.
1.What is the 'wet-bulb temperature'? 2.What is the 'wet-bulb depression'? 3.On what instrument for measuring atmospheric moisture can you find a wet and dry bulb?
1.This is the lowest temperature that can be reached by evaporating water into the air. 2.The temperature difference between the wet bulb and dry bulb (air temperature) is called the wet-bulb depression. 3.On an aspirated or sling psychrometer.
In a volume of air, how does the 'actual vapor pressure (e)' differ from the 'saturation vapor pressure (es)'?
Actual vapor pressure indicates the air's total or current water vapor content, whereas saturation vapor pressure describes how much water vapor is necessary to make the air saturated at any given temperature, or it describes the maximum amount of water vapor the air could hold at a given temperature. The actual vapor pressure and saturation vapor pressure are the same when the air is said to be saturated or having a relative humidity of 100%. When the air is unsaturated , relative humidity values will be less than 100%. In this situation the saturation vapor pressure will always be greater than the actual vapor pressure.
What type of cloud formations are typically associated a warm front and cold front?
Air that is forced to ride up and over the gentle slope of a warm front will produce layered clouds in the stratus category because the atmosphere is mainly stable. Air that is forced upward along a more aggressive cold front will tend to build vertically and be in the cumulus category because the atmosphere is mainly unstable.
What conditions are most favorable for the occurrence of aircraft icing?
Aircraft icing occurs when an aircraft is flying through clouds that contain a significant amount of super-cooled liquid water droplets. The best aircraft icing conditions occur when the cloud temperature ranges from 0ºC (32ºF) to -10ºC (14ºF). At these temperatures a lot of super-cooled liquid water can be present within the cloud because of a lack of active ice nuclei at these temperatures.
What does the saturation vapor pressure (es) primarily depend upon?
At higher temperatures, it takes more water vapor to saturate the air. More vapor molecules will exert a greater pressure. Therefore, saturation vapor pressure depends primarily on the air's temperature because warmer air has the potential to hold more water vapor.
Explain why the air on a hot, humid day is less dense than the air on a hot, dry day.
At the same temperature and at the same atmospheric level (pressure), humid air weighs less than dry air. This is due to the fact that water vapor molecules weigh less than the dry air molecules that they are replacing.
Explain how the Bergeron process 'Ice Crystal Process or Cold Rain Process' increases the size of ice crystals?
Bergeron Process → Ice crystals grow larger at the expense of the surrounding super-cooled water droplets since the saturated vapor pressure over ice is less than the saturated vapor pressure over water at the same subfreezing temperature. The water vapor molecules will diffuse towards the ice crystal causing the ice crystal to grow while the super-cooled liquid water droplet will decrease in size due to evaporation since the water droplet must replace the water vapor molecules that it lost to the ice crystal.
What are the ideal weather conditions for the formation of dew and frost?
Both dew and frost can form on nights with clear to mostly clear skies and calm winds. During the overnight hours these conditions are favorable for rapid radiational cooling. When objects near the surface become colder than the dew-point temperature, dew will form (condensation) on those objects. When objects near the surface become colder than the frost-point temperature, frost will form (deposition) on those objects.
The temperature at the surface is 25˚C and the dew-point temperature is 15˚C. Cumulus clouds form in the afternoon. What will be the approximate base of these cumulus clouds?
Cloud Base = 4,000 ft AGL
Explain why the condensation process becomes more efficient when the air becomes colder.
Condensation occurs when water vapor molecules condense onto condensation nuclei (aerosols). These nuclei can consist of microscopic bits of dust, smoke, salt, and other solid particles. In warm air, fast moving vapor molecules strike the nuclei with such impact that they may simply bounce away. However, if the air is chilled, the molecules move more slowly and are more apt to stick and condense onto the nuclei.
What is the difference between dry and wet haze?
Dry haze consists of particles (aerosols) in the atmosphere that selectively scatter some rays of sunlight which will give the atmosphere a bluish, brownish, or yellowish color causing a decrease in visibility. Wet haze consists of particles (aerosols) in the atmosphere in which the condensation process has started to occur when relative humidity values reach 75%. Wet haze particles are slightly larger than dry haze particles and will scatter rays of sunlight more effectively than dry haze giving the atmosphere a dull gray or white appearance causing a greater reduction in visibility.
The surface temp of a parcel of air is 24°C and the dew-point temp is 16°C. Using the adiabatic process lift a parcel of air to the 2 km level. What is the temp and dew-point temp of the air parcel at the 2 km height?
First we need to know the various lapse rates. Dry Lapse Rate = 10°C/km Dew-Point Lapse Rate = 2°C/km Moist Lapse Rate = 6°C/km Next we need to know when to use them. If parcel is unsaturated use the Dry LR for parcel temp and Dew-Point LR for parcel dew-point temp. If parcel is saturated use the Moist LR for both the parcel temp and dew-point temp.
Why do hot, humid summer days usually feel hotter than hot, dry summer days?
From earlier readings, we learned that the process of evaporation takes energy and therefore is a cooling process. We also learned that the evaporation rate, in part, is dependent upon the moisture content of the air, the drier the air, the higher the evaporation rate. Putting these factors together, we can see that the evaporation rate from our bodies will be slower on hot, humid days versus hot, dry days, therefore we would feel warmer on hot, humid days because the evaporation rate would be slower.
How do the three states of water differ?
Gas, water vapor molecules move about freely, mixing well with neighboring atoms and molecules. Liquid, the water molecules are closer together (greater density than ice), and so they constantly jostle and bump each other. Solid, the molecules arrange themselves into an orderly pattern, with each molecule more or less locked into a rigid position, able to vibrate, but not able to move about freely.
Describe the orbit pattern for a 'Geostationary' and 'Polar-orbiting' weather satellite.
Geostationary satellites revolve around the earth at the same rate that the earth rotates, so it remains above a fixed spot on the equator and monitors the same area of the earth's surface constantly. Height of orbit is 22,300 miles. Polar-orbiting satellites scan north to south which closely align with the meridian (longitude) lines. They move over the southern and northern polar regions on each pass with one orbit taking approximately 90 - 100 minutes. As the earth rotates to the east beneath the satellite, each pass monitors an area to the west of the previous pass. Eventually, the satellite covers the entire earth moving over the same area twice daily. Height of orbit varies from 225 - 500 miles.
What is the difference between glaze and rime icing?
Glaze icing forms when large super-cooled liquid drops strike the aircraft and spread out before freezing. The solid sheet of ice that forms is smooth and transparent. Glaze ice can build up quickly, is heavy, and difficult to remove, even with modern de-icers. Rime icing forms when an aircraft flies through a cloud containing small super-cooled liquid droplets. These droplets will freeze before they have time to spread out, leaving a rough and brittle coating of ice on the wing and other exposed parts of the aircraft. Rime ice usually appears white since air is trapped between the frozen droplets. Thou lighter than glaze ice, rime icing will redistribute the air flow over the wing more than glaze icing will.
What is the difference between hygroscopic nuclei and hydrophobic nuclei?
Hygroscopic nuclei are 'water seeking' and water vapor condenses upon these surfaces when the relative humidity values are considerably lower than 100% (75%). These nuclei are made up of sulfates. Hydrophobic nuclei are 'water repelling' therefore relative humidity values must be near or above 100% to promote condensation.
It is raining. How can you tell if the cloud type is nimbostratus or cumulonimbus.
If the precipitation event is a light to moderate steady rain or snow with no lighting, then the cloud type would be nimbostratus. If the precipitation event consists of a moderate to heavy rain shower accompanied by lightning, then the cloud type is cumulonimbus.
During a summer day, explain why the Relative Humidity values will change significantly while the amount of water vapor remains fairly constant throughout the day.
In many places, the air's total water vapor (moisture) content varies only slightly during an entire day, and so it is the changing air temperature that primarily regulates the daily variation in RH. This would cause the highest RH values to occur during the coldest part of the day, early morning, and the lowest RH values to occur during the warmest part of the day, mid to late afternoon. From this we can see that RH does not tell us how much water vapor is actually in the air, rather, it tells us how close the air is to being saturated at a given temperature.
What is the primary difference between a cloud droplet and a raindrop?
Its size. An ordinary cloud droplet is extremely small having an average diameter of 20 μm (.0008 in). A rain drop on average, is 100 times larger at 2000 μm (.08 in).
What atmospheric conditions are necessary for a snowflake to remain a snowflake and not melt into a raindrop when falling into air temperatures below cloud base that are slightly above freezing?
In order for a falling snowflake to survive in air with temperatures much above freezing, the air must be unsaturated and the wet-bulb temperature must be at or below freezing. The snowflake will partially melt in the warmer air but due to the dryness of the air, the evaporation process will cool the air and snowflake. This will allow the snowflake to fall earthward before melting. Eventually the air will cool to the wet-bulb temperature and become saturated providing no warm air advection is taking place.
Calculate the stability of a parcel of air at the 1 km and 2 km level. The starting temp for the parcel is 30ºC and the dew-pt temp is 22ºC. The environmental temps are 22ºC at the 1 km level and 12ºC at the 2 km level. To answer this question you will need to first find the parcels temp at the 1 km and 2 km level, then compare the parcel's temp to the environmental temps to make the decision if the parcel is stable or unstable at the two different levels.
Initial Temp = 30°C and Dew-Point Temp = 22°C (The air parcel is unsaturated due to the spread in the Temp and Dew-Point Temp of 8°C). Let's just move the parcel up 1 km initially. The new parcel Temp will be 20°C (30 - 10 = 20) and the new parcel Dew-Pt Temp will be 20°C (22 - 2 = 20) at the 1 km level. At the 1km height the parcel is now saturated since the Temp and Dew-Pt Temp are equal at 20°C. So we must use the Moist LR for both the Temp and Dew-Pt Temp for the last km rise from the 1 km to the 2 km level. The new Temp at the 2 km level will be 14°C (20 - 6 = 14) and the new Dew-Pt Temp will be 14°C (20 - 6 = 14). Now compare the parcel temp at 1 km and 2 km level to the environmental temps at those two levels. 1 km Environment temp 22°C, Parcel temp 20°C (Stable) 2 km Environment temp 12°C, Parcel temp 14°C (Unstable)
North Dakota winters can be harsh. You should understand the local terminology. What is the difference between a 'Ground Blizzard' and a 'Blizzard'?
North Dakota is unique because it has a lot of open country. A Ground Blizzard is classified as an event when: -Blizzard conditions are occurring in the open country due to the blowing and drifting of existing snow. -Snow does not have to be falling to create these conditions. -Visibilities in cities will be much better than those in the open country A Blizzard is classified with the following definition: Issued for winter storms with sustained or frequent winds of 35 mph or higher with considerable falling and/or blowing snow that frequently reduces visibility to 1/4 of a mile or less. These conditions are expected to prevail for a minimum of 3 hours.
Why do we use 10˚C/km for the 'dry lapse rate' and only 6˚C/km for the 'moist lapse rate'?
Once the air parcel becomes saturated (100% RH), the latent heat of condensation (600 cal/g) will add sensible heat to the parcel which in turn will offset the cooling due to expansion and slow the rate of cooling within the rising parcel. Hence the cooling rate will decrease from 10°C/km (dry) to 6°C/km (moist). The difference of 4°C is due to the release of latent heat.
Explain why rain shadows form on the leeward side of mountains.
Precipitation falls on the windward side of the mountain. Lets take a closer look at the flow of an air parcel up and over a mountain.
Define the precipitation type "Virga".
Precipitation that falls from a cloud but evaporates before reaching the ground. Under the right conditions, the evaporation of the raindrops below cloud base can cause a significant low-level wind shear event on the surface.
An air parcel has a dew-point temp of 30˚F and an air temp of 80˚F. The actual vapor pressure is 5.6 mb and the saturated vapor pressure is 35.0 mb. What is the Relative Humidity?
RH = actual vapor pressure (e) saturated vapor pressure (es) RH = 5.6 mb / 35.0 mb x 100% RH = 16%
Calculate the relative humidity (RH) for an air parcel with a dew-point temperature of 45˚F and an air temperature of 70˚F. You will need to use the appropriate table on page 105 (12th Edition) of your lecture book to figure this problem out.
RH = e/es x 100% or 10.2 mb/25.0 mb x 100% = 40.8%
So what exactly does the Relative Humidity Value tell us?
Relative Humidity only tells us how close an air mass is to saturation (100%). Warm air with a high relative humidity value would contain a lot of moisture but cold air with a high relative humidity would not contain a lot of moisture. Therefore, relative humidity values are not a good indicator of how much moisture is actual in the air.
Why is it foolish to perform a cloud seeding operation with silver iodide or any of the other seeding agents when the sky is clear?
Seeding does not generate clouds. The first ingredient in any seeding project is the presence of clouds. For the best results, 1) the cloud must be cold enough in the upper portions to contain super-cooled liquid water, and 2) be lacking in ice crystals and ice nuclei. Cloud seeding adds the necessary ice nuclei that will enhance ice crystal growth and the number of ice crystals within the cloud. With the increase in ice crystals, the Bergeron process can create precipitation particles.
When the 'Relative Humidity' is given, why is it also important to know the air temperature?
Since relative humidity (RH) values indicate the amount of water vapor in an air mass relative to its temperature, and that warmer air has the capacity to hold more water vapor, a high RH value in a cold air mass could actually contain less actual water vapor than a low RH value in a warm air mass.
How is the difference between dew-point temperature and air temperature (dew- point depression) related to the Relative Humidity?
Since the dew-point temperature is a direct measure of actual water vapor content in the air, the difference between air temperature and dew-point temperature can indicate whether the Relative Humidity value is low or high. When the two are far apart, the Relative Humidity is low, when the two are close together, the Relative Humidity is high.
How do the atmospheric conditions that produce sleet differ from those that produce hail?
Sleet forms when there is a layer of above freezing temperatures below cloud base but the temperatures at the surface are below freezing. A snowflake falling out of the cloud will melt in the above freezing layer producing a rain drop. The below freezing surface layer must be thick and cold enough to refreeze the raindrop before reaching the ground. Hail is produced inside a cumulonimbus cloud by accretion of super-cooled liquid water onto a large frozen embryo caught in a strong updraft.Strong updrafts hold the frozen embryo in areas of super-cooled liquid water which will cause the hailstone to increase in size until it can overcome the vertical velocity of the updraft and eventually fall to the earth's surface
What is the difference between sleet and freezing rain?
Sleet is usually a transparent or translucent ice ball around .2 inches or less in diameter. When it hits the ground it can bounce. The formation of sleet was discussed in the previous question. It is a frozen raindrop. Freezing rain is liquid (super-cooled) that will freeze on contact with objects that are below freezing on the surface. The determining factor between sleet and freezing rain as a precipitation type, is the depth and coldness of the subfreezing layer near the surface.
So what exactly does the Dew-Point Temperature tell us?
The Dew-Point Temperature is the value we want to use to identify how much water vapor is available. When the dew-point temperature is increasing, the amount of water vapor available is increasing.
Define 'stable' and 'unstable' when relating the terms to the atmosphere.
Stability in the atmosphere relates to a comparison of temperatures between a parcel of air and the air surrounding the parcel. When a parcel of air is colder than the surrounding air, it will not be able to rise because it is more dense or heavier than the surrounding air. If the parcel is forced to rise, it will return to its place of origin once the lifting mechanism dissipates because the temperature of the parcel is still colder than the surrounding air. (Stable) When a parcel of air is warmer than the surrounding air, it will have buoyance because it is less dense or lighter than the surrounding air and it will be able to rise on its own freely. (Unstable)
Explain the difference between the 'dry lapse rate' and the 'environmental lapse rate'. How do we obtain the environmental temperatures in order to calculate the 'environmental lapse rates'?
The 'dry lapse rate' applies to the cooling or warming of a parcel of unsaturated air that is rising or descending through the atmosphere. The 'dry lapse rate' has a constant value (10°C/km). The 'environmental lapse rate' indicates the overall vertical temperature profile of the atmosphere. These temperatures are measured twice daily by the release of radiosonde balloons at the various National Weather Service Offices. The 'environmental lapse rates' can and do change regularly and can even change from one layer of the atmosphere to the next layer of the atmosphere.
What conditions cause an unstable atmosphere?
The 'environmental lapse rate' is large (steep) when unstable conditions prevail. In other words, the rate of change in temperature from the surface to those aloft is relatively large. Therefore, we need cold air aloft and warm air at the surface to steepen the 'environmental lapse rate'.
What conditions cause a stable atmosphere?
The 'environmental lapse rate' is small when stable conditions prevail. In other words, the rate the temperature changes with height is small resulting in the air temperature from the surface to those aloft being relatively small. Therefore, we need warm air aloft or cool air at the surface or a combination of both to achieve this relatively small temperature decrease with height.
What does the 'Relative Humidity' represent?
The Relative Humidity (RH) is the ratio of the amount of water vapor actually in the air to the maximum amount of water vapor required for saturation at a particular temperature (and pressure). Or in other words, it is the ratio of the air's water vapor current content to its potential full capacity.
A January snowfall covers central Arkansas with 5 inches of snow. The following day a south wind brings thick dense fog to this region. Explain what apparently happened and name the type of fog that formed.
The cold snowy surface cooled the relatively warm, moist air mass from the south to its dew-point temperature. Since the warm, moist air mass was advected over a colder region of snow by the south wind, the type of fog created was 'Advection Fog'.
What conditions are necessary for the formation of 'Advection Fog' ?
The method for the formation of 'Advection Fog' is lowering the air temperature to the dew-point temperature. This will occur when warm, moist air is advected over a colder surface. The colder surface could consist of an area of cold water or cold land. As the wind moves the warmer air over the colder surface, the air temperature will be drawn down to the dew-point temperature causing saturation to occur and the development of the fog. Advection Fog can be dense, widespread, and long lasting making it more dangerous than radiation fog.
Provide a brief explanation on the process involved in the formation of 'Radiation Fog' and a description of the characteristics of 'Radiation Fog'.
The method for the formation of 'Radiation Fog' is lowering the air temperature to the dew-point temperature. This will occur during the process of radiational cooling during the overnight hours. The best conditions for the formation of 'radiation fog' is when the overnight skies are clear and the wind is light. 'Radiation Fog' is shallow, patchy, sometimes referred to as 'ground fog'. It is located in low lying areas and is most commonly seen around sunrise.
What conditions are necessary for the formation of 'Upslope Fog'?
The method of formation is lowering the air temperature to the dew-point temperature. 'Upslope Fog' forms when moist air slowly rises, cools, and condenses over elevated terrain. The cooling process results from the air rising and cooling due to expansion. The Front Range of the Rocky Mountains is a prime area for 'Upslope Fog' development when a moist air mass is moved into the region by an easterly wind.
A cloud has an air temperature around -10˚C (14˚F). Why are there many more cloud droplets than ice crystals in this cloud even though the air temperature is well below the freezing temperature of 0˚C (32˚F)?
The number of ice-forming nuclei available in the atmosphere is small for temperatures between 0°C (32°F) and -10˚C (14˚F). Therefore a lot of super-cooled liquid water can exist in clouds with temperatures in this range. However, as the temperatures decrease, more particles become active and promote freezing. Particles of clay become active around -15˚C (5˚F).
When a cloud consists of super-cooled water droplets and ice crystals, is the saturation vapor pressure greater over the super-cooled water droplet or over the ice crystal?
The saturation vapor pressure above a water surface is greater than the saturation vapor pressure above an ice surface. This is true because it is easier for water molecules to escape from a water surface than an ice surface.
Explain why it takes longer to cook vegetables in the mountains than at sea level.
The saturation vapor pressure is directly related to the temperature of the water vapor in the bubbles, higher water vapor temps produce higher saturated vapor pressures values. Hence, any change in atmospheric pressure will change the temp at which water boils. An increase in air pressure raises the boiling point, while a decrease in air pressure lowers it. Since pressure decreases with height, the higher you go, the lower the boiling point, and the longer it would take to cook vegetables.
What is the dew point temperature?
The temperature to which air would have to be cooled (with no change in air pressure or moisture content) for saturation to occur.
Define the term 'ceiling' when referring to cloud conditions.
The term ceiling is defined as the height of the lowest layer of clouds above the surface that are either broken or overcast, but not thin.
List the lapse rate used for the vertical temperature profile of the atmosphere.
This lapse rate is called the 'Environmental Lapse Rate'. This lapse rate is not a constant number. Because the atmospheric temperatures are always changing, the calculation of the 'environmental lapse rate' will vary. To calculate the 'environmental lapse rate' we use the temperature data provided by a upper-level sounding that was collected during the ascent of a radiosonde balloon.
Define "Conditionally Unstable"?
This occurs when the 'environmental lapse rate' value is found between the numerical value of the 'moist' and 'dry lapse rate'. Conditionally Unstable means, if unsaturated air could be lifted to a level where it becomes saturated, instability would result. In other words, the higher the moisture content in the parcel, the quicker the parcel can reach saturation when lifted. Therefore the level where the parcel becomes unstable is conditioned on the initial water content of the parcel before lifting.
Describe how the process of collision-and- coalescence produces precipitation.
This process is known as the 'Warm Rain Process' since the temperatures within the cloud are above freezing 1) Cloud droplets have varying sizes within the cloud mass because there are varying strengths of updrafts in the cloud, 2) Coalescences occurs between the cloud droplets when the larger cloud droplets fall and collide with smaller droplets, 3) The drops will eventually grow to a size that overcomes the upward vertical velocity in the cloud enabling the drops to fall to the surface.
Why are IR images computer enhanced with color?
To increase the contrast between features and their backgrounds, a color scale was developed to enhance finer features within a cloud mass or surface objects.
Explain how visible (Vis) and infrared (IR) images can be used to distinguish: (a) thick clouds from thin clouds (b) high clouds from low clouds.
Visible measures sunlight reflected from the tops of the clouds (albedo). Thick clouds have a higher albedo so they appear brighter than thin clouds with a lower albedo. IR images measure the radiation emitted by the tops of clouds or the earth's surface if no clouds are present. Low clouds (warm) radiate more IR than high clouds (cold). An artificial gray scale is assigned to the various temperatures, gray for lower, warm clouds and white for higher, cold clouds.
What is an absolutely stable atmosphere?
When a lifted parcel of air remains colder than the surrounding air, we say the atmosphere is absolute stable. In other words, when the 'environmental lapse rate' is less than the 'moist adiabatic lapse rate' (6°C/km) the atmosphere is absolutely stable. Lifting the air parcel unsaturated or saturated will not achieve a parcel temperature warmer than the outside environmental air.
What is an absolutely unstable atmosphere?
When a lifted parcel of air remains warmer than the surrounding air, we say the atmosphere is absolutely unstable. In other words, when the 'environmental lapse rate' is greater than the 'dry lapse rate' (10°C/km) the atmosphere is absolutely unstable. Under this scenario, a parcel lifted dry or moist will always have a temperature warmer than the surrounding environmental air
Define what an adiabatic process is?
When a rising parcel of air expands and cools or when a sinking parcel of air compresses and warms with no exchange of heat with the surrounding air outside of the parcel, this situation is called an adiabatic process.
What kind of clouds are associated with a stable atmosphere?
When stable air is forced to rise it will have a tendency to spread out. The clouds that form under this condition will also spread out forming layers. Therefore clouds with this characteristic will be either cirrostratus, altostratus, stratus or nimbostratus. (stratus → 'layered')
Can the collision-coalescence (Warm Rain) and Bergeron (Ice Crystal/Cold Rain) process for precipitation production exist in the same cloud formation?
Yes, If the cloud has a vertical temperature structure that allows for regions of ice crystals, super-cooled liquid droplets and liquid droplets. This holds true for a cumulonimbus cloud. Temperatures in the mid and upper portion of the cumulonimbus cloud are cold enough to support ice crystals and super-cooled liquid water droplets while the lower portion of the cumulonimbus cloud is warm enough to support liquid droplets only.
On some occasions, you will walk outside during a cold morning and see your breath. What is happening that enables you to see your breath on a cold morning? Does the air temperature have to be below freezing for this phenomenon to occur?
You see your breath because warm, moist air form your mouth mixes with cooler air in the atmosphere. The mixture is super-saturated. Therefore, condensation occurs within the exhaled breath. You see the small water droplets that form during the condensation process. The air temperature does not have to be below freezing for this to occur.
It is 7:00 am, the skies are clear, the wind is calm, the air temperature is 37ºF, and the dew-point temperature is 34ºF. Your car is parked on the street and the windshield is covered with frost. Why?
Your car windshield was able to cool down to a temperature below freezing due to the infrared radiation loss during the overnight hours. Since the windshield temperature was colder than the dew-point temperature and at a temperature below freezing, frost formed on the windshield instead of dew.
List the (3) lapse rates, and their numerical values, that are used for a rising or descending parcel of air.
ØDry Lapse Rate (10°C/km) - For Temperature ØWhen parcel RH is less than 100% ØDew-Point Lapse Rate (2°C/km) - For Dew-Point Temperature Ø When the parcel RH is less than 100% ØMoist Lapse Rate (6°C/km) - For both Temperature and Dew-Point Temperature Ø When the parcel RH is 100%