Exam 2 Review

What is a diabatic process?

A diabatic process is one in which heat is exchanged with the change in temperature.

Vapor Pressure

A measure of atmospheric moisture, the partial pressure exerted by water vapor.

Specific Humidity

A measure of atmospheric moisture. The mass of water vapor per unit mass of air, usually expressed in grams per kilogram (g/kg).

Mixing Ratio

A measure of atmospheric moisture: the mass of water vapor per unit mass of dry air, usually expressed in grams per kilogram (g/kg).

What is the effect of solute on saturation?

A solute reduces the effect of the curvature of the water droplet. This reduces the tendency for the water droplet to evaporate.

What? is especially common at sea.

Advection fog

Advection fog

Advection fog is fog that is formed when moist air is transported over a cold surface. The cold surface causes the air in contact with it to cool. If the air cools to saturation, condensation occurs and dew is formed on the ground. Further cooling causes the air close to the surface to also become saturated, and the motion of the air causes a mixing of the air and causes the condensation to occur at higher levels above the surface until the fog covers the entire area.

What are the factors that can affect the environmental lapse rate?

Advection of air, entrainment of air, radiational cooling, subsidence.

What are ways to measure precipitation?

Air pillows for snow, rain gauges, tipping bucket gauges.

There are limits on lifting unstable air. What are they?

Any type of inversion

In what three ways can you achieve saturation?

By cooling the air temperature to the dewpoint temperature, by mixing cold air with warm moist air, and by adding water vapor to the air.

What is centripetal acceleration?

Centripetal acceleration is the acceleration associated with the flow in a curved direction. It is associated with the Centrifugal force. The centripetal acceleration is inward directed

What is sublimation?

Change from a solid into a vapor without passing through the liquid phase. Also used to describe the reverse (vapor to solid).

What is deposition?

Change from the vapor phase to the solid phase (frost is an example). Deposition releases the energy of vaporization and fusion.

With what cloud would you get a "halo"?

Cirrostratus

With which pressure system (High pressure or low pressure) would you expect the usually get clouds? Which one would you expect to usually get clear skies?

Cloud with low pressure because of convergence and rising motion. High pressure because of sinking motion and divergent flow.

How do ice crystals grow in the cold cloud precipitation process?

Cold clouds produce precipitation by the Bergeron process.5. A larger droplet colliding with a smaller droplet below it as it falls will coalesce with the smaller one, making a larger droplet.

What is condensation?

Condensation is the phase change of water from a gas to a liquid.

In what cloud does hail form?

Cumulonimbus.

What is a fair weather cloud?

Cumulus humulus

What is dew

Dew is the liquid form of water when condensation occurs at the dewpoint temperature.

What is evaporation?

Evaporation is the phase change of water from a liquid to a gas.

What does friction do the wind speed, the Coriolis force, the pressure gradient force?

Friction slows the wind, it weakens the Coriolis force (see the Coriolis force equation), and it does nothing directly to the pressure gradient force.

What is frost?

Frost is the result of deposition when the air is saturated. Frost is different from frozen dew.

What is frozen dew?

Frozen dew is the solid form of water that has formed when water condensed and further cooling resulted in the water freezing.

What is heterogeneous nucleation?

Heterogeneous nucleation is the process in which water droplets grow by condensation in the presence of a hygroscopic nuclei. Heterogeneous nucleation is easier to get droplet growth since the relative humidity does not have to be at 100 percent with respect to water to have this growth occur.

What are four cloud types?

High, middle, low, and clouds of vertical development.

What is homogenous nucleation?

Homogenous nucleation occurs when water droplets grow strictly through condensation with one another. No aerosol is present.

What is the role of ice nuclei?

Ice nuclei are needed for formation of ice crystals at temperatures near 0 degrees Celsius. Ice nuclei are more rare than are condensation nuclei.

What is an adiabatic process?

In an adiabatic process, temperature change can be effected by the change in the volume of a parcel. No heat exchange takes place.

What is an inversion? How does it affect the stability or instability of the air mass?

In inversion is a change in the lapse rate of the temperature, where the temperature increases with height. It makes the air more stable.

If you are above the surface, what force is non-existent?

In the free atmosphere, friction is essentially non-existent. In the planetary boundary layer (the first 1.5 km), the friction force is important.

In the Saturated process, what happens when an air parcel rises?

In the saturated process, when a parcel rises, it will cool via the saturated or moist adiabatic lapse rate.

Describe the process of warm cloud growth for precipitation.

In this process droplets of different sizes are falling with the larger one colliding with the smaller ones and coalescing. This is the collision-coalescence process. It occurs in a cloud where the temperature is above zero degrees Celsius. Therefore, no ice crystals are present.

Describe the process of cold cloud growth for precipitation.

In this process, the Bergeron Process, ice crystals that have a lower saturation vapor pressure than does water vapor, grow at the expense of the water vapor. The cloud has water droplets that are supercooled and ice crystals present.

What is riming?

Is growth of an ice crystal as it collides with a water droplet that freezes on contact.

What happens to density as you go up in the atmosphere?

It decreases.

What happens to pressure as you go up in the atmosphere?

It decreases.

Absolute Humidity

Mass of water vapor per unit volume of air, usually expressed in grams per cubic meter (g/m3).

The mixture may have a temperature low enough to produce saturation and condensation, producing ________.

Mixing fog

What occurs at fronts between air masses of maritime origin

Mixing fog

Mixing fog

Mixing fog is fog that occurs when warm moist air comes in contact with cool moist air.

What clouds give us precipitation?

Nimbostratus, cumulonimbus.

Why is growth by condensation not a precipitation producing process?

Once all the small droplets have combined with the larger ones, there is insufficient water vapor to grow the droplets anymore.

Know the mechanisms that lift air.

Orographic, Frontal, Convergence, Convection

What is pressure?

Pressure is a force per unit area. In our atmosphere, it is the force per unit area exerted by the gases.

Types of fog resulting from cooling

Radiation (Ground), Advection, Upslope, mixing fog

What is the difference between sleet and freezing rain? What is the common feature in the temperature profile for each of these precipitation types?

Sleet and freezing rain form in the presence of a frontal inversion. The difference is the sleet is frozen before reaching the ground and freezing rain freezes on contact with a super cooled surface.

Types of fog resulting from

Steam, Frontal

What is subgeostrophic flow?

Subgeostrophic flow is the gradient flow found around low pressure systems where the forces result in a wind speed slower than would be expected from the pressure gradient force.

What is supergeostrophic flow?

Supergeostrophic flow is the gradient flow found around high pressure systems where the forces result in a wind speed faster than would be expected from the pressure gradient force.

What is the Coriolis force? When the Coriolis force equal to zero?

The Coriolis force is the force that appears to deflect motion. It is an apparent force that arises because of the earth's rotation. It is always zero at the equator and when the wind speed is zero.

What is Guldberg-Mohn balance? What forces are in balance?

The Guldberg Mohn balance is a balance that arises because of the effect of friction on the wind. The forces in balance here are the friction force, the pressure gradient force and the Coriolis force. If we have a closed low pressure or high pressure system, we would add the centrifugal force.

Identify the direction of air flow around a high pressure in the Northern Hemisphere.

The air flow around an area of high pressure in the northern hemisphere is clockwise.

Identify the direction of air flow around a low pressure in the Northern Hemisphere

The air flow around an area of low pressure in the northern hemisphere is counterclockwise.

How do we determine when the air is absolutely stable?

The air is absolutely stable when the environmental lapse rate is less than the dry and the moist adiabatic lapse rates.

How do we determine when the air is absolutely unstable?

The air is absolutely unstable when the environmental lapse rate is greater than the dry and the moist adiabatic lapse rates.

How do we determine when the air conditionally unstable?

The air is conditionally unstable when the environmental lapse rate is between the dry and moist adiabatic lapse rates.

In the Guldberg-Mohn balance, how do we explain the cross isobar flow?

The cross isobar flow is the result of the friction reducing the wind speed which in turn weakens the Coriolis force. This cause the flow to cross isobars toward low pressure and cross isobars outward from high pressure.

What is the environmental lapse rate and how does it differ from the dry and saturated adiabatic lapse rates?

The environmental lapse rate is the change in temperature with height for a given location or area. It varies from day to day. The dry and moist adiabatic lapse rates are fixed.

What is terminal velocity?

The final speed obtained by an object falling through the atmosphere, when friction with the surrounding air bal ances the force of gravity.

What are the forces that move the air?

The forces are the pressure gradient force, the Coriolis force, the gravitational force, the centrifugal force and the friction force.

What is geostrophic balance? What forces are in balance?

The geostrophic balance is the balance found where the air is not accelerating and the forces in balance are the pressure gradient force and the Coriolis force.

What is gradient balance? What forces are in balance?

The gradient balance occurs where the air flows parallel to the isobars in a curved manner. The air accelerates as in the curved path. The forces in balance are the pressure gradient force, the centrifugal force and the Coriolis force.

What is the hydrostatic equilibrium? Why is it important?

The hydrostatic balance is the balance between the vertical pressure gradient force and the gravitational force. Without it, the atmosphere would have rapidly ascending air in all areas.

What is the difference between the lifted condensation level and the level of free convection?

The lifted condensation level is the point at which condensation occurs. Above this, if available, is the level of free convection where the air, which is all ready saturated, is positively buoyant.

Relative Humidity

The measure of the amount of water vapor in the air as a fraction of saturation, often expressed as a percent age. Because the saturation point is temperature-dependent, relative humidity depends on both the moisture content and the temperature of the air.

What is the effect of curvature on saturation vapor pressure?

The more curved the surface, the higher the saturation vapor pressure. This also holds for relative humidity which can be expressed as the ratio of the specific humidity and the saturation specific humidity * 100.

What is the planetary boundary layer, the free atmosphere?

The planetary boundary layer (PBL) is that part of the atmosphere within the first 1.5 km (approximately) where friction is important. The free atmosphere is the region above the PBL where friction is no longer important.

What is cloud seeding? How is it performed? What precipitation formation process is involved in cloud seeding?

The process of introducing "ice" nuclei into a cloud to create precipitation. It takes place by the Bergeron process, and can only occur in cold or cool clouds.

What is aggregation?

The process where ice crystals come together.

What is the frost point?

The temperature at which frost will form if the air is cooled at a constant pressure.

Dew Point

The temperature to which the air must be cooled to become saturated.

Why can you see your breath on a cold day?

The warm moist air expelled from your lungs mixes with the colder air. For a moment, the mixture becomes saturated and you can see the condensation in the air coming from your mouth. Of course, this process doesn't last long because the mixed air mixes with even more drier air until the air is no longer saturated and the water droplets from your breath quickly evaporate, mixed fog

What are lenticular clouds?

These are lens shaped clouds that form downwind of mountain ranges.

Pressure gradient force

This force is the result of pressure differences. The greater the pressure difference, the more closely drawn are the isobars. This means that the wind is very strong. The weaker the pressure gradient, the more spread are the isobars. This means that the wind is weak. This force is always pointed toward low pressure.

Friction force

This force is the result of the character of a surface. It causes the wind to slow down in speed and can change the direction of the wind.

Geostrophic Balance

This is a balance between the horizontal pressure gradient and the Coriolis force. In this balance, the horizontal pressure gradient force is pointed toward low pressure (it always is) and the Coriolis force is pointed in the opposite direction. The resultant wind is the geostrophic wind. This flow is generally occurring in flow that is not curved (that is non-accelerating).

What is a frontal inversion?

This is a type of inversion where warm air associated with a warm front overruns cold air as it is retreating, thus forming a frontal inversion.

What is the rain shadow?

This is formed by the adiabatic descent of air on the leeward side of a terrain feature.

Hydrostatic Balance

This is the balance between gravitational force directed down and the pressure gradient force which is pointed up.

Gradient Balance

This is the balance between the Pressure gradient force, the Coriolis force, and the Centrifugal force. This balance occurs in curved flow (accelerating flow) where the centrifugal force is always directed outward from the center, pressure gradient force points toward low pressure and the Coriolis force points in the opposite direction to the pressure gradient force.

What is the hydrologic cycle?

This is the cycle that explains the movement of water through the atmosphere.

Gravitational force

This is the downward directed force that is the result of the Earth's gravitational field.

What is entrainment?

This is the drawing in of air outside a cloud. It can change the stability of the air within the cloud.

Coriolis force

This is the force that occurs because the earth rotates. It causes a deflection of the air in a rightward direction in the northern hemisphere.

What is the Lifted Condensation Level?

This is the level at which a parcel of air rising at the dry adiabatic lapse rates reaches the dewpoint temperature and becomes saturated. At this point, the parcel rises at the moist adiabatic lapse.

What is the environmental lapse rate?

This is the rate of change of the temperature at some point on the Earth. It varies from point to point and day to day.

What is a subsidence inversion?

This is the result of sinking or subsiding air. The air dries and warms adiabatically.

Why do we need to reduce the pressure to sea level?

To plot maps of pressure, we have to take into account the terrain. Because pressure decreases with height, if we didn't reduce pressure to sea level, there would be constant areas of low pressure in elevated locations.

Upslope fog

Upslope fog is fog that forms when there is a gradual orographic ascension of moist air up a sloping plain or hilly region.

In a dry adiabatic process, what happens when an air parcel rises?

When an air parcel rises in the dry adiabatic process, the parcel expands and the parcel experiences a temperature decrease of 1 degree Celsius per 100 meters.

In the Saturated process, what happens when the air parcel sinks?

When the parcel descends, it will warm via the saturated adiabatic lapse rate.

In a dry adiabatic process, what happens when the air parcel sinks?

When the parcel sinks, the parcel contracts and the temperature of the parcel increases 1 degree Celsius per 100 meters.

What are some of the errors associated with measuring precipitation

Wind blown, overestimate using radar.

Gulberg-Mohn balance

balance between the friction force, coriolis force, and the pressure gradient force. This balance occurs in the planetary boundary layer and accelerates the wind by changing the speed and direction (velocity). It has no impact on the pressure gradient force.

What cloud gives us hail?

cumulonimbus.

Centrifugal force

represents the effects of inertia that arise in connection with rotation and which are experienced as an outward force away from the center of rotation.

The moist air will cool adiabatically to form _________ providing the air is already close to saturation.

upslope fig