Chapter 5

What does the environment lapse rate refer to?

(ELR) the rate of vertical temperature decrease in the air column

What are psychrometers? How do they work?

A pair of thermometers, one of which has a cotton wick around the bulb that is saturated with water, the other with no covering. Swinging the device will cause evaporation of water on the wet bulb, giving the wet bulb temperature. This is compared to the dry bulb temperature to determine the amount of water vapor present in the air.

When rubbing alcohol is applied to a person's skin, it feels colder than the application of water would. Why?

Alcohol is very volatile; it evaporates more quickly than water and therefore carries away body heat more rapidly

What are the numerical values of dry and saturated adiabatic lapse rates? Under what circumstances are they applicable?

As long as air is unsaturated it will heat or cool when ascending or descending, respectively, at a rate of 1.0oC/100 m, the dry adiabatic lapse rate. Once saturated, ascending air will cool at the saturated adiabatic lapse rate which on average is 0.5oC/100m.

Why is relative humidity a poor indicator of the amount of water vapor in the air?

Because it is temperature dependent and it is inversely proportional to air temperature. Therefore, high relative humidity values in cold air actually relate to minuscule absolute humidity values. Conversely, low relative humidity values in warm air may relate to rather large absolute humidity values.

What are deposition and sublimation?

Both terms refer to a change of state which skips a step. Specifically, deposition refers to the changed of state from a gas to a solid while sublimation indicates the reverse.

What are the three general methods by which the air can become saturated?

By adding water vapor to air, mixing cold air with warm, moist air, and/or lowering the temperature of air to the dew point.

What are condensation nuclei and ice nuclei? Are they typically made of the same materials? Which is more abundant in the atmosphere?

Condensation nuclei are small, airborne particles that enhance condensation and ice nuclei are particles onto which ice crystals can form when the air becomes saturated. No, they are not typically

Define dew point. What characteristics make this measure superior to relative humidity?

Dew point is the temperature at which saturation is reached. It is useful in that the dew point can be compared directly to the current temperature to determine the amount of water vapor present. When the dew point is close to the actual temperature then the air is near saturation, when it is far from the air temperature, it is far from saturation.

Explain the difference between diabatic and adiabatic processes.

Diabatic processes refer to temperature changes that involve a direct exchange of heat energy. Adiabatic processes refer to temperature changes without an exchange of heat.

Why can't the dew point temperature exceed the air temperature? What happens if the air temperature is lowered to a value below the initial dew point?

If air temperature is lowered to the dew point, saturation will occur. If the temperature dips below the dew point, then the dew point will decrease as well. This is offset by the condensation of water vapor in the air. Because of this, the dew point can never exceed the air temperature.

Describe the various processes that can lead to the formation of dew.

Lowering of temperature to the dew point near the surface. Favored under clear skies and no wind.

Define relative humidity.

Relative humidity is the amount of water vapor in the air compared to the maximum amount possible at the current temperature.

Explain the concepts of equilibrium and saturation.

Saturation is an equilibrium state denoting proportional loses of water from the surface to the atmosphere through evaporation and gains from the atmosphere to the surface through condensation. When energy is available and evaporation occurs, the low water vapor content of the atmosphere keeps condensation from occurring. With increasing water vapor content, the rate of condensation increases. Eventually, the amount of water vapor in the air is enough for the rates of condensation and evaporation to be equal. The resulting equilibrium state is termed saturation.

What is the difference between frozen dew and frost?

Structure and manner of formation

Define dry bulb temperature, wet bulb temperature, and wet bulb depression.

The dry bulb temperature is the temperature of the dry thermometer, the wet bulb temperature is the temperature of the wet thermometer. The wet bulb depression is the difference between the two temperatures, which is used to measure water vapor content of the air.

What is the first law of thermodynamics and how does it apply to cloud development?

The first law of thermodynamics states what happens when heat is added to or removed from gases. Specifically, if heat is added, there will be some combination of an expansion of the gas and an increase in its temperature. This is important towards a proper understanding of the adiabatic process.

What is the heat index?

The heat index is a measure of the high air temperature with the effect of humidity factored in. This gives an indication of how high heat and high humidity will affect the human body.

What is vapor pressure? In what units of measure is it expressed?

The pressure exerted on the atmosphere by the presence of water vapor. Expressed another way it is the part of the total atmospheric pressure due to water vapor. It is expressed in millibars in the US and kilopascals in Canada.

Describe the distribution of average dew point across the united states in summer and winter.

The total amount of water vapor generally decreases with distance from the Gulf of Mexico, the primary source of water vapor. This is true in both seasons as well as in north-south and east-west directions. During winter the amount of moisture extending into the Great Plains is low and only a minimal amount of east-west variation exists. In summer, a decline is seen in a north-south direction and also moving westward from about the Mississippi River to the Rocky Mountains. Obviously, more water vapor is present during the summer months.

What is supercooled water?

Water having a temperature below the freezing point of water but nonetheless existing in a liquid state.

Describe the various processes that can lead to the formation of fog.

cooling of layer of air with light winds, evaporating water from falling precipitation or by mixing warm moist air with cold air