Moisture Flashcards
What dictates how much moisture/vapour a pocket of air can hold?
The air’s temperature
What are the three changes of states of matter?
What are the terms for:
- Liquid to solid
- Solid to liquid
- Freezing
- Melting
What are the terms for:
- Solid to gas
- Gas to solid
- Sublimation
- Deposition
What are the terms for:
- Gas to liquid
- Liquid to gas
- Condensation
- Evaporation
What is deposition?
- When a gas becomes solid, this is called deposition.
- This is a process that releases energy
- This is how hoarfrost and snow are formed
What is sublimation?
- When a solid skips the melting stage and goes right into being a gas, this is sublimation.
- This process absorbs heat/energy
- Dry ice is an example of this
What is Dew Point?
This is the temperature at a given pressure that air must be cooled to in order to reach 100% saturation. Knowing the dew point gives us a measure of how much water the atmosphere is currently holding.
Why can warm air hold more moisture than cold air?
In cold air, molecules are very tightly packed and there isnt much room left over for water molecules to fit themselves in.
What is relative humidity?
Given as a percentage, this is the amount of water vapour present in the air compared to what it could hold.
Rememeber this changes based on temperature. A colder parcel of air can hold less moisture than warm.
At 100% relative humidity the air is saturated (like a sponge, it is holding 100% of the water that it can). If the air then cools, the air molecules essentially shove out some of the moisture as the pack closer together.
This moisture is expelled in the form of clouds or precipitation
What is the environmental lapse rate and how do we find it?
Inlike the ISA, this is the actual lapse rate of how much the temperature drops per 1000 ft
What does adiabatic mean?
- Refers to a parcel of air in which the air inside the parcel cannot interact with or be influcenced or changed by the atmosphere surrounding it
What is dry and wet adiabatic cooling
So we have our sealed parcel of air and water molecules that is warmer than the air around it. As this parcel starts to rise it will still cool, but much slower, at 3°C / 1000ft. This is the dry adiabatice lapse rate (called dry because the water is still in vapour form and not visible)
As it rises this parcel will expand (because the air gets thinner as you gain altitude). This expansion will caused a cooling of the parcel.
As it cools, it will eventually become saturated, forcing the water molecules out as visibe moisture. This is of course condensation, which means the water malecules released their latent heat to become visible moisture. This latend heat is still trapped in the parcel and causes the lapse rate to drop considerably. Now we have the wet lapse rate of 1.5 / 1000ft
If a parcel of dry (no visible moisture yet) is rising, expanding, and cooling, what is the relative humidity within that parcel doing?
Realtive himidity is increasing
What are the three main types of rainfall?
- Convergent / Cyclonic Rainfall
- Orographic / Relief Rainfall
- Convectional Rainfall
What is orographic (relief) rainfall?
When warm, moist air is forced up and over an obstacle (mountain), it cools. This cooling allows condesation to form clouds and precip
What is convectional rainfall?
- When the ground is heated and the air over it rises and expands.
- During its climb, the air mass remains warmer than the air surrounding it and continues to rise
- Thunderstorms
