Part 1 - what is snow? Flashcards
What shape are snowflakes?
Hexagonal
What are the size of snowflakes dependent on?
The temperature and amount of water vapour available at the time of development
At what temperature can snowflakes form?
-40 degrees
What percentage of the earth do snowflakes cover?
23%
How do snowflakes form?
Ice crystals form around a small particle of dust or chemical substance in the air.
If the air is humid the the crystals tend to grow more rapidly, develop branches and clump together. In colder, drier air the particles remain small and compact
Define the term ‘snow’
It is the solid form of water that crystallises in the atmosphere
What is air from ear the earths surface made up of approximately?
Nitrogen
Oxygen
Argon
Very small traces of other gases including carbon dioxide and water vapour
What percentage of nitrogen makes up air?
78%
What percentage of oxygen makes up air?
21%
What percentage of argon is air made from?
1%
Up to what percentage of water vapour may air contain in hot tropical rain forests?
4%
What happens to the molecules and pressure of the air with altitude?
It decreases
How thick is the earths atmosphere?
It is a difficult question to answer but it is said to be about 100 km
What thickness of the atmosphere does weather take place in?
15 km of the earths atmosphere
Why does a helium balloon rise?
Helium is lighter than air
In a video a helium balloon was sent into the atmosphere, as it rose it expanded to around 3 times its size, why did it expand?
The balloon expanded because of the pressure of the helium gas inside the balloon was higher than the pressure of air outside the balloon
Why did a helium balloon that was sent into the atmosphere fall back down once the ballon had burst?
Because of the force of gravity
What is the abbreviation for volume?
V
What is the abbreviation for mass?
m
In mathematical terms what is the abbreviation for density?
p
In mathematical terms if two symbols are put next to each other what does this mean?
It is accepted that this means that they should be multiplied together
On average how much does the temperature drop every 1000 m of ascent?
6 degrees Celsius
Though these values vary considerably with location, season and time of day
Assume the temperature drops 6 degrees for every 1000 m of ascent. If it is 15 degrees at sea level(0m altitude). What is the atmospheric temperature on the summit of Mount Everest (8848 m) ?
There are 8.848 sets of 1000 m. 8.848 multiplied by 6 degrees = 53.088 degrees 15 - 53.088 = 38.088 degrees Rounded to 1 sig fig -40 degrees
What is the troposphere?
It is the lowest region of the atmosphere
It is bounded by the earth beneath and the stratosphere above
10-18km
Characterised by decreasing temperature with increasing altitude
Which layer of the atmosphere are most of the weather and cloud systems held?
Within the troposphere
What is the lowest temperature that is reached in the troposphere?
-57 degrees Celsius
What are the three main transfer of heat?
Thermal conduction
Convection
Radiation
How is heat transferred through thermal conduction?
This happens when two objects are in contact with each other.
Heat can be transferred from an object at one temperature to an object at a lower temperature when the two objects come into contact with each other.
How is heat conducted from the ground to the atmosphere?
Air is a poor heat conductor, but heat is nevertheless transferred by conduction from the ground to the lowest layer of the atmosphere when the ground is hotter.
Explain how convection heat transfer works?
The bottom part to a heat source heats up first, as it gets hot it rises and liquid/gas moves down in its place to warm it up.
Explain how radiation heat transfer works?
It is heat being transferred through the air by radiation. We can feel it as heat, or we can see it (sunlight) or it can be invisible.
What two types of radiation does the sun emit?
Visible radiation - sunlight
Invisible radiation - the heat from the sun and ultraviolet light
How is the heat from the sun transferred to the top of the atmosphere?
Both through visible radiation (sunlight) and invisible radiation UV light
How is the troposphere mainly heated and how does this play a major role in one of the main characteristics of this layer?
The lower part of the troposphere is mainly heated from below and it’s heated is mainly redistributed to higher levels by convection. The result is that the temperature of the troposphere decreases with altitude. Altitude in this context is equivalent to height above sea level
What is the layer in the atmosphere above the troposphere?
Tropopause
What is the main characteristic of the tropopause?
The temperature here remains roughly constant with increasing altitude.
What layer of the atmosphere comes after the tropopause?
Stratosphere
What happens with the temperature and altitude of the stratosphere?
Temperature increases with altitude
What is the increase in temperature with altitude mainly due to in the stratosphere?
The radiation from the sun entering the atmosphere from above
What layer in the atmosphere comes after the stratosphere?
Stratopause
What layer of the atmosphere comes after the stratopause?
Mesosphere
What layer in the atmosphere comes after the mesosphere?
Mesopause
What is an endothermic process?
It is a reaction that occurs with the absorption of heat. It need an input of energy to occur
What is the main heating process for the lower atmosphere?
Convection
Apart of transferring heat from rising warm air to colder air further up, what does convection also move?
Convection also moves water vapour in the form of moist air, around the atmosphere.
What is latent heat?
It is the energy required for evaporation or sublimation
The heat absorbed or radiated during a change or phase at a constant temperature and pressure
What is a cloud?
It is a collection of droplets or crystals, of which its base is above the ground.
What is mist?
A mass of small drops of water in the air close to the ground
What is fog?
A thick cloud that forms close to the ground or to water and is difficult to see through.
Fog is thicker than mist
How are clouds formed?
When rising air that contains water cools to a point that the vapour condenses in to a liquid
What is dew point?
It is the temperature when vapour condenses in to liquid
How long do small cumulus clouds last?
On average, small cumulus clouds last only 10 mins
What are the 4 main classifications of clouds?
Cirrus
Stratus
Cumulus
Nimbus
Why does the cooling of air slow down in a cloud?
Heat is being generated in the cloud to stop the rate of cooling.
Clouds generate heat, when water condenses out of air, it releases a huge amount of energy. This energy warms the air around it and create big bursts of energy. This is what helps to keep the cloud afloat. This energy is called latent heat.
The cloud base is at 3000 ft which is 1000m. The temperature at this height is approx 21 degrees Celsius.
What would you expect the temperature on the ground to be?
It is 1000 m to the ground so we would expect the temperature to be 6 degrees warmer than the base of the cloud. The temperature would be 27 degrees
What is lapse rate?
It is the time/rate at which atmospheric temperature increases with decreasing altitude
What is precipitation?
It is the name given to water in any solid or liquid form that falls from a cloud and reaches the ground
What is considered as precipitation?
Rain, drizzle, hail, snow
What is not considered as precipitation?
Dew, frost, mist, fog
According to size what is considered to be classified as rain?
Droplets at least 0.5 mm in diameter
But is usually 1 mm to 2 mm
What are drops less than 0.5 mm in diameter called?
Drizzle
What is meant by the term coalescence?
It is when a cloud droplet in a warm cloud rises and grows bigger until it is heavy enough to drop down as a raindrop
What is condensation nuclei?
Minute particles of matter(dust, salt) that are present in the atmosphere, water vapour sticks to these and condenses. Further water vapour then stick to these surfaces and condense until droplets of liquid water form.
What are freezing nuclei?
Minute solid particles that promote the formation of ice crystals from water droplets.
What are cold clouds?
These clouds have an atmospheric pressure of 0 degrees and this is where raindrops turn to ice
How does atmospheric temperature change with altitude?
Atmospheric temperature decreases approximately 6 degrees per 1000 m of altitude
What helps water turn in to ice crystals?
The addition of bacteria helps the ice crystals to nuclear. Dust also helps the water to freeze. Pure water requires the lowest temperatures and it’s the hardest to freeze.
What does most rain start off with?
Most rain starts as ice crystals, inside a cloud the temperatures are often below freezing. As those snow crystals get heavy they fall, as they fall they melt to become rain.
Define the term supercooling?
It is water that does not freeze below the normal freezing temperature of 0 degrees Celsius
In clouds where the is an absence of freezing nuclei, at what temperature can water droplets still exist?
- 40 degrees Celsius
What is the mechanism for the formation of precipitation in cold cloud s called?
Bergeron process
What clouds often have a high number of ice crystals required to produce snow?
Nimbostratus
Describe the process of the formation of snow and rain in a cloud ?
Water vapour in clouds condense/freeze onto ice crystals and the crystals grow at the expense of a droplet
Once the crystals are large enough they can no longer be held aloft by up draughts they start to fall through the cloud of supercooled droplets
If the cloud contains many ice crystals some may break up as the fall through the cloud and form secondary crystals
Small falling crystals collide with and stuck to one another and this process forms snowflakes
If the snowflakes melt in lower warmer parts they emerge as rain
Describe the process of how hail is produced in a cloud?
Ice crystals drift through the cloud several times with a crystal partially melting and moisture freezing onto the crystals to form ‘rimed’ or graupel ice
The up and down motion through the cloud means that the ice will be deposited on the growing hail pellet under a number of different temperature conditions and hailstones are often layered, with some transparent ice (glaze) and some opaque ice (time/graupel)
The precipitation finally seen on the ground depends on the conditions at the base of the cloud and below it. Hail usually reaches the ground as hail because their isn’t time for it to melt completely even if it falls in warm air. Snow falls more slowly so it may have turned to rain by the time it reaches the ground
Why does the snow cover in the northern hemisphere advance towards the equator and then retreat throughout the year?
As winter progresses, the North Pole points away from the Sun and the energy received at the surface of the earth is reduced. As temperatures fall, snow advances towards the equator. As the earth continues to orbit, the north pole begins to face the sun and the amount of energy received attire surface of the earth increases.
As the northern hemisphere warms the snow retreats northwards
Is there any seasonal snow cover in the Southern Hemisphere away from the Antarctica?
The only snow visible in the Southern Hemisphere away from Antarctica is in a relatively small region along the west coast of South America.
