Snow hydrology part 1

Question 1

What are the two key questions in snow hydrology?

Answer 1

1) How much snow is there?
2) How fast it’s going to melt

Question 2

What is the SWE?

Answer 2

It’s snow water equivalent, it’s the amount of liquid water you would obtain if you melted a certain amount of snow

Question 3

What is the SWE equation? What are the two things you need to know to calculate the SWE?

Answer 3

SWE = density of snow/density of water x Depth
You need to know the density of the snow and the depth of the snow

Question 4

What’s the density of water?

Answer 4

1000 kg/m^3

Question 5

What is SWE measured in?

Answer 5

usually mm

Question 6

How do you determine SWE using a snow core sampler?

Answer 6

Take the snow core sampler, stick it into the snowpack, pull it out to get the core of snow, uses gages to determine depth of snow pack, and then use the depth of the corex the area to find the volume of snow, divide it by the weight and then get density. With both depth and density of snow you can then find SWE.

Question 7

What are snow pit/density samples used for?

Answer 7

You take the cube and get snow and then use that to find density of snow, than proceed with SWE calculations

Question 8

How can you find the SWE over large areas?

Answer 8

Can use a snow depth probe in which you make depth measurements every metre over 100 metres and then using snow pits get density and then calculate SWE.

Question 9

What are the four ways to make automatic SWE measurements?

Answer 9

heated tipping bucket
sonic ranger
snow pillow
gamma ray counter

Question 10

How does a heating tipping bucket work?

Answer 10

the bucket is set out and copper funnel gets warmed, any snow that lands on the funnel melts and then runs into the bottom of the bucket, gives you an immediate measurement of snow water equivalent

Question 11

How does a sonic ranger work?

Answer 11

emits sound wave that bounces over surface of snow pack and the amount of time it takes to come back shows you the snow depth, as the snow depth increases the signal returns faster (cause it’s bouncing off a higher elevation)

Question 12

What is a benefit of the snow pillow?

Answer 12

It reduces drift over the landscape

Question 13

How does a snow pillow work?

Answer 13

gives a measurement over small area, is a flexible pad filled up with antifreeze, as the snow lands on the pad it displaces glycol into a tube and the height of the tube is measured relating to the weight of the snow on the pillow. Can then use weight/area to get density and then divide that by density of water to get SWE.

Question 14

How does a gamma ray counter work?

Answer 14

most places on earth contain small levels of radioactive isotopes, the sensor counter measures radiation as it leaves the earths surface, snow decreases signal, so the SWE is found bases on the reduction of the signal from isotopes.
Advantage here is that it measures over very large areas, however it does not provide info directly on depth and density of snow

Question 15

How does snow form in clouds?

Answer 15

By the bergeron process, this occurs in cold clouds that become supersaturated and cool below their saturation vapor pressure so the water vapour moves to the lower sat vapor pressure in these clouds and condense over previous ice crystals or CCN.

Question 16

What two things does the initial shape of the crystal depend on?

Answer 16

Temperature in the cloud and the degree of supersaturation

Question 17

To get the classic dendritic snowflake, what conditions do you need?

Answer 17

Moderately cold temperatures and high supersaturation

Question 18

What is destructive metamorphism, how will it change snow density, grain size, and grain form?

Answer 18

Destructive metamorphism is when the snow grains blow around, smash into things and break up, this causes snowflakes over time to erode, become smaller, rounded, and increase in density (as they get compacted).

Question 19

What is constructive metamorphism (ex: sintering)?

Answer 19

Is when snow crystal his the ground and as pressure increases on the snowpack they snow grains weld together and increase in density.

Question 20

What is constructive metamorphism (ex faceting)?

Answer 20

Occurs when there’s large temp gradients in the snowpack which lead to diff saturation vapor pressures (higher at bottom due to more warmth) so water evaporates and moves up ad then refreezes created big grains. This decreases density, increases snow grain size, and changes the form into a striated one.

Question 21

Why does snow metamorphism matter?

Answer 21

Because it effects density (destructive metamorphism and sintering increasing density, faceting decreases) (how much snow) and effects albedo (destructive metamorphism decreases it) (which determines how fast the snow will melt).

Question 22

What is the driver of how fast snow will turn into melt?

Answer 22

the energy balance

Question 23

How much incoming solar radiation does snow reflect through albedo?

Answer 23

40 -90%

Question 24

What is the total energy available for melt or warming of the snow eqn?

Answer 24

delta Qm= Q* (energy balance) + Qh (sensible heat) + Qe (latent heat)

Question 25

How do you find the snow melt rate in mm/hr?

Answer 25

Have Qm (W/m^2)/100 = m/s and convert to mm/hr

Question 26

Say the energy available to melt was negative and the snow pack temp reached 0 degree, would the snow be freezing or melting? What if Qm was positive?

Answer 26

first scenario, it would freeze, second scenario it would melt

Question 27

How does longwave radiation both contribute to cooling and warming of a snow pack?

Answer 27

If albedo or clouds is high the long wave might reflect back and make the snowpack lose energy, but clouds can also reradiate energy which causes a energy gain and leads to warming of the snowpack