precipitation

Question 1

generally winter is getting _______ and summer is getting _________. though annually it doesn’t make that much of a difference

Answer 1

wetter

drier

Question 2

why is summer drier?

Answer 2

warm air can hold more water

Question 3

what are the Met Office Standards for rain gauges

Answer 3

• funnel and bottle
• there must be a standard height above the ground
• narrow spout of funnel to limit evaporation.
• standard diameter 5inches

Question 4

explain briefly how tipping bucket rain gauges work

Answer 4

-funnel to collet water then to a metal scope on a pivot.
-when one side of the scope is full, it then tips and fill water on the other scoop
-the rate at how fast It tips measure how much water there is.
each tip is equivalent 0.5mm of rainfall
-can measure the amount of rain over a period of time to find rat
-on graph, one bar=pne tip

Question 5

explain briefly how weighing rain gauges work

Answer 5

• it has a sensor that measure the mass of water collected, hence record the rate of rainfall in a period of time
• it can measure both liquid and solid precipitation
• big container, doesn’t need to be empty often
• oil floats on top of water to reduce evaporation

Question 6

why do rain gauges have to be set on short grass

Answer 6

vegetation will shelter the rain gauge if its not short, hence will affect accuracy as vegetation absorbs water

Question 7

why does the height at which the rain gauge is set matter

Answer 7

closer to surface- more splash in and splash out

higher up- no splashes but more Windfield. less blown in and blown out.

Question 8

how can splash in and blow out be reduced

Answer 8

• the rain gauge is levelled with the ground to reduce splashing
• shielded to reduce windfield

Question 9

true or false

raindrops have a higher velocity than snowflakes

Answer 9

True. snowflakes has a lower density hence lower velocity

Question 10

what are the techniques to measure snowfalls

Answer 10

• need shielded gauges, can capture more snow

- snow gauges can’t be built too low; can be buried

Question 11

how do we find the snow mass per unit area?

Answer 11

snow depth x snow density

Question 12

why does snow density vary

Answer 12

snow can be compacted. therefore density is fresh snow is lower than old compacted snow

Question 13

how does a visibility sensor work

Answer 13

• made up of two sensor, one is to shine light, another is to receive
• clear day- light will shined to the ground from the first sensor, no reflection will be picked up at the detector
• foggy day; particles in the air will reflect the light and the detector will pick this up. less light resulted on the ground

Question 14

how does precipitation detector work

Answer 14

circuit is work when rain touches the electrodes. the amount of water running across the surface gives the rate of rainfall.

Question 15

compare how the optical disdrometer and impact disdrometer work

Answer 15

optical- 2 sensors; one to emit radiation dn one to pick it up. when there’s rainfall in between, radiation gets interfered and rainfall rate will be given
impact- measure the sound of the rain and generate electrical impulse

Question 16

true or false

larger drops correspond with higher rainfall rate

Answer 16

True

Question 17

how does rainfall radar work

Answer 17

• a pulse electromagnetic radiation is transmitted
• signal is reflected back from the raindrops
• distance of rain is given by the time of return signal
• size of drops is given by the strength of signal.
• stronger strength = larger raindrops = higher rainfall rate.

Question 18

True or false 
Radar scans by rotating about vertical
axis at four elevation angles between
0.5 and 4 – one complete scan takes
5 minutes

Answer 18

True

Question 19

true or false

both rain and drizzle can be detected by radar

Answer 19

false. drizzle is too small to be detected

Question 20

what are some rainfall radar errors

Answer 20

• echoes can be from birds or a group of insects
• echoes due to permanent obstacles (mountains)
• rain detected at high levels may evaporate before it reaches the ground. so data not useful for public
• wet snowflakes at melting stage looks like large raindrops and can give false results

Question 21

why can we eliminate rainfall radar errors

Answer 21

• use a network of rainfall radar to create overlapping of radar, this helps us to recognise the pattern
• compare the results with rain gauges

Question 22

why is rainfall radar useful

Answer 22

helps us to get immediate data on the amount and location of the rainfall. helps us to forecast events like flash-floods

Question 23

how can satellite measure rainfall and humidity

Answer 23

measure radiation field at particular wavelength and relate it to rainfall

Question 24

how can doppler radar be used to monitor storms and tornado

Answer 24

• doppler radar measure how fast a target (eg. storm) is moving towards or away from the radar
• it does it using the frequency shift of the return signal

Question 25

1mm rainfall = _____ kg m^-2

Answer 25

1