Precipitation (fact sheets 3&4)

Question 1

Precipitation

Answer 1

The water reaching a catchment as rainfall, snow, hail, dew or occult (i.e. mist, fog) forms.

Question 2

Average annual rainfall for the world and Lancaster

Answer 2

1000m

Question 3

Rainfall measurement is based on…

Answer 3

areal integration of a network of point rainfall measurements (individual rainguage catches)

Question 4

Measuring rainfall

2 types

Answer 4

1. storage gauge

2. rainfall recorders

Question 5

two types of storage gauge

Answer 5

daily and monthly

Question 6

Example of a daily storage gauge

Answer 6

met office mark 2 daily storage gauge

Question 7

Errors associated with storage gauges

2

Answer 7

outsplash and insplash

Question 8

adaptation to reduce in-splash

met office mark 2 daily storage gauge

Answer 8

the gauge orifice is located 1ft above the ground surface

Question 9

adaptation to reduce out-splash

met office mark 2 daily storage gauge

Answer 9

drop between orifice and collection funnel of 4 inches

Question 10

adaptation to reduce uncertainty in the collected area

met office mark 2 daily storage gauge

Answer 10

the orifice has a ‘knife edge’

Question 11

adaptation to reduce evaporation of collected water

met office mark 2 daily storage gauge

Answer 11

the collection funnel has a narrow neck

Question 12

adaptation to extreme rainfall

met office mark 2 daily storage gauge

Answer 12

the collection bottle sits within an outer can that will catch extreme rainfall (slightly less accurately though)

Question 13

adaptation to further reduce evaporation and increase stability
(met office mark 2 daily storage gauge)

Answer 13

the gauge is dug into the ground

Question 14

When are met office mark 2 daily storage gauge monitored in the UK

Answer 14

9am GMT / 10am BST

Question 15

two types of rainfall recorders

Answer 15

siphoning-tank raingauge

tipping-bucket raingauge

Question 16

siphoning-tank raingauge

Answer 16

collects water in a funnel, directs this into a cylindrical tank, as the tank fills a float is raised which lifts a pen on a chart (autographic chart)

Question 17

what happens when a siphoning-tank raingauge reaches a certain water level?

Answer 17

the float-pen mechanism releases a catch and the tank tips over and empties from a pipe aided by a siphoning mechanisms

Question 18

name of autographic chart produced by a siphoning-tank raingauge

Answer 18

hyetogram

Question 19

disadvantage of a siphoning-tank raingauge

Answer 19

the chart requires digitising to obtain rainfall intensity data

Question 20

Tipping-bucket raingauge

water collection

Answer 20

collects water in a funnel then delivers it to a pivoted double bucket device, one bucket is filled first, which causes it to tip, empty and bring the second bucket below the funnel

Question 21

Tipping-bucket raingauge

data collection

Answer 21

as each bucket tips, a magnet passes a reed switch causing an electrical contact to close, the time of the voltage pulse can then be recorded with a datalogger

Question 22

when are the tipping-bucket raingauge buckets set to tip?

Answer 22

after receiving 0.5mm of rainfall

Question 23

Tipping-bucket raingauge are sensitive to

Answer 23

freezing

Question 24

what is a reed switch

Answer 24

two pieces of metal which are very close together, close to a magnet, makes a circuit when closed

Question 25

how to mitigate freezing of tipping-bucket raingauges

2

Answer 25

use resistors as heaters
or
accept freezing on cold days and have a check gauge which records monthly total next to it

Question 26

how can raingauge sheltering be avoided?

Answer 26

sit the gauge at a distance 2x the height of the nearest obstacle, which is equivalent to a 30 degree angle between the gauge and the building top

Question 27

how can turbulence at the gauge orifice be reduced?

2

Answer 27

sit the gauge within a Huddleston turf wall and slope the banks
or
gauge in a ground-level pit with an anti-splash grid around

Question 28

how is precipitation in forest measured?

2

Answer 28

sitting rain gauges in clearings

connecting a canopy-level funnel to a standard raingauge (canopy gauge)

Question 29

how is snowfall measured?

Answer 29

heated gauges at 1m above ground with shields around the gauge orifice to reduce turbulance effects