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h...PowerPoint/.../precipitation.
h...PowerPoint/.../precipitation.p
                 t
                pt
Have you ever just looked
       at clouds?
Wh do
Why d we
have clouds?
Why are there
different
shapes?
What can they
tell us about
the weather?
    Take Good Notes!



There will be
a quiz on
thi
this
information
Understanding Clouds
           Clouds form as
           warm air is
           forced upward
           As the air is
           forced upward,
           it expands and
           cools
Understanding Clouds
                      cools
           As the air cools,
           the relative
           humidity
           reaches 100%
           For more information on
            e at e u d ty click
           Relative Humidity c c ☼
 Water vapor begins to condense
        y    p
  in tiny drops around nuclei.
Nuclei are small particles of dust,
     salt
     salt, and smoke in the
           atmosphere
      Cloud Types

There are
many
different
        yp
cloud types
       Cloud Types
Can you think
of the two
main ways
that clouds
     l   ifi d?
are classified?
Shape, Height,
Shape, Height,
and
       i
sometimes
Rain Capacity
       By Shape!
  There are three main cloud
types that are based on shape
   Think you know any of them?

            Stratus
           Cumulus
            Cirrus
    Stratus Clouds
Stratus
clouds form
  smooth,
a smooth
even sheet
They usually
form at low
altitudes
     Stratus Clouds
When air is
cooled and
condenses near
the ground, a
stratus cloud
know as _______
forms
Know the
name?
Cumulus Clouds
        These are
        masses of
        puffy,
        puffy white
        clouds, often
        with flat bases
        They form
          hen
        when air
        currents rise
Cumulus Clouds
        Th
        They can bbe
        associated
        with both fair
        weather
        and…….when
         h          ll
        they get really
        tall ___!
Thunderstorms!
      Cirrus Clouds
Ci       l d
Cirrus clouds
are high, thin,
white,
feathery
clouds
containing ice
  y
crystals
     Cirrus Clouds
Cirrus clouds
are usually
associated
with fair
weather, but
they may
indicate
         hi
approaching
storms
      By Height
Th      fi f l d
The prefix of cloud names can
 describe the height of cloud
             bases
                      above
   Cirro: High clouds abo e
            6000m
        By Height

Alto: Middle elevation clouds
between 2000 to 6000m

Strato: Low level clouds below
2000m
       Rain Clouds
Nimbus
Ni b
clouds are
dark clouds
associated
with
precipitation
        Rain Clouds
When a nimbus
cloud is also a
towering
cumulus cloud,
it’    ll d
it’s called a
cumulonimbus
cloud
Cirrus
Clouds
Cl d
Cumulostr
  atus
 Clouds
 Ready for a quick review?

1. Cl d         f     h th
1 Clouds can form when the
relative humidity reaches ____%
2. In order for clouds to form,
  ater apor
water vapor begins to condense
around ____of dust, salt, and
smoke
3. Clouds are classified by ____
   d       d        i
and____ and sometimes rain i
capacity
4. Puffy, white clouds are called?
5
5. Mid elevation clouds between
2000 and 6000m
Let s
Let’s see how you did!

        1.
        1 100
      2. Nuclei
 3. Shape and height
     4. Cumulus
        5.
        5 Alto
Forms of Precipitation
Precipitation (pre-sip-uh-
P i it ti     (      i  h
              (pre-sip-uh-
tay-
tay-shun) is any form of
water that falls to the
Earth's surface.
Types of Precipitation
The type of precipitation that
Th t        f    i it ti   th t
              g        p
falls to the ground depends
upon the formation process
   d th temperatures of the
and the t         t      f th
environment between the
cloud and the surface
Can you name the different
  types of precipitation?
            Rain
            R i
            Snow
             Hail
            Sleet
        Freezing Rain
         Rain
    Rain develops when
  growing cloud droplets
  g      g            p
    become too heavy to
 remain in the cloud and
           ,
as a result, fall toward the
      surface as rain
R i        l
Rain can also   As th f lli
                A the falling
begin as ice    snow passes
crystals that   through the
collect each    freezing level
other to form   into warmer
l
large                 h flakes
                air, the fl k
snowflakes      melt
Rain from snow!
          Snow
Snow is formed when ice
S      i f     d h i
  y
crystals form from water
vapor that is in the clouds
directly b           h d !
di tl above your heads!
This process is called
sublimation
             Hail
Hail is formed
when updrafts
         i d
carry raindrops
upwards into
extremely cold
areas of the
atmosphere
              Hail
There the
raindrops
merge and
freeze. When
the frozen
clumps get to
heavy they fall
to earth
            Hail
H il
Hail can vary
in size, from
the size of a
small stone to
that of a
baseball! So
b    b ll
be careful
          Sleet
                raindrops
Sleet is frozen raindrops.
Sleet begins as rain or snow
and falls through a deep
layer of cold air that
contains temperatures below
freezing th t exist near the
f    i    that i t       th
surface.
Sleet
    Rain that falls
    R i th t f ll
    through this
    extremely cold
    layer has time
    to freeze into
         ll
    small pieces off
    ice
      Freezing Rain
F    i      i is f lli    i th t
Freezing rain i falling rain that
             0°
cools below 0°C, but does not
turn to ice in the air
      ater “supercooled”
The water is “supercooled”
When the drops hit anything
 they instantly turn to ice!
1.
1 Nuclei for the formation of rain
   drops can be small particles of: A)
   salt     smoke     dust
   salt, B) smoke, C) dust, D) all the
   above
2 Whi h of these cloud types is not
2. Which f th       l dt       i     t
   based on the clouds shape: A)
    t t         i b              l
   stratus, B) nimbus, C) cumulus,
   D) cirrus
         l   ti    l d b t
3. Mid elevation clouds between
 2000 and 6000m: A) nimbus, B)
 alto, C) cirro, D) strato
4. This form of precipitation is
 supercooled: A) rain, B) snow,
 C) sleet, D) freezing rain
5. This form of precipitation
5 Thi f       f     i it ti
 stays frozen all the way to the
 ground: A) rain, B) snow, C)
 sleet,
 sleet D) freezing rain

Let’s see how you did!
The Answers!
    1.
    1 D
    2
    2. B
    3
    3. B
    4. D
    5. B
        Weather Modification

• Weather modification is deliberate human
  intervention to influence atmospheric processes
  that constitute the weather.
• Weather modification falls into three categories:
    (1) the use of energy to forcefully alter the weather,
    (2) modifying land and water surfaces to change their
                                         atmosphere,
    natural interaction with the lower atmosphere and
    (3) triggering, intensifying, or redirecting atmospheric
    processes.
Intentional Weather Modification
           Techniques
• The focus of intentional weather
  modification using modern weather
                   g
  technology is on:
   cloud seeding,
          seeding,
   fog and cloud dispersal,
                  dispersal,
   hail suppression, and
        suppression,
   frost prevention
 Cloud
 Cl d
seeding
    What if you need to know the
        i f ll i      t h   t?
      rainfall in a catchment?
           yourself
Measure it yourself….
– Type of rain gauges?
            p gauges?
– Where to put g g
– How many gauges?
– How do you map it?
2.3. Measurement of Rainfall

   Rainfall and other forms of precipitation are
                              depth,
   measured in terms of depth, the values being
                  millimeters.
   expressed in millimeters.
   One millimeter of precipitation represents the
   quantity of water needed to cover the land with a
   1mm layer of water, taking into account that
            y              ,      g
   nothing is lost through drainage, evaporation or
   absorption.
   absorption.
   Instrument used to collect and measure the
                           raingauge.
   precipitation is called raingauge.
Rain:
  Is      i it ti i the form of water drops of size
– I precipitation in th f         f t d      f i
  larger than 0.5 mm to 6mm
– The rainfall is classified in to
    Light rain – if intensity is trace to 2.5 mm/h
                                 2.5           7.5
    Moderate – if intensity is 2 5 mm/hr to 7 5 mm/hr
    Heavy rain – above 7.5 mm/hr
           Rain Measurement
  Rain,                          precipitation,
• Rain the most common form of precipitation is
  probably the easiest to measure.
• The most common instruments used to measure
  rain are:
                                                  y,
    the standard rain gauge, which is read directly, and
                       g g
                       gauge,
    the tipping bucket gauge and weighing gauge, both
                                            gauge,
    of which record the amount of rain.
   A
standa
rd rain
gauge
        Rainfall measurement…




           Precipitation gauge
                 1 - pole
                     ll t
              2 - collector
              3 - support-
               galvanized
               g
                  metal sheet
               4 – funnel
              5 - steel ring


1. Non recording gauge
1 N         di
2. Recording gauge / graphic raingauge
The instrument records the graphical
                          p     p    ,
variation of the fallen precipitation, the total
fallen quantity in a certain time interval and
            y                 (
                              (mm/hour).
                                      )
the intensity of the rainfall (mm/hour).
It allows continuous measurement of the
rainfall.
rainfall.
                          The graphic rain gauge
                                 1-receiver
                                  2-floater
                                  2 floater
                                 3-siphon
                            4-recording needle
                           5-drum with diagram
                            6-clock mechanism
   Tele-
3. Tele-rain gauge with tilting baskets
     tele-
The tele-rain gauge is used to transmit
                    p    p
measurements of precipitation through   g
electric or radio signals.
The sensor device consists of a system with
two tilting baskets, which fill alternatively with
                           funnel,
water from the collecting funnel establishing
the electric contact.
The number of tilting is proportional to the
quantity of precipitation hp
Tele-
Tele-rain gauge ……



  The tele-rain-gauge

   1 - collecting funnel
    2 - tilting baskets
    3 - electric signal
      4 - evacuation
4. Radar measurement of rainfall

The meteorological radar is the powerful instrument
                         extent,
for measuring the area extent location and
movement of rainstorm.
The amount of rainfall overlarge area can be
determined through the radar with a good degree of
accuracy
The radar emits a regular succession of pulse of
electromagnetic radiation in a narrow beam so that
                                     beam,
when the raindrops intercept a radar beam its
intensity can easily be known.
Raingauge Network
 Since the catching area of the raingauge is
      y              p
 very small as compared to the areal extent
 of the storm, to get representative picture of
 a storm over a catchment the number of
    i           h ld be
 raingauges should b as l                  ibl
                            large as possible,
 i.e. the catchment area per gauge should
      small.
 be small.
 There are several factors to be considered
                           gauge:
 to restrict the number of gauge:
 – Like economic considerations to a large extent
                                       extent.
 – Topographic & accessibility to some extent.
                                            Raingauge Network…..

World   Meteorological                 Organization      (WMO)
recommendation:
recommendation:
– In flat regions of temperate, Mediterranean and tropical
  zones
     Ideal  1 station for 600 – 900 km2
     Acceptable 1 station for 900 – 3000 km2
– In mountainous regions of temperate , Mediterranean and
  tropical zones
     Ideal   1 station for 100 – 250 km2
     Acceptable    1 station for 250 – 1000 km2
– In arid and polar zone
                          10,
     1 station for 1500 – 10,000 km2
                 g g                          g
10 % of the raingauges should be self recording to
know the intensity of the rainfall
Weather Station
         Placement of Rain Gauges
Gauges are affected by wind pattern, eddies, trees and
the       it lf therefore it is i
th gauge itself, th f               t tt h       th
                             i important to have the
gauge located and positioned properly.


           • 1m above ground level is standard -
   all gauges in a catchment should be the same height

  • 2 to 4 times the distance away from an isolated object
      (                          g)                        g
      (such as a tree or building) or in a forest a clearing
      with the radius at least the tree height or place the
                     gauge at canopy level
                            g
       Placement of Rain Gauges
 shielded to protect gauge in windy sites
                                                      wind-
 or if obstructions are numerous they will reduce the wind-
speed, turbulence and eddies.
Raingauge with
      g
 wind guards
      Placement of Rain Gauges
•For sloping ground the gauge should be placed with the
opening parallel to the ground
•Th rainfall catch volume (
 The i f ll t h l                 is then divided by the
                            (mm3) i th di id d b th
opening area that the rain can enter
Number and Distribution of Gauges

 Need to consider:
   size of area
   prevailing storm type
   form of precipitation
   t
   topographyh
   aspect
   season
                           g
        Distribution of Gauges
The distribution of gauges should not be random.
                                         random.
        only fi ed
      – onl fixed characteristics of areas can be sampled
        randomly. Random events must be sampled by a
        systematic arrangement of sampling points


Practical considerations of access and exposure mean
that some pragmatism is required in designing a
network.
      – It is useful to locate gauges so that isohyetal maps can
             drawn                             near
        be drawn. Some gauges need to be near, or outside the
        catchment boundary in order to cover the catchment
        completely.
                             g
                Number of Gauges

Depends on Storm type

  Cyclonic storms (large areas, low intensities) -small
  number of gauges may be O.K.
            g g       y

  Convective storms (local, intense, uneven
                                needed
  distribution) -denser network needed. Convective
  storms may have seasonal dominance -need to
  consider this as well.

  Orographic rainfall due to mountains (not fronts) -may
  need denser network than flatter area.
         Snow Measurement
• The two most common measurements of
                                equivalent.
  snow are depth and water equivalent.
  Although th quantity of water i a given
• Alth      h the      tit f     t in    i
  volume of snow is not constant, a general
    ti f          it f       to     it f    t i
  ratio of 10 units of snow t 1 unit of water is
  often used when exact information is not
      il bl
  available.
2.2 Temporal and Spatial Variation of Rainfall

   Rainfall varies greatly both in time
   and space
    – With respect to time – temporal variation
    – With space – Spatial variation


   The temporal variation may be defined as
   hourly, daily, monthly,
   hourly daily monthly seasonal variations
                        (long-
   and annual variation (long-term variation of
   precipitation)
Things to know about rainfall
 Where to get rainfall information
 Rainfall sites in the area of interest
 Seasonal rainfall trends
 Variability of rainfall across the state and between
 towns
 Area specific rainfall
 Site specific rainfall
                      g
 – Methods of measuring rainfall
 – Where to place rainfall gauges - depends on the site
 – How many gauges to place in area - depends on the
        i   t
   experiment
 – What to do with the rainfall data
         Farming Scenario
   What information do you need?
Seasonal rainfall
Long term average rainfall
Risk of drought
Chance of rain
Southern Oscillation Index effect on rainfall
prediction
                                     Temporal Variation of rainfall at a particular site

                                             Total Rainfall amount = 6.17 cm


                            14
                     m/hr




                            12
             nsity, cm




                            10

                            8
Rainfall Inten




                            6

                            4

                            2

                            0
                                 0      20        40       60       80       100      120   140
                                                            Time, min
                                                        Long term Precipitation variation at Arba Minch

                              45
                              40
                              35
A n n u a l ra i n f a l l , m m




                              30
                              25
                              20
                              15
                              10
                                   5
                                   0
                                   1986   1988   1990   1992      1994     1996      1998     2000        2002       2004      2006
                                                                             Years
                                                                                                                 Annual Precipitation
                                                                                                                 average precipitation
 2.4 Preparation of Data
   Before using rainfall d
   B f       i                  it is             h k
                   i f ll data, i i necessary to check
   the data for continuing and consistency
    – Missing data              Nx   ⎡ P1   P2         Pm ⎤
    – Record errors        Px =      ⎢    +    + ... +    ⎥
                                M    ⎣ N1 N 2          Nm ⎦
  Estimation of Missing Data
 • Given annual precipitation values – P1, P2, P3,… Pm at
         i hb i          i     f     i
      neighboring M stations of station X 1, 2, 3 & m
                        respectively
• The normal annual precipitation given by N1, N2, N3,…,
               Nm, Ni… (including station X)
   • To find the missing precipitation, Px , of station X
Test for consistency record
 (Double mass curve techniques)

      • Let a group of 5 to 10 base stations in the
       g                    p
    neighbourhood of the problem station X is selected
 • Arrange the data of X stn rainfall and the average of
    the neighbouring stations in reverse chronological
                d (from recent to old record)
              order (f           t t ld       d)
• Accumulate the precipitation of station X (∑ Px ) and
       the average values of the g
                 g                 group base stations (∑ Pavg )
                                        p
               starting from the latest record.
• Plot the (∑ Px ) against (∑ Pavg ) as shown on the next
                             fi
                             figure
  • A decided break in the slope of the resulting plot is
                                      g    p     p
     observed that indicates a change in precipitation
           regime of station X, i.e inconsistency.
• Therefore, is should be corrected by the factor shown
                          th      t lid
                                                                Double Mass Curve Analysis                               Test for consistency
                                                                                                                                    record….
                                                   5
      ulated annual rainfall of X st in 10^3 cm




                                                  4.5

                                                   4
                                   tn




                                                  3.5
                                                  35
                                                                                                                                  Mc c
                                                   3
                                                                                                                       a            =
                                                  2.5

                                                   2
                                                                                                                     c            Ma a
                                                  1.5

                                                   1
 accumu




                                                  0.5

                                                   0
                                                        0     0.5               1              1.5               2          2.5
                                                            Accumulated annual rainfall of neigbouring stns in 10^3 cm


                                                                    Pcx – corrected precipitation at any time period t1 at
         Mc
Pcx = Px                                                                                    stationX
                                                                      Px – Original recorded precp. at time period t1 at
         Ma                                                                                 station X
                                                                       M – corrected slope of the double mass curve
2.5 Mean Precipitation over an area

 Raingauges rainfall represent only point sampling
 of the areal distribution of a storm
 The important rainfall for hydrological analysis is a
                  area,
 rainfall over an area such as over the catchment
 To convert the point rainfall values at various
                                         catchment,
 stations to in to average value over a catchment
 the following methods are used:
  – arithmetic mean
  – the method of the Thiessen polygons
  – the isohyets method
Arithmetic Mean Method

    h     h       is h i ll       d li    i ll
• When the area i physically and climatically
   homogenous and the required accuracy is
   small,
   small the average rainfall ( ) for a basin
                     P
 can be obtained as the arithmetic mean of the
     hi values recorded at various stations.
   • Applicable rarely for practical purpose

     P1 + P2 + ..... + Pi + .....Pn     1   N
 P =
                   N
                                    =
                                        N
                                            ∑P
                                            i =1
                                                   i
   Method of Thiessen
       polygons
  The      h d f Thiessen polygons consists of
• Th method of Thi              l          i   f
  attributing to each station an influence zone
  in which it is considered that the rainfall is
  equivalent to that of the station.
• The influence zones are represented by convex
  polygons.
• These polygons are obtained using the
  mediators of the segments which link each
  station to the closest neighbouring stations
Thiessen polygons ……….
                   Thiessen polygons ……….


           P               P
          A7       A
            P              6
          7 A
        A 2        A
                   6
                       P       A
P            2
               A   1               P
        A
        8                      5
8   P                  1
                                   5
    3
        3     4    P
                   4
                                  Thiessen polygons ……….

     P1 A1 + P2 A2 + ..... + Pm Am
 P =
        ( A1 + A2 + ..... + Am )
Generally for M station
             M

             ∑ PA     i   i         M
                                             Ai
 P     =     i =1
               Atotal
                              =    ∑
                                   i =1
                                          Pi
                                             A

        Ai
The ratio           is called the weightage factor of
        A
                          t ti
                         station i
    Isohyetal Method
• An isohyet is a line joining points of equal
  rainfall magnitude.
               1
        8
               0. D
   6       C      a5
                   1
          9    0 a 1
        7 . a3
       B 7         24
  4                2
        . 2A    E
           .a2 9 1
     4 a1
        0
     F     2    . 0.
     .         8
     04   6    1 0
       Isohyetal Method

                           the  l     f the isohytes
   • P1, P2, P3, …. , Pn – th values of th i h t
   • a1, a2, a3, …., a4 – are the inter isohytes area
     respectively
   • A – the total catchment area
      P
   •     - the mean precipitation over the catchment
        ⎛P +P ⎞ ⎛P +P ⎞                 ⎛ P −1 + P ⎞
      a1⎜ 1  2
               ⎟ + a2 ⎜ 2 3
                            ⎟ +...+ an−1⎜  n      n
                                                    ⎟
   P=   ⎝ 2 ⎠ ⎝ 2 ⎠                     ⎝ 2 ⎠
                          A

NOTE h method iis superior to the other two methods
  Th i
  The isohyet h d      i       h    h          h d
       especially when the stations are large in number.
                       gg
  Methods of determining grid data
In the example station X is the station with data
 missing
 Inverse distance squared
     – The closer a station is to station X the greater the
       weight assigned to that station's precipitation.

     – The inverse of the squared distance between a
       station and station X is used as a weighting
                                                     X.
       factor in determining the rainfall at station X
 2.6 Intensity – Duration – Frequency (IDF) Relationship
Mass Curve of Rainfall

                                                   Mass curve of rainfall
accum ulated pr ecipitation, mm




                                  60

                                  50

                                  40



                                            1st
                                  30

                                  20

                                  10       sto              2nd
                                  0
                                           rm, ,           stor
                                       0      20    40         60           80   100   120


                                            16              m,
                                                           Time, hour


                                                            16
Hyetograph                                                        IDF ….
                                                              time
         - is a plot of the accumulated precipitation against time,
                         plotted in chronological order

                                Hyetograph of a storm

                   0.5                               Total
 ntensity cm /hr
               r




                                                    depth =
                   0.4

                   0.3
                                                    10.6
                                                    10 6 cm
        y,




                   0.2
                   0.1
In




                    0                                  Duratio
                         0–8   8 – 16   16 – 24 24 – 32 32 – 40 40 – 48
                                           Time, hours n = 46

                                                           hr
IDF ….
In
I many d i           bl       l t d to     t h d   h
           design problems related t watershed such as
runoff disposal, erosion control, highway construction,
culvert design, it is necessary to know the rainfall
intensities of different durations and different return
periods.
periods.
                              inter-
The curve that shows the inter-dependency between i
(cm/hr),                                    curve.
(cm/hr) D (hour) and T (year) is called IDF curve.
                                               as:
The relation can be expressed in general form as:

                 x
           kT                   i – Intensity (cm/hr)

i =                             D – Duration (hours)

        (D + a )     n      K, x, a, n – are constant for a
                                   given catchment
IDF ….
                                 Typical IDF Curve

                    14
                                                                 T = 25 years
                    12
In tesit cm / h r




                                                                        y
                                                                 T = 50 years
                    10                                           T = 100 years
                    8
       ty,




                    6                                           k = 6.93
                    4                                           x = 0.189
                                                                a = 0.5
                    2                                               0.878
                                                                n = 0 878
                    0
                         0   1   2        3         4   5   6
                                     Duration, hr
Rainfall Measurement
 Why do we need to measure rainfall?
   Agriculture – what to plant in certain areas, where
           and when to plant, when to harvest

    Horticulture/viticulture - how and when to irrigate

   Engineers - t design structures for runoff control
   E i          to d i    t t       f       ff   t l
         i.e. storm-water drains, bridges etc.

  Scientists - hydrological modelling of catchments



          courses.nres.u
          iuc edu/nres4
          p
    Site Specific Rainfall Information

n – annual rainfall distribution
           p
     Site Specific Rainfall Information

me – annual rainfall distribution
   (note change in distribution of rainfall and change in scale
          p
    Site Specific Rainfall Information

                    Tasmania
ebery West coast of Tasmania–
  (note change in distribution of rainfall and change in scale
         p
   Site Specific Rainfall Information

gin – variation in rainfall
          p
    Site Specific Rainfall Information

gin – probability of rainfall
        p
     Comparison of rainfall sites

What if you live
                                                   300
                                                                   y = 1.0431x
                                                                   R2 = 0.8563
                                                   250
between Wagin




                                 onthly rainfall
                                                   200

and Katanning?                                     150




                      Katanning mo
Can you use their                                  100


rainfall data to                                   50


predict rainfall at                                 0
                                                         0   50   100      150       200   250   300

your farm?                                                        Wagin monthly rainfall
Humidity and Relative Humidity

 H    idit i th
 Humidity is the amount oft f
 water vapor in the air
 Relative humidity is a measure
                     ater apor
 of the amount of water vapor
 that the air is holding,
 compared to the amount it can
 hold at a specific temperature
Humidity and Relative Humidity

 Wh th i i h ldi
 When the air is holding as
 much moisture as it can, it’s
 said to be saturated
Can you explain this graph?
I th       l f th      i    th
In the cool of the morning, the
air can’t hold as much
moisture. We often have dew on
a summer morning
Once the air has warmed, the
relative humidity drops since
the air can hold more moisture
HUMIDITY, PRECIPITATION AND CLOUDS
                                     �   Air is formed of 99%
   Warmer air can hold              nitrogen and air, the rest
                                           g           ,
   MORE water vapour                being trace gases such as
                                       argon, CO2 and water
                                                vapour.
   The rate of increase is             � The amount of water
     EXPONENTIAL (it                vapour is called humidity.
 increases by a factor of 3            � The amount of water
        every 10°C)                vapour that can be held by
                                         air depends on the
                                                p
                                             temperature.
                                      � The actual amount of
                                   vapour held in air is called
                                     absolute humidity (in gm
                                            per kg of air).
                                    � The % that this forms of
                                     the capacity of the air to
                                        hold vapour is called
                                         relative humidity.
                                      � Points A 1-5 are all at
                                   100% relative humidity. B3
                                      is 80%, C3 is 33%, M is
                                                 50%.
       atschool.eduweb.co.uk/rad     � For air at temperature

       geog/metlink/ppt/rain/H     and humidity of B3, C3 and
           um_Ppt_Cloud.pp             M to reach saturation
You’ve seen water on the outside
        of a cold drink?
                  The ld i
                  Th cold air
                  around the
                  glass causes a
                  lower
                  temperature
                       h h h
                  at which the
                  air is
                  saturated
You’ve seen water on the outside
        of a cold drink?

                  The
                  temperature
                  at which air is
                  saturated and
                  condensation
                  takes place is
                  the dew point
                  To return click
                  here ☼

				
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