CH4 – humidity, condensation
and clouds
Water:
1- vital for life
1
2- phase change releases or absorbs large
amounts of energy
gy
3- a greenhouse gas
Issues include:
1- what are key aspects of the hydrologic cycle?
2- what is the water vapor capacity of the air?
3- what is the actual water vapor content?
4- estimates of water vapor: RH, dew point T
5- basic cloud types are?
Stepped Art
Fig. 2-3, p. 28
Stepped Art
Fig. 4-1, p. 80
oceans 97%, glaciers 2%, groundwater 0.6%
p
0.001% ((326 million cubic miles total))
atmosphere
Fig. 4-2, p. 81
there are 2 measurements to obtain:
1 how
1h
much
h vapor iis present?
t?
2- how much can the air hold (capacity)?
think of your gas tank - it can hold 15 gal but your
gage suggests
t you have
h
7
7.5
5 or h
half
lf
in the container experiment we waited till
saturation was reached, in nature clouds and fog
are two examples of saturated conditions
How does one measure what water vapor is
present and how much the air could hold?
p
Pressure, P, is the weight
g of all the molecules
above your level of observation….each molecule
would contribute
N2 would
ld contribute
t ib t tto P th
the most,
t then
th O2
P = Pd + e , dry components + water vapor
For Hawaii at the surface Pd = 1000 mb, e = 20 mb
e = what is present, es = max amount possible
Fig. 4-5, p. 83
vapor pressure, e is what is actually present
saturation vapor pressure
pressure, es f (T)
the public typically talks about:
1- relative humidity = e/es x 100%
RH = 100% in cloud
note that it does not tell actual amount
pyap
percent
units? none, simply
2- dew point T: the T at which dew forms, to find
this value simply cool the air and leave P and e
constant
t t
in cloud: T = Tdew
3 mixing ratio and specific humidity (g/kg)
3-
Fig. 4-8a, p. 86
Fig. 4-8b, p. 86
Can you change RH without adding or subtracting
water vapor?
RH = e/es….change the T and you change the
denominator…and RH varies
How does one change e?
1- evaporate water into the air (increase e)
2 if clouds develop and rain out (decrease)
2-
Fig. 4-7, p. 85
Cloud types – 6 general types
1 fog: radiation,
radiation advection
advection, evaporation
2- low: stratus bases < 2000 m (6500 feet)
stratus,
t t
nimbostratus,
i b t t
cumulus,
l
stratocumulus
t t
l
3- middle: 2000 m < bases < 6000 m
altostratus,
lt t t
altocumulus
lt
l
4- high: bases > 6000 m
cirrus, cirrostratus, cirrocumulus
5- clouds with significant vertical development
cumulus congestus, cumulonimbus
6- rare clouds at extreme altitudes
Fig. 4-32, p. 104
Fig. 4-29, p. 102
Fig. 4-27, p. 101
Fig. 5-12, p. 119
Fig. 4-30, p. 103
Fig. 4-31, p. 103
Fig. 7-7, p. 176
Fig. 4-21, p. 99
Fig. 5-27, p. 129
Fig. 4-22, p. 99
Fig. 4-23, p. 100
Fig. 4-25, p. 100
Fig. 4-24, p. 100
Fig. 4-26, p. 101
Fig. 4-17, p. 94
Fig. 4-19, p. 95
Fig. 5-5, p. 114
Fig. 4-16, p. 93
Table 4-4, p. 105
Fig. 4-33, p. 105
Fig. 4-34, p. 106
Fig. 5-CO, p. 110
Fig. 7-CO, p. 168
Fig. 4-35, p. 106
Fig. 7-19, p. 183
Unusual clouds at extreme altitudes
nacreous ~ 30 kkm ((stratosphere)
t t
h )
noctilucent ~ 75 km (mesosphere)
both are seen in polar regions, believed to be
ice
Aurora: ~ 100 km (thermosphere)
not a cloud, but interaction of charged particles
from the sun with atoms in the uppermost part of
th atmosphere
the
t
h
Fig. 4-37, p. 107
Fig. 4-38, p. 107
Summary CH4
H idit – the
Humidity
th amountt off water
t vapor in
i the
th air
i
Humidity can be quantified several ways:
1- vapor pressure (mb)
2- relative humidity (%, no units)
3- dew point temperature (°C or °F)
Saturation vapor pressure: the maximum amount
of vapor that air can hold, f (T)
(warm air can hold much more vapor than cold air)
Saturated air is in balance, but if you:
1- cool air further more vapor condenses to liquid
2- warm air and more droplets evaporate
To reach saturation one could:
1 add more water vapor
12- cool the air
3 lower
3l
th
the P (thi
(this cools
l th
the air,
i ttoo))
Know how to use the e, es diagram
Cloud classification:
1 layered (stratiform) or heaped (cumuliform)
12- what level is it at or is it tower-like
f
fog,
low,
l
middle(alto),
iddl ( lt ) hi
high,
h vertically
ti ll d
developed
l
d
3- Key terms to describe clouds:
stratus=layered,
t t
l
d cumulus
l =h
heaps
cirrus = filament or hair-like
nimbus = rain, alto = middle
haze: RH< 100% but water collects on nuclei,
scatters light in all directions
Fig. 4-4, p. 82
Fig. 4-20, p. 96
Table 4-2, p. 98
Figure 2, p. 173