1.
Cloud
Development
a.
Convection (Figure 5.10a-5.13)
b.
Topographic uplift
(Figure 5.10b, 5.14-5.16)
c.
Convergence (Figure 5.10c)
d.
Fronts (Figure 5.10d)
2.
Adiabatic
Cooling and Warming
a.
Adiabatic - impassable
to heat; involving neither loss nor acquisition of heat [f. Gr.a
not + dia through + batoz passable].
A very
useful concept in atmospheric sciences giving rise to the notion of an
“air
parcel” that is thermally distinct/isolated from its immediate
environment.
b.
Dry (i.e., non-saturated)
air cools at about 10°C/km as it
rises. It warms at the same rate as it sinks.
This is called the dry adiabatic lapse rate (the rate of change of
temperature with height; Figure 5.2, 5.3).
c.
In English units, the dry
adiabatic lapse rate is
equal to about 3°F/1000
ft.
d.
Moist (i.e., saturated,
cloudy) air cools at about 6°C/km as it
rises (Figure 5.6). This is the moist
adiabatic lapse rate.
e.
The environmental
lapse rate is the actual
change in temperature with altitude out in the atmosphere, e.g., the
skew-T
sounding.
3.
Atmospheric
Stability
a.
Compare the environmental
lapse rate to the adiabatic
bench marks (dry or moist, depending on conditions).
i.
The
atmosphere is stable if the environmental
lapse rate is more positive than -10°C/km
(Figure 5.3). So a skew-T of -9°C/km
would indicate a stable atmosphere. Note that Ahrens omitted the
negative signs
from all the lapse rates, e.g., 4°C/1000 m
should read -4°C/1000
m, etc.
ii.
The
atmosphere is unstable if the environmental
lapse rate is more negative than -10°C/km . So a skew-T of -11°C/km
would indicate an unstable atmosphere.
4.
Precipitation
Processes
a.
Warm clouds where only
liquid water exists (warmer
than about -15°C, i.e.,
many tropical and subtropical clouds, including some
i.
Collision
and coalescence
·
Need to
grow from CCN (0.1 mm
diameter) to cloud droplets (10 mm
diameter), which is
easy; then to rain drops (1000 mm
diameter), which is
difficult (most clouds do not rain) (Fig 5.17).
·
Some how a
larger than average cloud
droplet grows and then falls through the cloud, colliding with
the
“average” 10 mm
droplets; and most often coalescing into a much bigger droplet
that
falls even faster, colliding and coalescing with many more “average”
droplets (Fig. 5.18, 5.19).
b.
Cold clouds (Bergeron or
ice crystal process) where
ice crystals can coexist (temporarily) with supercooled liquid
droplets, i.e.,
about -20°C.
i.
In mixed
phase clouds liquid droplets
grow on CCN while ice crystals grow on ice nuclei (IN) (Figure 5.21, 5.22).
ii.
The vapor
pressure exerted by the liquid
droplets is higher than that exerted by the solid crystals (Figure 4.5)
with
the net result that vapor is “driven” from the droplets to the
crystals, i.e.,
the ice crystals grow while the liquid droplets evaporate (Figure 5.22).
iii.
The growing
crystals fall through the
remaining cloud of liquid droplets, where they collide and instantly
freeze the
droplets thereby growing into much bigger ice crystals (snow flakes)
(Figure
5.23).
5.
Some Types of
Precipitation
a.
Freezing Rain (Figure
5.32)
b.
Snow crystals,
graupel, etc.
c.
Hail (Figure 5.33-5.34)
6.
Precipitation
Gauges
a.
Standard gauge (Figure
5.37)
b.
Tipping bucket (Figure
5.38; ASOS)
7.
Radar
a.
Radio detection and
ranging
b.
Doppler radar (Figure
5.39, 5.40; NOAA
NEXRAD
WSR-88D; NWS, TUS
Doppler
radar)