Transcript Document

(C, B, A, C, D, D, B, A)
x
x
x
x
x
x
x
x
CISK & air/sea interaction
Evaporation from the earth’s Surface
Condensation in clouds and precipitation
Photochemical reaction at 20-60km
Reaction with plants at the
surface and dissolution in water
Mixing
Mixing due
due to
to fluid
fluid motion
motion
and molecular diffusion
downward
decreases
increases
geostrophic
right
ITCZ
pa=Rd T
pa=Rd Tv
CCN
Collision and coallescence
Riming and aggregation
Coriolis force vanishes on the equator, and hurricane growth needs the Coriolis force
Physically, it means that the upward pressure gradient
force is Balanced by the downward gravitational force.
The first law of thermodynamics is: dq=du+dw: heat absorbed by a system is used to increase its internal
Energy (du) and do external work (dw). For adiabatic processes,
Dq=0. So, du=-dw. When an air mass comes down a big mountain, it experiences adiabatic compression
because pressure increases toward the earth’s surface. Compression reduces its volume and thus
dw=pda<0, and du=-dw>0. Internation energy increae indicates temperature increase. This is why
we often observe warm air at foothills.
The entropy is higher in the case with precipitation. This is because when there isn’t precipitation,
The process is adiabatic and reversible, wherease with precipitation the process is
Pseudoadiabatic and irreversible. For irreversible process, its entropy increases.
The second law of thermodynamics says
The = sign hlods for reversible and > sign for irrervisble process.
Convection will not occur because the atmosphre is under an absolutely stable stratification.
Yes. Convection will occur if the air parcel is lifted above the level of free
convection. This is because the atmosphere is conditionally unstable. Below
the level of free convection bouyancy of the air parcel is smaller than its weight (it is heavier than
Surrounding iar). Above the level of free convection the air parcel is more buoynant than its surrounding
air and thus can go up without external lifting.
See figure 1 for level of free convection. We expect convective clouds because of the free
Convection. Layered clouds requires stable stratification.
It is evident that the two curves coincide well: high (low) nuclei concentration corresponds to high
(low) electric field. This is because aerosols are much bigger than electrons, and thus aerosols
move much slower than electrons under the same electric fields. The slow motion reduces
electrical currents and and thus reduces the neutralization between the positive and negative
Charges that generates the electric fields, resulting an increase in the electric field.
The major difference between air mass thunderstormand the squall line is
that the former has no shear but the latter has a strong shear between their
updraft and downdraft winds. In the airmass thunderstorm, precipitation
causes downdraft, which cuts off the moisture source provided by the
updraft. It has a self-destroying mechanism and thus this type of
thunderstorm seldom causes severe damagement. In the squall line,
updraft and downdraft winds strengthen each other: the cold downdraft
lifts up the warm air and thus increases the updraft; moisture brings
up by the updraft condenses and precipitates. Precipitation increases the
downdraft by drag effect, and by evaporative cooling which increases
density and thus increases the sinking of air. This type of thunderstorm can
be very destructive because winds /precipitation are strong due to the
self-enhancing mechanism.
•Weak disturbances containing vorticity in tropical ocean surface (5-20N(S) latitudes) when SST
is >26.5; for example, a low pressure prturbation;
•Geostrophic adjustment (Coriolis force tends to balance pressure gradient force) will generate
a cyclonic circulation; Ekman layer frictional convergence forces the warm air to go up, which
will cause convection, condensation, and thus latent heat release;
•Latent heat will increase air temperature and thus further reduce the low pressure perturbation;
•Reduced low pressure results in faster rotation and increased frictional convergence, results
in increased convection and latent heat release and even warmer air temperature;
•Increased reduction of low pressure.
B
D
Level of free convection
x
LCL
A
Temperature
Figure 1
C
Height (km)
Nuclei
Figure 2.
Electric field
Figure 3: Hurricane Andrew, 1992