GEOL 1301.
Principles of Earth Sciences
Instructor: Dr.
Nandigam
Chapter 16-MOISTURE, CLOUDS, AND PRECIPITATION
1.
Formation of a single average raindrop
requires water from nearly a million microscopic cloud droplets
2.
Changes of State
a.
Calorie: amount of het
required to raise the temperature of 1 gram of water by 1C.
b.
Latent heat: Heat energy which is not associated with a
temperature change Ex: melting of ice
c.
Evaporation: process of converting a liquid to a gas, Ex:
evaporation of sea water (600 calories per gm of water)
d.
Condensation: process whereby water vapor changes to the liquid
state, Ex: formation of fog and clouds
e.
Melting: process by which a solid is changed to a liquid Ex:
melting of ice (80 cal/gm of ice)
f.
Freezing:
process by which a liquid is changed to a solid
Ex: water to ice
g.
Sublimation: conversion of a solid directly into gas Ex: dry ice
(frozen Co2)
h.
Deposition: Conversion of gas directly into solid Ex: frost on
grass and windows
3.
Humidity
a.
Humidity: amount of water vapor in air
b.
Saturation: state of air at which it contains
maximum amount of water vapor
c.
Specific Humidity: weight of water vapor per weight of a chosen mass of air
d.
Relative
Humidity: ratio of the air’s actual
water vapor content to its potential water vapor capacity at a given
temperature
e.
Dew Point: the temperature to which air would have to be cooled
to reach saturation
f.
Hygrometer:
instrument that measures Relative Humidity
g.
Psychrometer: consists
of two thermometers mounted side by side; dry-bulb, gives the present air
temperature, wet-bulb, with thin muslin wick tied around the end aids in measuring
the relative humidity
4.
Cloud
Formation
Addition
of water vapor to air Saturation of
air with Condensation DEW, FOG
Cooling of air to its dew point water vapor of air OR
CLOUDS
5.
Adiabatic
Temperature Changes
Change of temperature without the addition or subtraction
of heat
Ex: Cooling of air when it expands and
warming when it gets compressed
6.
Dry
adiabatic lapse rate: 10°C per 1kilometer
Wet adiabatic lapse rate: 5°C per 1000 meters to 9°C per 1000 meters
7.
Processes
that lift air
Orographic lifting:Lifting of air when elevated terrains, such as mountains, act
as barriers to flowing air
Frontal Wedging: Occurs when cool air acts as barrier over which
warmer, less dense air rises
Convergence: Occurs whenever air masses flow together and result
in general upward movement
8.
The basis of
cloud formation: Adiabatic Cooling
- Condensation: may form dew, fog or clouds
- Adiabatic
Temperature Change: Temperature
change that occurs when heat is neither added nor subtracted
- Dry and Wet Adiabatic Rate:
Ø
Dry: Cooling or heating of unsaturated air ascending or
descending through the atmosphere at the rate of 10 C per 1000 meters
Ø
Wet:
Slower rate of cooling of a parcel of air ascending through the atmosphere
after reaching dew point than before; varies from 5 to 9 C per 1000 meters;
caused by the release of latent heat of condensation
9.
Stability
of air:
a.
Stable air: produces widespread
clouds with little vertical thickness and results in light precipitation
a.
Absolute
stability: occurs when environmental
lapse rate is less than the wet adiabatic rate
b.
Temperature
Inversion: occur on clear and calm
nights as a result of radiation cooling of earth’s surface when warm air acts
as a lid and prevents appreciable vertical mixing
b. Unstable air: produces cauliflower-shaped
clouds and result in heavy precipitation
Ø
Absolute
instability: occurs when
environmental lapse rate is greater than the
dry adiabatic rate; produces fluffy clouds
Ø
Conditional
Instability: Occurs when
environmental lapse rate is between the
dry and wet adiabatic rates; may cause thunder storms
10.
Processes that lift air:
a.
Orographic lifting: occurs when elevated terrains act as barriers to
flowing air
Associated with rainshadow
desert on the lee ward side of the mountains; ex:
b.
Frontal Wedging:
occurs when cool air acts as a barrier over which warmer, less dense air rises;
important in producing clouds; stable warm air eproduces
layered clouds; unstable warm air produces towering clouds
c.
Convergence:
Occurs whenever air masses flow together and result in general upward movement
ex:
11.
Types of clouds:
Clouds: visible aggregates of minute droplets of water or
tiny crystals of ice; classified based on their form and height:
a.
Cirrus:
high, white and thin
b.
Cumulus:
globular individual cloud masses, have flat base and have the appearance of
rising domes or towers
c.
Stratus:
sheets or layers that cover much or all of the sky
12.
a.
High Clouds:
above 6000 meters; not precipitation makers; cirrus, cirrostratus, cirrocumulus
b.
Middle Clouds:
2000 to 6000 meters; procude infrequent light snow or
drizzle; Altocumulus, Altostratus
c.
Low Clouds:
less than 2000 meters; stratus, stratocumulus, nimbostratus; nimbostratus which
form in association with stable conditions are chief precipitation producers
d.
Clouds of vertical displacement: Cumulonimbus clouds, towering clouds which are
associated with unstable conditions, may produce rain showers or a
thunderstorm, have their bases in the low height range but extend upward into
the middle or high altitudes
13. Rain Gauge:
Open container having a consistent cross section throughout can be a rain gauge
Standard
Rain Gauge: Receiver, funnel and
measuring tube; Receiver is 8 inches diameter at the top; funnel conducts the
collected rain water to measuring tube; measuring tube with cross-sectional
area one-tenth as large as the receiver, the narrow opening minimizes the
evaporation; rainfall depth is magnified ten times