Marine meteorology 2 nd November 2011 Precipitation Marine Science Department Fisheries and Marine Science Faculty Padjadjaran University
Marine meteorology
2nd November 2011
Precipitation
Marine Science DepartmentFisheries and Marine Science Faculty
Padjadjaran University
Outline
Overview: precipitation & condensation
Precipitation’s Importance
Types
Steps of Precipitation
Frontal systems
Precipitation data
Rainfall
Terms
Condensation
• Condensation occurs when water vapor changes to a
liquid.
• For condensation to take place, the air must be saturated
and there must be a surface on which the vapor can
condense.
• In the air above the ground, tiny hygroscopic (water-
absorbent) particles known as condensation nuclei
serve as the surfaces on which water vapor can condense.
Cloud Heights
• Cloud heights can be either:
high, with bases above 6000 meters.
middle, from 2000 to 6000 meters, or
low, below 2000 meters.
• Based on the two criteria, ten basic cloud types,
including such types as cirrostratus, altocumulus,
and stratocumulus, are recognized.
Precipitation Types
• The two most common and familiar forms of
precipitation are:
RAIN (drops of water that fall from a cloud and
have a diameter of at least 0.5 millimeter) and
SNOW (precipitation in the form of ice crystals or,
more often, aggregates of ice crystals).
Flicker.com Warebuzz.com
Precipitation Types
• Other forms include: Sleet (falling small particles of ice that are clear to translucent),
Glaze (formed when supercooled raindrops turn to ice on
colliding with solid objects),
Hail (hard, rounded pellets or irregular lumps of ice produced in
large cumulonimbus clouds), and
Rime (a deposit of ice crystals formed by the freezing of
supercooled fog or cloud droplets on objects whose surface
temperature is below freezing).
• Drizzle (smaller droplets of rain, yet larger than mist)
• Mist (smallest water droplets visible)
• Gaupel (watery hail)
Hailhard, rounded pellets or irregular
lumps of ice produced in large
cumulonimbus clouds
climate.met.psu.edu
•Gaupel (watery hail)
Drizzle
(smaller droplets of
rain, yet larger than
mist)
Mist : smallest water droplets visible
dsumantriphotography.wordpress.com
Rime Ice
Hail
Sleet formation
Rime (a deposit of ice
crystals formed by the
freezing of supercooled fog
or cloud droplets on
objects whose surface
temperature is below
freezing).
Steps:
Precipitation occur when 3 conditions met :
1. Atmosphere is saturated.
2. Small particles are present ; dust, ocean salt,
etc.
3. Drops are big enough to reach the surface.
Atmosphere Saturated
Atmosphere becomes saturated When the air masses is
cooled by lifting.
Air masses lifting caused by:
- Frontal system (warm fronts/cold fronts)
- Orographic effect (induced by mountain); rain shadow
produces deserts.
- Convection ; summer thunderstorms
Frontal System
Cold Fronts
- High intensity
- Short duration
- Narrow zone
Warm Fronts
- Gentle rainfall
- Long term
- widespread
Orographic precipitationMechanisms of orographic
precipitation:
(a) Seeder-Feeder mechanism;
(b)upslope condensation;
(c) upslope triggering of
convection;
(d)upstream triggering of
convection;
(e)thermal triggering of
convection;
(f) leeside triggering of convection;
(g) leeside enhancement of
convection. Slanted lines below
cloud base indicate
precipitation.
[From Fig. 12.24 of Houze, 1993].
Convective Precipitation
High intensity
Short duration
Limited area
It results from the heating of
the earth's surface that causes
air to rise rapidly. As the air
rises, it cools and moisture
condenses into clouds and
precipitation. This type
of precipitation is common in
the prairie provinces.
Precipitation Terms
Hystograph : a plot of rainfall intensity vs time
Isohyete : Contours of constant rainfall, similar to contours
of constant elevation.
Isohyetal map : Map with contours of constant rainfall.
Rainfall (mm) at Bantar Dewa Ciamis station
Rain Measurement
• Rain, the most common form of precipitation, is
probably the easiest to measure.
• The most common instruments used to measure
rain are:
the standard rain gauge, which is read directly, and
the tipping bucket gauge and weighing gauge,
both of which record the amount of rain.