Evaporation from:

1

• Evaporation from
• 1. Snow ice, 2. Plants, 3. Pools and lakes
• 4. Rivers streams, 5. Lands, 6. Water vapor
  molecules

2

• 1. Warm area heats the air above, 2. Bubble of
  warm air rises slowly
• 3. As it rises, the air expands and cools,
• 4. When air has cooled, water droplets form
  around the condensation nuclei
• 5. Clouds form High (. 6000m), medium
  (2000-6000m), and low ( 2000m) level clouds

3
Cirrus CloudsHigh-level

• The most common form of high-level clouds that
  are thin and often wispy. Typically found at
  heights gt 6,000 m, in fair weather and point in
  the direction of air movement at their elevation,
  cirrus clouds compose of ice crystals originated
  from the freezing of supercooled water droplets.

Cirrus Cloud, Australia
4
Altocumulus Cloud (Mid-Level)

• Altocumulus may appear as parallel bands (top) or
  rounded masses (bottom). Typically a portion of
  an altocumulus cloud is shaded.
• It usually form by convection in an unstable
  layer aloft, which may result from the gradual
  lifting of air in advance of a cold front. The
  presence of altocumulus clouds on a warm and
  humid summer morning is commonly followed by
  thunderstorms later in the day.

• Cumulonimbus

5
Nimbostratus Cloud (low level)

• Dark, low-level clouds accompanied by light to
  moderately falling precipitation. Low clouds are
  primarily composed of water droplets since their
  bases generally lie below 2,000m. If temperature
  is cold enough, these clouds may also contain ice
  particles and snow.

When cloud particles become too heavy to remain
suspended in the air, they fall to the earth as
hail, rain, freezing rain, or snow.
6

• 1. Winds flow from high pressure to low pressure
  areas, picking up moisture (water vapor) from the
  ocean, bringing rain and storms along the way.

7

• When water droplets grow to 0.1 mm or larger,
  they begin to fall as rain because air currents
  can no longer keep them in suspension. Darker
  clouds tend to give rise to heavy rainfall. Ice
  crystals fall as snow or hails can melt as they
  warm up.

8

• At low temperature, water droplets freeze to ice
  crystals that can come in infinite numbers of
  form give rise to snowflakes, which accumulates
  on mountain tops. Snow can melt as weather
  warms, or turn into ice and flow down the valleys
  as glaciers.

9

• 1. Warm air rises over cold air, 2. Cirrus
  clouds form
• 3. Cirrostratus signal that it will soon rain,
  4. It normally rain in here first, 5.
  altostratus clouds bring rain, 6. Cold air
  passes below warm air.

10

• 1. 2. Warm air rises as 3. cold air descends
  below forcing the warm air upwards,
• 4. Cumulonimbus clouds bring heavy rains, 5.
  Anvil-shaped clouds on top.

11

• 1. As warm front passes over, nimbostratus
  disappears is replaced by stratus and
  stratocumulus clouds.
• 2. Clear patches begin to appear in the sky
• 3. rain stops intermittently
• 4. Poor visibility, 5. High humidity in air

12
Orographic Storms

• Warm moist air rises over, say, a mountain,
  condenses form precipitation. Windward slope
  has more rain. Leeward slope has less rain.

13

• 1. Heavy storms bring bad weather to sea,
• 2. Low visibility because of heavy rains
• High waves created by winds

14
Radar Image of Pacific Canada

• Radar echoes are processed to provide real time
  information on rainfall distribution and
  intensity.

15
MOTIVATION
Acquire detailed spatial rainfall fields over
large aerial coverage frequently. e.g. Weather
Surveillance Radar-1988 Doppler (WSR-88D)
Hourly
16
IR/MW TB rainfall measurement

• IR measures CLOUD TOP Brightness Temperature (TB)
• The colder the IR TB ? high rain rate
• MW TB penetrates clouds The colder the MW TB (at
  85.5 GHz) gt high rain rate

17
Total rainfall accumulation field (mm) in 168
hours for Medium Stratiform event
GAUGE mean51 std4mm
RADAR mean34 std10mm
STRATIFORM-MEDIUM EVENT (8-14 December, 1994)
plotted from 0.5mm contour interval
18
Total rainfall accumulation field (mm) in 168
hours for Medium Stratiform event
Mean51 std4mm
Mean34 std10mm
RADAR
GAUGE
Mean52 std6mm
Mean44 std10mm
WAVELET
SOA
19
Satellite data availability
Tropical Rainfall Measuring Mission (TRMM)
satellite Coverage (350N 350S) 12 or 24-hr
resolution Microwave TB 5 km res. (channels 8
9 at 85.5GHz) IR TB 2.4 km res. (channel at
10.8um)
20
Satellite data availabilityGOES IR TB Hourly,
4km res. (ch4 at 10.7um)