Transcript Monsoon

Monsoon
Part Ⅰ
What is a monsoon
What makes a monsoon
What is a monsoon
• A term from early Arabs called the "Mausin," or "the
season of winds."
• The seasonally shifting winds in the Indian Ocean
and surrounding regions, including the Arabian Sea
and the Bay of Bengal.
monsoon—A monsoon results
from the circulation induced by
temperature contrasts between
a warm (cold) continent and a
cold (warm) ocean.
Ramage (1971) based on wind directions
• It is now more applied to tropical and
subtropical seasonal reversals in both
winds and associated precipitation.
• People are more concerned about the
precipitation for two reasons:
a：natural disasters, like flooding and
drought ;
b: latent heat in the global diabatic heating.
The hydrologic cycle and latent heat
release latent heat
absorb latent heat
ice
Condensation
release latent
heat
This heat anomalies produce circulation anomalies
vapor
evaporation
Absorb latent heat
Liquid
Monsoonal or non-monsoonal?
Total summer
precipitation
Annual range
of rain
Ratio of summer rain to yearly rain
TAO. 1987
Members in the Asian-Australian
summer monsoon system
B: trade wind
C: crossequatorial flow
D: SW
monsoon
L
EASM
L
L
c
H
A
India monsoon, East Asian monsoon, Meiyu front
H
Austrilian high
A
Mean onset date of the summer monsoon
Monsoon is a mixed blessing
Life-giving rain & Wild storms
It annually shapes the lives of both the
people and the wildlife of the monsoon
regions.
In late spring, the grassy plains and forested hillsides of
southwestern India are among the hottest places on the
earth.
"The air is on fire and the leaves are perfectly still as if holding
their breath."
"there is a curious sense of anticipation.“
——— Shantipriya
Animals and human alike await the
monsoon
Monsoon onset
Monsoon Race
Clouds : Ci, Sc, Ns, Cu
As clear blue
sky just gives
its way to
white clouds,
the dark clouds
that carry rains
are coming.
Before monsoon hits the Arabian coast, the
fishing boats are pulled on the coast,
packed, and tightly tied with the ropes for
the support.
Monsoon break
Crocodiles
spawn
Weaver birds build their
nests during monsoon
break.
Monsoon withdrawal
Farmers plant rice paddies after monsoon rains.
Wild storms: People rest on the
pavement of a flooded street in Bombay.
Monsoon rains have killed 41
people across India over the
past two days. (Yahoo News.
Wed,Jul 5,2006)
Monsoon peak
India's financial capital Bombay came to a
virtual standstill Tuesday in the torrential
rainfall, killing 7 people. (Yahoo News.
Jul.4,2006)
Yangtzs valley in China
East Asian monsoon area
Meiyu front
Monsoon rains come too late this year
(2006).
Monthly rainfall
anomaly:-80%
Mei-yu front does
not come to the
middle-lower
reaches of Yangtzs
River this year.
Monthly precipitation anomaly in Jun.2006
Flooding 1998
Global population distribution
1.03b in
India
1.37b in
China
The most densely populated areas are in
monsoon regions.
Regional summer monsoon domains
North African monsoon from Reddiman
2001
From Simona 2004
From Berbery et al. 2005,
From Ramage 1971
Global summer monsoon
rainy season
Summer rain
Winter rain
Global summer monsoon rainy season
Summary
• Monsoon means seasonal reversals both in
winds and precipitation
• Monsoon’s onset, peak and withdrawal
• Monsoon rainy season has inter-annual
variations (floods, droughts)
What makes a monsoon
• How is the atmosphere heated at
the earth’s surface?
• Energies driving the atmosphere to
move are primarily come from the
sun.
Nearly half of the total sun’s energy is concentrated
within the visible light wavelength
Solar radiation
Solar radiation absorbed
by atmosphere
Visible solar radiation
is not absorbed by air
About 51% of solar radiation is absorbed by surface
How is the atmosphere heated
Energy gained by
atmosphere: +160
Energy lost by
atmosphere: -160
+19
+7
+23
+111
51% of the solar radiation is absorbed by the earth
Ocean currents move heat downward into deep water
Temperature at 1000hPa
summer (JJA)
winter (DJF)
Land-sea distribution makes the imbalance of
the heat
Just as sea breeze
Warmer air
High pressure
Low pressure
Warmer air
The earth’s rotation around the sun produces
the heat imbalance between the two
hemispheres .
Seasonal variations of solar
radiation
• The pattern
of Absorbed
Solar
Radiation
has a strong
zonal
component
that is
dominated by
orbital effects.
Tibetan Plateau, the third
pole of the earth. It is a heat
source at its surface.
Average elevation is 4500m.Total
area is about 2,400,000km2
Rainfall center
Latent heat
is most
intense over
Tibet
Interaction between the two hemispheres
ISM
H
EASM
H
Three factors contribute to monsoon
Tibetan Plateau
60
50
40
Interactions between the two
hemispheres
30
East Asian monsoon regions
20
North American monsoon regions
10
North African monsoon regions
0
-10
South American monsoon regions
-20
Australian monsoon regions
South African monsoon regions
-30
-40
-50
-60
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
20
40
Summer Monsoon Domain
60
80
100
120
140
160
180
Seasonal overturning in winds
Summary
• The first driving force is solar radiation
• The second driving force is land-sea
distribution
• The three is the huge topography.