Transcript NE Monsoon of SE Asia

Monsoon Weather
North Easterly Monsoon
NE Monsoon of SE Asia
– In January, the pressure is as high as 1030 mb or more in the Siberian
High.
– Causes a NW or north wind over Japan and a NE wind over much of
China, Indo-China, the Phillipines, Malaya and India.
– This is known as the NE monsoon and it blows from November to March.
It starts as a very cold, dry continental air mass.
– It warms as it moves south. Following a long land track it produces
clear, cool and dry weather conditions, but,
– When it swings across the China Sea and the Bay of Bengal, it is
warmed and moistened from below to produce Cu/Cb and
moderate/heavy showers to eastward-facing areas of SE Asia, Malaysia,
the Phillipines and India, with the cloud build-up being aided by
orographic uplift.
– As the air tracks further south it crosses the equator behind the ITCZ and
changes its direction to NW by Northern Australia (Darwin area) as is
known as the North Westerly Monsoon in this area.
South Westerly Monsoon
SW Monsoon of SE Asia
• July chart, the dominating pressure feature is the large thermal low of India
and central Asia. The intense surface heating of Southern Asia and the
Indian sub-continent causes an outflow of air aloft. There is a subsequent fall
in surface pressure over NW India, Pakistan and Southern Iran.
• The SE trade winds diverging from the South Indian Ocean anticyclone feed
into the equatorial trough, cross the equator, and are drawn towards the
Indian Low. They are then turned by geostrophic force to become the SW
Monsoon.
• The airmass has tracked over thousands of tropical ocean so it is moist and
warm. It is however shallow (5000 - 7000 ft) and growth of cumulus cloud is
inhibited by warm, dry air above. When within 100 - 200 miles of the Indian
coastline, the monsoon flow thickens up (11,000 - 13,000 ft), allowing the
cumulus to develop. Further lifting over the hills of India, Indo-China and
Malasia, and strong surface heating causes further development into CB/TS,
and copious rainfall, which penetrates well inland.
• The weather is intensified when the ITCZ sweeps through the area
northwards from May to July to the Himalayas and southwards from August
to early October. To the west of Karachi in Pakistan, cloud ceases to thicken
and there is sudden reduction in rainfall. Away from the narrow coastal strip,
the areas of Arabia, Iran, western Pakistan and NW India are quite arid.
SW Monsoon of West Africa
– A similar situation to the SW monsoon of SE Asia
occurs in the South Atlantic in the summer. Again
the SE trade winds cross the equator and are
deflected to the right to cross the Gulf of Guinea
from the SW behind the ITCZ, producing similar
weather conditions to the Indian monsoon. On the
ITCZ itself, violent storms with line squalls and
heavy rain occur over the coastal regions north of
the Gulf and over the Gulf itself.
Monsoon Coast Avr. Monthly Rainfall
Sumatras
• During the SW monsoon, the Malacca Strait
between Sumatra and Malaysia is subject to
violent thundery squalls which feature archshaped cumulonimbus clouds. They are
known as Sumatras and usually occur at
night. They are caused by katabatic winds
blowing down on the eastern side of the
mountains of Sumatra. Between June and
September they bring heavy rain to
Singapore around dawn or later in the
morning.