Download Climate controls

Climate Varies around the Globe:
How and Why?
Yongqin David Chen (陳永勤)
Department of Geography and Resource Management
The Chinese University of Hong Kong
Shatin, NT, Hong Kong
Presentation Outline
• Climate controls: latitude dominates, others also work
• Classification of irregularly distributed climates
• Similar latitudes, but very different climates: Somalia vs
Malaysia, Shandong vs Xinjiang
Climate controls
(1) Latitude – fluctuations in the amount of solar radiation received at earth’s
surface, represents the single greatest cause of temperature differences.
(2)
Land and water – marine and continental climates
(3)
Ocean currents – poleward-moving warm currents (Gulf Stream and Kuroshio
Current in N Hemisphere and Brazilian and East Australian Currents in S
Hemisphere, more pronounced impacts in winter) and equatorward-moving cold
currents (Canaries and California Currents in N Hemisphere and Peruvian and
Benguela Currents in S Hemisphere, chilling effects stabilize air masses)
(4)
Pressure centers and prevailing winds - air mass movement and gain or loss
of heat and moisture, seasonal shifting. More maritime on the west coast of N
America and more continental on the east coast
(5)
Mountain barriers and highlands – windward and leeward sides and rain
shadow, Andes and Himalayan in S America and Asia, no mountain barrier in
western Europe leading to moderate temperatures and sufficient precipitation in
the entire region
•Latitudinal heat balance.
Average over the entire year, we see that equatorward from 36o , the
amount of incoming solar radiation exceeds the loss from outgoing
terrestrial radiation. The reverse is true for the middle and high (polar)
latitudes, where losses from outgoing terrestrial radiation exceed gains
from incoming solar radiation.
•Climate is a 3-D phenomenon:
latitudinal, longitudinal, and altitudinal
•An index of continentality
gauges the influence of oceans on air temperature over continents. In
this scheme, North America is divided into zones of increasing
maritime influence: continental, subcontinental, maritime, and
ultramaritime. The greater the maritime influence, the less is the
contrast between average summer and average winter temperatures.
[Adapted from D.R. Currey, “Continentality of Extratropical Climates.” Annals of Association of
American Geographers 64, No.2 91974):274]
•Major Ocean Currents:
1. Gulf Stream
2. North Atlantic Drift
3. Labrador Current
4. West Greenland Drift
5. East Greenland Drift
6. Canary Current
7. North Equatorial Current
8. North Equatorial
Countercurrent
9. South Equatorial Current
10. South Equatorial
Countercurrent
11. Equatorial Countercurrent
12. Kuroshio Current
13. North Pacific Drift
14. Alaska Current
15. Oyashio Current
16. California Current
17. Peru or Humbolt Current
18. Brazil Current
19. Falkland Current
20. Benguela Current
21. Agulhas Current
22. West Wind Drift
•Coastal upwellings
are important because they provide abundant nutrients and
therefore encourage rich fishing grounds.
Köppen system - Five principal climate groups
A) Humid tropical - Winterless climates; all months have a mean
temperature above 18oC.
B) Dry - Climates where potential evaporation exceeds precipitation;
there is a constant water deficiency.
C) Humid middle-latitude, mild winters - the average temperature
of the coldest month is below 18oC but above -3oC.
D) Humid middle-latitude, severe winter - the average temperature
of the coldest month is below -3oC and the warmest monthly mean
exceeds 10oC.
E) Polar - Summerless climates; the average temperature of the
warmest month is below 10oC.
•“The zone is a strange climatological phenomenon – a
desert (the Somali-Chalbi) on the eastern cost in tropical
latitudes. The extreme aridity is caused, in the main, by the
fact that the prevailing winds, during most months of the year,
have a northeasterly or southwesterly direction, thus making
moist air masses over the land an exception rather than the
rule (Fig.1).”
The Horn of Africa, by J.F. Griffiths
Climates of Africa, Vol. 10,
World Survey of Climatology, p. 134
•
Unusual aridity of the Horn of Africa caused Flohn (1964) to ask:
“why are the summer rains missing?”
(1) directional divergence produced by overheating at the Ethiopian
highlands,
(2) speed divergence produced by the northerly increase of the
pressure gradient,
(3) frictional divergence in coast-parallel winds,
(4) deflection of wind-driven ocean surface current and cold upwelling
along the coast.
Flohn, H., 1964. On the causes of the aridity of northeastern Africa. Würzburger
Geograph. Arb., 12: 17 pp. (English translation by East African Meteorological
Dept., Nairobi, 1966.)
•“why are the summer rains missing?” (1) directional divergence
produced by overheating at the Ethiopian highlands; (2) speed divergence
produced by the northerly increase of the pressure gradient; (3) frictional
divergence in coast-parallel winds; (4) deflection of wind-driven ocean
surface current and cold upwelling along the coast.
•Amazing fluctuations of annual rainfall amounts at
Djibouti for 64 years
- Less than 30 mm for five years
- 250 mm or more for four years
•Seasons defined by rainfall patterns:
Jilal – December to March, the northeast monsoon is in
dominance and conditions are dry and relatively hot.
Gu – April and May, the transition period, relatively wet and
hot.
Hagar – June to September, the southwest monsoon
dominates, bringing relatively cool conditions with showers
along the coast but dry inland.
Der – October and November, the transition period, similar to
the Gu but there is the important rainy season in the north.
•Climate of Malaysia
Tropical; annual southwest (April to October)
and northeast (October to February) monsoons
• What
is the Malaysia's climate like?
Malaysia has two main seasons, the Northeast Monsoon
(November to March) and the Southwest Monsoon (May
to September),
separated by two relatively shorter intermonsoon periods.
The mean monthly rainfall amount shows drier weather
conditions from May to July and wetter weather conditions
from November to January. February is also a relatively dry
month. The date of the beginning and end of the monsoon
varies from year to year.They are determined by the
beginning of rain spell and predominant wind direction.