Climatology Introduction to Aspects of World Climatology

Factors Affecting Climate Latitude Geography such Land/sea disposition Effects of the world general circulation, including its seasonal changes Local effects (e.g. ocean currents, mountain ranges)

Factors Affecting Climate Intensity of solar radiation. Land/sea distribution. Ocean Currents. Prevailing Winds. Location of High/Low pressure systems. Mountain barriers. Altitude.

Ocean Currents

Global Sea Surface Temperatures

Untilted Non-rotating Earth EQUATORIAL TROUGH POLAR HIGH

Sir Isaac Newton 1st Law Conservation of Momentum

Untilted Rotating Earth

Worldwide Circulation Hadley Cell Ferre l Cell

Climate Zones

Climate Zones - Summary

Annual movement of the Earth around the Sun

Climatic Zones - Seasonal JanuaryJuly

Summary of Climatic Zones Polar: –quiet settled anticyclonic weather, low precipitation with a snow and ice surface. In the northern hemisphere, however, the 'pole of cold' is displaced to the Siberian land mass, and the polar area itself is often invaded by travelling depressions, increasing the snowfall.

Summary of Climatic Zones Boreal Zone (Subpolar climate) 40° - 60°: –exists only in the northern hemisphere between the cool disturbed temperate zone and the Polar zone in N. America, Scandinavia and N. Russia. Characterised by warm moist summers and very cold winters. Disturbed Temperate: –disturbed climate, travelling depressions, frontal weather, and no dry season. –Winds predominantly westerly with frequent gales

Climate Zones cont. Mediterranean/Sub-tropical transitional /Warm temperate zone: –under the influence of the sub-tropical high pressure areas in summer giving fine, dry, settled weather. Under the influence of the temperate zone depressions during winter giving rain and cool unsettled weather. Sub-Tropical: –influenced summer and winter by the sub-tropical highs. Pleasant weather over the sea but arid deserts over the land.

Climate Zones cont. Savannah/Tropical Transitional: –trade winds in winter with sub-tropical weather, equatorial rainbelt in summer. Equatorial: –two very wet seasons, with the transit of the sun/ITCZ, and uniformly high temperature, humidity, and rainfall throughout the year. No dry season

Average Global Surface Pressure - January

Average Global Surface Pressure - July

Sumatras S.E. Trade Winds Singapore Sumatera Malaysia Kuala Lumpur Straights of Malacca Early morning squalls

Sumatras During the SW monsoon, the Malacca Strait between Sumatra and Malaysia is subject to violent thundery squalls which feature arch- shaped 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 (Sumatera - Indonesia). Between June and September they bring heavy rain to Singapore around dawn or later in the morning.

SIBERIAN HIGH H H H HH H L L L L ITCZ

ASIATIC LOW L L L H H HHH HHH ITCZ Pampero

ITF in West Africa

S.E. Asia ITCZ plus secondary convergence line

Monsoons - July

S.W. Monsoon - October

REGIONAL CLIMATOLOGY NW Europe Mediterranean

30N 40E20E30E10E0 40N MEDITERRANEAN - JANUARY Mistral 20-50/70kt Bora 70G100kt L Sirocco KhamsinGhibli H Harmattan L L L L L

30N 40E20E30E10E0 40N MEDITERRANEAN - JULY L Etesian winds Shamal Haboobs L Levanter (March + July-October)

Mediterranean Area - Local Winds –Mistral The Mistral is a northerly wind blowing into the Mediterranean. It is principally a valley or funnel wind, blowing down the Rhone Valley and through the Toulouse Gap. It is enhanced by katabatic effect on the sides of the valley to speeds of kts with gusts up to 70 kts. It occurs mainly in winter and early spring, often in conjunction with a Gulf of Genoa depression and/or a cold front moving south into the Mediterranean. –The Bora The Bora is a cold northerly or north-easterly wind in winter and early spring from the high ground to the north of the Adriatic. A depression moving eastwards along the Mediterranean brings a northerly gradient behind it, and the resultant wind is intensified primarily by katabatic and, to a much lesser extent, funnel effects. It reaches an average speed of 70 knots with gusts up to 100 knots, and prohibits aircraft operations on coastal airfields in Italy and the former Yugoslavia around the Adriatic.

Mediterranean Area - Local Winds –Sirocco The Sirocco occurs in the winter and is a warm, dry, dust-laden, southerly wind off N. Africa into the western Mediterranean, usually in advance of a travelling depression. Crossing the sea it is cooled from below, so that it is made stable but also moistened. It tends to produce dust-laden advection fog or shallow stratus if it penetrates as far as the northern Mediterranean. Such conditions are known as ‘the Marin’ in the south of France. –Khamsin The southerly wind in winter which blows into the Mediterranean off the eastern part of Libya and Egypt, also in advance of depressions moving along the eastern Mediterranean, is known as the Khamsin, which comes from the Arabic word for 50. A hot dry wind, it is often associated with sandstorms on the N. African coast. Such a wind is also known as the Ghibli in western Libya.

Mediterranean Area - Local Winds –Levanter The Levanter is an easterly wind which blows in the western Mediterranean and affects the southern coast of Spain, Gibraltar and the north coast of Africa. As it moves westward, it moistens and cools at the surface and advection fog or low status results. It is most frequent from July to October and in March. –Etesians The Etesian winds blow from a northerly direction around the asiatic low pressure in summer. They affect the Eastern Mediterrean between 20° and 30°E (mainly across Greece, the Aegean Sea and Western Turkey, but they can reach the North African coast). Their speed is normally kts but they can gust to gale force in the height of summer. Their name comes from the Greek word for ‘annual’ but the Turks call them the Meltemi..

Middle East - Local Winds –Shamal The Shamal is a North/NW wind which blows in June to August around the Indian low pressure area and across Iraq. It brings dust or sandstorms which reduce visibility to 1,000-3,000 m.

Local Duststorms - Africa –Haboobs During the ITCZ’s movement northwards across the Sudan in July, the strong up-currents and squally winds associated with its Cbs cause severe duststorms known as Haboobs. Dust impregnates the clouds to over 10,000 feet and the apparent wall of dust can be seen at distances in excess of 50 miles. –Harmattan The cooling of the Sahara during the months November- March leads to high pressure and to a north-east wind towards the Atlantic coast. This is the Harmattan, and it is a very dust-laden wind, with visibilities from 4,000 m down to 1,000 m, which adversely affects aircraft operations on the coastal airfields of NW Africa to as far south as Lagos and other nearby areas.