Geography

Geography

 

Krong Preah Sihanouk – Sihanoukville

Sihanoukville is located at the [[Gulf of Thailand]] and rises up to {{convert|15|m|ft}} [[Above mean sea level|above sea level]].

TOWN: As a result of its clearly defined purpose, its very brief but turbulent history and its location Sihanoukville is unlike any other urban center in Cambodia. Established after the period of the [[French Protectorate]] bourgeois colonial style quarters as in [[Kampot]], [[Siem Reap]] or Phnom Penh do not exist. Architecture and street layout are dedicated to modern concepts of functionality. Planning of the city’s layout in particular did hardly be a subject of aesthetic considerations or applied sciences. Beginning at the port a moderate raster of streets spans up to the Weather Station Hill (Victory Hill)and along the local beach. Between the Communal Bank and Victory beach pier is one of the few spots in town, that seem to have been thought over in advance. The area connects via typical rather irregular successions of residential buildings, bare of any landmarks,  along a single highway. These highways were meant to connect the very few and widely dispersed actual settlement centers, its neighborhhoods lack intimacy in a one-dimensional infrastructure. The city’s center is to a great deal an alternating sequence of single blocks of solid urban edifices, such as banks, middle-class hotels, gas stations, pharmacies, Chinese bakeries and electronic retailers followed alternatingly by long rows of low-end food stalls, umbrella shops, motor-bike repair services, mini-markets,  laundry services, lock-picker services and – too many – mobile phone shops.


Geography, Geology

The area is mainly composed of sedimentary rocks from the Mesozoic and Cenozoic age, including heterogeneous conglomerate composition, layering thick, quartz pebbles, silica, limestone, riolit and felsit. The Mesozoic rocks are classified in Phu Quoc Formation (K pq). The Cenozoic sediments are classified in formations of Long Toan (middle – upper Pleistocene), Long My, (upper Pleistocene), Hau Giang (lower – middle Holocene), upper Holocene sediments, and undivided Quaternary.

 


 

Geography, Climate and Hydrology – Gulf of Thailand and South -East Asia

The International Hydrographic Organization defines the southern limit of the Gulf of Thailand as a line running from the Camau Point (8°36’N) in Vietnam, to the eastern side of the estuary of the Kelantan River (6°14′N 102°15′E).

The whole of the Southeast Asian waters are considered principally as part of the Pacific Ocean and their southern boundary is placed at the southern entrances of the Savu and Timor Seas.

The waters and islands between Asia and Australia and between the Pacific and the Indian Oceans form a geographical and oceanographical unit because of their special structure and position. Geographically the whole region is a part of Asia and is denoted as South-east Asia; oceanographically, the waters are part of the Pacific Ocean. This is justified not only by the position of the most obvious boundary between the Pacific and the Indian Oceans formed by Malaya, Sumatra, Java, and the Lesser Sunda Islands, but also by the fact that these seas are filled with water from the Pacific, to which they have the readier access.

The distribution of water and land alone characterizes the Southeast Asian Waters as one of the regions with the most complex structure on the earth. Numerous large and small islands subdivide the region into different seas, which are connected with each other by many passages and channels. When considering in addition the structure of the bottom of the seas, and that of the surface of the land, this unusual character appears still more pronounced. Deep trenches, high mountain chains, rows of volcanoes, deep sea basins and innumerable coral islands form a complexity of phenomena which are not found over such an extended area in any other part of the world.


“The Gulf of Thailand is a shallow sea (~50 m avg.) in Southeast Asia. It, like the Gulf of Carpentaria which has been shown to have a strong connection to the MJO – Madden–Julian Oscillation  (Oliver and Thompson, 2011), lies within the tropical regions strongly influenced by the MJO.”


THE WIND SYSTEMS AND THE CIRCULATION AT THE SURFACE

Because they are situated between the land masses of Asia and Australia, the South-East Asian Waters are the ideal monsoon region. The equatorial pressure trough moves according to the position of the sun, crossing the equator twice each year. In the summer hemisphere a low develops over the continent in prolongation of the equatorial pressure trough, while in the winter hemisphere a high is formed over the continent, belonging to the subtropical high. Between the high and the low the monsoons develop. Because the pressure distribution is very stationary, the winds have a high constancy, especially over the sea. The wind forces are generally small; storms and typhoons are observed only over the northern parts of the China Sea and the Philippines, over the Andaman Sea and north of Australia. When the equatorial trough passes the equator the winds are extremely variable, but in the full monsoon they temporarily deviate over land from the direction of the monsoons because of thermal influences.

SURFACE CURRENTS IN THE SOUTHEAST ASIAN WATERS

The development of a strong circulation within the South-East Asian Waters is favored by their geographical situation. The area formed by the China Sea, the passages between Sumatra and Borneo, the Java Sea, the Flores Sea and the Banda Sea lies with its axis exactly in the main wind direction of both monsoons. The China Sea between Formosa and Singapore extends in a north-east-south-west direction, and the north-east as well as the south-west monsoon blow along its axis. The waters between Sumatra and Borneo situated just below the equator form a north-south connection between the China and Java Seas and the monsoons blow here in a northerly and in a southerly direction. The area formed by the Java, Flores and Banda Seas, extending from west to east lies again in the direction of the monsoons, which blow here from west-north-west and from east-south-east. This situation conditions a strong circulation in this whole region during both monsoons. Moreover this circulation is favored by the great constancy of the winds, even if they are relatively weak, this is important for the development of a stationary system of currents.

THE MONSOONS

In January the north monsoon is fully developed. Over Asia a high is formed and the equatorial trough lies just north of Australia. Over the whole China Sea and over the Andaman Sea the northeast monsoon blows, and continues towards the Pacific Ocean as the northeast trades. In the China Sea wind force 5 is often exceeded. The monsoon passes the equator as a north wind and south of it turns to the east, where it appears as the northwest monsoon. The equatorial trough lies over the Indian Ocean at about 10°S, south of which the southeast trades are found. Off the northwest coast of Australia the trades are deflected and blow almost parallel to the coast towards the northeast with only a small force. In February the equatorial trough moves northwards and lies over Java and the Lesser Sunda Islands. Over the whole region between Java and Australia southwest winds now prevail branching off from the southeast trades. North of the equator conditions have not changed, but the strength of the monsoon has decreased. In March the southeast trades of the Indian Ocean extend further northwards and eastwards, while over the Timor and Arafura Seas northwest winds still prevail. Over the China Sea the northeast monsoon has weakened.
In April the equatorial trough moves quickly to the north and lies over the equator. The southeast trades always reach to about 5°S, that is, towards the north of the Lesser Sunda Islands, where it is normally called the southest monsoon. North of the equator, over the China Sea and over the Philippines weak northeast winds still prevail, while over the Gulf of Bengal southwest winds are blowing, introducing the monsoon for Burma and Thailand. May brings a complete change of conditions. The system of the northeast winds over the China Sea and the Philippines collapses, and the south monsoon succeeds over the whole of Southeast Asia. South of the equator the southeast monsoon blows, continuing to the Indian Ocean as the southeast trades. At the equator south winds prevail, and north of it the southwest monsoon. In the area of the Philippines and of the Celebes Sea the winds are still weak and unsteady. In June the distribution changes slightly; the winds become stronger, and reach force 4 and more over the Arafura Sea, over the Indian Ocean, and especially over the Gulf of Bengal. In July and August the south monsoon reaches its full development. In these months the low over Asia and the high over Australia are strongest and the circulation reaches its 17 greatest strength. Over the open sea wind force 4 is often exceeded, but over the Indonesian Archipelago and over the Philippines the wind remains on the average below force 4. In September over the waters around Formosa and Hong Kong the first northeast winds occur, indicating a weakening of the Asian low. In the other parts of the region the south monsoon loses only slightly in strength. In October the equatorial trough begins to move rapidly southwards, and by the middle of the month, lies along a line from the center of the Gulf of Bengal to the north coast of New Guinea. North of this line northeast winds prevail, south of it still the southeast monsoon. In the Indian Ocean between the equator and 10°N the southwest monsoon has turned so far, that it comes almost from the west.
In November the equatorial trough runs clearly south of the equator. The northeast monsoon has intensified especially over the China Sea and normally exceeds wind force 4. Over the Indian Ocean the system of the southeast monsoon has collapsed, and the southeast trades are confined to south of about 5°S. By December the equatorial trough moves further to the south and lies at about 5°S. The northeast monsoon reaches its maximal force over the China Sea, crosses the equator as a north wind and temporarily reaches Java and the Lesser Sunda Islands. Over the Java Sea west winds prevail. The southeast trades of the Indian Ocean have retreated further to the south and reach just up to 10°S, and near the Australian northwest coast, south winds prevail. This variation of the atmospheric circulation finds its parallel in a corresponding variation of the oceanic circulation. Because of the high constancy of the monsoons and of their regular appearance the ocean currents show the same characteristics.
Just as the monsoon changes direction twice a year and the winds are practically reversed at the time of their strongest development, the oceanic circulation is also reversed in large areas. Thus, this complete reversal is really typical of the circulation in these waters.

South-West Monsoon

June-September

The south-west monsoon usually blows in from the Indian Ocean from June-September, but it can sometimes start early in May (as it has done this year, 2008). In simplistic terms, the heat of March-May brings about a significant difference between land and sea temperatures. This causes hot air to rise creating low pressure which in turn causes the monsoon wind to blow towards land. As the wind blows it attracts moisture from over the oceans which may fall as rainfall on the mainland. Coming in from a south-westerly direction, it is the Andaman Coast of Thailand which is hit the hardest. Downpours can be torrential and may be accompanied by gusty winds and high waves. Some boat services are temporarily suspended during May-October on the Andaman Coast, but it should be noted that it doesn’t rain all day, every day. There is still plenty of sunshine and temperatures remain high.

Although the period from June-September sees more rain on the Andaman Coast, the Gulf Coast doesn’t escape completely, but there is still less rainfall here than the Andaman Coast.


North-East Monsoon

November-March

The north-easterly wind brings cooler temperatures and generally less humidity .

However, the north-east monsoon has a slightly different effect on the more exposed Gulf Coast. As the wind blows from the north-east it travels across the Gulf of Thailand picking up moisture.


Pre-Monsoon (summer)

March to mid-May

The transitional period from the north-east monsoon to the south-west monsoon can result in extremely high temperatures.