Warm fronts

A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient. Warm fronts lie within broader troughs of low pressure than cold fronts, and move more slowly than the cold fronts which usually follow because cold air is denser and harder to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale.
Clouds ahead of the warm front are mostly strati form, and rainfall gradually increases as the front approaches. Fog can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the strati form clouds ahead of the front, and after frontal passage thundershowers may continue. On weather maps, the surface location of a warm front is marked with a red line of semicircles pointing in the direction of travel.

Development

Air masses are large bodies of air with similar properties of temperature and humidity that form over source regions, and the warm air masses behind warm fronts are not only warmer but higher in humidity than the colder air preceding them. Because of a warm air mass’s higher temperature and thus lesser density, mixing between the two air masses is unlikely. Being lighter, the warm air mass is unable to displace the cooler air mass and instead is forced upward along the upper boundary of the colder air in a process known as overrunning. The boundary between the two air masses has a gradual slope of 130 and lifting is slow but persistent. As the air mass rises into regions of lower pressure, it expands and cools. As it cools, water vapor condenses and forms extensive cloud coverage. The first clouds to form along the sloping surface of the cold air are high cirrus, which thicken to cirrostratus and altostratus. Once the clouds have thickened to 2,500 metres (8,200 ft) from the earth’s surface, rain can begin to fall from the heavy nimbostratus cloud.

References:  http://passporttoknowledge.com/scic/jetstreams/educators/fronts.pdf

HOT WEATHER! -due to season changing

Today, I would explain why our weather recently is SO HOT! Yet, do you realize it is only really really hot during the morning to afternoon, then suddenly at around 5pm it starts to rain? Well, below is an explanation for it. (This relates to Singapore’s seasons.)

Singapore is currently going through something called the inter-monsoon season, which means a season between two monsoons. This season is characterized by hot, intense heat during the afternoons followed by short but heavy thunderstorms later in the day. The atmosphere is also very humid, with weak winds in the afternoon but heavy winds during the thunderstorms.

Contrary to much belief, Singapore does have seasons! The uniform weather in Singapore is affected by two specific season-Northeast Monsoon Season (December-March), where the season north easterly winds blow through Singapore and Southwest Monsoon Season (June-September), south easterly or south westerly wind blow through the country. Between each monsoon season, there is another kind of season called the inter-monsoon season which occurs during May-April and October-November.

The difference between the Monsoon seasons and inter-monsoon seasons is the strength of the wind as well as the effect of the sun. During monsoon seasons, the wind is constant and strong and it blows from a uniform direction. This uniform direction of wind leads to a more predictable and fairly constant weather. However, during the inter-monsoon period, the winds are weaker and they do not come from a fixed direction, leading to more erratic weather, which is occurring now.

Furthermore, during this season, due to the earth’s tilt, the equator is directly below the sun, which explains the hot noon temperature.  This hotter temperature would then lead to the heavy downpour later in the day. As said above, as the surface heats up, the warm air would rise and cool to form water vapor, which would condense to produce clouds that form rain. Since there are higher temperature in the afternoon, it would likely result in heavier rains later in the day as more hot air rise to form clouds. Hence, the weather now is not only hot, but it also has a high humidity, with drastic weather changes.

Taken from: http://www.climatetemp.info/singapore/

Breakdown/ Summary of graph:

Months with high average temperature: March, APRIL, MAY, June

Months with high humidity: Jan, APRIL, MAY, November, December

Well, now we can see why it is so hot and so humid!

Bibliography

http://wildsingaporenews.blogspot.com/2011/04/singapore-hot-and-wet-days-may-last.html

http://wildsingaporenews.blogspot.com/2011/05/singapore-hottest-days-of-year.html

http://monsoonseason.com/

http://weather.about.com/od/monsoons/f/monsoons.htm

Done by: Tay Li Lin (14)

River Delta

River delta is defined as the place where river unload their deposits, which is built up from primarily river-borne sediment. It is usually formed when the amount of sediment delivered at the mouth of a river exceeds the amount removed by waves and tidal currents, decreases the current velocity and also the transport capacity of the river.

There are a lot of types of river delta:

Fig 1: An arcuate delta

• Arcuate (fan-shaped) delta - e.g., Nile River.  Has many active, short distributaries taking sediment to their mouths.  The receiving (ambient) waters are rather shallow and have relatively even wave action arriving perpendicular to the shore with minimal longshore current.  As the sediment exits the many distributary mouths, the waves push it back, so the coastline is rather smooth.

Fig 2: a bird-foot delta

• Bird-foot (shaped like a bird foot) delta - e.g., Mississippi River.  Tend to have one or a very few major distributaries near their mouths.  The receiving basin has currents that carry the sediment away as it exits the distributary mouth.  There is a broad, shallow shelf that deepens abruptly, so the trend is to grow long and thin like a bird's toe.

Fig 3: a cuspate delta

• Cuspate (tooth-shaped) delta - e.g., Tiber River of Italy.  Usually has one distributary emptying into a flat coastline with wave action hitting it head-on.  This tends to push the sediment back on both sides of the mouth, with a "tooth" growing out onto the shelf.

Fig 4: an estuarine delta

• Estuarine delta - e.g., Seine River of France.  This type of delta has a river that empties into a long, narrow estuary that eventually becomes filled with sediment (inside the coastline).

Reference:

http://home.swipnet.se/valter/main%20Ri.htm

http://web.bryant.edu/~dlm1/sc366/deltas/deltas.htm

http://www.americaswetlandresources.com/background_facts/detailedstory/RiverDelta.html