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

Wrap-up with Term 2 Booklet

Hey guys, Luo Yang here.

My post would a summary of the things we had done this term using mindmap :)

Luo Yang (22)

Made using https://bubbl.us/

Chapter 3: Rivers

Hello everyone,

This post is about the stages of the river and how they are formed.

                                  Fig 1.   Overall of three main stages of river

1. Upper course

                                 Fig 2. The V-shaped Valley of the upper couse

    Most of the rivers begin from the top of the hills and mountains. Since the clouds move upwards air will cool down and form the rain, there will be a lot of rain. When rain falls on the land, some of the water will seep into the soil, and some of it stays on the surface. The water on the surface will flow down and form tiny streams. These streams will gradually join with other streams to form the beginning of the river. The beginning may be a spring, or a marsh or even a glacier. When the river flows down the steep and rocky sides of the hill or mountain, it will get faster and wilder as well as pick up and carries along with the large boulders and rocks. This wearing away of the land is called erosion.

2. Middle course

                                    Fig 3.  The meanders of the middle course
                                      

    As the river continues on its journey the ground starts to have a gentler slope. The river carries on eroding the land, making the river wider and deeper. Bends and turns called meanders then start to form, as the water begins to wears away the sides. The volume of water also increases, as smaller rivers called tributaries also flow in.

3. Lower course

                                               Fig 4.  The lower course and end of the river

    The river is very wide and deep by the time it reaches its final stage which is lower course. The surrounding land will have also flattened out, making the water slow down, and stones that have been carried along will drop down to the riverbed. It is also at this stage that the river meanders into large horse-shoe shapes, and this is where flooding is most likely to cause problems. When the river comes to an end, it will either flow into a loch or into the sea. This parts is known as the mouth of the river.

Done by Yu Jiacheng (25)

Human influences on Hydrograph

Urbanization

Urbanization replaces permeable land surface with impermeable one, which is covered by streets, parking lots, buildings etc. Water will run off the surface rather than being absorbed by soil. Base flow will decrease while overland flow will increase. With more overland flow, river will respond more quickly to rainfall, resulting in a shorter lag time. The construction of sewers during urbanization effectively increases the drainage density, resulting in a higher peak discharge.

Deforestation

Trees lengthen the lag time by intercepting the water. They also increase water infiltration by taking up water by their roots. Deforestation will reduce the interception and water-taking up; there will be more overland flow. Rivers in areas that have been cleared by deforestation will also respond quicker to rainfall, resulting in a higher peak discharge and shorter lag time.

Building of dams

The presence of a dam, will allow flow to be controlled, reducing the risk of flooding and allowing rivers to gradually respond to heavy rainfall in a controlled way; the river has a longer lag time.

Done by Nguyen Trung Hieu (23)

REFERENCE:

Channel Geometry and Flow Characteristics. The Physical Environment. Retrieved on 26 April 2011.URL: http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/fluvial_systems/channel_geometry_and_flow.html

Factors affecting Hydrographs / Lag Time. Retrieved on 26 April. URL: http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes/GCSE%20Revision/Unit%201/Rivers/rivers_factors_affecting_hydrographs.htm

Hydrographs

Hi guys, today I'll be blogging about hydrographs.

Recap: a hydrograph is a graph that shows the discharge of a point in the river over a period of time, usually to show the change in discharge caused by rainfall. Discharge is just the amount of water that flows through that certain point and is measured in cumecs - cubic meters per second. The significance about hydrographs is that we can find out about the patterns in a certain drainage basin, how much water passes through a point and how long it takes for the water to get there, and from there we can implement protective measures to ward against floods and things like that.

Since all that water has to come from somewhere, let's look back to the hydrological cycle.
Overland flow and through flow all contribute to the amount of water in the drainage basin. The amount of overland flow/surface runoff is dependent on rainwater intensity and the infiltration capacity of the soil. If it's been raining heavily for a while and the soil is already saturated, then it stands to reason that there would be more overland flow. Throughflow is the water that flows horizontally in the soil (it's different from groundwater flow, that is in, well, groundwater but this is in the soil).The factors that would affect the amount of water would be:

1. Urbanisation
In this case, we're assuming urbanisation doesn't include drains. (But if there were, it would lead to a longer lag time, because the water takes a longer time to get to the river, or if the drains lead to reservoirs or water storage areas, then a lower peak). Urbanisation would basically entail a concrete jungle, and concrete has really poor permeability. As a result, there would be a lot more water flowing on the surface. 
2. Reforestation
Reforestation would mean more trees, and more interception (and also more evapotranspiration). So there would be less water reaching the surface, and less overland flow. And of course, it would offset some of the carbon in the atmosphere, and become a carbon sink.
3. Deforestation
The lack of trees would conversely mean less interception, and more water would reach the surface.
4. Permeability of soil
Very permeable soil means that it is more likely to absorb water and not so permeable soil means that more water would "pass" over it rather than being absorbed. This is assuming that infiltration capacity is constant, because the soil could be very permeable but cannot absorb a lot of water.  

(If you can think of some more factors, leave it in the comments :>)

Since we've already went through in class the factors that affect the lag time and shape of hydrographs, I won't talk about them here.

But I think the thing to note here is that, a lot of human activity is affecting not only the hydrological cycle, but also the discharge in the rivers. In reality, a lot of the floods and water-related disasters could be due us, our need to build buildings, cut down trees and so on. So we should balance our activity with our environmental conscience - because the environment can only take so much and bring the conditions back to equilibrium.

Chapter 2: The Hydrological Cycle

Fig 1. Overview of the Hydrological Cycle

1.       Overview of the Hydrological Cycle

The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation. Once the water reaches the ground, one of two processes may occur;

1) Some of the water may evaporate back into the atmosphere or

2) The water may penetrate the surface and become groundwater. Groundwater either seeps its way to into the oceans, rivers, and streams, or is released back into the atmosphere through transpiration of the plants. The balance of water that remains on the earth's surface is runoff, which empties into lakes, rivers and streams and is carried back to the oceans, where the cycle begins again.

2.  Different Processes of Hydrological Cycle

-   Evaporation and Condensation:

Evaporation is the phase change of liquid water into a vapor (gas). Evaporation is an important means of transferring energy between the surface and the air above. The energy used to evaporate water is called "latent energy". Latent energy is "locked up" in the water molecule when water undergoes the phase change from a liquid to a gas. Eighty-eight percent of all water entering the atmosphere originates from the ocean between 60^o north and 60^o south latitude. Most of the water evaporated from the ocean returns directly back to the ocean. Some water is transported over land before it is precipitated out. When water vapor condenses back into a liquid it releases latent heat, which is converted into sensible heat warming the surrounding air. The warming of the surrounding air fuels uplift to help promote adiabatic cooling and further condensation. As droplets of water coalesce into larger droplets they attain a size big enough to fall towards the earth as precipitation. Located high in the troposphere, rain drops possess a high degree of potential energy that is converted into kinetic energy once they begin to fall toward the surface. Impacting the surface they convert this kinetic energy into work done on the surface (erosion for example). 

-   Interception and Infiltration

As water reaches the surface in various forms of precipitation, it is intercepted by plants or falls directly to the surface. Precipitation that collects on the leaves or stems of plants is known as interception. The amount of water intercepted by a plant largely depends on plant form. Water is held on the leaf surface until it either drips off as through fall or trickles down the leaf stem finally reaching the ground as stem flow. Interception of falling rain buffers the surface against erosion. Coniferous trees tend to intercept more water than deciduous trees on an annual basis because deciduous trees drop their leaves for a period of time.

Figure 2. Droplets of water intercepted by tree leaf. 

Upon reaching the ground, some water infiltrates into the soil, possibly percolating down to the groundwater zone or it may run across the surface as runoff. Infiltration refers to water that penetrates into the surface of soil. Infiltration is controlled by soil texture, soil structure, vegetation and soil moisture status. High infiltration rates occur in dry soils, with infiltration slowing as the soil becomes wet. Coarse textured soils with large well-connected pore spaces tend to have higher infiltration rates than fine textured soils. However, coarse textured soils fill more quickly than fine textured soils due to a smaller amount of total pore space in a unit volume of soil. Runoff is generated quicker than one might have with a finer textured soil.

Vegetation also affects infiltration. For instance, infiltration is higher for soils under forest vegetation than bare soils. Tree roots loosen and provide conduits through which water can enter the soil. Foliage and surface litter reduce the impact of falling rain keeping soil passages from becoming sealed.

3.       Importance of the Hydrological Cycle

All the creatures cannot live without water. Approximately three-fourths of the Earth is covered with water. However, of this water, only one percent is the fresh water on which we depend. The fresh water that we use and its continuous replacement are results of the hydrological cycle. Due to hydrological cycle, the quantity of water level in the oceans, rivers, ponds etc are maintained properly. The earth have limited amount of fresh water and if water that evaporate never return back to earth, we would not be living now.

Done by Zeng Jingxuan (16)

Reference:

1. Alguo Dai & Kevin Trenberth, Clouds-Hydrological Cycle Retrieved 23^rd April from http://www.tiimes.ucar.edu/highlights/fy06/dai.html

2. Hydrological Cycle. Retrieved 23^rd April from http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/hydrosphere/hydrologic_cycle.html

1.2 Singapore's Water

Hello everyone, this is Rachel Tan (12).

In this post, I will touch on the efforts of the Singapore government in sustaining our water resources, such as the 4 national taps.

The First Tap (Reservoirs):
Currently, Singapore have 17 reservoirs to collect rainwater and used water as our supply is low, hence it is necessary for us to maximize all resources we have.
I think that this idea is excellent, as well as the government's efforts to build more barrages and reservoirs since the past years.
However, I feel that perhaps they should put a little bit more focus on maintainance of our drainage systems, especially those in low lying areas like Orchard Road, which is probably the worst place for a floods to occur as shops will suffer big losses. Everybody, remember those Birkin bags floating out of their shops and Milk Tea everywhere, I'm sure we don't want that to occur again right!

To tackle that problem the stretch of Orchard Road will be raised to decline this issue and so on. Check this video out for a more comprehensive explanation.

The Second Tap (Malaysia):
This is the import of water from Johor, Malaysia to increase our supply, and is under two agreements signed years ago.
These agreements will expire in 2011 and 2061, which Malaysia may not choose to renew them.
Hence, Singapore government is indeed taking measure now to ensure our sustainability even if Malaysia do cut-off our water supply from them.
This is good, as it is better to prepare in advance for the future, then panic in a couple of years time. A method would be the 3rd tap.

The Third Tap (NEWater):
This is a technology developed locally and is our Singapore pride. It makes use of ultra-filtration to recycle used water from our sewage system and is highly sustainable. This is due to that it "cleans" used water, which cannot be used for much purposes, thus after going through the NEWater treatment, not only is it able to be reused again, it will also be contributing to saving the environment, by following 2 of the 3 "R"s, reuse and recycle! In fact, this technology is so highly feasible that oil plants are in Saudi Arabia are said to be using it as well!
Another video I found which briefly shows the processes in this treatment ina cute way:
<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/K1rb13g6dTU" frameborder="0" allowfullscreen></iframe>

The Fourth Tap (Desalination Plant)
At this plant, sea water undergoes a pre-treatment process likewise to NEWater to purify it for new consumption.
This is very feasible as Singapore is a island, surrounded by nothing but sea water. What better way than to make use of these vast resources into consumable water for our resources right!
After all, the resource of sea water can be said to be impossible to use up and after all the worries of Singapore sinking due to rising sea levels from global warming, perhaps this is a way to counter that problem!

Just a Quick Note:
Comments on Azirah's post on the Importance of Water:
I feel that her post is very good in listing out all the different uses of water, from in the system(our human bodies) to the universe(the Earth).
I would particularly like to highlight that water makes up around 65% of our bodies, and without it, we will die! Like by dehydration. I feel that this is of the utmost important use of water, as if we mammals don't exist, Earth will be like empty, then there will be no point in tis existence.
Also, I like that she brought up that water is also in our DNA, as we learnt in our biology lesson, the hydrogen bonds between the two nitrogenous bases in the DNA molecule is necessary for DNA replication to occur.

I would also like to add on that without water, water transport will not be possible. Thus this affects globalization!

Continue on Precipitation

1/ Orographic Precipitation:

-Orographic precipitation takes place at mountainous places.

-Some processes take place during Orographic Precipitation: (in order)

            -Evaporation:

                        - of the ocean water creating moist air over ocean surface.

                        - of ice crystals and air moisture in the cloud when it moves down the leeward slope, creating hot and dry air region at the base of the mountain.

            -Adiabatic cooling: (Refer to Chelsia's post for definition) 

            - Condensation of the water vapour when air rises on the windward slope since air is cooled adiabatically. (Condensation is the change of the physical state of matter from gaseous phase into liquid phase)

- Precipitation of water vapour occuring when air continues to rise higher on the windward slope. Precipitation will start to fall to the surface, creating a rain shadow.

- Evaporation of the moisture in clouds when the air travels down the slope of the mountain makes air hot and dry. Hence, dry and hot deserts are observed at the end of the leeward slope.

2/ Frontal Precipitation:

Summary of mechanism of Frontal Precipitation

-       Warm front: warm air advances towards cold air -> warm air rises and coolds adiabatically -> condensation -> rain

-       Cold Front: heavier cold air advances and pushes beneath warm air -> warm air is forced upwards and cools adiabatically -> condensation -> rain

Since the text book mentioned the differences between warm front and cold front but did not specifically state them out, I would touch on those differences as well as types of weather may be produced. 

Differences between warm front and cold front:

-       By definition,

o   Warm front is the boundary between cold air and warmer air that's replacing the cold air

o   Cold front is the boundary between warm air and colder air that's replacing the warm air.

-       A cold front is associated with colder weather and a warm front is associated with warmer weather. Cold front is usually found at a temperature drop's leading edge. Meanwhile, warm front is usually found at a homogenous warm air mass's leading edge.

-       Cold fronts can move up to twice as fast as warm fronts can, since cold air is denser and harder to be removed from the earth’s surface than warm air. As a result, cold fronts can produce sharper changes in weather than warm fronts.

-       Due to the difference in mechanism, different types of weather are created:

Weather conditions associated with a cold front.

Weather Phenomenon	Prior to the Passing of the Front	Contact with the Front	After the Passing of the Front
Temperature	Warm	Cooling suddenly	Cold and getting colder
Atmospheric Pressure	Decreasing steadily	Leveling off then increasing	Increasing steadily
Winds	South to southeast	Variable and gusty	West to northwest
Precipitation	Showers	Heavy rain or snow, hail sometimes	Showers then clearing
Clouds	Cirrus and cirrostratus changing later to cumulus and cumulonimbus	Cumulus and cumulonimbus	Cumulus

Weather conditions associated with a warm front.

Weather Phenomenon	Prior to the Passing of the Front	Contact with the Front	After the Passing of the Front
Temperature	Cool	Warming suddenly	Warmer then leveling off
Atmospheric Pressure	Decreasing steadily	Leveling off	Slight rise followed by a decrease
Winds	South to southeast	Variable	South to southwest
Precipitation	Showers, snow, sleet or drizzle	Light drizzle	None
Clouds	Cirrus, cirrostratus, altostratus, nimbostratus, and then stratus	Stratus, sometimes cumulonimbus	Clearing with scattered stratus, sometimes scattered cumulonimbus

Please correct me if I'm wrong. If you have any question, please feel free to comment. :) Hope this help your further understanding. 

 Done by: Nguyen Xuan Quynh (9)

Chapter 1: Water

1.1 Importance of Water for Life

From the article, the words associated with water, as discussed in class, are listed below.

Water

1. Boiling point of 100˚C

2. Can act as a shield

3. DNA

4. Dissolves minerals

5. Electron hog

6. Forms crystal lattice

7. Hydrogen bond

8. Less dense in solid form (i.e. ice)

9. High specific latent heat

10. H2O is a polar molecule

11. Absorbs UV rays

12. Dipole

13. Oxygen covalent bond

14. Indicator of life

15. Large (i.e. large enough to insure that water in cells will neither freeze nor boil off) range of temperature. Doesn’t boil/freeze easily.

16. Transporting molecules

17. Density decreases when frozen

18. Versatile and unique

19. Maintains stable climate on Earth

20. Most abundant liquid in the universe

21. Pond will not freeze entirely so life forms can survive

Hence, I will be touching on the main roles of water on Earth.

Water is needed for:

1. Replication

Water allows organic compounds to react in ways that ultimately allow replication.

2. Metabolism for life

Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules for the growth of larger molecules while in catabolism, water is used to break bonds for the generation of smaller molecules. 

3. Photosynthesis in plants

During photosynthesis, carbon dioxide and water are needed for the production of glucose.

4. Continuity of underwater ecosystems

Fishes and marine mammals, and plants live and grow in the water respectively. Some of these animals are the foundation of the ocean food chain while the plants provide aquatic vertebrates with oxygen to survive.

5. Agriculture

Water is used for irrigation in agriculture. 

6. Drinking

The human body contains 55%-78% water. To function properly, the body requires at least two liters of water per day to avoid dehydration. 

7. Washing

Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances. 

8. Chemical uses

Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst.

9. Heat exchange

Water and steam are used as heat transfer fluids in diverse heat exchange systems, due to its availability and high heat capacity, both as a coolant and for heating.

10. Fire extinction

Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. Hence, the evaporation of water carries heat away from the fire.

11. Recreation

Humans use water for recreational purposes, exercising and sports. Lakesides, beaches and water parks are also popular places for people to go to relax. Besides that, some keep life in aquariums or ponds for show, fun, and companionship.

12. Industrial applications

Hydroelectric power comes from water driving a water turbine connected to a generator. Besides that, pressurized water is used in water blasting and water jet cutters. Also, very high pressure water guns are used for precise cutting. In addition, water is used in the cooling of machinery to prevent over-heating.

13. Food Processing

The level of water activity affects bacterial growth while water hardness affects the quality and sanitation of a product as well as its pH balance. Besides that, some cooking methods involve the immersing of food in water or steam. Water is also used for dishwashing.

Wikipedia (25-03-2011 16:11) Water. Retrieved March 29 2011, from http://en.wikipedia.org/wiki/Water

Nurul Azirah Binte Johari (11)