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Topic Review
Tropospheric Ozone
Ozone (O3) is a trace gas of the troposphere, with an average concentration of 20–30 parts per billion by volume (ppbv), with close to 100 ppbv in polluted areas. Ozone is also an important constituent of the stratosphere, where the ozone layer exists which is located between 10 and 50 kilometers above the earths surface. The troposphere is the lowest layer of the Earth's atmosphere. It extends from the ground up to a variable height of approximately 14 kilometers above sea level. Ozone is least concentrated in the ground layer (or planetary boundary layer) of the troposphere. Ground level or tropospheric ozone is created by chemical reactions between oxides of nitrogen (NOx gases) and volatile organic compounds (VOCs). The combination of these chemicals in the presence of sunlight form ozone. Its concentration increases as height above sea level increases, with a maximum concentration at the tropopause. About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. Although tropospheric ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects. Ozone in the troposphere is considered a greenhouse gas, and may contribute to global warming. Photochemical and chemical reactions involving ozone drive many of the chemical processes that occur in the troposphere by day and by night. At abnormally high concentrations (the largest source being emissions from combustion of fossil fuels), it is a pollutant, and a constituent of smog. Its levels have increased significantly since the industrial revolution, as NOx gasses & VOCs are some of the byproducts of combustion. With more heat and sunlight in the summer months, more ozone is formed which is why regions often experience higher levels of pollution in the summer months. Although the same molecule, ground level ozone can be harmful to our health, unlike stratospheric ozone that protects the earth from excess UV radiation. Photolysis of ozone occurs at wavelengths below approximately 310–320 nanometres. This reaction initiates the chain of chemical reactions that remove carbon monoxide, methane, and other hydrocarbons from the atmosphere via oxidation. Therefore, the concentration of tropospheric ozone affects how long these compounds remain in the air. If the oxidation of carbon monoxide or methane occur in the presence of nitrogen monoxide (NO), this chain of reactions has a net product of ozone added to the system.
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  • 24 Nov 2022
Topic Review
Geodetic Datum
A geodetic datum or geodetic system (also: geodetic reference datum or geodetic reference system) is a coordinate system, and a set of reference points, used for locating places on the Earth (or similar objects). An approximate definition of sea level is the datum WGS 84, an ellipsoid, whereas a more accurate definition is Earth Gravitational Model 2008 (EGM2008), using at least 2,159 spherical harmonics. Other datums are defined for other areas or at other times; ED50 was defined in 1950 over Europe and differs from WGS 84 by a few hundred meters depending on where in Europe you look. Mars has no oceans and so no sea level, but at least two martian datums have been used to locate places there. Datums are used in geodesy, navigation, and surveying by cartographers and satellite navigation systems to translate positions indicated on maps (paper or digital) to their real position on Earth. Each starts with an ellipsoid (stretched sphere), and then defines latitude, longitude and altitude coordinates. One or more locations on the Earth's surface are chosen as anchor "base-points". The difference in co-ordinates between datums is commonly referred to as datum shift. The datum shift between two particular datums can vary from one place to another within one country or region, and can be anything from zero to hundreds of meters (or several kilometers for some remote islands). The North Pole, South Pole and Equator will be in different positions on different datums, so True North will be slightly different. Different datums use different interpolations for the precise shape and size of the Earth (reference ellipsoids). Because the Earth is an imperfect ellipsoid, localised datums can give a more accurate representation of the area of coverage than WGS 84. OSGB36, for example, is a better approximation to the geoid covering the British Isles than the global WGS 84 ellipsoid. However, as the benefits of a global system outweigh the greater accuracy, the global WGS 84 datum is becoming increasingly adopted. Horizontal datums are used for describing a point on the Earth's surface, in latitude and longitude or another coordinate system. Vertical datums measure elevations or depths.
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Topic Review
Convective Boundary Layer
The Convective Boundary layer (CBL), also known as the daytime Planetary boundary layer, is the part of the atmosphere most directly affected by solar heating of the earth's surface. This layer extends from the earth surface to a capping inversion that typically locates at a height of 1–2 km by midafternoon over land. Below the capping inversion (10-60% of CBL depth, also called entrainment zone in the daytime), CBL is divided into two sub-layers: mixed layer (35-80% of CBL depth) and surface layer (5-10% of CBL depth). The mixed layer, the major part of CBL, has a nearly constant distribution of quantities such as potential temperature, wind speed, moisture and pollutant concentration because of strong buoyancy generated convective turbulent mixing. Parameterization of turbulent transport is used to simulate the vertical profiles and temporal variation of quantities of interest, because of the randomness and the unknown physics of turbulence. However, turbulence in the mixed layer is not completely random, but is often organized into identifiable structures such as thermals and plumes in the CBL. Simulation of these large eddies is quite different from simulation of smaller eddies generated by local shears in the surface layer. Non-local property of the large eddies should be accounted for in the parameterization.
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Topic Review
1968 Burma Cyclone
The 1968 Burma cyclone was regarded as the worst to strike the country during the 20th century before it was surpassed by another unnamed cyclone in 2004 and further, Cyclone Nargis in 2008, respectively. The first tropical cyclone of the 1968 North Indian Ocean cyclone season, it started as a depression on May 7 on the northern Andaman Sea. With low wind shear and warm sea surface temperatures, the storm intensified in the waters near Burma before heading northwestwards. It then started to rapidly intensify, with an eye becoming apparent on satellite imagery on May 9. Also that day, it reached its peak intensity, with 3-minute maximum sustained winds of 220 km/h (140 mph) by the Indian Meteorological Department, which is equivalent to a super cyclonic storm; however, the agency treated the system as a severe cyclonic storm. Little to no changes happened on the cyclone as it turned northeastwards, making landfall near Akyab (now Sittwe) between 18:00 and 21:00 UTC on that day. Land interaction rapidly weakened the storm, dissipating on May 10 as an area of low-pressure in south Chin State. The predecessor to the cyclone caused light to moderate downpour to the Andaman Islands; however, no deaths were reported. Winds reported from the cyclone inland Burma reached an estimate of 60–100 mph, altogether with heavy rainfall and large storm surges. The former flooded the crops, submerging them in floodwaters in the process while the latter washed out villages near the path of the storm. Schools and hospitals throughout Akyab were destroyed by high winds and large waves, while the port suffered major damages. The town was almost destroyed due to the storm. In addition, some ships in the said harbor, including the Greek freighter Geros Michalos were reportedly sunk in the Bay of Bengal. Houses were destroyed during the storm and many livestock died, mainly due to drowning. The death toll from the cyclone was finalized on May 1968 at 1,307 individuals, while 2,000 more were reportedly missing. The property damages were estimated at K15 million kyat ($3.248 million United States dollar ). After the cyclone, the Government of Burma started to release aid to the victims, altogether with food supplies and cotton blankets. The Red Cross Society of the country donated cases of medicines to the country, while the United States Government released over 25,000 blankets to be transferred to the area. In addition, many countries and organizations including the UNICEF contributed over $121,291 (1968 USD) to Myanmar, following the disaster.
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Topic Review
2020–2021 Taal Volcano Eruptions
Taal Volcano in Batangas, Philippines began to erupt on January 12, 2020, when a phreatomagmatic eruption from its main crater spewed ashes over Calabarzon, Metro Manila, and some parts of Central Luzon and Ilocos Region, resulting in the suspension of school classes, work schedules, and flights in the area. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) subsequently issued an Alert Level 4, indicating "that a hazardous explosive eruption is possible within hours to days." Volcanic activity continued into 2021, when smaller eruptions occurred in July 2021.
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Topic Review
Tropical Savanna Climate
Tropical savanna climate or tropical wet and dry climate is a type of climate that corresponds to the Köppen climate classification categories Aw (for a dry winter) and As (for a dry summer). Tropical savanna climates have monthly mean temperatures above 18 °C (64 °F) in every month of the year and typically a pronounced dry season, with the driest month having less than 60 mm (2.36 inches) of precipitation and also less than [math]\displaystyle{ 100-\left (\frac{Total\ Annual\ Precipitation\ (mm)}{25} \right) }[/math] of precipitation :200–1 This latter fact is in direct contrast to a tropical monsoon climate, whose driest month sees less than 60 mm of precipitation but has more than [math]\displaystyle{ 100-\left (\frac{Total\ Annual\ Precipitation\ (mm)}{25} \right) }[/math] of precipitation. In essence, a tropical savanna climate tends to either see less rainfall than a tropical monsoon climate or have more pronounced dry season(s). In tropical savanna climates, the dry season can become severe, and often drought conditions prevail during the course of the year. Tropical savanna climates often feature tree-studded grasslands, rather than thick jungle. It is this widespread occurrence of tall, coarse grass (called savanna) which has led to Aw and As climates often being referred to as tropical savanna. However, there is some doubt whether tropical grasslands are climatically induced. Additionally, pure savannas, without trees, are the exception rather than the rule.
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Topic Review
WISDOM Project
The WISDOM Project is a bilateral research project between Germany and Vietnam, focusing on the creation of a Water related Information System for the Mekong Delta. Initiated by the Vietnamese and the German Government it was started in the year 2007, and is planned to continue until the year 2013. Water-related Information System for the sustainable Development of the Mekong Delta in Vietnam
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Topic Review
Burmese Amber
Burmese amber, also known as Burmite or Kachin amber, is amber from the Hukawng Valley in northern Myanmar. The amber is dated to around 99 million years old, during the earliest part of the Cenomanian age of the Late Cretaceous. The amber is of significant palaeontological interest due to the diversity of flora and fauna contained as inclusions, particularly arthropods including insects and arachnids but also birds, lizards, snakes, frogs and fragmentary dinosaur remains. The amber has been known and commercially exploited since the first century AD, and has been known to science since the mid-nineteenth century. Research on the deposit has attracted controversy due to its role in funding internal conflict in Myanmar and hazardous working conditions in the mines where it is collected.
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Topic Review
Water Quality Observations from Space
Water is the basis of all life on this planet. Yet, approximately one in seven people in the world do not have access to safe water. Water can become unsafe due to contamination by various organic and inorganic compounds due to various natural and anthropogenic processes. Identifying and monitoring water quality changes in space and time remains a challenge, especially when contamination events occur over large geographic areas. Remote sensing makes it possible to monitor and identify large land and water bodies that suffer from quality problems more effectively and efficiently. 
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Topic Review
Biochronology
In paleontology, biochronology is the correlation in time of biological events using fossils. In its strict sense, it refers to the use of assemblages of fossils that are not tied to stratigraphic sections (in contrast to biostratigraphy, where they are). Collections of land mammal ages have been defined for every continent except Antarctica, and most are correlated with each other indirectly through known evolutionary lineages. A combination of argon–argon dating and magnetic stratigraphy allows a direct temporal comparison of terrestrial events with climate change and mass extinctions.
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