Category Weather & Climate

            El Nino is Spanish for “Boy Child” — a reference to Jesus. It was named in the 17th century by Spanish-speaking fishermen who lived in Peru, South America. It was given this name because the unusual weather associated with El Nino began around Christmas.

            El Niño Spanish is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (between approximately the International Date Line and 120°W), including the area off the Pacific coast of South America. The ENSO is the cycle of warm and cold sea surface temperature (SST) of the tropical central and eastern Pacific Ocean. El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific. El Niño phases are known to occur close to four years, however, records demonstrate that the cycles have lasted between two and seven years. During the development of El Niño, rainfall develops between September–November. The cool phase of ENSO is La Niña, with SSTs in the eastern Pacific below average, and air pressure high in the eastern Pacific and low in the western Pacific. The ENSO cycle, including both El Niño and La Niña, causes global changes in temperature and rainfall.

            Developing countries that depend on their own agriculture and fishing, particularly those bordering the Pacific Ocean, are usually most affected. In American Spanish, the capitalized term El Niño means “the boy”. In this phase of the Oscillation, the pool of warm water in the Pacific near South America is often at its warmest about Christmas. The original name of the phase, El Niño de Navidad, arose centuries ago, when Peruvian fishermen named the weather phenomenon after the newborn Christ. La Niña, chosen as the “opposite” of El Niño, is American Spanish for “the girl”.

            Originally, the term El Niño applied to an annual weak warm ocean current that ran southwards along the coast of Peru and Ecuador at about Christmas time. However, over time the term has evolved and now refers to the warm and negative phase of the El Niño–Southern Oscillation and is the warming of the ocean surface or above-average sea surface temperatures in either the central and eastern tropical Pacific Ocean. This warming causes a shift in the atmospheric circulation with rainfall becoming reduced over Indonesia and Australia, while rainfall and tropical cyclone formation increases over the tropical Pacific Ocean. The low-level surface trade winds, which normally blow from east to west along the equator, either weaken or start blowing from the other direction.

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          Fog is cloud that forms close to the ground. It appears when the wind is light, the air is damp and the sky is relatively clear. It often forms when moisture in the air close to the ground condenses and spreads upwards — this is called radiation fog. It is most common at the beginning or end of the day, when the ground cools down quickly.

          Fog is a natural weather conditions that can cause visibility to become zero. It can cause accidents on normally safe roads and is such a serious weather condition that schools delay the start of the day until the sun burns it off. So how does fog form? First it is important to understand that fog is basically a cloud on the ground. This means like clouds it is a collection of tiny water droplets formed when evaporated water is cooled. The way it is cooled determines how fog is formed.

          The first way that fog is formed is by infrared cooling. Infrared cooling happens due to the change of seasons from summer to fall and winter. During the summer the ground absorbs solar radiation. As air passes over it is made warm and moist. When the seasons change this mass of warm moist air collides with the cooler that is now prevalent. This cause is the water vapor in the air mass to condense quickly and fog is formed. This fog is often called radiation fog due to the way it forms. This kind is the most common type of fog. It also happens when an unseasonable day of warm weather combined with high humidity is followed by dropping temperatures.

          The next way that fog forms is through advection. Advection is wind driven fog formation. In this case warm air is pushed by winds across a cool surface where it condenses into fog. There are also other kinds of fog like hail fog or freezing fog. Each of these conditions is where condensed water droplets are cooled to the point of freezing. There is also fog formed over bodies of water. One type is sea smoke. This is a type of fog that forms when cool air passes over a warm body of water or moist land.

          In general we see that fog is formed whenever there is a temperature difference between the ground and the air. When the humidity is high enough and there is enough water vapor or moisture fog is sure to form. However the kind of fog and how long is last and its effects will depends on the different conditions mentioned. One interesting kind of fog actually helps to make snow melt faster.

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          One of the simplest ways to measure humidity is to use a hair hygrometer. This uses a piece of human hair, which stretches or contracts according to the amount of water in the air. In a weather house — a type of hair hygrometer — a hair attached to a turntable stretches and contracts, making the man appear in humid conditions and the woman appear when it is drier.

          These devices use a human or animal hair under some tension. The hair is hygroscopic (tending toward retaining moisture); its length changes with humidity, and the length change may be magnified by a mechanism and indicated on a dial or scale. In the late 17th century, such devices were called by some scientists hygroscopes; that word is no longer in current use, but hygroscopic and hygroscopy, which derive from it, still are. The traditional folk art device known as a weather house works on this principle. Whale bone and other materials may be used in place of hair.

          In 1783, Swiss physicist and geologist Horace Bénédict de Saussure built the first hair-tension hygrometer using human hair.

          It consists of a human hair eight to ten inches long, b c, fastened at one extremity to a screw, a, and at the other passing over a pulley, c, being strained tight by a silk thread and weight, d.

          The pulley is connected to an index which moves over a graduated scale (e). The instrument can be made more sensitive by removing oils from the hair, such as by first soaking the hair in diethyl ether.

 

 

 

 

 

 

 

 

 

 

 

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          To Measure humidity accurately, meteorologists look at relative humidity. This is the amount of water in the air, relative to the maximum amount of water that it can hold at that temperature. To measure relative humidity, a wet and a dry thermometer are used. The wet bulb is covered with wet muslin. The water in the muslin evaporates, making the temperature around the wet bulb cooler than that around the dry bulb. The amount of water that evaporates increases along with the dryness of the air — the greater the difference in temperature, the lower the humidity. A smaller difference means higher humidity. The thermometers are housed in a Stevenson screen, to shade them from the Sun.

           Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air. A related parameter is the dew point.

              Climate control refers to the control of temperature and relative humidity in buildings, vehicles and other enclosed spaces for the purpose of providing for human comfort, health and safety, and of meeting environmental requirements of machines, sensitive materials (for example, historic) and technical processes.

              A hygrometer is a device used for measuring the humidity of air.

             The humidity of an air and water vapor mixture is determined through the use of psychrometric charts if both the dry bulb temperature (T) and the wet bulb temperature (Tw) of the mixture are known. These quantities are readily estimated by using a sling psychrometer.

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           Desert regions have very low levels of humidity — often less than 10%. The low levels of water vapour in the air and, indeed, the general scarcity of water makes conditions for life very difficult. Agriculture is practically impossible in such areas and is only really successful in places where levels of humidity tend to be moderate.

           Deserts cover 20 percent of the earth’s surface yet are the driest regions in the world. Their lack of humidity is particularly striking because hot areas can hold so much moisture. Rainforests, for instance, combine warm air and high precipitation to produce some of the highest areas of humidity in the world. Deserts, on the other hand, are very dry, so they’re antithetical to most life.

          Deserts are prone to having long periods of little to no rain before receiving short bursts of precipitation, but the amount of humidity that does enter the air is rare. The desert air is so dry that the rate of evaporation regularly exceeds the rainfall rate, and the rainfall may even evaporate before it hits the ground.

          Desert conditions are also exacerbated by the fact that desert organisms respond to the low humidity by preserving as much water as they can without losing it to evaporation. Many desert plants have evolved a waxy structure called a cuticle that can keep water inside. Small leaves and white hairs that reflect heat may also be strategies for dealing with desert conditions.

         Humidity also affects human health conditions in general (some more and some less of course). For example, high humidity levels in the hot temperatures will make the feeling of heat much worse, since the sweat which regulates our body temperature cannot evaporate as quickly. The best relative humidity, that feels the most comfortable is somewhere around 45%. But nor extremely high neither extremely low humidity is good for human health, even though both high and low humidity climate conditions have pros and cons. 

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