CommunityMedicine

Topic:Meteorology and Its Elements

Submitted By:Muhammad Arslan Yasin

Subject:Community Medicine

SUKHERA ILLUSTRATORZ

Meteorology and Its Elements

Definition:

The branch of science concerned with the processes and phenomena of the atmosphere,especially as a means of forecasting the weather.

Meteorology is the science that deals with the study of changes or phenomena occurring inthe atmosphere.

Commonly known as 'weather,' meteorology focuses on the atmospheric variables relatedto current or near-future conditions. Several weather elements describe the atmospheresuch as temperature, humidity, precipitation amount and type, wind direction and strength,atmospheric pressure, and cloud cover.

Elements of Meteorology:The elements of meteorological environment are:

1. Atmospheric pressure

2. Air temperature

3. Humidity

4. Air movement (Air velocity, Direction and speed of the wind)

5. Rain fall.

6. Precipitation

7. Visibility

8. Cloudiness (cloud type and cover)

9. Sunshine duration

Meteorology:The word meteorology is from the Ancient Greek and

meaning "the study of things high in the air."

Luke Howard has been called “the father of meteorology” because of his comprehensiverecordings of weather in the London area from 1801 to 1841 and his writings, whichtransformed the science of meteorology.

1.Atmospheric pressure:

Atmospheric pressure, also known as barometric pressure (after the barometer), is thepressure within the atmosphere of Earth (the pressure exerted by the weight of theatmosphere).

The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa.

101,325 Pa=760 mm Hg

The atmospheric pressure falls as the altitude increases as in high mountains and rises asaltitude decreases as in deep mines.

Atmospheric pressure∝Altitude1

i.e. When aperson descends 33 feet (as inmines), he is exposed to an atmosphericpressure of 2 atmospheres, i.e. 760 × 2 = 1520 mm Hg.

Measurement of atmospheric pressure:

The instrument used to measure atmospheric pressure is called ‘Barometer.

- ‘Kew Pattern’ station barometer is widely Used.

- Others are Fortin’s barometer, Aneroid barometer and Barograph.

Effects of Atmospheric Pressure:

The influence of atmospheric pressure on health is considered under two headings:

I. Effects of diminished atmospheric pressure.

II. Effects of increased atmospheric pressure.

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I.Effects of Diminished Atmospheric Pressure:

This occurs in high altitudes. Sudden exposure to high altitude above 10,000 feet, resultsin ‘Acute mountain sickness’ (or aviator sickness) due to rarity of atmosphere and deficiency inoxygen.

- This is characterized by headache, mental fatigue, irritability, irrational behavior, loss ofmuscular coordination, insomnia, nausea, vomiting, breathlessness, and in severe cases theremay be bleeding from the nose, ringing in the ears, palpitation and even collapse.Later asthe pulmonary edema develops, the respiration becomes deep andirregular(Cheyne-Stokes breathing) the person also develops oliguria, mental confusion,hallucinations, later develops stupor, convulsions, coma and death supervenes.

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Acclimatization:

Human body has a remarkable power of adjusting itself to low oxygen pressure providedthe change is made slowly and persons can live for long period at heights of 15,000 to20,000 feet without ill effects. This adjustment of the body is called ‘Acclimatization.’

The physiological changes are:

• Increase in rate and depth of respiration (to minimize the

difference between the oxygen of the air andoxygen of the blood).

• Increase in the hemoglobincontent of the blood.

• Increase in the cardiac output.

II.Effects of Increased Atmospheric Pressure:

This occurs in low altitudes. The effects are best observed in persons Working in divingbells, compressed air chambers (Caisson’s), etc. and the symptomsproduced is knownas ‘Caisson’s disease,’ where in the personexposed to high pressure, the gases inthe air such as oxygen, carbon dioxide andnitrogen are dissolved in the blood and tissues,depending upon their partial pressures and the whole body is thus saturated with air.

Decompression sicknes:

As a rule, the workers do not suffer while they are in the caisson but grave symptomsoccur after they return to the outside air. It is called ‘Decompression sickness,’characterized by euphoria, sensation of increased strength, respiration becomesdeeper andquicker and the heart becomes stronger and slower. These may be followed bynasal voice, disturbance in hearing, changed sense of smell or taste, rarely hemorrhages fromthe mouth, tympanic cavity and even from the lungs.

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2.AIR TEMPERATURE:

Not only it has a direct impact on the health of the individual but also it has an importantbearing in the natural history of certain diseases, especially vector borne diseaseslike malaria, filariasis, Kyasanur forest disease, Japanese encephalitis, etc. For example, themalarial parasites cease to undergo deve lopment in the stomach of the femaleanopheline mosquito when the mean temperature remains below 16°C.

Optimum air temperature for the development of malarial parasites is between 20 and30°C,i.e. 68 and 86°F.

Measurement of Air Temperature:

Air temperature is recorded by using thermometers. There are two types—Mercurythermometer and Spirit (or alcohol) thermometers.

Effects of Temperature:

This can be studied under two heads—of high temperature and of low temperature.

A)Effects of High Temperature:

Local effects—are blackening of skin, prickly heat (i.e. Heat rash or miliaria rubra), sunburn anddermatitis.

General effects—are heat exhaustion, heat cramps and heat stroke.

(Heat–strain:

The patho-physiological effects of heat on body system is called ‘Heat–strain’.)

I.Heat exhaustion:

This term includes heat syncope, water depletion exhaustion andsalt depletionexhaustion.

Heat syncope: It is characterized by giddiness and fainting due to pooling of blood inthe lower limbs following prolonged standing in the hot sun, Which is common among

soldiers.

Water depletion exhaustion: It is characterized by excessive loss of water dueto profuse sweating. If water is not replaced, it leads to a reduction of intracellular fluid,resulting in excessive thirst, oliguria, oligemic shock andeven in death.

Salt depletion exhaustion: Along-with the perspiration, there will be a loss of sodiumchloride, leading to reduction in the extra-cellular fluid and signs of dehydration.

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II.Heat cramps:

This is another acute clinical condition resultingfrom exposure to heat. It ischaracterized by sudden and severe painful, spasmodic contractions of the skeletal

muscles, due to loss of sodium and chloride from the body.

III.Heatstroke (Sun stroke):

It is usually due to radiant heat from the sun. It is characterized by very high bodytemperature of above 106°F, rapid pulse, rise of blood pressure,dry andhot skin,delirium, convulsions, partial or total unconsciousness, stupor, coma followed by death.

B)Effects of Decreased Atmospheric Temperature:

General effects: Initially, there will be shivering and tensing of the muscles resulting in riseof BP, pulse rate and respiration rate followed by decrease in BP, pulse rate and respirationrate. Later, there will be hemoconcentration, oliguria and muscular weakness. With

hypothermia at 80°F, coma sets in. At 75°F, death occurs following ventricularfibrillation.

Local effects: Local changes occur in the extremities (hands and feet).

The conditions are:

I. Acute transient inflammatory reaction.

II. Trench foot.

III. Frost bite

I.Acute transient inflammatory reaction:

When the body is exposed to cold temperature, there will beVaso-constriction of the superficial blood vessels followed by intermittent vaso-dilatation. This iscalled ‘Hunting’ phenomenon, due to the release of chemical substance locally in the tissues.There will be pain, numbness and loss of sensation.

II.Trench foot (or immersion foot):

It is so called because it used to be common among those soldiers, who used to stand intrenches for long periods during Ist World-War. Prolonged exposure to cold initiallyresults in acute transient inflammatory reaction, later followed by vaso-dilatation, transudation,hemoconcentration, platelet conglomeration, tissue edema and gangrene may follow.

III.Frost bite:

This occurs when exposed to temperature of 0 to – 5°C. There is actuallyfreezing of the tissues and crystals of ice are formed between the cells. The skinappears pale, dull, opaque andyellowish.

3.HUMIDITY:

Atmospheric humidity means the moisture content of the air.

Atmospheric humidity ∝eTemperatur

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(Dew point:

The temperature at which the moisture precipitates is called ‘Dew point.’)

Humidity may be expressed as absolute humidity or relative humidity.

-Absolute Humidity:

It is the actual amount of moisture (or water vapor) in an unit

volume of air.

-Relative Humidity:

Relative humidity (RH) is the percentage of moisture present n the air,complete saturation being taken as 100. Greater the relative humidity, the nearer theair to saturation.

Measurement of Humidity:

The humidity of the air can be measured by an instrument called ‘Hygrometer’, of whichthere are two kinds—namely direct and indirect hygrometers.

Direct hygrometers are Danniell’s Hy, Regnault’s Hy and Dine’s Hy.

Indirect hygrometers are dry and wet bulb hygrometer, Sling psychrometer and Assmannpsychrometer.

Effect of humidity on human body:

I.Health Risks of High Humidity:

When the air has a high moisture content, as is the case in humid weather, this sweatcannot evaporate, leaving our bodies feeling hot and sticky. To cool off, our bodies must workeven harder.It can contribute to feelings of low energy and lethargy. In addition, hyperthermia,or over-heating as a result of your body’s inability to effectively let out heat, can negativelyimpact your health in conditions of high humidity.

II.Health Risks of Less Humidity:

Eyes become dry and irritated, skin gets flaky and itchy and the low humidity inflames anddries out the mucous membrane lining the respiratory tract. As a result, the risk of cold, flu andother infections is substantially increased.

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4.AIR MOVEMENT:

Even with disruptions like weather fronts and storms, there is a consistent pattern to how airmoves around our planet’s atmosphere. This pattern, called atmospheric circulation, is causedbecause the Sun heats the Earth more at the equator than at the poles. It's also affected by thespin of the Earth.

Measurement of Air Movement:

The best instrument used to record the velocity of air and also the pressure of the wind isRobinson’s wind anemometer.

Effect of AIR Movement:

The way the air moves affects the weather, because winds move heat and coldtemperatures as well as moisture from one place to another, transporting conditions from onegeographical zone to another. The way winds pass each other, and the direction they move,also affects what weather a region will see on any given day.

5.Rain Fall:

Rain is liquid water in the form of droplets that have condensed from atmospheric watervapor and then become heavy enough to fall under gravity.

Measurement of Rain Fall:

The standard instrument for the measurement of rainfall is the 203mm (8 inch) rain gauge.

Effects of Rain Fall:

Heavy rainfall can lead to numerous hazards, for example: flooding, including risk to humanlife, damage to buildings and infrastructure, and loss of crops and livestock. landslides, whichcan threaten human life, disrupt transport and communications, and cause damage to buildingsand infrastructure.

When little or no rain falls, soils can dry out and plants can die. When rainfall is less thannormal for several weeks, months, or years, the flow of streams and rivers declines, waterlevels in lakes and reservoirs fall, and the depth to water in wells increases.

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6.Precipitation:In meteorology, precipitation is any product of the condensation of atmospheric water vapor

that falls under gravity from clouds. The main forms of precipitation include drizzle, rain, sleet,snow, ice pellets, graupel and hail.

Measuremet of precipitation:

Precipitation is measured as the amount of water that reaches horizontal ground or thehorizontal ground projection plane of the earth's surface, and is expressed as a vertical depth ofwater or the water equivalent of solid precipitation.

Effects of Precipitation:

Global Climate Change. comes from precipitation. Too little precipitation can result in drysoil, shallow streams, and shortages of municipal water supplies. However, too muchprecipitation can also have a negative impact on human activities, business and industry,agriculture, and the environment.

7.Visibility :In meteorology, visibility is a measure of the distance at which an object or light can be

clearly discerned. It is reported within surface weather observations and METAR code either inmeters or statute miles, depending upon the country. Visibility affects all forms of traffic: roads,sailing and aviation. Meteorological visibility refers to transparency of air: in dark,meteorological visibility is still the same as in daylight for the same air.

Measurement of visibility:

Visibility is limited to about 296 km.One classical method to measure visibility is to measurehow much light that is transmitted from a light source to a receiver located a distance- forinstance 50 meters away. In foggy weather less light (compared to during clear weather) willreach the receiver because of the scattering along the ray path.

Effects of Visibility:

Visibility is a measure of how well an observer can view a scene. This includes how farone can see in the atmosphere as well as the ability to see the textures and colors of thescene.Unfortunately, these views are sometimes obscured by haze, which consists of fineparticles and gaseous air pollution in the atmosphere. Although haze does occur naturally,due to things such as dust and wildfire smoke, it is primarily caused by air pollution fromanthropogenic sources.

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8.Cloudiness :The state of being cloudy (e.g. weather). Expect considerable cloudiness with occasional

rain showers.

Measurement of Cloudiness:

In meteorology, an okta is a unit of measurement used to describe the amount of cloudcover at any given location such as a weather station. Sky conditions are estimated in terms ofhow many eighths of the sky are covered in cloud, ranging from 0 oktas (completely clear sky)through to 8 oktas (completely overcast).

Effects of cloudiness:

Effects of Cloud Cover: on forecasted temperatures. During the day, the earth is heated by thesun. If skies are clear, more heat reaches the earth's surface. This leads to warmertemperatures.

9.Sunshine Duration:Sunshine duration is the length of time that the ground surface is irradiated by direct solar

radiation (i.e., sunlight reaching the earth's surface directly from the sun).

Measurement of Sunshine Duration:

Measurement is performed by instruments called sunshine recorders. For the specificpurpose of sunshine duration recording, Campbell–Stokes recorders are used, which use aspherical glass lens to focus the sun rays on a specially designed tape. When the intensityexceeds a pre-determined threshold, the tape burns.

Effects of sunshine duration:

Energy from the Sun is very important to the Earth. The Sun warms our planet, heating thesurface, the oceans and the atmosphere. This energy to the atmosphere is one of the primarydrivers our weather. Our climate is also strongly affected by the amount of solar radiationreceived at Earth.

The Sun is the source of most of the energy that drives the biological and physicalprocesses in the world around us—in oceans and on land it fuels plant growth that forms thebase of the food chain, and in the atmosphere it warms air which drives our weather.

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