Meteorological EnvironmentDr Rupesh Sahu, M.D.

Assistant ProfessorDepartment of Community Medicine

BMC, Sagar

Objectives

• To know about various Meteorological elements

• To know how are they measured• To know what are their effects on health

Meteorology

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

Meteorological Environment

• Following Elements comprise Meteorological Environment1. Atmospheric pressure2. Air Temperature3. Humidity4. Rainfall5. Direction & speed of wind6. Movement of clouds & character of weather

‘Climate’

• A geographical concept representing a summation of the whole range of meteorological environment

Measurement

• By Barometer.• 3 types

– Fortins b– Kew pattern station b: used in Indian Meteorological

dept

– Barograph

Kew Pattern Station Barometer

Effect of exposure to High Altitude (Low Pressure)

• Human is physiologically adapted to live at One atm pressure.

• Air is less dense- partial pressure of O2 is also less.

• Physiological Effects– Increase in respiration– Increase in concentration of Hb– Increase in Cardiac output.

Effect of sudden exposure to High Altitudes

Acute Mountain sickness• Relatively common,

harmless, transient condition

• c/b– Headache– Insomnia– Breathlessness– N,V– Impaired vision

High altitude pulmonary oedema• Appear on about 3rd day

of high altitude.• As PE develops there

also develops– Cough– Irregular breathing (cheyne

stokes breathing)– Oligouria– Mental confusion– Hallucination, stupor, coma

Effect of exposure to Low Altitude (High Pressure)

Increased Depth

Gases in blood (O2, N2, CO2) dissolve increasingly

N2: Narcotic actionCO2: increase narcotic action of N2

O2: Convulsions, death.

Person Comes up: gases released (undissolved)—Air embolism

2. Air Temperature

• Represents Degree of hot/coldness of air.• Influenced by

– Latitude of place– Altitude – Direction of wind– Proximity to sea

Air Temperature

• Measurement : Thermometer• Commonly used are Mercury thermometers

– Boils at high temperature (356.73 degree celcius)– Has regular expansion– Levels can be seen easily.

• Alcohol thermometer used at many places since it has advantage of not solidifying even at lowest known temperatures.(*freezing point of mercury: -38.83 degree celcius)

Air Temperature

• Essential conditions for use of thermometers:– Air should have free access to the bulb– Should be protected against radiant heat.

Stevenson screenUsed in all meteorological observatories in India

Stevenson’s Screen

Types of Thermometers

1. Dry bulb thermometer2. Wet bulb thermometer3. Maximum thermometer4. Minimum thermometer5. Six’s maximum and minimum thermometer6. Globe thermometer7. Wet globe thermometer8. Silvered thermometer9. Kata thermometer

Dry & Wet bulb thermometer

Six’s Maximum and Minimum thermometer

Max min thermometer

Globe Thermometer

Globe Thermometer

Wet bulb globe thermometer

Wet Bulb Globe Temperature

• It is used by industrial hygienists, athletes, and the military to determine appropriate exposure levels to high temperatures.

• In hot areas, some US military installations display a flag to indicate the heat category based on the WBGT.

• The military publishes guidelines for water intake and physical activity level for acclimated and unacclimated individuals in different uniforms based on the heat category.

Heat stress indices

• Include– Equatorial comfort index– Heat stress index– Predicted four hour sweat rate

Effects of Heat stress

1. Heat stroke2. Heat hyperpyrexia 3. Heat exhaustion4. Heat cramps5. Heat syncope

Preventive measures

– Replacement of water– Regulation of work– Clothing– Protective devices– Work environment

Effects of Cold stress

• Hypothermia : – c/b numbness, loss of sensation, muscular

weakness, desire for sleep, coma and death.• Immersion/ trench foot• Frostbite

3. Humidity

• Moisture• Amount of moisture which air can hold

depends upon its temperature.• Humans are very sensitive to humidity, as

the skin relies on the air to get rid of moisture.

• Expressed as– Absolute humidity– Relative humidity

Absolute humidity

• Weight of water vapor in a unit volume of air

• Expressed as gms per cubic meter of air

Relative humidity

• Most common way of describing atmospheric moisture.

• Relative humidity is the ratio of the amount of water vapour actually in the air to the maximum amount of water vapour for saturation at that particular temp & pressure.

• A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain.

Relative humidity• The process of sweating is our body's attempt to keep

cool and maintain its current temperature. • If the air is at 100-percent relative humidity, sweat will

not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high.

• If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling us off.

• Very low RH causes skin cracks, dry flakes, itch, irritates mucous membrane in nose, throat (itchy throat).

• Dry nasal passages permit bacteria to incubate causing persistent infection.

Dew point

• Represents TEMPERATURE to which air would have to be cooled (with no change in pressure/moisture) for saturation to occur.

• High Dew point indicates high water vapour content and low dew point indicate low water vapour content.

• Frost point

Measurement of Humidity

• Dry & wet bulb Hygrometer• Sling Psychrometer• Assmann Psychrometer

Dry & wet bulb Hygrometer

Relative Humidity chart

Sling Psychrometer

4 revolutions per second=15 m/s air speed

4. Precipitation

• Collective term used for rain, snow, hail, dew, and frost i.e. all forms of water precipitated from the atmosphere.

• Measured by rain guages

Rain guage

*Rim should be exactly horizontal*one foot above the ground level

5. Air velocity

• Measured by Anemometer & Kata thermo.• Measured in meter/s : described as

– 0.5 m/s: complete calm, smoke rising vertically– 3.3 m/s: slight breeze, leaves rustling– 10 m/s: Strong wind, larger branches of trees

moving– 15-20 m/s: Storm– 25-30 m/s: Gale– 30-50 m/s: Hurricane

Anemometer

Wind direction

6. Clouds

• Are observed for their form, amount, direction, height.

• Gives insight into sequence of weather.• From the state of sky and evolution of

clouds, weather is described as fine, fair, unsettled, bad, thunderous.