Relative Humidity,Dewpoint, Heat and UV Index
The amount of moisture air can hold is dependent on its temperature and pressure. The warmer the air the greater the quantity of water vapour it can contain. The air temperature is measured with a normal thermometer this is the Dry-Bulb reading.The actual amount of moisture known as the mixing ratio is measured in grams of water per kilogram of dry air. When air at a certain temperature is saturated it cannot hold any more moisture. The relative humidity of the air is the ratio of the actual amount of moisture in the air to the saturated amount.
We can use evaporation to measure the amount of moisture in the air. A wet cloth is placed over the bulb of a thermometer and then air is blown over the cloth causing the water to evaporates. Since evaporation takes up heat, the thermometer will cool to a lower temperature than a thermometer with a dry bulb at the same time and place. The depression in Wet-Bulb temperature allows the humidity to be calculated.
If the air is fully saturated (100% relative humidity) the water cannot evaporate, so both the wet and dry bulb temperatures are the same. The dew point is the temperature at which air is saturated with water vapor, which is the gaseous state of water.
If the air is fully saturated (100% relative humidity) the water cannot evaporate, so both the wet and dry bulb temperatures are the same. The dew point is the temperature at which air is saturated with water vapor, which is the gaseous state of water.
When air has reached the
dew-point temperature at a particular pressure, the water vapor in the air is
in equilibrium with liquid water, meaning water vapor is condensing at the same
rate at which liquid water is evaporating.
Below the dew point, liquid water will begin to condense
on solid surfaces (such as blades of grass) or around solid particles in the
atmosphere (such as dust or salt), forming clouds or fog..
Dew point is closely linked to relative humidity which is the ratio of the
pressure of water vapor in a parcel of air relative to the saturation pressure
of water vapor in that same parcel of air at a specific temperature. Relative
humidity (RH) is expressed as a percentage.
The relative humidity is 100
percent when the dew point and the temperature are the same. If the temperature
drops any further, condensation will result, and liquid water will begin to
form.
Compared to relative humidity,
dew point is frequently cited as a more accurate way of measuring the humidity
and comfort of the air, since it is an absolute measurement (unlike relative
humidity).
Most people are comfortable with
a dew-point temperature of 60 degrees Fahrenheit (16 degrees Celsius) or lower.
At a higher dew point of, for example, 70 F (21 C), most people feel hot or
"sticky" because the amount of water vapor in the air slows the
evaporation of perspiration and keeps the body from cooling.
1.Increase respiration
2.Increase blood circulation
3.Increase sweating
Sweating,
one of the key cooling mechanisms of the body, only works to cool us down if the
water that is excreted
through the skin, evaporates. This is where humidity comes in. The
concentration of water in the air, relative to the temperature (relative
humidity) determines the rate at which the water can evaporate from the skin.
When the air is holding more moisture (relative to the total moisture it could
hold at that temperature), it is harder for the air to absorb the sweat from
our skin. The result? We sweat and sweat but instead of feeling any relief, we
simply feel hot and sticky. With high relative humidity subverting the cooling
ability of sweating, the body is eventually forced to do other things to cool
us down.
With High humidty sweating cannot cools our body and body temperature goes up ,loosing salts,water,chemicals from body. dehydration depletes water in blood and it becomes thick requires more pressure to pump and increase blood pressure. Less blood flow through brain,muscles and other organs and more blood flows through skin which cause fatigue and physical strength declines and mental faculties will get affected.
When humidity goes down the reverse action happens we will loose more water through evaporation since the ambient air accepts more water. Water is lost through breathing, skin ,urination when you exhale in to glass during winter you will notice fog which shows the amount of water leaving your body.. The less humidity in air you breathe the more water your body will try to put back in to it. During respiration, the body actually humidifies the air you
breathe. Starting in the nose but continuing throughout the respiratory tract,
mucus membranes not only help to filter out debris and particles in the air,
but they also moisten the air. When you exhale, this moisture is lost. The less
humidity in the air you breathe, the more moisture your body attempts to put
back into it. There is also one other process at work during respiration and
that deals directly with the lungs. The body keeps the lungs moist, and as
drier air enters it naturally draws moisture out. So, the combination of the
humidifying that the lungs and the respiratory passages perform not only makes
the air breathable but also contributes to the slow but steady loss of moisture
from the body..
The effects of low humidity are best
expressed in two areas, the skin and respiratory system.
· Dry Nasal Passages: As more moisture is drawn from the mucus membranes
to moisten dry air, the membranes can dry out quicker than the moisture can be
replenished by the body. This can manifest itself as dry and even painfully
cracked sinuses. It can become so severe that the cracked sinuses bleed. This
is partly why many experience nosebleeds during the drier, cooler fall and
winter months.
· Sore or Scratchy Throat: The same process that is drawing moisture from the
nasal passages can also effect your throat.
· More Illness: As the nasal passages dry out from low humidity, the
body's ability to trap and filter out viruses and microbes that cause illness
dips. When the sticky membranes lose their ability to filter, more microbes can
pass through. Even worse, as the mucus membranes dry and crack, they provide a
direct path to the bloodstream for pathogens. This is often why the flu is so
prevalent during the fall and winter.
. Tear glands excretes excessively due to more evaporation due to low humidity which causes the eyes to be less moisturized and feel itching.
. Skin absorbs moisture when it is exposed to it ,and vice versa when you dip your hands in water your hands get wrinkled due to water absorption at 100% relative humidity .
UV Index
UV index denotes an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time.UV Index is designed as an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn on human skin.
If a light skinned person(without sunscreen) begins to sunburn in 30 minutes at UV Index 6, then that individual should expect to sunburn in about 15 minutes at UV Index 12 – twice the UV, twice as fast.UV ray intensities are higher between 11:30 and 12:30, or between 12:30 and 13:30 in areas where day light saving time is observed.
Below mentioned report shows UV and Heat Index in trivandrum city dated 04-05-2018 , UV index is 8 which is near extreme and Heat index is 104 deg F which is also extreme and cause heat stroke ,muscle cramps,heat exhaustion possible with prolonged exposure .
