DASK

METEOROLOGY FOR EVERYONE

Prepared by: Dr. Ahmet KILIÇ

AIR TEMPERATURE

DEW-POINT TEMPERATURE

The hotness or coldness of a substance is called its temperature and is measured with a thermometer. To ensure that the temperature of the surrounding air is the same as the thermometer, it must be shaded from sunlight and be exposed to adequate ventilation. These conditions are provided by enclosing the thermometer within a white wooden box.

Most temperature scales today are expressed in degrees Celsius (°C). The Celsius scale is fixed by two points, the freezing and boiling point of water, which at normal atmospheric pressure are 0°C and 100°C respectively. The scale is then divided into 100 units. Special thermometers are used to indicate the maximum and minimum temperatures reached over a period, usually one day.

SENSIBLE HEAT AND HEAD INDEX

HEAD INDEX CHART

DEW-POINT TEMPERATURE

All air contains water vapour of varying quantities. The dew point indicates the amount of moisture in the air. The higher the dew point, the higher the moisture content of the air at a given temperature. Conversely, the dew point of humid air will be higher than the dew point of dry air.

Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapour content) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapour possible at the existing temperature and pressure.

The dew point may be measured directly by a dew-point hygrometer, or indirectly from wet-and dry-bulb thermometer readings.

SENSIBLE HEAT AND HEAD INDEX

How Heat Affects the Body ? Human bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and -- as the last extremity is reached -- by panting, when blood is heated above 98.6 degrees. The heart begins to pump more blood, blood vessels dilate to accommodate the increased flow, and the bundles of tiny capillaries threading through the upper layers of skin are put into operation. The body's blood is circulated closer to the skin's surface, and excess heat drains off into the cooler atmosphere. At the same time, water diffuses through the skin as perspiration. The skin handles about 90 percent of the body's heat dissipating function.

Sweating, by itself, does nothing to cool the body, unless the water is removed by evaporation -- and high relative humidity retards evaporation. The evaporation process itself works this way: the heat energy required to evaporate the sweat is extracted from the body, thereby cooling it. Under conditions of high temperature (above 90 degrees) and high relative humidity, the body is doing everything it can to maintain 98.6 degrees inside. The heart is pumping a

torrent of blood through dilated circulatory vessels; the sweat glands are pouring liquid -- including essential dissolved chemicals, like sodium and chloride -- onto the surface of the skin.

HEAT INDEX CHART

Heat Index Chart
% Relative Humidity
T E M P E R A T U R E		15	20	25	30	35	40	45	50	55	60	65	70	75	80	85	90
	43	42	44	47	51	55
	41	39	41	42	45	47	50	55
	38	36	37	39	40	42	43	46	49	52
	35	33	34	35	36	37	38	40	41	43	45	48	51	55
	32	30	31	31	32	33	33	35	36	37	38	39	41	43	46	47	49
	29	27	28	28	29	29	30	31	31	32	32	33	34	36	36	38	39
	27	25	25	26	26	26	26	27	27	28	28	29	29	30	31	31	32
	27 - 32 degrees				Fatigue is possible with prolonged exposure and/or physical activity.
	32 - 40 degrees				Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or physical activity.
	41 - 54 degrees				Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity.
	55 + degrees				Heatstroke/sunstroke is highly likely with continued exposure.