“The average kinetic energy of gas molecules is known as temperature”
Measurement of Temperature:
- The thermometers must be placed where air circulation is relatively unobstructed,
- They must be protected from the direct rays of the sun and from precipitation.
Min & Max Temperature
The minimum thermometer, of the alcohol in glass type, has an index which remains at the lowest temperature occurring since its last setting.
The maximum thermometer has a constriction near the bulb which prevents the mercury from returning to the bulb as the temperature falls and thus registers the highest temperature since its last setting.
Instrument of Measuring Temperature
- Electrical-resistance thermometers,
- Gas-bulb thermometers,
other types of instruments are used for special purposes.
- The mean daily temp is the average of the daily maximum and minimum temperatures.
- The normal daily temp is the average daily mean temperature for a given date computed for a specific 30-yr period.
- The mean monthly temp is the average of the mean monthly maximum and minimum temperatures.
- The mean annual tem is the average of the monthly means for the year.
- The degree day is a departure of one degree for one day in the mean daily temperature from a specified base temperature.
- lapse rate is the rate of change of temperature in vertical direction
- The mean lapse rate is a decrease of about 3.6 Fo per 1000 ft increase in height.
- The greatest variations in lapse rate are found in the layer of air just above the land surface.
- Dry-Adiabatic lapse rate (5.4 Fo per 1000 ft. )
- Saturated-Adiabatic lapse rate(3.0 Fo per 1000 ft)
- Pseudo-Adiabatic lapse rate
Geographical Distribution of Temp
- In general, temperature tends to be highest at low latitudes and to decrease poleward
- However, this trend is greatly distorted by the influence of land and water masses, topography, and vegetation.
- The heat from a large city, which may roughly equal one-third of the solar radiation reaching it, produces local distortions in the temperature pattern so that temperatures recorded in cities may not represent the surrounding region.
Time Variation of Tem
- The daily variation of temperature lags slightly behind the daily variation of solar radiation
- The temperature begins to rise shortly after sunrise, reaches a peak 1 to 3 hr (about ½ hr at. oceanic stations) after the sun has reached its highest altitude, and falls through the night to a minimum about sunrise.