in Centimeters of Mercury
Electrical thermometers
1. Thermoelectric: two metal types, electrons flow across from one to the other depending on temperature
2. Resistance: flow of electricity depend on temperature
Air is a good insulator- does not conduct heat well
Diurnal cycles have 2 peaks
Max 10AM and 10PM
Min 4AM and 4PM
Torricelli in 1643 designed the Barometer in Centimeters of Mercury
Conversion to millibars: p of mercury at 0oC = 13.6 X103 kg/m3
correct for expansion of Hg with temperature change
Varies from 0 -4%
Water is constantly added and removed (evaporation submlimation and condensation)
The amount of water in the atmosphere is extremely important.
1. The amount of condensation is imporatant aspect of weather ---rain fall, transfer of energy
2. Water vapor is the most important absorber of radiation in the air and thus affects the energy balance in the atmosphere
3. The release of energy when vapor condenses to form rain is an important source of energy for atmospheric circulation.
Energy lost to the atmosphere when ice melts. All of the heat energy supplied to the ice acts to break the bonds that hold the crystalline structure together. The ice does not gain any temperature during this process.
Latent heat is required to evaporate water,
melt ice or sublimate ice (convert ice directly to vapor).
1. Absolute Humidity:
= density of water vapor; expressed at mass/unit volume
Usually no more than 12g/m3 but can reach 40g/m3 at higher temperatures
2. Partial Pressure
Contribution to pressure of atmosphere by H20; usually expressd in
inches of Hg or mbars
usually no more than 15mbars but can reach 30mb
3. Saturation Vapor Pressure
When no more water can be added to the atmospheric volume. Varies with temperature and pressure
4. Dew Point; temperature at which air is saturated.
5. Relative Humidity; Ratio in % of:
Actual Vapor Pressure X 100
Saturation Vapor Pressure
1. Vapor Pressure is the amount of atmospheric pressure attributable to water vapor.
extract all water per unit volume of air
p=m X p X height
not practical
2. Hair Hygrometer
Human blond hair extend 2.5% from 0 to 100% humidity
3) psychrometer; liquid in glass thermometers
muslin over a thermometer. No muslin over other thermometer. The difference in temperature is a function of difference in humidity. Calibrations used.
Wind acts to mix the atmosphere. It transports components such as dust, chemicals moisture etc, from one place to another thereby redistributing concentratins.
Measured and reported using convention; From (example, if wind is blowing from the northeast we say it is a Northeasterly wind).
1. Wind vanes tell us direction
2. Anemometers exist for measurement of wind speed. The cup anemometer is the most widely used.
3. Gustiness and Diurnal Wind Variations are the normal pattern of winds
Speed varies much more horizontally than it does vertically. Usually the horizonatall speed is 10X more variable than the vertical speed.
cool link