LAB I: Temperature Phenomena  



There are three types of mechanisms to transfer energy: conduction, convection, and radiation.  Conduction is the transfer of heat through matter by molecular activity.  If someone were to touch a hot pan, energy from the hot pan transfers to the person’s hand, thus burning the hand.  If you were to hold an ice cube in your hand, energy from your hand is transferring to the ice cube, thus melting the ice cube and cooling off your hand.  Metals, of course, are good conductors of energy.  Poor conductors, which do not transfer energy very well, are called insulators.  Wine corks, plastic foams, and even air are some examples of poor conductors.


Convection is the transfer of heat by mass movement or circulation within a substance.  For the atmosphere, gases and liquids would be the substance.  A pot of boiling water is a great example of convection.  As the water is heated on the bottom of the pot, it rises towards the surface.  Then as it cools, it sinks back down towards the bottom of the pot to get re-heated again.  The atmosphere works in the same way.  As air is heated at the surface of the earth, it rises into the atmosphere, cools, and then sinks.  Energy is transferred from the surface to the atmosphere.


How is the surface of the earth heated initially?  By the sun’s radiation.  Solar radiation is energy that is released by the sun in the form of particles or electromagnetic waves, and there is no need of a substance for transport.  All forms of radiation coming out from the sun can be seen on the electromagnetic spectrum. 


Visible light energy coming from the sun is the only solar radiation wave that we can see naturally, and is made up of all colors (Red, Orange, Yellow, Green, Blue, Indigo, and Violet or ROYGBIV).  43% of the solar radiation output is visible light, 49% is infrared radiation, and 7% is ultraviolet radiation.  The remaining 1% is in the form of x-rays, gamma rays, and radio waves.  As solar energy reaches the Earth, much of the ultraviolet radiation is absorbed by the ozone layer.  Some of the infrared radiation gets absorbed by the clouds and other atmospheric gases.  Therefore most of the energy that reaches the Earth’s surface is in the visible part of the electromagnetic spectrum.  The Earth’s surface absorbs the radiation, and then re-emits the radiation in the form of long-wave infrared.  The infrared radiation that the earth emits is a longer wavelength of infrared than what the sun emits.  So the earth emits long-wave radiation (long-wave infrared) and the sun emits short-wave radiation (ultraviolet, visible, and short-wave infrared).


The radiation emitted by the earth, can then be absorbed by clouds and other atmospheric gases.  The two primary gases that absorb long-wave radiation in the lower atmosphere are water vapor and carbon dioxide.  Methane, ozone, and chlorofluorocarbons can also absorb some of the long-wave radiation.  The gases can then re-emit the energy again and send the energy back down towards the Earth’s surface.  The emitting long-wave radiation from the earth and gases heats our planet from the surface up into the atmosphere.  The sun’s short-wave energy DOES NOT directly heat up the atmosphere.  If that were the case, then outer space would be very warm and not extremely cold.  




Reflection is when energy (radiation) is bounced off of an object at the same angle and intensity.  Albedo is the percent of radiation that is reflected by a surface.  Surfaces that reflect a lot of energy have a high albedo.  Energy that is reflected does not get absorbed by the surface and changed into the long-wave infrared radiation.  Therefore, the gases in the atmosphere can’t absorb it and the temperature remains cool.  Surfaces that absorb a lot of energy have a low albedo.  The energy is re-emitted as long-wave infrared radiation which heats the atmosphere.



Albedo is calculated as the amount of energy reflected from a surface divided by the total amount of incoming energy to the surface, multiplied by 100 to get a percentage.


            Albedo (%)  =   Reflected energy   x 100

                                      Incoming energy


For example: if the amount of energy hitting a surface is 645 units and the amount of energy being reflected by that surface is 135 units, then the albedo of that surface would be:


135 units  x 100    or   0.209 x 100 =  20.9%

645 units


This means that 20.9% of the energy that is hitting the surface is getting reflected back into the atmosphere, while 79.1% (100-20.9%) of the energy is being absorbed by the surface.  The earth’s surface heats up, emits the long-wave infrared radiation which the gases absorb and radiate energy back to us.  This surface will have a warm air temperature over it.


EXERCISE 1:  For each of the examples listed on the worksheet, calculate the albedo of the surfaces.  Rank the surfaces from 1 to 3, with 1 being the surface with the warmest air temperature above it and 3 being the surface with the coolest air temperature above it.





In the lab itself you will be asked to calculate the daily mean temperature and the daily temperature range.  The daily mean temperature or average temperature is calculated by averaging the 24 hour readings from each hour of the day or by averaging the high and low temperature throughout the day. 


            Maximum Temp. + Minimum Temp        =   Daily Temperature Mean



The daily temperature range is simply the difference between the high and low temperatures.  Under normal conditions, the smaller the temperature range the more humid an observing station is.  The greater the temperature range, the less humid an observing station is.



EXERCISE 2 – For each example listed on the worksheet, calculate the daily mean temperature, the daily range, and rank the three cities from 1 to 3, with 1 being the most humid and 3 being the least humid.