Chapter 3 Notes-Temperature
- Surface temperature is measured 1.5 meters above the ground (usually on a grass surface) in the shade to avoid solar heating of the thermometer. Avg. global temp=15 C.
- Over short periods of time and regions, imbalances in surface energy budget can result in temperature increasing or decreasing when energy is either stored or removed from the system.
- Temperature changes are driven by the difference in incoming solar radiation gains versus outgoing terrestrial energy losses.
- The surface exchanges energy with the air by conduction, convection, turbulent mixing of the winds, and radiative and latent heat fluxes.
- Diurnal Temperature Cycle- the repeating pattern of daily temperatures.
- Diurnal Temperature Range- the differences between the minimum and maximum temperatures on any given day.
- Daily Mean Temperature- averaging the maximum and minimum temperature for a 24 hour period.
- Similar temperature cycles also occur on monthly, annual, and interannual time scales.
- 5 major factors cause energy imbalances for annual temperature cycle: Latitude, Surface Type, Elevation and Aspect, Relation to large bodies of water, and cloud cover.
o Latitude- angle of inclination affects incoming solar energy and causes the seasonal cycle in temperature. The amount of energy at the top of the atmosphere is called Insolation. **Higher insolation=Higher temperatures. Insolation levels affected by latitude.
o Surface Type- Because the atmosphere is heated by the Earth’s surface, the surface type plays an important role in the surface air temperature.
o Elevation and Aspect- Higher altitude generally has colder temps b/c the air is less dense and there are fewer molecules to absorb incoming solar radiation.
§ Aspect is the direction that a mountain slope faces-south facing slopes receive more solar energy and are warmer than north-facing.
o Large Bodies of Water- Act to thermally stabilize the temperature of the surrounding air, so that differences between months are reduced. Due to water’s high specific heat (more heat required to increase the temperature of water and it cools down much slower than land). Temperature of nearby water also modifies a region’s temperature.
o Cloud Cover- clouds reflect and absorb solar energy. They reduce the amount of solar radiation at the surface causing daytime cooling and have a warming effect, which can be very pronounced at night, when they emit longwave radiation toward the surface.
- Global temperatures have increased approximately 6 degrees C over the last 120 years.
- Same 5 factors affect diurnal temperature cycle: latitude, surface type, elevation and aspect, relationship to large bodies of water, and cloud cover.
- Diurnal temperature cycle has air temperature increasing all morning long to an incoming solar energy peak at noon. After noon, the energy gains still exceed the losses until around 4 pm when maximum daily temperature is reached. The energy losses then exceed the gains all night long, with a minimum temperature around sunrise.
- Larger diurnal temperature ranges are seen in equatorial regions, deserts, higher elevations and regions directly facing the sun, regions far from bodies of water, and clear sky areas.
Changing Temperature with Height
- Lapse Rate- change of temperature with height.
- Air that moves up and down in the atmosphere undergoes temperature changes.
- A rising parcel always expands because atmospheric pressure always decreases with altitude and the parcel loses kinetic energy when converting it to potential energy, which also results in a cooling in temperature of the parcel.
- **A rising parcel always cools. ** A descending parcel always warms.
- Adiabatic Process- a process in which no heat energy is gained or lost by the system.
- Dry Adiabatic Lapse Rate- a 10 degree C/km rate of cooling resulting from expansion.
- Environmental Lapse Rate- the specific change of temperature with altitude at any particular time and location.
- In order to find out if air will rise and keep rising, we must compare the dry adiabatic lapse rate to the lapse rate of the air surrounding it.
- A parcel of air that is warmer than the air around it will continue to rise because it is also less dense than the air surrounding it. As long as the temperature of the parcel does not drop lower than the air around it, the parcel will continue to rise.
- *Environmental Lapse Rate > Dry Adiabatic Lapse Rate – parcel will keep rising.
o Also, called Absolutely Unstable
- *Environmental Lapse Rate < Dry Adiabatic Lapse Rate – parcel will stop rising.
o Also, called Statically Stable-inhibits vertical movements of air parcels.
- Temperature Inversions- regions of the atmosphere in which temperature increases with altitude. This produces a very stable atmosphere.
- Nocturnal Inversion- inversion that develops at the ground during the night—often occur on clear, calm nights and are more prevalent in winter. Clouds, wind, length of night, and the condition of the ground all control the development of it.
- Wind chill factor- cooling power of wind, describes the increased loss of heat by the movement of the air.
- Frost protection of agriculture is done through mechanical mixing of the air, plastic covering, orchard heaters, or spraying them with water.