110 Chapter 3

How would you construct an instrument shelter that holds thermometers to measure atmospheric temperature?

painted white, face north, 5ft off of ground, under gray surface

Describe each of the controls of temperature. Time of Year Latitude Land vs Water Distribution Ocean Currents Elevation

Time of Year - location of the earth (season) Latitude - amount of incoming solar radiation Land vs Water distribution - more water (Southern) will have smaller seasonal temperature variations Ocean Currents - warm vs cold currents will affect coastal temperatures Elevation - higher elevations are colder due to decreasing temperatures with height but they also experience smaller temperature variations.

What weather conditions are best suited for the formation of a cold night and a strong radiation inversion

during the winter months when, skies are clear, winds are calm, air is dry, and snow is on the ground.

Frost vs Freeze

Frost - Air temp. ground is freezing but air temp. above ground is above freezing Freeze - both air temp. ground and above is freezing level.

What is a 'sensible temperature'?

A wind-chill temperature and heat index temperature are both considered sensible temperatures. These are temperatures that the body feels like in contrast to the actual temperature of the environment as measured with a thermometer.

Name three methods that farmers can use to protect their crops against the cold. Explain the physical principle behind each method.

1. Orchard Heaters - They circulate the air by setting up convection currents 2. Wind Machines - They mix cooler surface air with warmer air above 3. Coat with Ice - Sprinklers emit a fine spray of water which freezes to the vegetation. The release of latent heat when the water changes to ice keeps the ice at ≈ 32˚F, protecting the vegetation beneath the ice.

In the Northern Hemisphere, why are summers warmer than winters, even though the earth is actually closer to the sun in January?

23.5˚ tilt in the earth's axis the sun angle is at its lowest point in the Northern Hemisphere during winter. Also daylight hours are shorter in the Northern Hemisphere during the winter months.

Explain why the daily range of temperature is normally greater (a) in dry regions than in humid regions and (b) on clear days than on cloudy days.

Dry regions have clearer skies and less water vapor in the atmosphere versus a humid region, therefore, incoming solar radiation is greater during the day in dry regions because the sun's energy is not reflected by clouds (higher temps) and radiational cooling is greater during the overnight hours in a dry regions because less water vapor is available to re-radiate outgoing infrared radiation back to the surface (lower temps). Clear days maximize daytime incoming solar radiation and nighttime radiational cooling (maximum daily temp range) while cloud cover will decrease daytime incoming solar radiation and hamper radiational cooling (minimal daily temp range).

Sun directly overhead

Sep 22 - Autumn Equinox - 0˚- Equator Dec 21 - Winter Solstice - 23 1/2 ˚S Tropic of Capricorn Mar 20 - Vernal Equinox - 0˚- Equator Jun 21 - Summer Solstice - 23 1/2˚N - Tropic of Cancer

Explain why the warmest time of the day is usually in the afternoon, even though the sun's rays are most direct at solar noon.

Solar noon depicts the time when incoming solar radiation is the greatest. But there continues to be a surplus of incoming solar radiation versus outgoing infrared radiation until late afternoon.

What are the main factors that determine seasonal temperature variations?

The 23.5˚ tilt in the earth's axis combined with the earth's elliptical orbit around the sun.

Explain how radiational cooling at night produces a radiation temperature inversion.

The ground and air near the ground will cool quicker than the air above by radiating infrared radiation (radiation cooling). The warmer temperatures aloft do transfer some heat downward but the process is slow due to the air's poor thermal conductivity. Therefore, by late night or early morning, the coldest air is found next to the ground, with slightly warmer air above (radiational inversion).

The earth is closer to the sun in January when the Southern Hemisphere is experiencing their summer season. So why are the Southern Hemisphere summers are not warmer than Northern Hemisphere summers?

the larger amount of water in the Southern Hemisphere (81%) versus the Northern Hemisphere (61%) causes summer temperatures to be cooler in the Southern Hemisphere. But the water's larger heat capacity will also cause the Southern Hemisphere winters to be warmer than the Northern Hemisphere winters, with the exception of the Antarctic due to its large snow and ice pack.

During the Northern Hemisphere's summer, the daylight hours in the far northern latitudes are longer than those in the mid-latitudes, but the temperatures are not warmer farther north. Why?

the sun angle is still considerably low, more solar radiation at the top of the atmosphere, but the sunlight penetrating through the northern will be partially scattered by fine dust and air molecules, reflected by clouds, and absorbed by atmospheric gases. These factors combined, reduce the amount of solar radiation reaching the ground. The solar radiation that does reach the ground, is partially reflected by ice and snow, is used to melt ice, snow and frozen ground and heat the lower atmosphere.