Meteorology 110 Chapter 3 Review

Calculate the Cooling Degree-Day (CDD) for Grand Forks on a day with a minimum temperature of 65˚F and maximum temperature of 95˚F.

You must first calculate the mean (average) daily temperature. In this example, with a high of 95˚F and low 65˚F the average temperature is 80˚F. Then subtract the base temperature (65˚F) from the mean daily temperature (85˚F) and you get a cooling degree-day of: 85˚F - 65˚F = 20 CDD.

Define terms used to describe the Daily, Monthly, and Yearly temperature values. 1. Daily or Diurnal Range of Temperature 2. Mean or Average Daily Temperature 3. Mean or Average Monthly Temperature 4. Annual Range of Temperature 5. Mean or Average Annual Temperature

1. Daily or Diurnal Range of Temperature The difference between the daily maximum and minimum temperature 2. Mean or Average Daily Temperature The average of the highest and lowest temperature for a 24-hour period 3. Mean or Average Monthly Temperature The average of the mean daily temperatures for that month (GFK: Jan 6.7°F, July 68.6°F 4. Annual Range of Temperature The difference between the average monthly temperature of the warmest and coldest months GFK: 68.6 - 6.7 = 61.9°F 5. Mean or Average Annual Temperature The average temperature for the entire year which represents the average of the twelve average monthly temperatures GFK = 40.0°F

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

1. Paint the shelter white 2. Face it to the north 3. Put slots in the side for free air flow 4. Place it 5.5 feet above the ground 5. Make sure it is located above a grassy surface in this part of the country and keep it away from buildings and surface concrete and/or pavement

Identify and name the major lines of latitude starting north and working south.

90˚ N North Pole 66½˚ N Arctic Circle 23½˚ N Tropic of Cancer 0˚ Equator 23½˚ S Tropic of Capricorn 66½˚ S Antarctic Circle 90˚ S South Pole

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. In extreme cases, very low wind-chill and high heat index temperatures can be life threatening

What nighttime weather conditions would create the greatest temperature gradient from the surface to areas just a few feet above the surface?

Clear, dry, calm conditions. As night progresses, the ground and the air in contact with it continue to cool more rapidly than the air a few meters higher. This is due to the ground and air above the ground radiating infrared energy, a process called radiational cooling. Radiational cooling is most efficient when the skies are clear, the air is dry, and the winds are calm. An increase in cloud cover and/or an increase in wind will decrease the effects of radiational cooling.

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. Radiational cooling is greater during the overnight hours in a dry regions because less water vapor is available to absorb and re-radiate outgoing infrared radiation back to the surface. 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).

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?

Even though the far northern latitudes are receiving more hours of sunlight in the summer, the sun angle is still considerably low. It is true that the northern latitudes are receiving more solar radiation at the top of the atmosphere, but the sunlight penetrating through the northern atmosphere 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. Solar radiation that does reach the ground is: 1) partially reflected by ice and snow, 2) is used to melt ice, snow, and frozen ground. Therefore with less incoming solar radiation reaching the surface and being used for phase change processes, less solar radiation is available for surface heating.

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

Grand Forks will experience its coldest nights and strongest radiational inversions during the winter months when, skies are clear, winds are calm, air is dry, and snow is on the ground.

The earth is closet to the sun in January when the Southern Hemisphere is experiencing their summer season. So why are the Southern Hemisphere summers not as warm as the Northern Hemisphere summers?

It is true that the sun is closet to the earth during the period when the Southern Hemisphere is experience summer (January 4th) but the large 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 cause the Southern Hemisphere winters to be warmer than the Northern Hemisphere winters, with the exception of Antarctica due to its large area of snow and ice.

Why does Grand Forks, ND have colder winter temperatures than Seattle, WA even though they are both located at roughly the same latitude (48˚N)?

Mid-ocean surface temperatures change relatively little from summer to winter compared to the much larger annual temperature changes over the middle of a continent. This is due to the difference in specific heat values between water (1.0 Cal/gr˚C) and land (0.3 Cal/gr˚C). Water will heat and cool slower than land due to its larger heat capacity. Therefore winter air temperatures in Seattle will be influenced by the surrounding water and stay warmer than temperatures in Grand Forks that is located in the middle of the North American continent.

What is a Wind Chill Temperature?

Once the wind starts to blow, the insulating layer of warm air is swept away and heat is rapidly removed from the skin by the constant bombardment of cold air. When all other factors are the same, the faster the wind blows, the greater the heat loss, and the colder we feel. How cold the wind makes us feel is usually expressed as a Wind-Chill Index (WCI)

Identify the major dates that correspond to the change of astronomical seasons in the Northern Hemisphere.

Sept 22nd Autumn Equinox 0˚ Equator Dec 21st Winter Solstice 23½˚S Tropic of Capricorn Mar 21st h Vernal Equinox 0˚ Equator June 21st Summer Solstice 23½˚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. Note: Solar noon is the half way point between sunrise and sunset.

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. Therefore maximum temperatures are usually reached 2-4 hours later than the time of peak incoming solar radiation.

What daytime weather conditions in the summer would create the greatest temperature gradient from the surface to an area just a few feet above the surface?

Sunny, calm conditions. The sun heats the ground which in turn heats the air in contact with the ground by conduction. Because air is such a poor conductor of heat, there exists a thermal boundary separating the hot surface air from the slightly cooler air above. On windy days however, turbulent eddies are able to mix hot surface air with the cooler air above reducing the temperature gradient from the surface upward.

If it is winter and January in New York City, what is the season in Sydney, Australia?

Sydney, Australia (33½˚ South Latitude) is in the Southern Hemisphere, therefore it would be summer but the month of the year is still January.

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 are the main factors that determine seasonal temperature variations. The angle at which a beam of light strikes the earth and the length of daylight hours are directly related to the tilt of the earth's axis and the earth's location in its orbit around the sun.

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

The earth is 3.1 million miles closer to the sun in January than in July but due to the 23.5˚ tilt in the earth's axis the sun angle is at its lowest point in the Northern Hemisphere during the end of December and first part of January. The sunlight that strikes at an angle is spread over a greater surface area, and therefore is a less intense heat source than a beam striking the earth surface directly. Another important factor is that the amount of daylight hours is less in the Northern Hemisphere during the winter months.

Can a thermometer measure a Wind Chill Temperature?

Thermometers can only measure the 'ambient' air temperature. A wind-chill temperature is a 'sensible' temperature or a temperature that we perceive. In the case of wind-chill, the 'sensible' temperature is a temperature in which 'we feel' colder than it actual is outside.

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

Time of Year - determines the location of the earth in its orbit around the sun which determines what season you are in. Latitude - determines the amount of incoming solar radiation, slant angle of sun, and duration of daylight hours, at a given time of year. Land vs Water distribution - areas with more water (Southern Hemisphere) will have smaller seasonal temperature variations. Areas located in the middle of continents (Grand Forks) will have a much greater seasonal temperature variation than areas along the coast. 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.

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

Under the right conditions, clear skies, dry air, and calm winds, the ground will cool quicker than the air above by the loss of outgoing 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 into the early morning hours, the coldest air is found next to the ground with slightly warmer air above (radiational inversion).

Calculate the Heating Degree-Day (HDD) for Grand Forks on a day with a minimum temperature of -30˚F and maximum temperature of -10˚F.

You must first calculate the mean (average) daily temperature. With a high of -10˚F and low of -30˚F, the average temperature for the day would be -20˚F. Then subtract the mean daily temperature (-20˚F) from the base temperature of (65˚F) and you get a heating degree-day of: 65˚F - (-20˚F) = 85 HDD.