Earths Seasons Presented by Rob Snyder

Three different sets of seasons each have their own calendars. Astronomical Seasons Meteorological Seasons Heating and Cooling Seasons

Astronomical seasons begin and end on an equinox or a solstice.

The 2008 astronomical summer (in the Northern Hemisphere) began at 23:59 GMT (19:59 EDT) on June 20 th. On that day and at that moment, the midday sun was directly overhead at a location on the Tropic of Cancer. A United States Naval Observatory web site can indicate where the sun was directly overhead on that day. A United States Naval Observatory web site can indicate where the sun was directly overhead on that day.

Seasonal changes in the lengths of daytime is the most dramatic in the Polar Regions.

A variety of learning experiences helps students develop an understanding of the affect of Earths axial tilt and orbital motion on the changes in sunlight reaching Earths surface at different latitudes.

The Globe Walk Demonstrations and activities guides students toward an understanding of the influence of Earths axial tilt on the angle of incidence of sunlight and length of daytime. Demonstrations and activities guides students toward an understanding of the influence of Earths axial tilt on the angle of incidence of sunlight and length of daytime.

Animations also can reveal the changes in sunlight reaching Earths surface at different Latitudes.

This animation reveals the affect of Earths orbital motion and its axial tilt on seasonal temperature changes This animation reveals the affect of Earths orbital motion and its axial tilt on seasonal temperature changes

The Encyclopedia of earth web site provides images and a description of changes in solar insolation at different Latitudes. The Encyclopedia of earth web site provides images and a description of changes in solar insolation at different Latitudes.

Seasonal changes in solar insolation is the most dramatic in Polar Regions.

Meteorological Seasons A meteorological winter is an alternative to an astronomical winter and consists of the three, consecutive, coldest months in a region. A meteorological winter is an alternative to an astronomical winter and consists of the three, consecutive, coldest months in a region. In some regions like the Northeast and Great Lakes, a meteorological winter begins on December 1 st and ends on the last day of February. In some regions like the Northeast and Great Lakes, a meteorological winter begins on December 1 st and ends on the last day of February.

A recent history of Pioneer Valley snowstorms that occurred before a winter solstice. 2003: December 6 th (20 inches of snow)2003: December 6 th (20 inches of snow) 2004: December 20 th (8 inches of snow)2004: December 20 th (8 inches of snow) 2005: December 3 rd (14 inches of snow)2005: December 3 rd (14 inches of snow) 2007: December 14 th and 15 th (20 inches of snow)2007: December 14 th and 15 th (20 inches of snow)

NOAAs false color images reveal how water evaporating from ocean water at lower Latitudes interacts with Continental Polar and Continental Arctic air masses.

A NOAA web site can be used to monitor the flow of Polar and Arctic air masses into the lower Latitudes. A NOAA web site can be used to monitor the flow of Polar and Arctic air masses into the lower Latitudes.

Polar fronts move further south during the Northern Hemispheres fall and winter.

A rhetorical question So, do you wait until the very first day of an astronomical or meteorological winter to use a heating system? So, do you wait until the very first day of an astronomical or meteorological winter to use a heating system?

Heating and Cooling Seasons Heating Seasons begin on July 1 st of one calendar year and end on June 30 th of the next calendar year so that the coldest months are in the middle of the heating season. Heating Seasons begin on July 1 st of one calendar year and end on June 30 th of the next calendar year so that the coldest months are in the middle of the heating season. Cooling Seasons begin on January 1 st and end on December 31 st of a calendar year so that the warmest months are in the middle of the cooling season. Cooling Seasons begin on January 1 st and end on December 31 st of a calendar year so that the warmest months are in the middle of the cooling season.

Heating and Cooling Seasons and the school year The school year includes the months when the majority of heating degree days accumulate. The school year includes the months when the majority of heating degree days accumulate. The first few months of a school year include the last few months of a cooling season. The last few months of a school year include the first few months of the next cooling season. The first few months of a school year include the last few months of a cooling season. The last few months of a school year include the first few months of the next cooling season.

The Cooling and Heating Season Assumptions Cooling systems are used on days when the average temperature is above 65º Fahrenheit. Heating systems are used on days when the average temperature is below 65º Fahrenheit.

A Degree Day formula is used to analyze cooling seasons and heating seasons degree days = # of days x (65º - average temp.) Positive answers = heating degree days. Positive answers = heating degree days. Negative answers = cooling degree days. Negative answers = cooling degree days. Note: Daily calculations are required when temperatures fluctuate above and below 65º during a heating or cooling season. Note: Daily calculations are required when temperatures fluctuate above and below 65º during a heating or cooling season.

A sample heating degree day calculation A days high temperature was 47º F. A days low temperature was 23º F. degree days = # of days x (65º - average temp.) degree days = 1 day x (65º - 35º) degree days = 30 The daily average temperature was below 65º, so 30 heating degree days accumulated on that day and 30 units of energy could be used by a heating system. The daily average temperature was below 65º, so 30 heating degree days accumulated on that day and 30 units of energy could be used by a heating system.

A sample cooling degree day calculation A days high temperature was 97º F. A days low temperature was 73º F. degree days = # of days x (65º - average temp.) degree days = 1 day x (65º - 85º) degree days = -20 The daily average temperature was above 65º, so 20 cooling degree days accumulated on that day and 20 units of energy could be used by a cooling system. The daily average temperature was above 65º, so 20 cooling degree days accumulated on that day and 20 units of energy could be used by a cooling system.

Degree day calculations serve as a proxy for average temperatures. Degree day calculations serve as a proxy for average temperatures. Energy suppliers use degree day data to schedule energy purchases and deliveries for heating and cooling systems. Energy suppliers use degree day data to schedule energy purchases and deliveries for heating and cooling systems. The amount of money spent on energy corresponds to the number of degree days that accumulate in a heating or cooling season. The amount of money spent on energy corresponds to the number of degree days that accumulate in a heating or cooling season.

Heating and Cooling Degree Days Accumulate TheNational Weather Service provide the number of heating or cooling degree days that have accumulated: The National Weather Service provide the number of heating or cooling degree days that have accumulated: during the most recent 24 hour period.during the most recent 24 hour period. so far during the present month.so far during the present month. so far in the present heating or cooling season.so far in the present heating or cooling season. so far in the previous heating or cooling season and during a normal season.so far in the previous heating or cooling season and during a normal season.

What is a normal heating or cooling season? The normal number of degree days that accumulate during a heating season or cooling is a 30 year average. The present 30 year period includes data from 1971 to The next 30 year period will be from 1981 to The normal number of degree days that accumulate during a heating season or cooling is a 30 year average. The present 30 year period includes data from 1971 to The next 30 year period will be from 1981 to 2010.

There are many ways to analyze heating and cooling degree day data. Make daily calculations of heating and cooling degree days.Make daily calculations of heating and cooling degree days. Maintain a running total of degree days.Maintain a running total of degree days. Compare the present season with a normal season.Compare the present season with a normal season. Determine how far we are through the present season.Determine how far we are through the present season. Monitor the severity of season in a region.Monitor the severity of season in a region. Compare the severity of seasons in several regionsCompare the severity of seasons in several regions Evaluate factors that affect the severity of a season.Evaluate factors that affect the severity of a season.

A Heating Season Map ( A District Heating Factor of 1.0 = 4000 heating degree days in an entire heating season) Source: Project RetroTech; U.S. Department of Energy

A Heating Season Map for Alaska (a DHF of 4 = 16,000 heating degree days in an entire heating season) Source: Project RetroTech; U.S. Department of Energy

A Cooling Season Map (the web site includes the scale)

An Antarctic Heating Season Monthly average temperatures can be obtained for research stations in Antarctica from WeatherReports.com. That data can be used to determine the number of heating degree days that accumulate during a heating season. That data can be used to determine the number of heating degree days that accumulate during a heating season.

August in McMurdo, Antarctica There are 31 days in August.There are 31 days in August. The average temperature is -22º F.The average temperature is -22º F. degree days = # of days x (65º - average temp.) degree days = 31 days x [65º - (-22)] degree days = 31 days x [87º] degree days = heating degree days accumulated that month heating degree days accumulated that month. A Reminder: This is accurate only if there were no days when the average temperature was above 65º F.

Midwinter Celebrations The U.S. Antarctic Program provides information about the midwinter celebrated in Antarctica. The U.S. Antarctic Program provides information about the midwinter celebrated in Antarctica. Midwinter in the Antarctic is celebrated on the same day of Shakespeares Midsummer in the Northern Hemisphere. Midwinter in the Antarctic is celebrated on the same day of Shakespeares Midsummer in the Northern Hemisphere.

Continental polar air masses are sometimes a component of a cold front that breaks a summer heat wave at lower Latitudes.

In Summary There are three categories of seasons.There are three categories of seasons. Heating Seasons describe 12 months of colder weather.Heating Seasons describe 12 months of colder weather. Cooling Seasons describe 12 months of warmer weather.Cooling Seasons describe 12 months of warmer weather. A degree day calculation is a proxy for average temperature.A degree day calculation is a proxy for average temperature. Heating and cooling degree days indicate the demand for heating and cooling systems.Heating and cooling degree days indicate the demand for heating and cooling systems. 30 year averages of data are used to analyze heating seasons.30 year averages of data are used to analyze heating seasons. Arctic air masses have more of an impact on heating seasons than on cooling seasons in the Northern Hemisphere.Arctic air masses have more of an impact on heating seasons than on cooling seasons in the Northern Hemisphere.