Earth’s SeasonsEarth’s SeasonsPresented by Rob SnyderPresented by Rob Snyder

Three different sets of Three different sets of seasons each have seasons each have

their own calendars.their own calendars.

Astronomical SeasonsAstronomical Seasons

Meteorological SeasonsMeteorological Seasons

Heating and Cooling SeasonsHeating and Cooling Seasons

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

http://okfirst.mesonet.org/train/meteorology/Seasons.html

The 2008 astronomical summer (in the The 2008 astronomical summer (in the Northern Hemisphere) began at Northern Hemisphere) began at

23:59 GMT (19:59 EDT) on June 2023:59 GMT (19:59 EDT) on June 20thth..

On that day and at that moment, theOn that day and at that moment, the

midday sun was directly overhead at amidday sun was directly overhead at a

location on the Tropic of Cancer.location on the Tropic of Cancer.

A United States Naval Observatory A United States Naval Observatory web site can indicate where the sun web site can indicate where the sun was directly overhead on that day.was directly overhead on that day.

http://aa.usno.navy.mil/data/docs/earthview.php

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

http://www.eoearth.org/article/Earth-Sun_relationships_and_insolation

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

““The Globe Walk”The Globe Walk”

Demonstrations and activities Demonstrations and activities guides students toward an guides students toward an understanding of the influence understanding of the influence of Earth’s axial tilt on the angle of Earth’s axial tilt on the angle of incidence of sunlight and of incidence of sunlight and length of daytime.length of daytime.

http://www.cs.sbcc.cc.ca.us/~physics/flash/LengthofDay.swf

Animations also can Animations also can reveal the changes in sunlight reveal the changes in sunlight reaching Earth’s surface at reaching Earth’s surface at different Latitudes.different Latitudes.

This animation reveals the affect of This animation reveals the affect of Earth’s orbital motion and it’s axial tilt Earth’s orbital motion and it’s axial tilt on seasonal temperature changeson seasonal temperature changes

http://geography.uoregon.edu/envchange/clim_animations/gifs/tmp2m_web.gif

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

http://www.eoearth.org/article/Earth's_energy_balance

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

http://www.eoearth.org/article/Earth-Sun_relationships_and_insolation

Meteorological SeasonsMeteorological Seasons

A meteorological winter is an A meteorological winter is an alternative to an astronomical winter and alternative to an astronomical winter and consists of the three, consecutive, consists of the three, consecutive, coldest months in a region.coldest months in a region.

In some regions like the Northeast and In some regions like the Northeast and Great Lakes, a meteorological winter Great Lakes, a meteorological winter begins on December 1begins on December 1stst and ends on the and ends on the last day of February.last day of February.

A recent history of Pioneer Valley A recent history of Pioneer Valley snowstorms that occurred before a snowstorms that occurred before a

winter solstice.winter solstice.

• 2003: December 62003: December 6thth(20 inches of snow)(20 inches of snow)

• 2004: December 202004: December 20thth(8 inches of snow)(8 inches of snow)

• 2005: December 32005: December 3rdrd (14 inches of snow) (14 inches of snow)

• 2007: December 142007: December 14thth and 15 and 15thth (20 inches (20 inches of snow)of snow)

NOAA’s false color images reveal how water evaporating NOAA’s false color images reveal how water evaporating from ocean water at lower Latitudes interacts with from ocean water at lower Latitudes interacts with

Continental Polar and Continental Arctic air masses.Continental Polar and Continental Arctic air masses.

http://maps.fsl.noaa.gov/http://www.goes.noaa.gov/enhanced.html

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

http://www.hpc.ncep.noaa.gov/dailywxmap/index.html

Polar fronts move further south during the Polar fronts move further south during the Northern Hemisphere’s fall and winter.Northern Hemisphere’s fall and winter.

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/weather_systems/fronts.html

A rhetorical questionA rhetorical question

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

Heating and Cooling SeasonsHeating and Cooling Seasons

Heating Seasons begin on July 1Heating Seasons begin on July 1stst of of one calendar year and end on June 30one calendar year and end on June 30thth of the next calendar year so that the of the next calendar year so that the coldest months are in the middle of the coldest months are in the middle of the heating season.heating season.

Cooling Seasons begin on January 1Cooling Seasons begin on January 1stst and end on December 31and end on December 31stst of a calendar of a calendar year so that the warmest months are in year so that the warmest months are in the middle of the cooling season.the middle of the cooling season.

Heating and Cooling Seasons Heating and Cooling Seasons and the school yearand the school year

The school year includes the The school year includes the months when the majority of heating months when the majority of heating degree days accumulate.degree days accumulate.

The first few months of a school The first few months of a school year include the last few months of a year include the last few months of a cooling season. The last few months cooling season. The last few months of a school year include the first few of a school year include the first few months of the next cooling season.months of the next cooling season.

The Cooling and Heating Season The Cooling and Heating Season AssumptionsAssumptions

Cooling systems are used on Cooling systems are used on days when the average days when the average temperature is above 65temperature is above 65º º Fahrenheit.Fahrenheit.

Heating systems are used on Heating systems are used on days when the average days when the average temperature is below 65temperature is below 65º º Fahrenheit.Fahrenheit.

A Degree Day formula is used to analyze A Degree Day formula is used to analyze cooling seasons and heating seasonscooling seasons and heating seasons

degree days = # of days x (65degree days = # of days x (65º -º - average temp.) 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 Note: Daily calculations are required when temperatures fluctuate above and below 65º during a temperatures fluctuate above and below 65º during a heating or cooling season.heating or cooling season.

A sample heating degree day calculationA sample heating degree day calculation

A day’s high temperature was 47A day’s high temperature was 47º F.º F.A day’s low temperature was 23A day’s low temperature was 23º F.º F.

degree days = # of days x (65degree days = # of days x (65ºº - average temp.) - average temp.)

degree days = 1 day x (65degree days = 1 day x (65º º - 35- 35º)º)

degree days = 30degree days = 30

The daily average temperature was below 65º, so 30 The daily average temperature was below 65º, so 30 heating degree days accumulated on that day and 30 units heating degree days accumulated on that day and 30 units of energy could be used by a heating system.of energy could be used by a heating system.

A sample cooling degree day calculationA sample cooling degree day calculation

A day’s high temperature was 97A day’s high temperature was 97º F.º F.A day’s low temperature was 73A day’s low temperature was 73º F.º F.

degree days = # of days x (65degree days = # of days x (65ºº - average temp.) - average temp.)

degree days = 1 day x (65degree days = 1 day x (65º º - 85- 85º)º)

degree days = -20degree days = -20

The daily average temperature was above 65º, so 20 The daily average temperature was above 65º, so 20 cooling degree days accumulated on that day and 20 units cooling degree days accumulated on that day and 20 units of energy could be used by a cooling system .of energy could be used by a cooling system .

Degree day calculations serve as a Degree day calculations serve as a proxy for average temperatures.proxy for average temperatures.

Energy suppliers use degree day Energy suppliers use degree day data to schedule energy purchases and data to schedule energy purchases and deliveries for heating and cooling deliveries for heating and cooling systems.systems.

The amount of money spent on The amount of money spent on energy corresponds to the number of energy corresponds to the number of degree days that accumulate in a degree days that accumulate in a heating or cooling season.heating or cooling season.

Heating and Cooling Heating and Cooling Degree Days AccumulateDegree Days Accumulate

TheThe National Weather Service provide National Weather Service provide the number of heating or cooling degree the number of heating or cooling degree days that have accumulated: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 so far in the present heating or cooling

season.season.• so far in the previous heating or cooling so far in the previous heating or cooling

season and during a “normal” season.season and during a “normal” season.

http://www.nws.noaa.gov/

What is a “normal” What is a “normal” heating or cooling season?heating or cooling season?

The normal number of degree days The normal number of degree days that accumulate during a heating that accumulate during a heating season or cooling is a 30 year season or cooling is a 30 year average. The present 30 year period average. The present 30 year period includes data from 1971 to 2000. The includes data from 1971 to 2000. The next 30 year period will be from 1981 next 30 year period will be from 1981 to 2010.to 2010.

There are many ways to analyze heating There are many ways to analyze heating and cooling degree day data.and cooling degree day data.

• Make daily calculations of heating and Make daily calculations of heating and cooling degree days.cooling degree days.

• Maintain a running total of degree days.Maintain a running total of degree days.• Compare the present season with a “normal” Compare the present season with a “normal”

season.season.• Determine how far we are through the present Determine how far we are through the present

season.season.• Monitor the severity of season in a region.Monitor the severity of season in a region.• Compare the severity of seasons in several Compare the severity of seasons in several

regionsregions• Evaluate factors that affect the severity of a Evaluate factors that affect the severity of a

season.season.

A Heating Season MapA Heating Season Map( A District Heating Factor of 1.0 = 4000 heating ( A District Heating Factor of 1.0 = 4000 heating

degree days in an entire heating season)degree days in an entire heating season)

Source: Project RetroTech; U.S. Department of Energy

A Heating Season Map for AlaskaA Heating Season Map for Alaska(a DHF of 4 = 16,000 heating degree days(a DHF of 4 = 16,000 heating degree days

in an entire heating season)in an entire heating season)

Source: Project RetroTech; U.S. Department of Energy

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

http://cdo.ncdc.noaa.gov/climaps/cdd0913.pdf

An Antarctic Heating SeasonAn Antarctic Heating Season

Monthly average temperatures can be Monthly average temperatures can be obtained for research stations in obtained for research stations in Antarctica from WeatherReports.com.Antarctica from WeatherReports.com.

That data can be used to determine the That data can be used to determine the number of heating degree days that number of heating degree days that accumulate during a heating season.accumulate during a heating season.

http://www.weatherreports.com/_/Antarctica

August in McMurdo, AntarcticaAugust in McMurdo, Antarctica• There are 31 days in August.There are 31 days in August.• The average temperature is -22The average temperature is -22º F.º F.

degree days = # of days x (65degree days = # of days x (65ºº - average temp.) - average temp.)

degree days = 31 days x [65degree days = 31 days x [65º º - (-22- (-22)])]

degree days = 31 days x [87degree days = 31 days x [87º]º]

degree days = 2697degree days = 2697

2697 heating degree days accumulated that month. 2697 heating degree days accumulated that month. A Reminder: This is accurate only if there were no days A Reminder: This is accurate only if there were no days

when the average temperature was above 65º F.when the average temperature was above 65º F.

Midwinter CelebrationsMidwinter Celebrations

The U.S. Antarctic Program The U.S. Antarctic Program provides information about the provides information about the midwinter celebrated in Antarctica.midwinter celebrated in Antarctica.

“ “Midwinter” in the Antarctic is Midwinter” in the Antarctic is celebrated on the same day of celebrated on the same day of Shakespeare’s “Midsummer” in the Shakespeare’s “Midsummer” in the Northern Hemisphere.Northern Hemisphere.

http://www.usap.gov/usapgov/news/contenthandler.cfm?id=1046

Continental “polar” air masses are sometimes a Continental “polar” air masses are sometimes a component of a cold front that breaks a summer heat component of a cold front that breaks a summer heat

wave at lower Latitudes.wave at lower Latitudes.

In SummaryIn Summary

• There are three categories of seasons.There are three categories of seasons.• Heating Seasons describe 12 months of colder Heating Seasons describe 12 months of colder

weather.weather.• Cooling Seasons describe 12 months of warmer Cooling Seasons describe 12 months of warmer

weather.weather.• A degree day calculation is a proxy for average A degree day calculation is a proxy for average

temperature.temperature.• Heating and cooling degree days indicate the Heating and cooling degree days indicate the

demand for heating and cooling systems.demand for heating and cooling systems.• 30 year averages of data are used to analyze heating 30 year averages of data are used to analyze heating

seasons.seasons.• Arctic air masses have more of an impact on heating Arctic air masses have more of an impact on heating

seasons than on cooling seasons in the Northern seasons than on cooling seasons in the Northern Hemisphere.Hemisphere.