Earth’s Seasons Explained by Rob Snyder | Understand Astronomical and Meteorological Seasons

1. Earth’s Seasons Presented by Rob Snyder

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

3. Astronomical seasons begin and end on an equinox or a solstice. http://okfirst.mesonet.org/train/meteorology/Seasons.html

4. 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. The 2008 astronomical summer (in the Northern Hemisphere) began at 23:59 GMT (19:59 EDT) on June 20th. http://aa.usno.navy.mil/data/docs/earthview.php

5. Seasonal changes in the lengths of daytime is the most dramatic in the Polar Regions. http://www.eoearth.org/article/Earth-Sun_relationships_and_insolation

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

7. Demonstrations and activities guides students toward an understanding of the influence of Earth’s axial tilt on the angle of incidence of sunlight and length of daytime. “The Globe Walk”

8. Animations also can reveal the changes in sunlight reaching Earth’s surface at different Latitudes. http://www.cs.sbcc.cc.ca.us/~physics/flash/LengthofDay.swf

9. This animation reveals the affect of Earth’s orbital motion and it’s axial tilt on seasonal temperature changes http://geography.uoregon.edu/envchange/clim_animations/gifs/tmp2m_web.gif

10. The Encyclopedia of earth web site provides images and a description of changes in solar insolation at different Latitudes. http://www.eoearth.org/article/Earth's_energy_balance

11. Seasonal changes in solar insolation is the most dramatic in Polar Regions. http://www.eoearth.org/article/Earth-Sun_relationships_and_insolation

12. 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 1st and ends on the last day of February. Meteorological Seasons

13. 2003: December 6th(20 inches of snow) 2004: December 20th(8 inches of snow) 2005: December 3rd (14 inches of snow) 2007: December 14th and 15th (20 inches of snow) A recent history of Pioneer Valley snowstorms that occurred before a winter solstice.

14. NOAA’s false color images reveal how water evaporating from ocean water at lower Latitudes interacts with Continental Polar and Continental Arctic air masses. http://www.goes.noaa.gov/enhanced.html http://maps.fsl.noaa.gov/

15. A NOAA web site can be used to monitor the flow of Polar and Arctic air masses into the lower Latitudes. http://www.hpc.ncep.noaa.gov/dailywxmap/index.html

16. Polar fronts move further south during the Northern Hemisphere’s fall and winter. http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/weather_systems/fronts.html

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

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

19. 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. Heating and Cooling Seasons and the school year

20. 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.

21. degree days = # of days x (65º - average temp.) Positive answers = heating 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. A Degree Day formula is used to analyze cooling seasons and heating seasons

22. A day’s high temperature was 47º F. A day’s 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. A sample heating degree day calculation

23. A day’s high temperature was 97º F. A day’s 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 . A sample cooling degree day calculation

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

25. TheNational Weather Service provide the number of heating or cooling degree days that have accumulated: during the most recent 24 hour period. so far during the present month. so far in the present heating or cooling season. so far in the previous heating or cooling season and during a “normal” season. Heating and Cooling Degree Days Accumulate http://www.nws.noaa.gov/

26. 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 2000. The next 30 year period will be from 1981 to 2010. What is a “normal” heating or cooling season?

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

28. 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

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

30. A Cooling Season Map(the web site includes the scale) http://cdo.ncdc.noaa.gov/climaps/cdd0913.pdf

31. 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. An Antarctic Heating Season http://www.weatherreports.com/_/Antarctica

32. There are 31 days in August. 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 = 2697 2697 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. August in McMurdo, Antarctica

33. The U.S. Antarctic Program provides information about the midwinter celebrated in Antarctica. “Midwinter” in the Antarctic is celebrated on the same day of Shakespeare’s “Midsummer” in the Northern Hemisphere. Midwinter Celebrations http://www.usap.gov/usapgov/news/contenthandler.cfm?id=1046

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

35. In Summary • There are three categories of seasons. • Heating Seasons describe 12 months of colder weather. • Cooling Seasons describe 12 months of warmer weather. • A degree day calculation is a proxy for average temperature. • Heating and cooling degree days indicate the demand for heating and cooling systems. • 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.