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  • Irish Chronicles Document Links Between Volcanoes and Weather
    A study of over 40,000 written entries in Irish Annals and ice core measurements shows a strong corr...Read more

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    Irish Chronicles Document Links Between Volcanoes and Weather

    A study of over 40,000 written entries in Irish Annals and ice core measurements shows a strong correlation between the occurrence of volcanic eruptions and extreme cold weather in Ireland over a 1200 year period. Data analyzed in this study cover the period from 431 to 1649, during which time up to 48 volcanic eruptions are identified in Greenland ice core records through deposition of volcanic sulfate in annual layers of ice. You can find the study (open access), published on 6 June 2013 in IOP Publishing's journal Environmental Research Letters, at http://iopscience.iop.org/1748-9326/8/2/024035/article. Find out more about how volcanoes can influence climate.
  • EF-5 Tornado in El Reno, Oklahoma Widest Ever Recorded in US
    The EF-5 tornado that hit El Reno, Oklahoma on May 31st was the widest ever recorded in the US, acco...Read more

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    EF-5 Tornado in El Reno, Oklahoma Widest Ever Recorded in US

    The EF-5 tornado that hit El Reno, Oklahoma on May 31st was the widest ever recorded in the US, according to the National Weather Service in Norman Oklahoma. The tornado, which remained on the ground for 40 minutes and reached 2.6 miles across (4.2 km), took the lives of 18 people including storm chasers Tim Samaras, Paul Samaras and Carl Young. For more information on the tornado, visit http://ow.ly/i/2hfDG.
  • Atmospheric CO2 Level Tops 400 ppm
    During the week of May 13th, the CO2 level at the Mauna Loa Observatory in Hawaii topped 400 ppm rep...Read more

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    Atmospheric CO2 Level Tops 400 ppm

    During the week of May 13th, the CO2 level at the Mauna Loa Observatory in Hawaii topped 400 ppm repeatedly. Daily levels of CO2 can vary due to weather, and there are seasonal trends as well. The level of atmospheric greenhouse gases continues to increase, now over 120 ppm since the Industrial Revolution began. For more on the Keeling Curve, see http://keelingcurve.ucsd.edu/. Find out more about greenhouse gases and warming.
A diagram of how the Sun moves through the sky on the winter solstice.
Click on image for full size

The Winter Solstice

Let's pretend, for the moment, that you're the person standing on the Earth in the picture to the left, living in Topeka, Kansas, around 40° N latitude. The picture on the left shows the view from the solar system (upper panel), and from on the surface of the earth (lower panel). Notice that some of the same features are labelled on each panel.

The upper panel shows that on the winter solstice (which occurs around December 21), the northern half of the Earth is tilted away from the Sun. Notice that the Sun is south of the equator. For you in Topeka, the altitude of the Sun at noon is 26.5°, which is pretty low in the sky. That is the lowest the Sun gets at that latitude. It has been getting lower and lower in the sky since the summer solstice and through the autumnal equinox. The bottom panel shows how the Sun moves through the sky for someone standing on the ground in Topeka.

So, on the winter solstice, the northern hemisphere is getting less direct sunlight than the southern hemisphere. This is winter for people in the northern hemisphere. During the winter, the Sun is also above the horizon for a shorter time than it is during the summer (the nights are long). The winter solstice is the shortest day of the year.

At this same time, the southern half of the Earth is tilted toward the Sun. If you were living in Valdivia, Chile (about -40° S latitude) you would be enjoying a nice warm summer.

How high the Sun get's in your sky, and how long it is above the horizon during the day, depend not only on the season, but also on your latitude.

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