One full orbit
around the sun- the period of a year- serves as a fundamental force of
climate variability as well as a measure of time. The essential cause
of seasonal climate change during the year is the tilt of Earth's axis,
currently 23.5 degree tilt off its axis, which alters the angle of solar
radiation and thus its intensity over the course of the year.
In Climate Science we dig deeper into how Earth's
tilted axis results in climate changes that can be seen in such climate
signatures as patterns of precipitation and temperature or the flow of
creeks and rivers, which are important considerations for water managers
in charge of controlling reservoirs or developing conservation plans.
In Climate History, we focus on the annual
migration patterns of birds and marine animals in the western hemisphere,
while in Resources there are links to websites
with information relating to the annual cycle and ideas for further inquiry
into our yearly journey around the sun.
Dec. 21 or 22, shortest day in Northern Hemisphere,
longest in Southern
Hemisphere tilts away from sun, receiving less direct solar radiation,
while the Southern Hemisphere tilts towards the sun.
Blizzards andice storms can occur throughout the boreal (Northern
Hemisphere) winter months in higher latitudes and elevations.
Image of Crater Lake by NPS.
March 20 or 21 in Northern Hemisphere
the sun's direct rays pass the equator, the length of day and night
are the same. (Equinox means " equal night"). Without
sufficient spring precipitation, droughts may occur later in the
year as evapotranspiration increases. In regions where winter and
spring precipitation falls as snow, runoff peaks start in the Spring
in the southern regions and progresses northward and upward in elevation
as the season progresses.
Image of New River by NPS
June 21 or 22, shortest day in the Southern Hemisphere,
longest day in Northern Hemisphere
Hemisphere tilts toward the sun, receiving more intense direct solar
radiation, while the Southern Hemisphere tilts away from the sun
and experiences winter.
where winter and spring precipitation falls as snow, there is often
a peak in snow melt runoff around the solstice. Droughts, flash
floods, forest fires and hurricanes are all climate-related events
that usually occur during the summer months and into the fall.
Wet season during the Indian Monsoon generally begins in June and
goes through September.
Image of Death Valley by NPs
Sept. 22 or 23 in
direct rays pass the equator and length of day and night are the same.
The seasonal cooling of the climate during autumn may include the
end of the growing season in some climates. Hurricane activity may
extend well into the Autumn season.
Image of Black Rock State Park, GA by Tom Wilson, USFS.
Changes in the Salt Lake region of Utah
Images of central Utah
were taken by NASA Terra satellite using a Multi-angle Imaging SpectroRadiometer
(MISR) camera on February 8, 2001 and June 16, 2001.
Salt Lake City is surrounded by mountains
including the Wasatch Range to the east, and the temperature difference
between the Great Salt Lake and the overlying atmosphere enhances the
moisture content of winter storms. These factors, in combination with
natural cloud seeding by salt crystals from the lake, are believed to
result in greater snowfall in neighboring areas compared to more distant
In addition to the obvious
difference in snow cover between the winter and summer views, water
color changes in parts of the Great Salt Lake are apparent in these
images. The distinctly different coloration between the northern and
southern arms of the Great Salt Lake is the result of a rock-filled
causeway built in 1953 to support a permanent railroad. The causeway
has resulted in decreased circulation between the two arms and higher
salinity on the northern side.