Summer solstice - Answers Approximately June 21 in the Northern Hemisphere when the sun is highest
in the sky and directly overhead at latitude 23 1/2 N, the Tropic of Cancer.
Autumnal Equinox - Answers The equinox at which the sun approaches the Southern Hemisphere and
passes directly over the equator. Occurs around September 23.
Indian summer - Answers An unreasonably warm spell with clear skies near the middle of autumn.
Usually follows a substantial period of cool weather.
Winter solstice - Answers Approximately Dec. 21 in the Northern Hemisphere when the sun is lowest in
the sky and directly overhead at latitude 23 1/2 S, the Tropic of Capricorn.
Vernal equinox - Answers The equinox at which the sun approaches the Northern Hemisphere and
passes directly over the equator. Occurs around March 20.
Radiational cooling - Answers The process by which the earth's surface and adjacent air cool by emitting
infrared radiation.
Radiation Inversion - Answers An increase in temperature with height due to radiational cooling of the
earth's surface.
Nocturnal inversion - Answers An increase in temperature with height due to radiational cooling of the
earth's surface.
Thermal belts - Answers Horizontal zones of vegetation found along hillsides that are primarily the result
of vertical temperature variations.
Orchard heaters - Answers Oil heaters placed in orchards that generate heat and promote convective
circulations to protect fruit trees from damaging low temperatures.
Wind machines - Answers Fans placed in orchards for the purpose of mixing cold surface air with
warmer air above.
Freeze - Answers A condition occurring over a widespread area when the surface air temperature
remains below freezing for a sufficient time to damage certain agricultural crops. A freeze most often
occurs as cold air is advected into a region, causing freezing conditions to exist in a deep layer of surface
air. Also called advection frost.
Controls of temperature - Answers The main factors that cause variations in temperature from one place
to another.
Isotherms - Answers A line connecting points of equal temperature.