GEOG 111 1st Edition Lecture 4 Outline of Last Lecture I. Solar and Terrestrial RadiationII. Radiation Lawsa. Stefan-Boltzmann Lawb. Weins LawIII. SunspotsIV. Earth-atmosphere influences on radiationa. Absorptionb. Reflectionc. ScatteringOutline of Current Lecture I. Two components of solar radiationa. Direct beamb. Diffuse lightII. Factors of Atmospheric TransmissivityIII. Earth-Sun Geometry Current LectureI. Solar radiation can be partitioned into two components:a. Direct beam- divided into light and dark, directly from the sun (when clouds block direct beam they create shadows)b. Diffuse light- “sky light” from diffused radiationi. As wavelengths from the sun are scatteredc. Inverse relationship between direct beam and diffusei. Less scattering: high direct beam, low diffused light dark blue skyii. More scattering: low direct beam, high diffused light lighter blue skyII. Three controlling factors of atmospheric transmissivity (the ease with which radiation is transmitted through the atmosphere; can be visible light or infrared radiation from the Earth):1. Clouds: no direct beam, all diffuse2. Haze (microscopic particles, aerosols in the sky): direct beam decreases, diffused light increasesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.3. Elevation (atmosphere is thinner at higher altitudes so less light gets scattered and the sky is a darker blue): direct beam increases,diffused light decreasesii. What color is the sky during a typical day on the moon?1. Black because there is no scattering taking placeII. Earth-Sun Geometrya. Seasonal changes in earth-sun geometry controls the intensity of solar radiation and the length of the dayb. Two independent motions affect earth-sun geometry:i. Rotation- counterclockwise (West to East); goes 360 degrees in 24 hours1. This is why we have time zones2. We go later in time to the east (Europe is ahead of us) and earlier in time to the west. The sun rises and sets later on the western edge of a time zone region and earlier on the eastern edge of a time zone region. ii. Revolution- the earth revolving around the sun on the plane of the ecliptic1. Takes 365.25 days2. Due to the earth’s elliptical path (not a perfect circle), the distancebetween the earth and sun varies during the year3. Perihelion- around January 3a. Earth is closest to the sunb. 147, 500, 000 km4. Aphelion- around July 4a. Earth is farthest away from sunb. 152, 500, 000
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