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Why Do the Seasons Lag In the northern hemisphere, June 21
Chapter 17, Problem 122P(choose chapter or problem)
Why Do the Seasons Lag? In the northern hemisphere, June 21 (the summer solstice) is both the longest day of the year and the day on which the sun’s rays strike the earth most vertically, hence delivering the greatest amount of heat to the surface. Yet the hottest summer weather usually occurs about a month or so later. Let us see why this is the case. Because of the large specific heat of water, the oceans are slower to warm up than the land (and also slower to cool off in winter). In addition to perusing pertinent information in the tables included in this book, it is useful to know that approximately two-thirds of the earth’s surface is ocean com-posed of salt water having a specific heat of 3890 J/kg · K and the oceans, on the average, are 4000 m deep. Typically, an average of 1050 W/m2 of solar energy falls on the earth’s surface, and the oceans absorb essentially all of the light that strikes them. However most of that light is absorbed in the upper 100 m of the Depths below that do not change temperature seasonally. Assume that the sunlight falls on the surface for only 12 hours per day that the ocean retains all the heat it absorbs. What will be the rise in temperature of the upper 100 m of the oceans during the month following the summer solstice? Does this seem to be large enough to be perceptible?
Questions & Answers
QUESTION:
Why Do the Seasons Lag? In the northern hemisphere, June 21 (the summer solstice) is both the longest day of the year and the day on which the sun’s rays strike the earth most vertically, hence delivering the greatest amount of heat to the surface. Yet the hottest summer weather usually occurs about a month or so later. Let us see why this is the case. Because of the large specific heat of water, the oceans are slower to warm up than the land (and also slower to cool off in winter). In addition to perusing pertinent information in the tables included in this book, it is useful to know that approximately two-thirds of the earth’s surface is ocean com-posed of salt water having a specific heat of 3890 J/kg · K and the oceans, on the average, are 4000 m deep. Typically, an average of 1050 W/m2 of solar energy falls on the earth’s surface, and the oceans absorb essentially all of the light that strikes them. However most of that light is absorbed in the upper 100 m of the Depths below that do not change temperature seasonally. Assume that the sunlight falls on the surface for only 12 hours per day that the ocean retains all the heat it absorbs. What will be the rise in temperature of the upper 100 m of the oceans during the month following the summer solstice? Does this seem to be large enough to be perceptible?
ANSWER:Solution 122P To find rise in temperature Step 1: Specific heat of Ocean water c = 3890 J/Kg Depth of the ocean where sunlight gets absorbed d = 100m Average solar energy falls on Earth’s surface Q = 1050 W/m 2 Time t = 12 h