Insolation and Net Radiation

Lab 4 Insolation and Net Radiation

Due: 11:59pm, Sept. 12, 2015

Please type your answers in Word, and print out the blank graphs, and draw the graphs by

hand, and then scan the completed graphs (or take pictures of your answers if you don’t have

a scanner) as images. And then insert the images into the Word file. Submit it to the folder of

Lab 4 in the Dropbox on the homepage of the course on D2L in the following format:

If Mary Smith is submitting lab 4, please name the file as MarySmith_lab4.doc.

Purpose

The purpose of this lab is for you to understand annual cycle of insolation and daily cycle of

net radiation.

Background

Insolation is the amount of solar radiation that reaches the earth surface. The annual cycle of

insolation at a given location on the globe depends on two factors: (a) the latitude at which the

observer is located and (b) the sun’s changing angle above the horizon at noon, which is caused

by the movement of subsolar point.

Net radiation is the difference between incoming and outgoing flows of solar radiation. The

daily cycles of net radiation at a given location on the global depends on the changing incoming

and outgoing flows of radiation in the course of a day. It is called radiation surplus when

incoming radiation is larger than outgoing; It is radiation deficit when outgoing larger than

incoming. Air temperature change is associated with the change in net radiation.

Assignment

1 The Annual Cycle of Insolation

(1) Table 1 gives the latitude of the subsolar point at ten-day intervals throughout the year. Plot

theses points on the blank graph (A) and connect them with a smooth curve. (10 points)

(2) Table 2 gives the intensity of insolation at various latitudes throughout the year. Plot these

monthly values for the following latitudes: 0°, 20°N, 40°S, 60°N, 90°N on the blank graph

(B). Enter the data point in the middle of the month as shown on the partially drawn line for

60°N. Connect the points with a smooth curve and label the latitude. (20 points)

2

Table 1 The latitude of subsolar point throughout the year

Table 2 Insolation throughout the Year (one unit is 889 gram calories per square

centimeter)

Date Subsolar Point Date Subsolar Point

3

S u

b so

la r P

o in

t

4

(3) Study the insolation curves in relation to the annual curve of the subsolar point.

Compare times of maximum and minimum values at 60°N and 40°S. Explain how these two

curves differ in timing. (10 points)

(4) Explain how the maximum and minimum of insolation at the equator are related to the

curve of the subsolar point. (10 points)

(5) Compare the insolation curves of 20°N and 90°N. Explain how these two curves differ

in timing. (10 points)

su b

so la

r p

o in

t

5

2 The Daily Cycle of Net Radiation

(1) Table 3 gives the net radiation at the ground and air temperature for a station in the

Midwestern US at about latitude 40°N on a day in mid-August. Sunrise occurred at 5:15am;

sunset about 6:50pm local time. Plot the data points on the blank graph C and connect them

with smooth curves. Use the upper graph for net radiation; use the lower graph for air

temperature. (20 points)

Table 3 Net radiation and air temperature for a station

(2) Please label the areas of radiation deficit and surplus on the upper graph

Estimate the time at which deficit changed to surplus: .

Estimate the time at which surplus changed to deficit: . (10 points)

(3) Estimate the time of occurrence of minimum temperature from the lower graph: .

Explain the time of minimum temperature in terms of net radiation curve. (5 points)

(4) Estimate the time of occurrence of maximum temperature from the lower graph: .

Explain the time of maximum temperature in terms of net radiation curve. (5 points)

14

6

Graph C