Solar zenith angles Summer

Figure 3.22 shows the solar angle 0 as a function of true solar time for several latitudes and different times of the year. As expected, only for the lower latitudes at the summer solstice does the solar zenith angle approach 0° at noon. For a latitude of 50°N even at the summer solstice, 0 is 27°. 

FIGURE 3.22 Effect of latitude on solar zenith angle. On the scale of true solar time, also called apparent solar time and apparent local solar time, the sun crosses the meridian at noon. The latitudes and seasons represented are as follows I, 20°N latitude, summer solstice II, 35°N latitude, summer solstice III, 50°N latitude, summer solstice IV, 20°N latitude, winter solstice V, 35°N latitude, winter solstice VI, 50°N latitude, winter solstice (from Leighton, 1961). 

The smaller the solar zenith angle is, the less atmosphere (particularly ozone) the total solar flux passes through before reaching the troposphere, and therefore the greater the incident flux. The solar zenith angle has its minimum in the summer and maximum in the winter. The variation of solar zenith angle with latitude for a given season is less important than the seasonal variation. 

The winter noontime values of n(0H), n(HC>2), and n(CH202) decrease by a factor 3.5 from those calculated for the summer. The primary cause is an increase in the solar zenith angle, which decreases the intensity of ultraviolet radiation required to produce 0(1D). Because of lower winter temperatures, n(H20) also decreases but... 

Figure 4. Examples of direct and diffuse solar irradiance and a correction factor for diffuse path length in measurements (Hargreaves, unpublished). (A) Diffuse fraction of irradiance as a function of solar zenith angle during summer, 1996, L. Lacawac, Pennsylvania (41.3°N) and August 2001, Crater Lake, Oregon (42.9°N). (B) Calculated correction [17] to remove effects of irradiance field from near-surface diffuse attenuation (K ) measurements, based on data in part (A).

The monitored site lies between 47 20" northern latitude and 27 bO" eastern longitude (Figure 1). At this latitude incident solar zenith angles between the solar radiation and the Earth s surface of about 19 23 during the winter and 66°17 during the summer, at midday, are reached with a variation of about 47°. 

Figure 5.30. Observations of the vertical distribution of the hydroxyl density (cm-3) in the mesosphere (adapted from Summers et al. 1997). From top to bottom, the average solar zenith angles for each panel were 62°, 44°, and 53°.

Figure IX-A-2b. Plot of the solar zenith angle as a function of latitude and local time of the day for June 22, Summer solstice. Note that the Sun is above the horizon all the day in the high latitudes (from Calvert et al., 2008).

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