Ambient Temperature Ambient temperature data are needed for the determination of the solar cell temperature, Equations (3-6). In this section we show yearly variation of the ambient temperature as well as diurnal variation of some particular Martian days. This information was supplied to us by Tillman [4]. Figure 3 shows the variation of the ambient temperature at Viking lander VL1 for part of the first year after landing. The top time coordinate (abscissa) has units of sol number, the number of Martian solar days from touchdown on sol 0 (1 sol = 24.65 h). The bottom abscissa is the seasonal date Ls. The diurnal ambient temperature variation at VL1 for sols 75 and 76 (summer), and sols 191 and 192 (autumn), are shown in Figs 4 and 5, respectively. The figures show large (60°) diurnal ambient temperature variation. Figure 6 shows the variation of the ambient temperature of Viking lander VL2 for the first year after landing. During dust storm events, the Martian atmosphere is strongly heated up by absorption of solar radiation due to the suspended dust. As a result, the maximum ambient temperature decreases significantly while the minimum increases, especially during the more intense 1977 B storm. The diurnal ambient temperature variation for sols 285 and 286 at the time of 1977 B global storm is shown in Fig. 7. The variation in temperature is rather small (16°). For the less intense 1977 A global storm, the diurnal temperature variation is larger (28°) as shown in Fig. 8, for sols 177 and 178; and for a local storm, the diurnal ambient temperature variation is still larger (38°), as shown in Fig. 9, sol 160. Insolation The insolation on the surface of Mars is composed of the direct beam and the diffuse components. The net solar flux integrated over the solar spectrum on the Martian surface was calculated by Pollack [5] based on multiple wavelengths and multiple scattering of the solar radiation. Derived data from this calculation are shown in Table I by the function f(z, r) where the parameters are the cosine of the zenith angle z and the optical depth t. This table pertains to albedo of 0.1 but can be used for higher albedo values to a first approximation. Using this data we calculated the global solar insolation. We assumed that the diffuse insolation is obtained by subtracting the beam from the global insolation, and we further assumed isotropic Martian skies.
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