Earth as a System | Class 9 Science Notes

13.1.1 Interaction of solar radiation on the Earth's surface

Different surfaces on Earth absorb and reflect solar radiation differently, affecting local temperatures. Land heats up faster than water because of differences in specific heat capacity. Dark-colored surfaces absorb more sunlight and become warmer, while light-colored surfaces reflect more and stay cooler. This property is quantified as albedo, the fraction of solar radiation reflected by a surface. High albedo surfaces like snow (0.80–0.90) and ice (0.50–0.70) reflect most sunlight, keeping polar regions cold. Low albedo surfaces like black soil and ocean water absorb more heat, making them warmer. Urban areas experience the 'urban heat island effect' where concrete, asphalt, and steel absorb and retain heat, raising city temperatures compared to rural surroundings. This effect increases energy demand for cooling and stresses urban ecosystems. The uneven heating caused by albedo differences and Earth's spherical shape leads to temperature variations with latitude, influencing atmospheric conditions and weather patterns. The Earth's tilt also causes seasonal changes in solar radiation received at different latitudes, further affecting climate and natural processes.

📊 Diagram: Fig. 13.5: Solar radiation and warming of the Earth illustrating absorption and reflection by different surfaces; Fig. 13.6: Urban heat island effect in a city showing temperature differences between urban and rural areas.

🧪 Activity: Activity 13.2: Complete Table 13.1 by researching albedo values of materials like snow, ice, crushed rock, light and black soil, and ocean water.

🔗 Connection: This section connects to the next discussion on how latitude and Earth's shape influence solar radiation distribution and atmospheric processes.