Question

This photo shows a snow-covered area in the middle latitudes on a sunny day in late winter. Assume that 1 week after this photo was taken, conditions were essentially identical, except that the snow was gone. Would you expect the air temperatures to be different on the two days? If so, which day would be warmer? Suggest an explanation.

Short answer

Yes, the day without snow would be warmer due to increased solar energy absorption by the ground.

Step-by-step solution

Analyze Surface Characteristics

Snow is highly reflective and has a high albedo, meaning it bounces back most of the sunlight instead of absorbing it as heat. Without snow, the surface (such as soil or vegetation) absorbs more sunlight and converts it into heat.

Examine Impact on Air Temperature

With the removal of snow, the surface absorbs more solar energy and has a lower albedo. This absorbed energy heats the ground, which in turn warms the air above it.

Compare Temperatures Between Two Days

Since the ground absorbs more energy without the snow, the temperature on the day without snow is likely to be warmer compared to the day with snow. The snow-covered day reflects sunlight, keeping the atmosphere cooler.

Provide an Explanation

The higher air temperature on the day without snow can be explained by the increased absorption of solar energy by the bare ground. The absence of snow allows the ground to heat up more than when the snow was present.

Key concepts

Solar Energy Absorption

Every day, the Earth receives energy from the sun, which we call solar energy. This energy is crucial because it keeps our planet warm enough to support life. However, how much of this solar energy is absorbed by the Earth depends on various factors, especially the type of surface that sunlight hits.
When sunlight reaches a surface, it can either be absorbed or reflected. If a surface absorbs sunlight, this energy is converted into heat, warming up the surface and, subsequently, the surrounding air. For example:

• Soil or vegetation can absorb a significant amount of sunlight.
• Dark surfaces tend to absorb more sunlight than light surfaces.
• Water bodies also absorb sunlight but reflect less than some surfaces like snow.
  

In contrast, reflective surfaces, like ice or snow, bounce back much of the sunlight, absorbing less energy. Therefore, the type of surface significantly affects solar energy absorption.

Surface Characteristics

The characteristics of a surface play a pivotal role in determining how much sunlight it absorbs or reflects.
For instance, snow is known for its high reflectivity due to its bright white surface. It has a high albedo, meaning it reflects a large percentage of the sunlight back into the atmosphere. Because of this reflection, less solar energy is absorbed, making the overall environment cooler than it would be without snow.
On the contrary, surfaces like soil or vegetation have a lower albedo and absorb more sunlight. Absorbing sunlight means these surfaces heat up quickly and pass this heat to the air above them, increasing atmospheric temperatures. When snow melts and reveals these surfaces, the increase in absorbed energy is considerable, leading to warmer ground and air temperatures.

Impact on Air Temperature

The temperature of the air is directly influenced by the energy absorbed by the Earth's surface. When a surface absorbs solar energy, it heats up and transfers this warmth to the air nearby through a process called conduction. This is why dark surfaces that absorb a lot of sunlight tend to make the environment warmer.
In scenarios where snow is present, the air temperature tends to remain cooler for a couple of reasons:

• Snow reflects sunlight, decreasing the overall absorption of solar energy.
• With less energy absorption, less heat is available to be transferred to the air.
  

Once the snow is gone, surfaces like soil or vegetation are exposed. These have a lower albedo than snow and absorb more energy, leading to increased ground temperatures. This rise in temperature is then transferred to the air, warming the overall environment.

Snow Reflectivity

Reflectivity, often measured by albedo, is a critical property of snow that affects climate and local temperatures.
Snow, especially fresh snow, can reflect up to 90% of the incoming sunlight. This means only a small fraction of solar energy is absorbed, and thus, snow-covered regions often remain much cooler than their snow-free counterparts.
The snow's ability to reflect sunlight plays a significant role in regulating the Earth's temperature. Consider the following:

• The high reflectivity leads to a lower temperature in regions covered by snow.
• This effect becomes more significant in larger areas, affecting climate patterns globally.
• When snow melts, the exposed dark surfaces absorb more solar energy, reducing the reflectivity and causing temperatures to rise.
  

The melt of snow is a transition phase where the Earth's surfaces move from high to low reflectivity, directly impacting air temperatures by increasing the amount of absorbed solar energy.