The air in the troposphere doesn't actually "heat up the sun." The sun is a giant ball of burning gas, and its heat comes from nuclear fusion in its core. The sun doesn't get heated by the Earth's atmosphere.

However, here's what happens to the air in the troposphere when it gets heated by the sun:

1. Expansion: When the air is heated, the molecules move faster and spread out, causing the air to expand. This makes it less dense.

2. Convection: As warm, less dense air rises, it creates areas of low pressure. Cooler, denser air from higher up flows in to fill the void, creating a cycle of convection currents. These currents drive weather patterns like winds and storms.

3. Evaporation: Heat from the sun also increases evaporation of water from oceans, lakes, and rivers, leading to increased humidity in the air. This water vapor can later condense to form clouds and precipitation.

4. Weather Patterns: The uneven heating of the Earth's surface, along with the rotation of the Earth, creates large-scale weather patterns like jet streams, which influence the distribution of heat and moisture around the globe.

So, the air in the troposphere doesn't heat the sun, but the sun's energy does cause the air to expand, rise, and circulate, creating the weather patterns we experience.