What is the expected descent behavior if a balloon inadvertently descends into stratus clouds and is shielded from the Sun?

When a balloon enters stratus clouds and is shielded from the Sun, its expected behavior is to descend more rapidly. This occurs because stratus clouds typically contain a significant amount of moisture and cooler air. When a balloon moves into this denser, cooler air, the overall buoyancy is affected.

In a cloud environment, the temperature generally lowers as altitude decreases, and since warm air is less dense and provides lift, the transition from warmer air to cooler, denser air leads to a reduction in lift. The balloon's helium or any lighter-than-air gas is less effective in providing buoyancy in this colder air, resulting in a quicker descent.

The other potential choices do not align with the physics of balloon flight in dense air currents typical of cloud layers. A balloon cannot maintain altitude while surrounded by cooler, denser air nor can it descend more slowly, as the cooling effect begins immediately upon encountering cloud cover. Similarly, it is not possible for the balloon to ascend slightly without a source of heating or lift to counteract the increased density of the surrounding air.