What would indicate that an aircraft is experiencing downdrafts in a thunderstorm?

The presence of growing raindrops is a strong indicator of downdrafts within a thunderstorm. In the context of a thunderstorm, downdrafts are caused by the cooling effects of precipitation and the descent of cool air from upper levels of the storm. As rain falls, the process can lead to the accretion of larger raindrops due to the collision and coalescence of smaller droplets. This increase in the size of raindrops typically signifies that the storm is producing stronger downdrafts, as the intense updrafts associated with the storm can create conditions favoring the growth of larger raindrops before they fall to the ground.

The other options do not accurately indicate downdrafts. An increase in temperature would generally suggest stable atmospheric conditions rather than the turbulent conditions associated with downdrafts. Clear skies would indicate a lack of thunderstorms and hence the absence of such downdraft activity. Dissipating clouds suggest that the thunderstorm is weakening and that downdrafts are likely decreasing rather than intensifying. Thus, observing growing raindrops provides the clearest indication of downdrafts in the context of thunderstorms.