Astudent who grew up in a tropical country and is studying in the united states may have no experience with static electricity sparcs and shocks until his or her first american winter. why is that so?

Since tropical countries have humid air, which is full of water vapor, it neutralizes charge and electricity, so it is usually impossible to experience static electricity sparks and shocks because it is always hot.
In America, however, especially during winter months, it is obviously not as hot, so the air is not humid, thus these sparks and shocks can be created.