What is the Harmattan wind, which frequently impacts aviation operations in Ghana and West Africa?

1. A dry, cool, and dusty northeasterly trade wind blowing from the Sahara Desert
2. A warm, humid southwesterly monsoon wind blowing from the Gulf of Guinea
3. A strong sea breeze that occurs along the coast of Accra during summer afternoons
4. A cyclonic wind storm that originates in the Indian Ocean and crosses East Africa