Notes: Equatorial region – Doldrums or equatorial belt of calms, area around the earth centered slightly north of the equator between the two belts of trade winds. The large amount of solar radiation that arrives at the earth in this area causes intense heating of the land and ocean. This heating results in the rising of warm, moist air; low air pressure; cloudiness; high humidity; light, variable winds; and various forms of severe weather, such as thunderstorms and squalls. Hurricanes originate in this region. The doldrums are also noted for calms, periods when the winds disappear, trapping sailing vessels for days or weeks.