el niño vs. la niña

whats the difference between el niño and la Nia? here are the definitions for both:

el niño: an irregularly occurring and complex series of climatic changes affecting the equatorial Pacific region and beyond every few years, characterized by the appearance of unusually warm, nutrient-poor water off northern Peru and Ecuador, typically in late December.

la Niña: a cooling of the water in the equatorial Pacific that occurs at irregular intervals and is associated with widespread changes in weather patterns complementary to those of El Niño, but less extensive and damaging in their effects.