северному

северному

"Северному" means "to the northern" or "northern" in the dative case.

Here, 'северному' is an adjective modifying the noun 'другу,' indicating the direction of northern residence of the friend.

Я отправлю письмо северному другу.

I will send a letter to my northern friend.

In this sentence, 'северному' describes the coast, emphasizing its geographical location.

Маршрут ведёт к северному побережью.

The route leads to the northern coast.

Here, 'северному' modifies 'горизонту,' showing the direction of the horizon as related to the north.

Мы направляемся к северному горизонту.

We are heading toward the northern horizon.