Japanese manner Greeting on the letter

  I  teach you something about Japanese letter.
When you write a private forman letter, Japanese people write
a certain phrase at the beginning of the letter.
Usually, the phrase is related to the season.
  For example, if you write a letter in winter,
you begin with the phrase, " It is getting colder, how are you doing?"
There are hundred kinds of  phrases in each season.
As you know, you can enjoy various changes of seasons.
Because of this cultural background, Japanese expressions
are formed.