Translation guide
In Japanese, 'this morning' is most naturally expressed as 今朝 (けさ). Unlike English, the word 'this' is not separately translated; it is built into the word 今朝. In many contexts, the time word alone is sufficient, and no additional particles like 'in' or 'on' are needed.
this morning
To talk about something that happened or will happen during the morning of today.
Do not translate 'this morning' as この朝 (このあさ). While grammatically possible, it is unnatural and rarely used. The standard word is 今朝 (けさ).
I woke up early this morning.
What did you eat this morning?
Literally 'today's morning'. It is less common than 今朝 but can be used for emphasis or in certain contexts. It may sound slightly more explanatory.
This morning was very cold.