What is "ba'Yom ha'Hu"?
Malbim The day of punishment.
What is the significance of breaking the bow of Yisrael?
Radak: I will break their strength and power. The prefix Vov in "v'Shabarti" is an addition to "v'Hishbati" (4).
Radak citing Targum Yonasan: I will break the strength of those who make war in Yisrael.
Malbim #1: This refers to Malchus Yehu. He became king via his bow ? he used it to kill Yehoram, and seized kingship (Melachim II, Perek 9).
Malbim #2: This refers to the bow that Elisha gave to Yo'ash Melech Yisrael (Yaravam's father) to shoot arrows; it will be an arrow of salvation to defeat Aram. Via this bow he defeated Aram and became powerful in his kingship.
Why will this be "b'Emek Yizre'el"?
Radak: The head of Malchus Efrayim was in Shomron and Yizre'el. Achav's palace was there, and also the kings after him.
Malbim: It is the place fixed to punish idolaters.
