1)
What arrows did Hashem send?
1.
Rashi: Refer to Shmuel II, 22:13:1:1 and the note there.
2.
Radak: They (and the lightning) are harsh decrees.
3.
Malbim: The lightning shattered the clouds, and they scattered and spilled their water. It is as if Hashem sent arrows to dispel the clouds.
2)
What is the meaning of "u'Verakim Rav va'Yhumem"?
1.
Radak: "Rav" is shooting arrows, like "va'Ymareruhu va'Robu" (Bereishis 49:23). He confounded the enemy via shooting arrows at them.
