What do we learn from "ha'Mekareh va'Mayim Aliyosav"?
Radak #1: This hints to the water above the Raki'a 1 .
Radak #2: This refers to clouds, which are Aliyos (upper stories); they are like a ceiling over the land.
Malbim: It begins to explain how the Raki'a was made. The water was made like a ceiling of a building. Above it is an upper story. From there and above pertains to Shamayim's domain. Living beings cannot breathe there. Also, they are called Aliyos due to the Aliyah (ascent) of the vapors.
Radak: Researchers say that there is no water above the Raki'a. They have another Perush of "ha'Mayim Asher me'Al la'Raki'a" (Bereishis 1:7). Refer to 104:3:1:2.
Why does it say "ha'Sam Avim Rechuvo"?
Radak: The matter is repeated in different words. "Rechuvo" teaches that through His Ma'amar and desire, the clouds go quickly back and forth, like an animal that goes like the desire of its rider.
Malbim: The vapors ascend and gathered in a place of rain. When they get hot, clouds form. It is as if Hashem rides on this light cloud - "Hinei Hashem Rochev Al Av Kal" (Yeshayah 19:1).
What do we learn from "ha'Mehalech Al Kanfei Ru'ach"?
Radak: This teaches that the wind pushes the clouds quickly to the direction that the wind is blowing. The wind goes according to Hashem's desire, as if it goes on His wings.
Malbim: This chariot [on which Hashem 'rides'] goes on wings of wind. In place of horses to pull the chariot, wings of wind pull it. I.e. they carry the clouds from place to place.