וַיֵּ֨ט מֹשֶׁ֣ה אֶת־מַטֵּהוּ֮ עַל־הַשָּׁמַיִם֒ וַֽיהוָ֗ה נָתַ֤ן קֹלֹת֙ וּבָרָ֔ד וַתִּ֥הֲלַךְ אֵ֖שׁ אָ֑רְצָה וַיַּמְטֵ֧ר יְהוָ֛ה בָּרָ֖ד עַל־אֶ֥רֶץ מִצְרָֽיִם׃
And Moses stretched forth his rod toward heaven; and the LORD sent thunder and hail, and fire ran down unto the earth; and the LORD caused to hail upon the land of Egypt.
Sforno on Exodus
ותהלך אש ארצה, the atmosphere which had already been heated descended earthward with the same speed as the hail. [Normally, fire has a tendency to rise into higher levels of the atmosphere. Here, the reverse happened. Ed.]
Tur HaArokh
ויט משה את מטהו על השמים, ”Moses stretched his staff heavenwards.” According to Ibn Ezra, the word שמים here is an alternate for the word “atmosphere.” We also find the expression רקיע השמים as referring to the atmosphere and not to celestial regions.