The banner like clouds and resembles the bow of Akhandal (Indra) which divides the sky and earth. See how Karna sends hosts of arrows like clouds pouring down rain as he is advancing fulfill the intention of Dhritarashtra's son.
आखण्डलधनुः प्रख्यमुल्लिशन्तमिवाम्बरम्। पश्य कर्ण समायान्तं धार्तराष्ट्रप्रियैषिणम्॥ शरधारा विमुञ्चन्तं धारासारमिवाम्बुदम्।