What was the easterly wind in Battle of Red Cliffs that night?

Based on the classic novel Romance of the Three Kingdoms. Jiang Gan was tricked into borrowing a knife by Zhou Yu for stealing a book. Cao Cao killed Cai Mao and Zhang Yun by mistake. Cao Cao regretted it, so he sent Cai Mao's brothers Cai Zhong and Cai He to surrender. Zhou Yu discovered his scam, so he played along and kept them. So, Yu and Dongwu veteran Huang Gai came up with a trick to cheat. Kong Ming borrowed an arrow to return to camp, and Zhou Yu gave a banquet to celebrate. Talking about military affairs during the dinner, Huang Gai deliberately insisted on Cao Cao; Zhou Yu pretended to be furious and hit Huang Gai. After Huang Gai was beaten, he asked the doctor Kan Ze to find Cao Cao's surrender. Cao Cao found that there was fraud in the letter and wanted to kill Kan Ze. But Kan Ze was quick-witted and calm, and answered calmly. At this time, Cai Zhong and Cai He told Cao Cao the news that Zhou Yu had beaten Huang Gai. Cao Cao told Huang Gai to surrender, but he was still not at ease. He ordered Jiang Gan to cross the river again to find out the truth. Zhou Yu and Kong Ming have already decided to attack Cao Cao with fire. Now that they have heard that Jiang Gan is coming again, they urgently called Pang Tong to make a series of plans. As soon as Jiang Gan arrived in Zhou Ying, he was sent to the Western Mountain Maoan by Zhou Yu. He wandered out at night and met Pang Tong. Tong deliberately said that Zhou Yu would not tolerate others, and Jiang Gan persuaded Pang Tong to return to Cao. The two sneaked back to Jiangbei overnight. Pang Tong advised Cao Cao to chain the warships of the Minjiang River in rows, so that the northern army, which was not used to sailing, could have a water fight and have a big celebration. The nail of the warship was locked, and Cao Cao went down the river this time to wipe out Wu Dong. General Yan Jiang. On Dongshan, Enemy at the Gates, Cao Cao looked ahead and wrote a poem. Zhou Yu was very proud to see Cao Cao's series of tricks and watch them from the river. This time, he will definitely break Cao Cao. Unexpectedly, a northwest wind woke him up. Wujun is in the southeast and Cao Jun is in the northwest. At this time, if you attack with fire, you will burn yourself instead of breaking the enemy, so you will become anxious. When Lu Su saw that the general was ill, he turned to Zhuge Liang for help. Kongming lied that he could cure the disease and wrote a letter to Zhou Yu, "If you want to break Cao Bing, you must attack with fire; Everything is ready, only the east wind. " When Zhou Yu saw it, the sick body suddenly recovered. Kong Ming said he could borrow the east wind. Ask Zhou Yu to build a platform for him to worship the wind in Nanping Mountain. On the day of Jiazi, the east wind really blew. Zhou Yuyuan sent soldiers to ambush behind the mountain. When the east wind gathered, he killed Kongming. When he saw the east wind blowing together, he quietly fled to the river and ordered the general to prepare a boat to meet him and turn to Xiakou.