How could Jesus be able to continue His miracle ministry after He ascended into heaven to sit down at the right hand of God the Father?

Answer 1

Basically, Jesus performed miracles so that people would believe He came from God (He said in John 14:11: "Believe me when I say that I am in the Father and the Father is in me; or at least believe on the evidence of the miracles themselves."). Now that He is with the Father, the Holy Spirit has taken over that job.

This is what Jesus said to His friends shortly before He died:

"Now I am going to him who sent me, yet none of you asks me, 'Where are you going?' Because I have said these things, you are filled with grief. But I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor {the Holy Spirit} will not come to you; but if I go, I will send him to you. When he comes, he will convict the world of guilt in regard to sin and righteousness and judgment: in regard to sin, because men do not believe in me; in regard to righteousness, because I am going to the Father, where you can see me no longer; and in regard to judgment, because the prince of this world {Satan} now stands condemned. I have much more to say to you, more than you can now bear. But when he, the Spirit of truth, comes, he will guide you into all truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. He will bring glory to me by taking from what is mine and making it known to you." (John 16:5-14)