What can I do to help my bipolar dad?

My dad has been depressed lately, not working because he's a Carpenter so in the winter time he doesn't get many calls, and he's been being very rude to my mom and taking out his anger on her and accusing her of cheating even though there is no way that she is. He just makes a big deal out of everything. Shes tried to talk to him about getting a more appropriate dose of antidepressant meds (which he takes but they aren't working) and shes talked to him about getting a small part time job for the winter, he just starts a fight every time she tries to talk to him about it. He's been this way for most of my life but right now it's been a lot worse. When he isn't depressed he is still bipolar, yelling at people for no reason out of the blue and bringing up anything he could possibly think of. I'm only fifteen and I don't know what I can do to help him. I just know I cannot put up with this much longer, because I'm starting to feel depressed. Any ideas to help me help my dad out?