 One of the important objectives from the lesson is to be able to calculate a simple radiation budget and interpret the calculations in terms of temperature trends for an object. So I want to walk you through the basic idea of a radiation budget and quick sample calculation. So to start with, radiation budgets are very simple. You can think about them just like the balance in your bank account. The balance in your bank account, to figure it out, you would just take the initial amount of money you have and you would add the deposits and subtract your withdrawals. So for example, if you start with $100 and you deposit another $100 and then withdraw 50, your balance would increase to $150 because you started with 100, you added 100 through a deposit and then you subtracted $50 through withdrawal to give you $150 and you would have a net gain of money because more money came into the account than you took out of the account. On the other hand, if you start with $100 again and then you deposit $50 and withdraw 100, your balance would decrease to $50 because you started with 100, you added 50, and then you subtracted 100 to give you 50. You would have a net loss of money because you took more money out of the account than you put into the account through deposits. Radiation budgets are very similar. If an object absorbs more radiation than it emits, then its temperature will increase. It will have a net warming because more radiation is coming in than is going out. On the other hand, if an object absorbs less radiation than it emits, its temperature will decrease. It will experience a net cooling because more radiation is going out than is coming in and being absorbed. So to figure out a net gain or loss of radiation, you would take your absorbed radiation and then subtract the emitted radiation. And a net gain in radiation or a positive value would yield a warming and a net loss of radiation would yield a cooling. That would be a negative result for that calculation. So here's an example. This graph is from Penn State University on December 12th, 2013, and the red curve shows downwelling solar radiation. That's incoming solar radiation that's coming to the ground and being absorbed. The blue curve shows downwelling infrared radiation, which is radiation coming into the earth from clouds and invisible gases in the atmosphere. And then the green curve shows upwelling infrared radiation, which is radiation that's being emitted from the earth. So we look at our calculation to figure out a net gain or loss of radiation. We just have to take our absorbed radiation and subtract the emitted radiation. And say we want to do this calculation at local noon, which is 17 Z at Penn State during standard time. So to figure out our equation, first we have to just figure out what our sources of incoming radiation are. Well, that would be downwelling solar and downwelling infrared, the red curve and the blue curve. And we just have to read values from the graph. So the incoming solar radiation would be about 470 watts per meter squared at local noon, that's 17 Z. And the downwelling infrared radiation would be about 180 watts per meter squared at 17 Z. Now the emitted radiation, that's the upwelling infrared on the green curve, would be about 280 watts per meter squared. So we would put that in our calculation to figure out our net gain or loss of radiation. And we would have our 470 watts per meter squared, that's the incoming solar. We would add the 180, that's our downwelling infrared, and we would subtract 280, which was our upwelling infrared. If you do the calculation, we get a positive result, that's 370 watts per meter squared. So since we had a positive result, that means we had a net gain in radiation, more radiation is coming in and being absorbed than is being emitted. So temperatures would increase at local noon on this particular day. Now there are other factors that impact temperature, but we're going to ignore those for the sake of this discussion. In this example we're just going to focus on radiation's contribution to temperature trends. So on this particular day, because on this particular time, more radiation is coming in than is going out, there's a net gain in radiation and temperatures would be increasing. Now note that there's a long period of time here where incoming solar radiation is zero. That corresponds to the nighttime hours when the sun's not up. So if you were doing a calculation at nighttime, your incoming solar value would be zero, and you'd be really looking at the downwelling infrared versus the upwelling infrared to do your calculations at nighttime.