Answer to Question 1
+SW is incoming shortwave radiation from the sun; -SW is outgoing shortwave radiation from the sun that has been reflected; +LW is incoming longwave radiation emitted by the Earth, absorbed by atmospheric gases, and reradiated to the Earth's surface. -LW is outgoing longwave terrestrial radiation.
Answer to Question 2
The latitudinal imbalance in insolation results from differences in the angle of incoming insolation, day length, seasonal variations, and albedo. The area between the tropics has high sun angle, consistent day lengths, and little seasonal variation, resulting in an energy surplus. The poles have a low sun angle, high albedo (due to snow and ice cover), long periods of darkness, and large daily and annual temperature ranges, resulting in an energy deficit. These differences drive the global circulation patterns.