The most abundant gas in the atmosphere by volume is ---. This gas comprises 78% of the Earth Atmosphere by volume. A. Oxygen B. Argon C. Carbon Dioxide D. Nitrogen - Answer- D. Nitrogen The definition of a variable gas is a gas that varies significantly from time to time and place to place. The most significant variable gas by volume in the PBL is: A. Ozone B. Oxygen C. Water Vapor D. Carbon Dioxide - Answer- C. Water Vapor An isobar is a line of constant --- - Answer- Pressure Which of the following best explains how pressure decreases with height in the Earth's atmosphere? A. It decreases at a constant rate (linear) B. It decreases quickly at first then more gradually (Exponential) C. It decreases at a rate 9.8 mb/km D. It decreases in the troposphere, increases in the stratosphere, then decreases to the top of the atmosphere - Answer- B. It decreases quickly at first then more gradually (Exponential) In the vertical dimension, the upper level jet stream is located closest to which mandatory synoptic scale pressure level? A. The 850mb level (1,500 meters) B. The surface C. The 500mb level (5,500 meters) D. The 300mb level (9,500 meters) - Answer- D. The 300mb level (9,500 meters) The seasons of Spring, Summer, winter, and Fall are a direct result of which phenomenon? A. The sun's energy output and the Earth's proximity to the sun B. Shifting of ocean currents C. The 23.5° tilt of Earth from vertical D. The jet stream - Answer- C. Th