Say a man has stolen enough of my money to make me angry enough to want to kill him. If I am 10 miles away with a loaded gun when this event happens, I would have a motive (reason), means (the gun), but no opportunity (be physically close enough).
If I was standing next to that same man with nothing in my hands, and he is locked inside his car: I have no means because I cannot get to him inside the car, I have a motive because of what he has done, and I have the opportunity because he is close enough for me to kill him if I had say a gun (means).
If I was sitting inside the car with the man with a gun: I have means (the gun), I have motive (stealing my money), and I have the opportunity (sitting next to him in the car).
Effects of Mean Flow Direction on Energy, Isotropy, and Coherence of Baroclinically Unstable Beta-Plane Geostrophic Turbulence
Jan 01, 2004; ABSTRACT The effects of mean flow direction on statistically steady, baroclinically unstable, beta-plane quasigeostrophic (QG)...