From the Old English word /bar/, meaning a straight piece of wood or metal that is longer than it is high or wide. More generally, /bar/ refers an object or mass of uniform composition that is greater in horizontal extent than vertical extent.

From the Latin and Greek stem /clino-/, meaning lean or slant. In meteorology, the state of the atmosphere in which layers of air having constant density intersect layers having constant pressure. On a weather chart, regions where isotherms are close together involve steep temperature and pressure gradients. Strong winds produce temperature advection (warming or cooling or air due to winds that cross the isotherms).

Also known as baroclinic wave, disturbance, or instability. Baroclinic instability is when a short wave disturbs the air flow, causing baroclinicity to arise instead of barotropism. There is a north to south temperature gradient and divergence aloft, contributing to the formation of mid-latitude cyclones.

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