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Junction-to-local-ambient thermal resistance typically exhibits appreciable variation with the velocity of the air flow on the component. Natural convection is influenced by the orientation of the component and its power dissipation; forced convection is affected by the local air pressure gradient. The isothermal surfaces in the vicinity of the component are specifically linked to the type of thermal resistance measured. For example, the isothermal surfaces in natural convection cooling are dramatically different than those in forced convection. Therefore, junction-to-ambient thermal resistance measurements must include specifications of the air flow conditions.