Mountain-Top Vortices as Causes of Large Errors in Altimeter Heights

Abstract

There have been uncontradicted reports of large altimeter errors in the vicinity of high mountains. A brief survey of pressure distributions over an airfoil with flaps shows a maximum pressure drop below static pressure of twice the velocity head. Applying this ratio to a 14,000-foot mountain in a 100-mph wind a maximum error of 700 feet is indicated. This is important, but not enough to explain the occasional reports of 2 to 3,000-foot errors. Pressure drops of this magnitude exist in tropical cyclones, and even greater depression is known in tornadoes. The pressure drop at the ground surface is seen to have an axial connection with the natural low pressure aloft. The strength of the vortex is shown to depend on the outside tangential input by the wind where the whirl velocity can be very moderate, and the superspeed spin inside a vortex is shown to be dependent on radial inflow of air which is discharged along the vortex axis. Procedures are suggested for locating mountain tornadoes and thorough investigation urged so that the great hazards of mountain vortices in a strong wind will become generally known.