Patent ID: 7654035

Claim:
A method for protecting crops in a first area of a stratified atmosphere from cold air in a surrounding area of the stratified atmosphere, the stratified atmosphere comprising a plurality of strata each of which has air of a different temperature with air in a stratum closest to the ground being coldest, the method comprising generating a pneumatic barrier to protect the crops (a) providing at least a first device for generating a pneumatic barrier in a stratified atmosphere to protect crops in a first area from cold air in a surrounding area, the stratified atmosphere comprising a plurality of strata each of which has air of a different temperature, the device comprising: a first structure comprising (i) a cylindrical portion with a circular or regular polygonal section, a lowermost rim and a vertical axis; (ii) a flared conic segment at the lowermost rim of the cylindrical portion and having a vertical axis that is the same as the vertical axis of the cylindrical portion, the conic segment flaring outwardly from the lowermost rim and ending in a flat, horizontal and open section; (iii) fan means disposed in the cylindrical portion for draining air from the stratified atmosphere through the open section and lowermost rim and for producing an outflow of air in an upward direction away from the lowermost rim and from the fan means; and (iv) outlet structure means disposed above the fan means for taking the upward outflow of air from the fan means and ejecting it from an outlet in the first structure with a mean velocity in an approximately horizontal direction to form a jet that has a horizontal plane of symmetry and a cross section that expands as it travels away from the outlet, contacts the ground and forms the pneumatic barrier to prevent cold air from the surrounding area from entering into the first area; and (v) support means for supporting the first structure on the ground in the first area with the open section of the flared conic section spaced above the ground a distance that causes the fan means selectively to drain into the first structure air from the stratified atmosphere that is coldest and (b) supporting the first structure of the device on the ground in the first area with the open section of the flared conic section spaced above the ground a distance that allows the fan means selectively to drain into the first structure air from the stratified atmosphere that is coldest; and (c) causing the fan means to drain the coldest air from the stratified atmosphere through the open section and lowermost rim and to produce an outflow of cold air in an upward direction away from the lowermost rim and through the outlet portion to form a first jet of cold air that has a horizontal plane of symmetry and a cross section that expands as it travels away from the outlet, contacts the ground at a boundary between the first area and a surrounding area and forms the pneumatic barrier at the boundary to prevent cold air from the surrounding area from entering into the first area.