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ON THE STRUCTURE OF PRESSURE SYSTEMS

G. J. HALTlNERU.S. Naval Postgraduate School, Monterey, Calif.

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LT. ROBERT F. ALDENU.S. Navy

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LT. GLENN C. ROSENBERGERU.S. Navy

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Abstract

The three-dimensional distribution of vertical velocity and “isobaric” velocity divergence are numerically evaluated for a number of synoptic situations using Northern Hemisphere data at 1000, 850, 700, 500, and 300 mb. The results indicate that in the typical migratory nondeveloping cyclone only moderate values of divergence exist both in the low and high troposphere with minimum values near 500 mb. On the other hand, a developing cyclone, which deepened markedly at sea level but only slightly in the upper troposphere, displayed much larger values of divergence and vertical velocity, about double; and the level of minimum divergence lowered to 600–700 mb.

In addition, a new pair of positive and negative divergence centers appeared parallel to the east coast of the United States prior to the intensification which took place in the immediate neighborhood.

Similar calculations for a blocking situation gave small values of vertical velocity and divergence in a broad area in the vicinity of the high pressure ridge as contrasted to the normal migratory anticyclonic system.

Finally, computations of thermal advection with the divergent wind showed it to be as much as half of the non-divergent advection at 850 mb., but relatively smaller at upper levels.

Abstract

The three-dimensional distribution of vertical velocity and “isobaric” velocity divergence are numerically evaluated for a number of synoptic situations using Northern Hemisphere data at 1000, 850, 700, 500, and 300 mb. The results indicate that in the typical migratory nondeveloping cyclone only moderate values of divergence exist both in the low and high troposphere with minimum values near 500 mb. On the other hand, a developing cyclone, which deepened markedly at sea level but only slightly in the upper troposphere, displayed much larger values of divergence and vertical velocity, about double; and the level of minimum divergence lowered to 600–700 mb.

In addition, a new pair of positive and negative divergence centers appeared parallel to the east coast of the United States prior to the intensification which took place in the immediate neighborhood.

Similar calculations for a blocking situation gave small values of vertical velocity and divergence in a broad area in the vicinity of the high pressure ridge as contrasted to the normal migratory anticyclonic system.

Finally, computations of thermal advection with the divergent wind showed it to be as much as half of the non-divergent advection at 850 mb., but relatively smaller at upper levels.

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