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- Author or Editor: E. Palmén x
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Abstract
Systematic studies of certain meridional cross sections carried out at the University of Chicago indicate that the westerlies in the upper troposphere and at the level of the tropopause often show a very narrow zone with extremely strong winds in the region above the frontal layer between the subtropical and the polar air. An example showing the method of analysis and its principal results is given. The stability of the strong westerly current (the “jet stream”) in this type of zonal air flow and the corresponding temperature distribution at the level of 200 mb are discussed.
Abstract
Systematic studies of certain meridional cross sections carried out at the University of Chicago indicate that the westerlies in the upper troposphere and at the level of the tropopause often show a very narrow zone with extremely strong winds in the region above the frontal layer between the subtropical and the polar air. An example showing the method of analysis and its principal results is given. The stability of the strong westerly current (the “jet stream”) in this type of zonal air flow and the corresponding temperature distribution at the level of 200 mb are discussed.
Abstract
The surface stress in tropical storms is computed as a function of the radius, from mean wind data in the troposphere. If only the symmetrical part of the circulation is considered, the stress ranges from 1 dyne per square centimeter in the outskirts to 20 dy/cm2 at a distance of 1 degree latitude from the center. Inclusion of the mean asymmetry of the wind field, resulting from superposition of steering current and vortex, yields values about 20 per cent higher.
The absolute angular momentum budget shows that most net inward momentum transport is carried by the symmetrical part of the circulation near the core, and that the asymmetrical part contributes up to 50 per cent at a distance of 6 deg lat from the center. Calculation of the angular momentum transport due to the earth's rotation in inflow and outflow layers shows that the vertical momentum transport is directed upward everywhere; outside the 2-deg radius, this transport is accomplished by eddies.
Generation and dissipation of kinetic energy are calculated. The generation depends on the vertical correlation between radial flow component and pressure gradient which, for production of kinetic energy, must be positive, i.e., the strongest inflow must occur at the strongest inward directed pressure gradient. This shows that kinetic energy production within the cyclone can take place only if the cyclone is of the warm core type.
Next, the importance of a local heat source at the ocean surface for production of the observed inward warming in the rain area is discussed, and a relation between the local heat source and the central pressure is given. A general energy balance shows that about 3 per cent of the latent heat released is converted to kinetic energy, and that a considerable export of potential plus internal energy takes place from tropical storms.
Abstract
The surface stress in tropical storms is computed as a function of the radius, from mean wind data in the troposphere. If only the symmetrical part of the circulation is considered, the stress ranges from 1 dyne per square centimeter in the outskirts to 20 dy/cm2 at a distance of 1 degree latitude from the center. Inclusion of the mean asymmetry of the wind field, resulting from superposition of steering current and vortex, yields values about 20 per cent higher.
The absolute angular momentum budget shows that most net inward momentum transport is carried by the symmetrical part of the circulation near the core, and that the asymmetrical part contributes up to 50 per cent at a distance of 6 deg lat from the center. Calculation of the angular momentum transport due to the earth's rotation in inflow and outflow layers shows that the vertical momentum transport is directed upward everywhere; outside the 2-deg radius, this transport is accomplished by eddies.
Generation and dissipation of kinetic energy are calculated. The generation depends on the vertical correlation between radial flow component and pressure gradient which, for production of kinetic energy, must be positive, i.e., the strongest inflow must occur at the strongest inward directed pressure gradient. This shows that kinetic energy production within the cyclone can take place only if the cyclone is of the warm core type.
Next, the importance of a local heat source at the ocean surface for production of the observed inward warming in the rain area is discussed, and a relation between the local heat source and the central pressure is given. A general energy balance shows that about 3 per cent of the latent heat released is converted to kinetic energy, and that a considerable export of potential plus internal energy takes place from tropical storms.
Abstract
The period of 3–7 February 1947 was marked by a radical change in the circulation over North America from westerly flow with only small perturbations to a pattern dominated by large warm anticyclones over the northern part of the continent and an unusually large cold cyclone covering the eastern part of the United States and southeastern Canada. Analyses, particularly of the 5OO- and 200-mb surfaces, and vertical cross sections for this period are shown, with an especially complete three-dimensional analysis for 5 February. The wind and temperature distribution during the period are discussed, with emphasis on the principal polar front, the tropopause surfaces, the jet stream, vertical motions (especially in the lower stratosphere), and the large-scale meridional exchange of air masses connected with the breakdown of the zonal flow and the formation of warm highs in the north and a cold low in the south.
Abstract
The period of 3–7 February 1947 was marked by a radical change in the circulation over North America from westerly flow with only small perturbations to a pattern dominated by large warm anticyclones over the northern part of the continent and an unusually large cold cyclone covering the eastern part of the United States and southeastern Canada. Analyses, particularly of the 5OO- and 200-mb surfaces, and vertical cross sections for this period are shown, with an especially complete three-dimensional analysis for 5 February. The wind and temperature distribution during the period are discussed, with emphasis on the principal polar front, the tropopause surfaces, the jet stream, vertical motions (especially in the lower stratosphere), and the large-scale meridional exchange of air masses connected with the breakdown of the zonal flow and the formation of warm highs in the north and a cold low in the south.
Abstract
An attempt is made to study, by means of a detailed synoptic analysis, the three-dimensional air-motion in a typical outbreak of a polar air-mass. The mean vertical velocities at different levels over the entire cold-air region south of latitude 45°N are computed by use of the principle of continuity of mass. The maximum mean subsidence is found to be nearly 2 km per day at about the 600-mb level. In addition, the distribution of vertical velocity in different parts of the cold tongue is computed by means of trajectories on isentropic surfaces, and some examples of characteristic three-dimensional air trajectories are given. The results show that a typical outbreak of cold air can be regarded as an effective cell for meridional exchange of mass, heat and angular momentum.
Abstract
An attempt is made to study, by means of a detailed synoptic analysis, the three-dimensional air-motion in a typical outbreak of a polar air-mass. The mean vertical velocities at different levels over the entire cold-air region south of latitude 45°N are computed by use of the principle of continuity of mass. The maximum mean subsidence is found to be nearly 2 km per day at about the 600-mb level. In addition, the distribution of vertical velocity in different parts of the cold tongue is computed by means of trajectories on isentropic surfaces, and some examples of characteristic three-dimensional air trajectories are given. The results show that a typical outbreak of cold air can be regarded as an effective cell for meridional exchange of mass, heat and angular momentum.
Abstract
The mean meridional circulation is computed for the northern hemisphere winter. The equatorward current in the low troposphere has a strength of l–3 mps near 10 to 15 deg lat, and the return current, centered near 200 mb, has about the same speed. An inactive layer without much net poleward or equatorward component extends from 700 to 400 mb.
Next, the release of kinetic energy by the meridional circulation is calculated, and it is shown that this release equals the kinetic energy export from the tropics to the middle latitudes. Finally, the mean meridional circulation exports heat from the tropics poleward; at 15 deg lat this heat transport has the right order of magnitude to balance the net heat loss in higher latitudes.
Abstract
The mean meridional circulation is computed for the northern hemisphere winter. The equatorward current in the low troposphere has a strength of l–3 mps near 10 to 15 deg lat, and the return current, centered near 200 mb, has about the same speed. An inactive layer without much net poleward or equatorward component extends from 700 to 400 mb.
Next, the release of kinetic energy by the meridional circulation is calculated, and it is shown that this release equals the kinetic energy export from the tropics to the middle latitudes. Finally, the mean meridional circulation exports heat from the tropics poleward; at 15 deg lat this heat transport has the right order of magnitude to balance the net heat loss in higher latitudes.
