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- Author or Editor: B. HAURWITZ x
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Abstract
It is shown that perturbations forming at wind discontinuities in the atmospheres of rotating planets are unstable, even though the distribution of the angular momentum of the rotating planet exerts a stabilizing influence. Consequently disturbances can develop spontaneously. Presumably at least some of the markings observed on planets, especially on Jupiter, represent such disturbances. The velocity of these perturbations is found not to differ greatly from the mean velocity of the fluid on both sides of the boundary. Therefore, the determination of planetary velocities of rotation from visual observations of such surface markings appears justified.
At a sharp current discontinuity the amplitude of a perturbation increases faster, the shorter the wave length. At shear zones of finite width only those waves are unstable whose length is greater than five times the width of the shear zone, and those waves will develop most rapidly whose length is about eight times the width of the shear zone. Since in the large-scale atmospheric circulations different wind belts are as a rule separated by finite shear zones rather than by sharp discontinuities very short waves cannot develop because they are not unstable. An empirical check of the relation between the width of the shear zone and the length of the developing perturbations is discussed.
Abstract
It is shown that perturbations forming at wind discontinuities in the atmospheres of rotating planets are unstable, even though the distribution of the angular momentum of the rotating planet exerts a stabilizing influence. Consequently disturbances can develop spontaneously. Presumably at least some of the markings observed on planets, especially on Jupiter, represent such disturbances. The velocity of these perturbations is found not to differ greatly from the mean velocity of the fluid on both sides of the boundary. Therefore, the determination of planetary velocities of rotation from visual observations of such surface markings appears justified.
At a sharp current discontinuity the amplitude of a perturbation increases faster, the shorter the wave length. At shear zones of finite width only those waves are unstable whose length is greater than five times the width of the shear zone, and those waves will develop most rapidly whose length is about eight times the width of the shear zone. Since in the large-scale atmospheric circulations different wind belts are as a rule separated by finite shear zones rather than by sharp discontinuities very short waves cannot develop because they are not unstable. An empirical check of the relation between the width of the shear zone and the length of the developing perturbations is discussed.
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It is shown on the evidence of observational material that the simplifications necessary in order to derive the equation for the isallobaric wind are not justified, because the neglected terms in the equations of motion, viz., the convective terms and the local derivatives of the geostrophic deviation, are of the same order of magnitude as the terms retained in the equations. Hence the concept of the isallobaric wind has to be abandoned. Consequently the convergence ahead of moving cyclones and the divergence behind, in the lower troposphere, cannot be explained by means of the isallobaric-wind relation. It is shown that the distribution of the acceleration of motion in moving pressure systems offers an explanation of the observed distribution of convergence and divergence.
Abstract
It is shown on the evidence of observational material that the simplifications necessary in order to derive the equation for the isallobaric wind are not justified, because the neglected terms in the equations of motion, viz., the convective terms and the local derivatives of the geostrophic deviation, are of the same order of magnitude as the terms retained in the equations. Hence the concept of the isallobaric wind has to be abandoned. Consequently the convergence ahead of moving cyclones and the divergence behind, in the lower troposphere, cannot be explained by means of the isallobaric-wind relation. It is shown that the distribution of the acceleration of motion in moving pressure systems offers an explanation of the observed distribution of convergence and divergence.
Abstract
Since the sea breeze is caused by the temperature difference between the air over land and that over water, its intensity might be expected not only to increase while the temperature difference increases to its maximum but also to continue increasing until the difference decreases to zero. It is shown that in a model taking friction into account the intensity of the sea breeze begins to decrease considerably earlier, in better agreement with the observations. The diurnal rotation of the sea breeze can be explained as an effect of the Coriolis force. The observations of the diurnal variations of the sea-breeze direction made at Boston agree reasonably well with the theory, especially insofar as the modifying effects of a superimposed general wind are concerned.
Abstract
Since the sea breeze is caused by the temperature difference between the air over land and that over water, its intensity might be expected not only to increase while the temperature difference increases to its maximum but also to continue increasing until the difference decreases to zero. It is shown that in a model taking friction into account the intensity of the sea breeze begins to decrease considerably earlier, in better agreement with the observations. The diurnal rotation of the sea breeze can be explained as an effect of the Coriolis force. The observations of the diurnal variations of the sea-breeze direction made at Boston agree reasonably well with the theory, especially insofar as the modifying effects of a superimposed general wind are concerned.
The effect of clear and cloudy days, and of days with large and small temperature ranges on the daily pressure variation at Bermuda is investigated. It is shown that the various harmonic components are not significantly affected by the different weather conditions contrary to what has been found for continental stations. Such an independence from the local weather situation is to be expected over the oceans, especially in the case of the semidiurnal pressure oscillation. The results strengthen the explanation given by Chapman for the occurrence of the semidiurnal pressure maximum two hours before solar transit through the meridian.
The effect of clear and cloudy days, and of days with large and small temperature ranges on the daily pressure variation at Bermuda is investigated. It is shown that the various harmonic components are not significantly affected by the different weather conditions contrary to what has been found for continental stations. Such an independence from the local weather situation is to be expected over the oceans, especially in the case of the semidiurnal pressure oscillation. The results strengthen the explanation given by Chapman for the occurrence of the semidiurnal pressure maximum two hours before solar transit through the meridian.
