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E. B. Kraus

Abstract

A simple analytical model relates the seasonal excursion of the Intertropical Convergence Zone to seasonal changes in hemispheric forcing. The maximum value of the excursion increases with the seasonal heating change; it decreases with the equator-pole heating difference and with the heat storage capacity of the system as indicated by the lag of the response after the forcing.

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E. B. Kraus

Abstract

Analysis of nine weathership records indicates that maritime precipitation is significantly more frequent at night. The effect varies with season and latitude. The diurnal variation is related to the absorption of solar radiation. Non-adiabatic heating may cause a reduction of liquid water production within rising clouds; this factor becomes important when vertical velocities are not too high. At the top of layer clouds, the diurnal rhythm of irradiation can also cause a time-lagged diurnal change of inversion levels and cloud thickness. The last inference is supported by observational data.

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E. B. Kraus

Abstract

Symmetry considerations indicate that in steady-state conditions, and in the absence of a sea current, a horizontal interface must move in the direction of the surface geostrophic wind. With currents present, the interface velocity is the vector mean of the surface geostrophic wind and the current velocity, weighted respectively by the fluid masses per unit surface area which are affected by the viscous diffusion of vorticity upward and downward from the interface. In turbulent flow with neutral stratification, the ratio of these masses equals the square root of the density ratio. In transient conditions, the surface drift velocity has components in the direction of the isallobaric gradient and down a steeping surface slope. Wave action is responsible mainly for the spreading and the breakup of surface films.

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E. B. Kraus

A field program to study the marine planetary boundary layer was carried out jointly by scientists and students from the Universities of British Columbia, Hamburg and Miami and by personnel from the NOAA Sea-Air Interaction Laboratory. The following article describes briefly the basic purpose, location, timing and execution of this work.

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E. B. Kraus

Abstract

No abstract available.

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E. B. Kraus

A simple sampling experiment gives a several octave range of values for the zonal surface stress obtainable from synoptic maps over the North Atlantic. Uncertainty about the value of the drag coefficient account for about half the variance. The different methods that have been used to specify this quantity are reviewed and an attempt is made to state explicitly the assumptions involved in each case.

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E. B. Kraus

Abstract

The spatial coherence of subtropical rainfall anomalies is documented by variance analysis. Major droughts repeatedly were felt at the same time around the globe along the arid margins of the tropical rainfall belt. The persistence of anomalies becomes apparent in precipitation time series which combine data from relatively large areas and in streamflow records. These can be used to demonstrate autocorrelations and unexpectedly long runs of wet or dry years.

The latest drought episode culminated in 1972 not only in the Sahel and the Sudan, but also along the borders of the Indian desert and in Central America. It is shown to have been accompanied by relatively low temperatures in the southern subtropics and by abnormally high temperatures in the antarctic. The meridional temperature gradient and the meridional slope of the 500 mb surface were correspondingly reduced. It is suggested that this was associated with a reduced demand for energy (and zonal momentum) exports from the tropics and therefore relatively weak direct tropical circulations. As a result, these circulations–which tend to straddle the equator–did not deliver the normal amount of precipitation along their northernmost borders in the monsoonal fringe area.

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E. B. Kraus and E. N. Lorenz

Abstract

Experiments with six different heating fields in a numerical general circulation model are described. Three different vertical heating gradients are each used once with and once without variations on the continental-oceanic scale along parallel circles. The zonal and the meridional heating fields are forced to vary seasonally. Integration has been carried out over a simulated period of one century for one particular configuration, and over periods of five years for each of the five other configurations.

Results which may be represented by an electrical analogue are rather similar to actual general circulation observations. They also show stronger summer westerlies and North-South temperature gradients in the model without schematic oceans and continents. Dynamic lag effects cause differences between the “climates” of spring and fall. In all experiments there was a breakdown in fall of a predominantly zonal circulation, accompanied by the development of “equinoctial storms.”

Lag correlations computed for the mean zonal thermal wind in the 100-year experiment show persistence in summer between successive ten-day means and significant negative values over longer lag periods. No significant lag correlations were found during the winter months.

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