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J. H. Joseph and A. Manes

Abstract

Two extensive sets of spectral pyrheliometric data taken at Jerusalem in the years 1930–34 and 1961–68 have been analyzed.

Seasonal and synoptic variations in the optical depth of the atmospheric aerosol and in its wavelength dependence in the visible part of the spectrum are given and compared with those at other locations.

A secular increase in the turbidity of about 10% per decade, since 1930, could be isolated in this study. Similar increases at various other stations throughout the world seem to indicate a global buildup of turbidity, at least in the Northern Hemisphere.

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Y. Mekler and J. H. Joseph

Abstract

No abstract available.

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J. H. LaCasce and Joseph Pedlosky

Abstract

The properties of baroclinic, quasigeostrophic Rossby basin waves are examined. Full analytical solutions are derived to elucidate the response in irregular basins, specifically in a (horizontally) tilted rectangular basin and in a circular one. When the basin is much larger than the (internal) deformation radius, the basin mode properties depend profoundly on whether one allows the streamfunction to oscillate at the boundary or not, as has been shown previously. With boundary oscillations, modes occur that have low frequencies and, with scale-selective dissipation, decay at a rate less than or equal to that of the imposed dissipation. These modes approximately satisfy the long-wave equation in the interior. Using both unforced and forced solutions, the variation of the response with basin geometry and dissipation is documented. The long-wave modes obtain with scale-selective dissipation, but also with damping that acts equally at all scales. One finds evidence of them as well in the forced response, even when the dissipation is weak and the corresponding free modes are apparently absent.

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N. Wolfson, J. H. Joseph, and Y. Mekler

Abstract

Four commonly used families of inversion techniques have been investigated. The accuracy and stability of the Chahine, Twomey–Phillips, Backus–Gilbert and non-linear regression techniques have been evaluated and compared. Practical and empirical rules for efficient use have been obtained.

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N. Wolfson, Y. Mekler, and J. H. Joseph

Abstract

A new way to assess the resolution of inversion methods is defined. The dependence of resolution on accuracy is broken into three parts, each of which has a distinct practical significance. Representatives of four commonly used inversion techniques are evaluated in this context.

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Edward J. Zipser and Joseph H. Golden

Abstract

On 14 August 1977, there was a mini-outbreak of three tornadoes about 40 km cut of Denver, Colorado. There were no significant synoptic-scale disturbances affecting Colorado on that day. Mesoscale analysis is used to establish several smaller scale systems that influenced storm development. The most notable feature of the mesoscale band of parent thunderstorms was the active growth along their northwest flank, in spite of cell movement toward the east. On the convective scale, the situation can be described as discrete propagation of multi-cell storms by new cell development on the left rear flank. Two of the three tornadoes were documented photographically, and post-analysis shows that they were of large size and long duration, but slow moving. Structural features of the largest tornado are analyzed in different portions of the life cycle, and compared with other cases in the literature. This tornado moved on a track curving toward the north-northwest, remaining at least 5–10 km distant from any significant precipitation. A dust band believed to represent an inflow jet was observed, which was in a different quadrant from similar features in other cases. Aspects of the tornadoes which could cause public confusion are noted, such as the disproportionately short condensation funnel from high-based cumulus clouds.

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J. H. Joseph, W. J. Wiscombe, and J. A. Weinman

Abstract

This paper presents a rapid yet accurate method, the “delta-Eddington” approximation, for calculating monochromatic radiative fluxes in an absorbing-scattering atmosphere. By combining a Dirac delta function and a two-term approximation, it overcomes the poor accuracy of the Eddington approximation for highly asymmetric phase functions. The fraction of scattering into the truncated forward peak is taken proportional to the square of the phase function asymmetry factor, which distinguishes the delta-Eddington approximation from others of similar nature. Comparisons of delta-Eddington albedos, transnmissivities and absorptivities with more exact calculations reveal typical differences of 0–0.022 and maximum differences of 0.15 over wide ranges of optical depth, sun angle, surface albedo, single-scattering albedo and phase function asymmetry. Delta-Eddington fluxes are in error, on the average, by no more than 0.5%0, and at the maximum by no more than 2% of the incident flux. This computationally fast and accurate approximation is potentially of utility in applications such as general circulation and climate modelling.

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JOSEPH VEDERMAN, GEORGE H. HIRATA, and EDMUND J. MANNING

Abstract

A series of barotropic forecasts has been prepared for several upper-air levels in the tropical Pacific. The governing equation is the vorticity equation for a barotropic non-divergent atmosphere. The input data are stream-function values derived from an objective tropical wind analysis. The area covered is the Pacific Ocean Tropics of both the Northern and Southern Hemispheres. Examples of tropical barotropic forecasts are shown. Verification data suggest that these barotropic forecasts have slightly less accuracy than subjective forecasts.

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P. L. Israelevich, J. H. Joseph*, Z. Levin, and Y. Yair

Abstract

No Abstract available.

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Joseph J. Cione, Peter G. Black, and Samuel H. Houston

Abstract

Composite analyses of marine surface observations from 37 hurricanes between 1975 and 1998 show that the difference between the sea surface temperature and the surface air temperature significantly increases just outside the hurricane inner core. This increase in the sea–air contrast is primarily due to a reduction in surface air temperature and is more likely to occur when sea temperatures are at least 27°C. Results show that 90% of the observed cooling occurs 3.25°–1.25° latitude from the hurricane center, well outside the region of strongest surface winds. Since surface pressure only decreases 3 mb over this interval, the ∼2°C drop in air temperature is not a result of adiabatic expansion.

For the subset of observations that contained moisture measurements, surface specific humidity decreased 1.2 g kg−1 4.5°–1.75° latitude from the storm center. This finding suggests that the observed reduction in surface air temperature is not simply a result of near-surface evaporation from sea spray or precipitation. An alternate explanation may be that outside the hurricane inner core, unsaturated convective downdrafts act to dry and evaporatively cool the near-surface environment.

Between 3.25° and 1.25° radius, composite analyses show that low-level inflow is not isothermal, surface moisture is not constant, and the near-surface environment is not in thermodynamic equilibrium with the sea. Calculations based on these observations show that θ e decreases between 4.0° and 1.25° radius and then quickly rises near the inner core as surface pressures fall and specific humidity increases. Surface fluxes of heat and moisture are also observed to significantly increase near the inner core. The largest increase in surface sensible heat flux occurs radially inward of 1.5°, where surface winds are strong and sea–air temperature contrasts are greatest. As a result, the average Bowen ratio is 0.20∼0.5° radius from the composite storm center. This increase in sensible heat flux (in conjunction with near-saturated conditions at low to midlevels) may help explain why average surface air temperatures inside 1.25° radius remain relatively constant, despite the potential for additional cooling from evaporation and adiabatic expansion within the high wind inner core.

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