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J. M. Austin

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J. M. Austin
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J. M. Austin

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J. M. Austin and R. Shapiro

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The hypothesis is investigated that there is a physical difference between the development and motion components of a surface pressure change. Temperature changes indicate that deepening and filling are accompanied by high-level heating and cooling, respectively, while the motion part of pressure changes is associated with low-level temperature variations.

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J. M. Austin and Collaborators

The results of an empirical study of 500-mb patterns are presented. It is shown that the prediction of the 24-hr and 48-hr intensification or weakening of troughs and ridges can be aided by a consideration of upstream changes. Qualitative rules for the prediction of a 24-hr change in the speed of troughs and ridges are included. Finally a climatological summary is presented of intensification, weakening and speed of troughs and ridges.

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D. R. Jackson, J. Austin, and N. Butchart

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In this paper results are presented from an improved version of the troposphere–stratosphere configuration of the Met Office Unified Model (UM). The new version incorporates a number of changes, including new radiation and orographic gravity wave parameterization schemes, an interannually varying sea surface temperature and sea ice climatology, and the inclusion of convective momentum transport. The UM climatology is compared with assimilated data and with results from a previous version of the UM. It is shown that the model cold biases in the January winter stratosphere and the January and July summer stratosphere are reduced, chiefly because the new radiation scheme is more accurate. The separation between subtropical and polar night jets in July is also better simulated. In addition, in the current version stratospheric planetary wave amplitudes in southern winter are less than half those in northern winter, which is in much better agreement with observations than the previous model version. Despite these improvements, the model still has a cold bias in the winter polar stratosphere, which suggests that the model representation of gravity wave drag is inadequate. Sensitivity tests were carried out and showed that the improved simulation of the separation of subtropical and polar night jets in July is due both to the different sea ice climatology and to the inclusion of convective momentum transport. The improved simulation of stationary wave amplitudes in July cannot be attributed to an individual model change, although it seems to be related to changed wave propagation and dissipation within the stratosphere rather than changes in the tropospheric forcing.

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B. J. Turner and G. L. Austin

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Three-dimensional radar data for three summer Florida storm are used as input to a microwave radiative transfer model. The model simulates microwave brightness observations by a 19-GHz, nadir-pointing, satellite-borne microwave radiometer.

The statistical distribution of rainfall rates for the storms studied, and therefore the optimal conversion between microwave brightness temperatures and rainfall rates, was found to be highly sensitive to the spatial resolution at which 0bservations were made. The optimum relation between the two quantities was less sensitive to the details of the vertical profile of precipitation.

Rainfall retrievals were made for a range of microwave sensor footprint sizes. From these simulations spatial sampling-error estimates were made for microwave radiometers over a range of field-of-view sizes. The necessity of matching the spatial resolution of ground truth to radiometer footprint size is emphasized. A strategy for the combined use of raingages, ground-based radar, microwave, and visible-infrared (YIS-IR) satellite sensors is discussed.

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H. G. Houghton and J. M. Austin

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Kenneth J. Voss and Roswell W. Austin

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Transmissometers always accept a certain portion of the forward-scattered light. The error in the beam-attenuation coefficient c(λ) due to this acceptance varies with the small-angle scattering function, single-scattering albedo, and instrumental design. This paper details methods to model error in measurements of c(λ) obtained with cylindrically limited and collimated-beam transmissometers. These models are used with real examples of beam attenuation and small-angle scattering function data to test how this measurement error varies.

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H. G. Houghton and J. M. Austin

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Surface pressure changes can occur only when an accelerational field exists. The regularity of occurrence, the distribution, and the magnitudes of the accelerational fields found in the atmosphere have been determined from the available data. The most direct method used was to plot maps of the deviation of the observed wind from the geostrophic wind. Charts of the horizontal divergence, as determined from the observed winds, were prepared for several levels. Charts were also drawn of the non-geostrophic temperature changes, which are defined as the difference between the actual 12-hour temperature changes and the temperature changes which would result from geostrophic advection of the temperature field. It is shown that the magnitudes of the divergence and the non-geostrophic temperature changes are consistent with the observed deviations from the geostrophic wind. The errors of each method are investigated and it is concluded that they are not sufficient to affect the order of magnitude of the results. All of the charts exhibit definite patterns which show a considerable degree of correspondence with the weather conditions. It is concluded that accelerational fields regularly occur in the atmosphere which are one order of magnitude greater than cyclostrophic accelerations and accelerations due to the variation of the Coriolis parameter.

The equation for the pressure tendency is discussed with reference to the observational data. Since the total divergence in a vertical column is the relatively small difference between large divergences of opposite sign, the divergence integral in the tendency equation apparently cannot be evaluated from the data. Furthermore the sum of the divergence and advective integrals yield only the surface pressure tendency, which is already available. It does not appear that the divergence can be prognosticated as accurately as the pressure field. It is pointed out that the vertical velocities associated with a field of divergence may cause large pressure and temperature changes aloft with no surface pressure change. This shows that it is not possible to determine the regions responsible for surface pressure changes by considering the changes in the several layers. The influence of vertical stability on surface pressure changes was investigated statistically with indeterminate results.

A model of a cyclonic development based on the latent heat of condensation is discussed. It appears that this mechanism is incapable of explaining pressure changes of the magnitude commonly observed. A mechanism by which additional accelerations and pressure changes might result from the deformation of the field of mass by an initial accelerational field is presented. Sufficient evidence has not been accumulated to determine whether this mechanism operates in the atmosphere.

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