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W. L. Smith

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Paul L. Smith
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WILLIAM L. SMITH

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An improved method for calculating tropospheric temperature and moisture from satellite radiometer measurements is developed. The troposphere is modeled by two temperature lapse rates and a single moisture lapse rate. These lapse rates as well as an optimum pressure level for dividing the two layers of constant lapse rate and surface temperature are calculated from three observations in the 15µ CO2 band, an observation in the rotational water vapor band, and an observation in the 11µ window region.

Radiances observed by a balloon-borne interferometer were used to approximate filtered radiometer measurements. Solutions for tropospheric temperature and moisture from the approximated radiometer observations are shown to agree favorably with radiosonde observations for both clear and partly cloudy conditions. The computations required are only 10 percent of those required by a previously developed method.

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Paul L. Smith Jr.

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Paul L. Smith

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Bartlett Smith and L. Mahrt

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An analytical two-layer approximation of atmospheric flow is developed to study boundary-layer production of vertical motion. The model consists of a boundary layer topped by a free-flow layer. Both layers am time-dependent and possess different values of stratification. The boundary-layer equations are layer-integrated over a fixed depth and surface stress is parameterized using a linearized surface drag law. The dynamics of this modeled flow are quite different from the case of constant eddy viscosity where the boundary layer depth is unrealistically sensitive to the dynamics.

Production of vertical motion is found to be most efficient in the region of the critical latitude where the forcing frequency is comparable to the natural internal frequency of the flow. This internal frequency depends not only on the Coriolis parameter, but also on stratification and boundary-layer properties. For a fixed value of these parameters, the boundary-layer produces vertical motion most efficiently when forced at a preferred horizontal length.

With sufficiently stratified mesoscale flows, significant boundary-layer pressure adjustments develop which decrease the circulation strength. Stratification is less effective in flows with large horizontal length scale. Results are interpreted for the case of flow forced by oscillating, differential boundary-layer heating.

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Paul L. Smith

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The antenna beam pattern for low elevation angles is examined in relation to the radar horizon to assess the impact of base-scan elevation angle on sensitivity to near-horizon weather features, as well as its effect on reflectivity measurements and ground clutter. The results from a simple model neglecting details of surface characteristics and multipath propagation suggest that a base elevation angle of about 0.3 beamwidth above the horizon would yield near-optimum sensitivity with acceptable degradation in reflectivity observations and ground clutter.

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Daniel L. Smith

The significance of Percent Correct Scores for National Weather Service (NWS) probability of precipitation (PoP) forecasts is examined. It is shown that the areal variability of rainfall and the nature of PoP forecasts preclude the achievement of a score of 100%—even for the best possible forecasts. A maximum possible percent correct is defined and radar estimates of rainfall coverage are combined with actual forecasts to determine how closely NWS forecasters approached this limit. Day- and nighttime percent correct scores were 75% and 85%, respectively, for the data examined. These values were close to the respective maximum possible scores of 83% and 90%. Relatively small changes in forecasters' percent correct scores are considered in light of these findings.

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WESLEY L. SMITH

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Clark L. Smith

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Low and high cloud motions derived from ATS-III satellite pictures, wind data from surface ships, vertical temperature profiles through the upper layer of the ocean, and sea-surface temperatures were used to examine intensity variations of Hurricane Celia.

Fields of radial and tangential wind components, absolute angular momentum flux, and absolute vorticity were computed from analyzed streamlines and isotachs. Radial and tangential velocities and absolute angular momentum flux were averaged around circles of several radii from the storm center. Average values of relative vorticity and divergence within these circular areas were also computed.

High-cloud motion computations were successful in identifying the intensification process in the outflow layer. The low-cloud motions, unfortunately, were not representative of the storm inflow layer.

An investigation of dynamic instability at the outflow level was made. The results did not indicate strongly that dynamic instability contributed to the intensification of the storm.

Final deepening followed a major change in direction of the surface inflow over warm shelf waters of shallow depths.

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