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J. C. King

Abstract

Surface pressure measurements from instruments deployed on ice floes in the southern Bellingshausen Sea were used to assess the accuracy of European Centre for Medium-Range Weather Forecasts (ECMWF) analyses in this region during February–May 2001. Despite the lack of in situ observations from this region, the analyses were found to be in very good agreement with the observed pressures and pressure gradients. The absolute difference between observed and analyzed pressures never exceeded 2.7 hPa over a pressure range of 965–1000 hPa. Standard deviations of the differences between observed and analyzed pressures were typically around 1 hPa. When additional in situ surface pressure observations from this region became available for use in the analyses, the agreement between analyzed and observed pressures improved only slightly. This suggests that atmospheric analyses are constrained well by satellite temperature soundings and other remotely sensed data in this region.

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J. C. King and J. Turner

Abstract

No abstract available

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Malcolm J. King and Christian Jakob

Abstract

Convection over the western equatorial Indian Ocean (WEIO) is strongly linked to precipitation over Africa and Australia but is poorly represented in current climate models, and its observed seasonal cycle is poorly understood. This study investigates the seasonal cycle of convection in the WEIO through rainfall and cloud measurements. Rainfall shows a single annual peak in early austral summer, but cloud proxies identify convective activity maxima in both boreal and austral summer. These diverging measures of convection during boreal summer are indicative of a reduction in the intensity of precipitation associated with a given cloud regime or cloud-top height during this time of year but an increase in the overall occurrence of high-top clouds and convectively active cloud regimes. The change in precipitation intensity associated with regimes is found to explain most of the changes in total precipitation during the period from May to November, whereas changes in the occurrence of convective regimes explains most of the changes throughout the rest of the year. The reduction in precipitation intensities associated with cloud regimes over the WEIO during boreal summer appears to be related to large-scale monsoon circulations, which suppress convection through forcing air descent in the midtroposphere and increase the apparent occurrence of convectively active cloud regimes through the advection of high-level cloud from monsoon-active areas toward the WEIO region.

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Michael D. King and Robert J. Curran

Abstract

The flux density measured at satellite altitude with a fixed field of view radiometer differs from the true flux density reflected by the earth-atmosphere system within the field of view of the radiometer. This difference is due to angular response characteristics of the radiometer, solid angle effects due to geometry, and angular reflectance effects of the earth-atmosphere system. All of these effects lead to uncertainties in the interpretation of instantaneous earth radiation budget measurements. The differences between the true flux density and the measured flux density are shown to be significant when the field of view of the radiometer is, large and when the atmosphere has a nonuniform, or spatially dependent, reflectance (albedo). A simulation experiment is described whereby the scene within the field of view of a nadir looking sensor is divided into a large number of equal area elements, each of which reflects radiation with one of two different reflectance models (corresponding to cloud-free and cloudy areas). The conditional mean values of the measured flux density, given values of the true flux density, are shown to differ significantly from the conditional means of the inverse problem, that of finding the mean value of the true flux density given a value for the measured flux density. The differences between the true flux density and the measured flux density are examined as a function of satellite altitude, field of view of the radiometer and solar zenith angle (including the effects of a terminator within the field of view) for both Lambertian and non-Lambertian reflectance models.

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Fred M. Vukovich and William J. King

Abstract

A three-dimensional primitive model was used to predict the early afternoon wind velocity field over St. Louis, Missouri. Four case studies were then performed where model results at various levels were compared with observed data from the METROMEX network. With proper initialization, the model very closely simulated actual conditions, the main feature of which was the urban heat island circulation. In-consistencies were due mainly to synoptic-scale changes and air mass anomalies, which the model is not designed to handle, and to limitations in the data associated with the network density.

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W. D. King and R. J. Handsworth

Abstract

It is shown that when liquid water contents are measured with the CSIRO hot-wire element, and cloud transmission measured in the UV with a simple optical system, then the two measurements can be combined to yield total droplet concentrations and average droplet size. Sizes and concentrations obtained from this technique are compared with those from an optical scattering probe, and reasonable agreement is found.

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J. C. King and W. M. Connolley

Abstract

Surface radiation measurements and other climatological data were used to validate the representation of the surface energy balance over the East Antarctic Ice Sheet in the U.K. Meteorological Office Unified Climate Model. Model calculations of incident and reflected shortwave radiation are in good agreement with observations, but the downward component of longwave radiation at the surface appears to be underestimated by up to 20 W m−2 in the model. Over much of the interior of Antarctica this error appears to be compensated for by an overestimate in turbulent transport of heat to the surface, while over the steep coastal slopes the heat flux is in good agreement with observations but the surface temperature is too low. The excessive heat flux over the interior results largely from the use of an inappropriately large bulk transfer coefficient under very stable conditions, suggesting that the surface heat flux scheme in the model is not ideally formulated for the conditions that prevail in the Antarctic boundary layer.

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E. W. Eloranta, J. M. King, and J. A. Weinman

Abstract

Vertical profiles of the horizontal radial wind component in the lowest kilometer of the atmosphere have been measured remotely with lidar. Wind speed determinations were made by observing the motion of naturally occurring aerosol density inhomogeneities. Lidar wind measurements compare favorably with simultaneous pilot balloon observations of the wind.

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Fred M. Vukovich, William J. King, J. W. Dunn III, and J. J. B. Worth

Abstract

The observed surface and upper air temperature and wind field patterns on 8 June 1976 in St. Louis, Missouri, were analyzed and compared with simulation results from a three-dimensional hydrodynamic model. An urban heat island (1–2°C temperature difference between the urban and rural regions) persisted during the day. The daytime temperature differential was relatively weak compared to that at night (∼5°C difference). In contrast, the urban heat island circulation was more intense during the day. This is thought to be due to the heating being distributed through a deeper layer. In the early evening, the heat island circulation dissipated due to the development of a surface-based inversion in the boundary layer.

The highest concentrations of O3 at the surface were found in the zone of convergence associated with the urban heat island circulation immediately downwind of the center of the city. As the heat island circulation dissipated during the early evening, the area of high O3 concentration was displaced further downstream.

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S. C. Ou, K. N. Liou, and J. F. King

Abstract

We have explored the applicability of the differential inversion (DI) method to temperature retrievals in both clear and cloudy atmospheres using red satellite data. The main theme of the DI is that the local Planck intensity can be exactly expressed by a linear combination of the derivatives of radiances in the logarithmic pressure coordinate. The inversion coefficients are obtained by fitting the weighting function to a generalized form. The higher-order derivatives of radiances are determined from polynomial fittings. The satellite dataset used in this work contains collocated brightness temperatures and radiosonde data that have been collected during the period of Baseline Upper Atmospheric Network (BUAN) experiments. These data include both cloudy and clear cases. A multispectral cloud-removal method using the principle of the N * method has been developed. This method uses radiances of High-Resolution Infrared Radiation Sounder channels 6, 7, and 8 to estimate clear radiances of these channels and the surface temperature simultaneously based on radiative transfer simulations. Subsequently, the quantity N * (the ratio of effective cloud cover over adjacent pixels) and the clear radiances of the rest of the channels are evaluated.

Retrieval results are presented in terms of rms temperature differences between retrieved and sounding profiles. Considering all clear and partly cloudy cases, the rms differences in temperature of approximately 2 K for retrievals using the DI are comparable to those using the minimum-variance scheme. The rms differences in temperature for retrievals using the multispectral cloud-removal scheme are slightly larger than those using the BUAN cloud-removal scheme by approximately 0.5 K. Finally, the rms temperature differences are much smaller than those for the first guess of the minimum-variance scheme. These results indicate fire that the DJ can achieve acceptable performance without first-guess or error covariance matrices; second, that the proposed multispectral cloud-removal method is also capable of generating reasonable cloud-removed clear radiances; and finally that the DI can be used as a tool to obtain first guesses in the current operational method and to perform large-volume temperature retrievals for climate studies.

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