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W. D. King, C. T. Maher, and G. A. Hepburn

Abstract

A further 400 h of flying experience with the CSIRO hot-wire probe has shown that it can accurately measure liquid water content in clouds. Computations and experiments suggest that when an epoxy coating is used for protection, it should be less than 50 μm thick, and that the wire should be operated around 160°C when such coatings are used. Comparisons of performance with the Axially Scattering Spectrometer Probe and in a wet wind tunnel indicate that splashing of drops up to 40 μm diameter is not a problem at speeds up to 80 m s−1.

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D. A. Parkin, W. D. King, and D. E. Shaw

Abstract

The CSIRO Division of Cloud Physics has designed and built 103 automatic recording raingages, at a cost of about $US600 each, for use in a cloud-seeding experiment. Each unit consists of a siphoned tipping bucket interfaced to a monophonic cassette tape recorder. The raingages have a resolution of 0.2 mm, and this can be recorded to an accuracy of ∼2 s. Each tape can store 3000 tip events, and with a battery drain of 500 μ A the units can be left unattended in the field for many months. Experience with the network has shown that ∼6% of the units have failed when left unattended for 4½ months. Some examples of the type and quality of the data that can be obtained from such a network are presented.

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W. D. King, D. A. Parkin, and R. J. Handsworth

Abstract

A liquid water sensor consisting of a thin copper wire wound on a hollow 1.5 mm diameter cylinder is described. Slave coils on either side of the master sensing coil reduce axial heat losses to an acceptable level, and allow for a simple relationship between power supplied to the wire and liquid water content. Wet wind-tunnel tests show that the system response to liquid water is easily calculable from a knowledge of the geometrical dimensions of the cylinder and the operating temperature of the hot wire. When operated at 100°C, the device has a sensitivity of 0.02 g m−3, a response time of better than 0.05 s and an accuracy of 5% at 1 g m−3.

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Patrick W. S. King, William D. Hogg, and Philip A. Arkin

Abstract

Data from the first Algorithm Intercomparison Project(AIP/1) collected over Japan and surrounding waters in June, July, and August 1989 are used in this study to assess the importance of visible data in satellite rain estimation techniques. The purpose of the project was to compare different methods for estimating rainfall using satellite measurements. Radar and surface gauge data provided the validation set.

RAINSAT, an estimation technique using both visible (VIS) and infrared (IR) data, achieved the highest correlation with the validation data. In this paper rainfall estimates from RAINSAT (VIS+IR) am compared with two IR-only techniques to deduce the effectiveness of VIS data. Some estimates are also made using a VIS-only technique. Comparisons am made on both a spatial and diurnal basis.

Cloud climatologies for a subset of the AIP/1 data and the southern Ontario data on which RAINSAT was trained showed a marked similarity. It is found that the total volume of rain as a function of albedo is very similar for both Japanese and Ontario data.

The VIS data generally produced higher correlations with the validation data than did the IR data. This was especially the case when rain fell from warm, orogaphically induced rainfall. When rain fell from cold bright clouds. especially over the ocean, the correlations of the two types of data with the validation data were similar.

It is also shown that normalization of VIS data by the cosine of solar zenith data was inadequate to remove diurnal variations in apparent brightness.

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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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C. M. Girod, G. C. Hurtt, S. Frolking, J. D. Aber, and A. W. King

Abstract

Fire risk and carbon storage are related environmental issues because fire reduction results in carbon storage through the buildup of woody vegetation, and stored carbon is a fuel for fires. The sustainability of the U.S. carbon sink and the extent of fire activity in the next 100 yr depend in part on the type and effectiveness of fire reduction employed. Previous studies have bracketed the range of dynamics from continued fire reduction to the complete failure of fire reduction activities. To improve these estimates, it is necessary to explicitly account for fire reduction in terrestrial models. A new fire reduction submodel that estimates the spatiotemporal pattern of reduction across the United States was developed using gridded data on biomass, climate, land-use, population, and economic factors. To the authors’ knowledge, it is the first large-scale, gridded fire model that explicitly accounts for fire reduction. The model was calibrated to 1° × 1° burned area statistics [Global Burnt Area 2000 Project (GBA-2000)] and compared favorably to three important diagnostics. The model was then implemented in a spatially explicit ecosystem model and used to analyze 1620 scenarios of future fire risk and fire reduction strategies. Under scenarios of climate change and urbanization, burned area and carbon emissions both increased in scenarios where fire reduction efforts were not adjusted to match new patterns of fire risk. Fuel reducing management strategies reduced burned area and fire risk, but also limited carbon storage. These results suggest that to promote carbon storage and minimize fire risk in the future, fire reduction efforts will need to be increased and spatially adjusted and will need to employ a mixture of fuel-reducing and non-fuel-reducing strategies.

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W. M. Porch, S. Barr, W. E. Clements, J. A. Archuleta, A. B. Fernandez, C. W. King, W. D. Neff, and R. P. Hosker

Smoke pot and oil fog smoke tracers have been used to plan meteorological instrument placement and quantitatively estimate air volume flow from a tributary during nocturnal drainage wind conditions. The estimated volume flow agrees well with estimates of the flow using tethered-balloon and remotely obtained wind velocity measurements. The smoke visualization shows a very complex flow structure caused by tributary flow interactions with the flow down the main valley. The magnitude of the outflow volume from the tributary was greater than expected. If the tributary studied is representative of the other tributaries in the valley, most of the volume flow in the main valley may enter through the tributaries.

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Guanglin Tang, Ping Yang, George W. Kattawar, Xianglei Huang, Eli J. Mlawer, Bryan A. Baum, and Michael D. King

Abstract

Cloud longwave scattering is generally neglected in general circulation models (GCMs), but it plays a significant and highly uncertain role in the atmospheric energy budget as demonstrated in recent studies. To reduce the errors caused by neglecting cloud longwave scattering, two new radiance adjustment methods are developed that retain the computational efficiency of broadband radiative transfer simulations. In particular, two existing scaling methods and the two new adjustment methods are implemented in the Rapid Radiative Transfer Model (RRTM). The results are then compared with those based on the Discrete Ordinate Radiative Transfer model (DISORT) that explicitly accounts for multiple scattering by clouds. The two scaling methods are shown to improve the accuracy of radiative transfer simulations for optically thin clouds but not effectively for optically thick clouds. However, the adjustment methods reduce computational errors over a wide range, from optically thin to thick clouds. With the adjustment methods, the errors resulting from neglecting cloud longwave scattering are reduced to less than 2 W m−2 for the upward irradiance at the top of the atmosphere and less than 0.5 W m−2 for the surface downward irradiance. The adjustment schemes prove to be more accurate and efficient than a four-stream approximation that explicitly accounts for multiple scattering. The neglect of cloud longwave scattering results in an underestimate of the surface downward irradiance (cooling effect), but the errors are almost eliminated by the adjustment methods (warming effect).

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S. Platnick, P. A. Durkee, K. Nielsen, J. P. Taylor, S.-C. Tsay, M. D. King, R. J. Ferek, P. V. Hobbs, and J. W. Rottman

Abstract

The authors investigate the extent to which the contrast brightness of ship tracks, that is, the relative change in observed solar reflectance, in visible and near-infrared imagery can be explained by the microphysics of the background cloud in which they form. The sensitivity of visible and near-infrared wavelengths for detecting reflectance changes in ship tracks is discussed, including the use of a modified cloud susceptibility parameter, termed the “contrast susceptibility,” for assessing the sensitivity of background cloud microphysics on potential track development. It is shown that the relative change in cloud reflectance for ship tracks is expected to be larger in the near-infrared than in the visible and that 3.7-μm channels, widely known to be useful for detecting tracks, have the greatest sensitivity. The usefulness of contrast susceptibility as a predictor of ship track contrast is tested with airborne and satellite remote sensing retrievals of background cloud parameters and track contrast. Retrievals are made with the high spatial resolution Moderate Resolution Imaging Spectroradiometer Airborne Simulator flown on the National Aeronautics and Space Administration’s high-altitude ER-2 aircraft, and with the larger-scale perspective of the advanced very high resolution radiometer. Observed modifications in cloud droplet effective radius, optical thickness, liquid water path, contrast susceptibility, and reflectance contrast are presented for several ship tracks formed in background clouds with both small and large droplet sizes. The remote sensing results are augmented with in situ measurements of cloud microphysics that provide data at the smaller spatial scales.

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L. C. Shaffrey, I. Stevens, W. A. Norton, M. J. Roberts, P. L. Vidale, J. D. Harle, A. Jrrar, D. P. Stevens, M. J. Woodage, M. E. Demory, J. Donners, D. B. Clark, A. Clayton, J. W. Cole, S. S. Wilson, W. M. Connolley, T. M. Davies, A. M. Iwi, T. C. Johns, J. C. King, A. L. New, J. M. Slingo, A. Slingo, L. Steenman-Clark, and G. M. Martin

Abstract

This article describes the development and evaluation of the U.K.’s new High-Resolution Global Environmental Model (HiGEM), which is based on the latest climate configuration of the Met Office Unified Model, known as the Hadley Centre Global Environmental Model, version 1 (HadGEM1). In HiGEM, the horizontal resolution has been increased to 0.83° latitude × 1.25° longitude for the atmosphere, and 1/3° × 1/3° globally for the ocean. Multidecadal integrations of HiGEM, and the lower-resolution HadGEM, are used to explore the impact of resolution on the fidelity of climate simulations.

Generally, SST errors are reduced in HiGEM. Cold SST errors associated with the path of the North Atlantic drift improve, and warm SST errors are reduced in upwelling stratocumulus regions where the simulation of low-level cloud is better at higher resolution. The ocean model in HiGEM allows ocean eddies to be partially resolved, which dramatically improves the representation of sea surface height variability. In the Southern Ocean, most of the heat transports in HiGEM is achieved by resolved eddy motions, which replaces the parameterized eddy heat transport in the lower-resolution model. HiGEM is also able to more realistically simulate small-scale features in the wind stress curl around islands and oceanic SST fronts, which may have implications for oceanic upwelling and ocean biology.

Higher resolution in both the atmosphere and the ocean allows coupling to occur on small spatial scales. In particular, the small-scale interaction recently seen in satellite imagery between the atmosphere and tropical instability waves in the tropical Pacific Ocean is realistically captured in HiGEM. Tropical instability waves play a role in improving the simulation of the mean state of the tropical Pacific, which has important implications for climate variability. In particular, all aspects of the simulation of ENSO (spatial patterns, the time scales at which ENSO occurs, and global teleconnections) are much improved in HiGEM.

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