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R. J. Purser and H-L. Huang

Abstract

An attempt is made to formulate consistent objective definitions of the concept of “effective data density” applicable both in the context of satellite soundings more generally in objective data analysis. The definitions based upon various forms of Backus-Gilbert “spread” functions are found to be seriously misleading in satellite soundings where the model resolution function (expressing the sensitivity of retrieval or analysis to changes in the background error) features sidelobes. Instead, estimates derived by smoothing the trace components of the model resolution function are proposed. The new estimates are found to be more reliable and informative in simulated satellite retrieval problems and, for the special case of uniformly spaced perfect observations, agree exactly with their actual density. The new estimates integrate to the “degrees of freedom for signal,” a diagnostic that is invariant to changes of units or coordinates used.

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William L. Smith, H. L. Huang, and Joe A. Jenney

Abstract

GOES high-resolution visible imagery is used to define the spatial resolution and scan geometry required for an advanced infrared sounder to fly on future polar-orbiting satellites. The definition is based on optimizing the probability of achieving one or more cloud-free infrared sounder fields of view within the footprint of an Advanced Microwave Sounding Unit (AMSU) assumed to have a linear resolution of 64 km. It is found that an instrument with about 8 km linear (10 km circular), or better, resolution that samples nine, or more, spatially independent fields of view within each AMSU footprint is needed to provide a high probability of achieving uncontaminated, by cloud, infrared sounding radiance observations.

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W. McKeown, F. Bretherton, H. L. Huang, W. L. Smith, and H. L. Revercomb

Abstract

Evidence for the radiometric determination of air–water interface temperature gradients is presented. Inherent radiometric characteristics in the water molecule cause variations in the absorption coefficient that allow radiation at near-infrared frequencies (2000–5000 wavenumbers, 2.0–5.0 μm) to carry information about subsurface water temperatures. This radiation leaving the surface is predominantly sensitive to water temperature in the layer between the surface and the “effective optical depth” (inverse of the absorption coefficient). Where atmospheric transmittance is high and/or the instrument is near the liquid, the radiance variations with frequency record temperature variations with depth. To measure the small radiance variations with frequency, an instrument must be radiometrically stable in suitable frequency bands with low instrument noise.

A simulation of this technique's use for airborne beat flux measurement indicated feasibility from low altitudes at night. Laboratory experiments produced radiometric signals that strongly indicated that the thermal structures in an air–water interface can be studied in detail. Corrected for variations of emissivity and reflectivity with frequency, the water spectra showed multiple correlations with those gradients inferred from bulk temperature measurements that assumed conductive heat loss. The use of high spectral resolution increased the vertical resolution of the interface thermal structures. Although high spectral resolution is not required for a field application, problems of system noise, atmospheric absorption, and solar reflection are more tractable with its use.

This technique may be useful in laboratory studies of thermal structures relevant to heat and gas flow that reside in the air–water interface.

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L. H. LinHo, Xianglei Huang, and Ngar-Cheung Lau

Abstract

Analysis of observations from 1979 to 2002 shows that the seasonal transition from winter to spring in East Asia is marked with a distinctive event—the onset of the south China spring rain (SCSR). In late February, the reduced thermal contrast between ocean and land leads to weakening of the Asian winter monsoon as well as the Siberian high and the Aleutian low. Meanwhile, convection over Australia and the western Pacific Maritime Continent is suppressed on the passage of the dry phase of a Madden–Julian oscillation (MJO). In conjunction with the seasonal march of monsoon circulation in the Indonesian–Australian sector, this MJO passage weakens the local thermally direct cell in the East Asia–Australia sector. This development is further accompanied by a series of adjustments in both the tropics and midlatitudes. These changes include attenuation of the planetary stationary wave, considerable weakening of the westerly jet stream over much of the central Pacific adjacent to Japan, and reduction of baroclinicity near the East Asian trough. The influence of concurrent local processes in midlatitudes on the SCSR onset is also important. The weakened jet stream is associated with confinement of frontal activities to the coastal regions of East Asia as well as with rapid expansion of the subtropical Pacific high from the eastern Pacific to the western Pacific. A parallel analysis using output from an experiment with a GFDL-coupled GCM shows that the above sequence of circulation changes is well simulated in that model.

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J. Mielikainen, B. Huang, H.-L. A. Huang, M. D. Goldberg, and A. Mehta

Abstract

The Weather Research and Forecasting model (WRF) double-moment 6-class microphysics scheme (WDM6) implements a double-moment bulk microphysical parameterization of clouds and precipitation and is applicable in mesoscale and general circulation models. WDM6 extends the WRF single-moment 6-class microphysics scheme (WSM6) by incorporating the number concentrations for cloud and rainwater along with a prognostic variable of cloud condensation nuclei (CCN) number concentration. Moreover, it predicts the mixing ratios of six water species (water vapor, cloud droplets, cloud ice, snow, rain, and graupel), similar to WSM6. This paper describes improving the computational performance of WDM6 by exploiting its inherent fine-grained parallelism using the NVIDIA graphics processing unit (GPU). Compared to the single-threaded CPU, a single GPU implementation of WDM6 obtains a speedup of 150× with the input/output (I/O) transfer and 206× without the I/O transfer. Using four GPUs, the speedup reaches 347× and 715×, respectively.

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J. L. Zhang, Y. P. Li, G. H. Huang, C. X. Wang, and G. H. Cheng

Abstract

In this study, a Bayesian framework is proposed for investigating uncertainties in input data (i.e., temperature and precipitation) and parameters in a distributed hydrological model as well as their effects on the runoff response in the Kaidu watershed (a snowmelt–precipitation-driven watershed). In the Bayesian framework, the Soil and Water Assessment Tool (SWAT) is used for providing the basic hydrologic protocols. The Delayed Rejection Adaptive Metropolis (DRAM) algorithm is employed for the inference of uncertainties in input data and model parameters with global and local adaptive strategies. The advanced Bayesian framework can help facilitate the exploration of variation of model parameters due to input data errors, as well as propagation from uncertainties in data and parameters to model outputs in both snow-melting and nonmelting periods. A series of calibration cases corresponding to data errors under different periods are examined. Results show that 1) input data errors can affect the distributions of model parameters as well as parameters’ correlation, implying that data errors could influence the related hydrologic processes as well as their relations; 2) considering input data errors could improve the hydrologic simulation ability for peak streamflows; 3) considering errors of temperature and precipitation data as well as uncertainties of model parameters can provide the best modeling simulation performance in the snow-melting period; and 4) accounting for uncertainties in precipitation data and model parameters can provide the best modeling performance during the nonmelting period. The findings will help enhance hydrological model’s capability for simulating/predicting water resources during different seasons for snowmelt–precipitation-driven watersheds.

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Norden E. Huang, Hsing H. Shih, Zheng Shen, Steven R. Long, and Kuang L. Fan

Abstract

Using a process denoted here as the empirical mode decomposition and the Hilbert spectral analysis, the ages of the seiches on the Caribbean coast of Puerto Rico are determined from their dispersion characteristics with respect to time. The ages deduced from this method are less than a day; therefore, the seiches could be locally generated.

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Maurice L. Blackmon, Y-H. Lee, John M. Wallace, and Huang-Hsiung Hsu

Abstract

The time variation of Northern Hemisphere wintertime 500 mb height fluctuations with short, intermediate and long time scales is investigated, using lag-correlation patterns derived from time-filtered data. Fluctuations with short (2.5–6 day periods) time scales propagate eastward at a rate consistent with the notion of a steering level around 700 mb, which supports an interpretation in terms of baroclinic waves. The mobile teleconnection patterns associated with the intermediate (10–30 day periods) time scales exhibit a pattern of time variation suggestive a Rossby-wave dispersion, with a predominance of southward dispersion from middle latitudes into the tropics. The geographically fixed teleconnection patterns characteristic of the longer time scales do not show a well-defined pattern of time variation, but their horizontal structure resembles that of the fastest growing normal mode associated with barotropic instability of the climatological mean wintertime flow.

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R. J. Bantges, H. E. Brindley, X. H. Chen, X. L. Huang, J. E. Harries, and J. E. Murray

Abstract

Differences between Earth’s global mean all-sky outgoing longwave radiation spectrum as observed in 1970 [Interferometric Infrared Spectrometer (IRIS)], 1997 [Interferometric Monitor for Greenhouse Gases (IMG)], and 2012 [Infrared Atmospheric Sounding Instrument (IASI)] are presented. These differences are evaluated to determine whether these are robust signals of multidecadal radiative forcing and hence whether there is the potential for evaluating feedback-type responses. IASI–IRIS differences range from +2 K in the atmospheric window (800–1000 cm−1) to −5.5 K in the 1304 cm−1 CH4 band center. Corresponding IASI–IMG differences are much smaller, at 0.2 and −0.8 K, respectively. More noticeably, IASI–IRIS differences show a distinct step change across the 1042 cm−1 O3 band that is not seen in IASI–IMG comparisons. This step change is a consequence of a difference in behavior when moving from colder to warmer scenes in the IRIS data compared to IASI and IMG. Matched simulations for the relevant periods using ERA reanalyses mimic the spectral behavior shown by IASI and IMG rather than by IRIS. These findings suggest that uncertainties in the spectral response of IRIS preclude the use of these data for quantitative assessments of forcing and feedback processes.

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W. L. Smith, H. E. Revercomb, H. B. Howell, H-L. Huang, R. O. Knuteson, E. W. Koenig, D. D. LaPorte, S. Silverman, L. A. Sromovsky, and H. M. Woolf

Abstract

A high spectral resolution interferometer sounder (GHIS) has been designed for flight on future geostationary meteorological satellites. It incorporates the measurement principles of an aircraft prototype instrument, which has demonstrated the capability to observe the earth-emitted radiance spectrum with high accuracy. The aircraft results indicate that the theoretical expectation of 1°C temperature and 2°–3°C dewpoint retrieval accuracy will be achieved. The vertical resolution of the water vapor profile appears good enough to enable moisture tracking in numerous vertical layers thereby providing wind profile information as well as thermodynamic profiles of temperature and water vapor.

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