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J. Y. Wang

Abstract

Information on atmospheric constituents is contained in the remotely measured spectral radiances. Two iteration methods, linear and nonlinear, are presented to demonstrate the possibility of inferring the water vapor profile from ground-based measurements. The linear inversion method which linearizes the radiative transfer equation is found to have a narrow range of convergence. A study of the vertical resolution of the inferred profile through the linear inversion technique indicates that fine-scale detailed structure of the profile cannot be reconstructed. The nonlinear iteration procedure, which minimizes the root-mean-squares residual of the random noise along the direction of “steepest” descent, is found capable of inferring a reasonably stable solution with wide range of convergence and is proven in numerical stability superior to the linear technique. The effects of the errors both in radiance measurements and in temperature profile on the inferred profile are also presented.

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J. Y. Wang and S. C. Wang

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G. T. J. Chen, Y. J. Wang, and C-P. Chang

Abstract

This study compares the systematic errors of 36-h surface cyclone and anticyclone forecasts for two operational numerical weather prediction models over East Asia and the western North Pacific Ocean: the U.S. Navy's Operational Global Atmospheric Prediction System (NOGAPS), and Japan Meteorological Agency's Fine-mesh Limited Area Model (JFLM). The study is carried out for the 1983 Mei-Yu season (May–July), which is the wettest season over East Asia based on nontyphoon-produced rainfall. All available 0000 and 1200 GMT forecast runs are evaluated against an independent dataset of subjective analysis produced operationally by the Central Weather Bureau, Taipei. The mean position errors, mean central pressure errors and forecast skill indices for both cyclones and anticyclones in the NOGAPS and JFLM models are examined.

Both NOGAPS and JFLM models are more likely to underforecast than to overforecast the existence and/or genesis of both cyclones and anticyclones. However, over the Tibetan Plateau and its vicinity, both models tend to overforecast the existence and/or genesis of cyclones. They also forecast both cyclones and anticyclones too slow and too far to the north.

Diurnal variations in central pressure errors suggest that the error source is the lack of radiation processes in the JFLM and too strong a diurnal cycle of radiation processes in NOGAPS. Also, the failure to treat adequately the bulk effects of cumulus convection seems to be primarily responsible for the poor forecasts of oceanic cyclone development.

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Y. J. Lin, T. C. Wang, and J. H. Lin

Abstract

Some dynamic and thermodynamic properties of a convective cell within a squall line that occurred on 6 June 1979 were studied based on dual-Doppler observations. The domain under investigation had a horizontal dimension of 27 km × 27 km with 12 levels in the vertical. The grid spacing used was 1 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Fields of deviation perturbation pressure, density and virtual temperature were recovered from a three-dimensional wind field using the thermodynamic retrieval method. These retrieved fields were then subjected to internal consistency checks to determine the level of confidence.

Our findings demonstrate that thermodynamic retrieval is feasible when random errors inherent in the radial wind components are minimized by proper smoothing. Errors in the computation of vertical velocity can be substantially reduced when a variational approach is used with the anelastic continuity equation applied to the vertically integrated horizontal mass divergence as an integral constraint. Results show that the gust front (GF) is primarily responsible for vigorous convection in the storm. Distinct features of strong wind shear, pressure change and temperature contrast are evident across the GF. The derived pressure and temperature perturbations are closely related to the updraft–downdraft structure. In particular, high pressure forms on the upshear side of an updraft with low pressure on the downshear side. The orientation of maximum pressure gradient across an updraft is in the direction of the environmental shear vector. Strong perturbation temperature gradients occur in the vicinity of an updraft with warning on its upwind side and cooling on its downwind side. The appearance of a downdraft in the immediate vicinity of an updraft is of importance in affecting the magnitude and distribution of pressure and temperature perturbations within the storm.

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J. Y. Wang, C. R. Claysmith, and M. Griggs

Abstract

A ground-based infrared spectroradiometer has been used to measure the vertical temperature profile of the lower atmosphere from 0 to 6 km. Eight measurements in the 15-μm carbon dioxide band have been used for the inversion in addition to three measurements in the 18-μm water vapor band for the water vapor corrections. One additional observation in the 11-μm window region is used to determine the presence of cloud. Twenty-one sets of clear sky data obtained in the summer of 1971 are used to verify the inversion technique. The resultant profiles have an accuracy comparable to that of radiosondes with an overall rms error of 1.58°C.

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Q.-S. Ge, J.-Y. Zheng, Z.-X. Hao, P.-Y. Zhang, and W.-C. Wang

Chinese historical documents that contain descriptions of weather conditions can be used for studying climate of the past hundreds or even thousands of years. In this study, the progress of reconstructing a 273-station quantitative precipitation dataset for 1736–1911—a period when records of the depth of rain infiltration (into the ground) and snow depth (above the surface) were kept in the Yu–Xue–Fen–Cun (which is part of memos routinely sent to the emperors during the Qing Dynasty) is reported. To facilitate the rainfall reconstruction, a field program of 29 sites covering different climate regimes and soil characteristics was designed for the purpose of establishing the transfer function between the rain infiltration depth and rainfall amount, while the relation between the snow depth and snowfall is obtained using instrumental measurements of recent decades. The results of the first site at Shijiazhuang (near Beijing) are reported here. The reconstruction shows that the summer and winter precipitation during 1736–1911 were generally greater than their respective 1961–90 means. Two years with extreme summer precipitation are identified—112 mm in 1792 and 1167 mm in 1801; the latter is larger than the 998 mm in 1996, which has been the most severe one of recent decades. The long-term high-resolution quantitative data can be used to study climate variability as well as to evaluate historical climate model simulations.

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Y.-C. Lin, L.-Y. Oey, J. Wang, and K.-K. Liu

Abstract

Annual Rossby waves in northern South China Sea had previously been studied using altimetry and model data; however, how they connect to subsurface temperature fluctuations has not been examined. This study analyzed a 22-month, surface to −500-m temperature time series at 18.3°N, 115.5°E, together with satellite and other data, to show the arrivals near z ≈ −300 m and deeper cool (warm) Rossby waves after their generation near the Luzon Strait in winter (summer). Temperature fluctuations with time scales of a few weeks, and with maximum anomalies near z ≈ −100 m, were also found embedded in the smooth Rossby waves and caused by propagating eddies. Eddy fluctuations and propagation past the mooring were of two types: southwestward from southwestern Taiwan, triggered by Kuroshio intrusion that produced anticyclone–cyclone pairs in late fall and winter, and eddies propagating westward from Luzon forced by annual anomalies of wind stress curl and Kuroshio path in the Luzon Strait

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X. Y. Zhang, Y. Q. Wang, W. L. Lin, Y. M. Zhang, X. C. Zhang, S. Gong, P. Zhao, Y. Q. Yang, J. Z. Wang, Q. Hou, X. L. Zhang, H. Z. Che, J. P. Guo, and Y. Li

Before and during the 2008 Beijing Olympics from June to September, ground-based and satellite monitoring were carried out over Beijing and its vicinity (BIV) in a campaign to quantify the outcomes of various emission control measures. These include hourly surface PM10 and PM2.5 and their fraction of black carbon (BC), organics, nitrate, sulfate, ammonium, and daily aerosol optical depth (AOD), together with hourly reactive gases, surface ozone, and daily columnar NO2 from satellite. The analyses, excluding the estimates from weather contributions, demonstrate that after the control measures, including banning ~300,000 “yellow-tag” vehicles from roads, the even–odd turn of motor vehicles on the roads, and emission reduction aiming at coal combustion, were implemented, air quality in Beijing improved substantially. The levels of NO, NO2, NOx, CO, SO2, BC, organics, and nitrate dropped by about 30%–60% and the ozone moderately increased by ~40% while the sulfate and ammonium exhibited different patterns during various control stages. Weather conditions have a great impact on the summertime secondary aerosol (~80% of total PM) and O3 formations over BIV. During the Olympic Game period, various atmospheric components decreased dramatically at Beijing compared to the same period in the previous years. This decrease was related not only to the implementation of rigorous control measures, but also to the favorable weather processes. The subtropical high was located to the south so that Beijing's weather was dominated by the interaction between a frequently eastward shifting trough in the westerlies and a cold continental high with clear to cloudy days or showery weather.

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J. Shen, M. Yu, A. J. Koivisto, H. Jiang, Y. Liu, L. Wang, and T. Hussein

Abstract

The inverse Gaussian distributed method of moments (IGDMOM) was developed to analytically solve the kinetic collection equation (KCE) for the first time. Using the IGDMOM, we obtained both new analytical and asymptotic solutions to the KCE. This is shown for both the free-molecular and continuum regime collision frequency functions. The new analytical solutions are highly suitable for demonstrating the self-preserving size distribution (SPSD) theory. The SPSD theory is considered one of the most elegant research works in atmospheric science for aerosols or small cloud droplets. It was initially discovered by Friedlander and then developed by Lee with an assumption of the time-dependent lognormal size distribution function. In this study, we demonstrate that the SPSD theory of coagulating atmospheric aerosols can be presented in a simpler and more rigorous theoretical way, which is realized through the introduction of the IGDMOM for describing aerosol size distributions. Using the IGDMOM, the new formulas for the SPSD, as well as the time required for aerosols to reach the SPSD, are analytically provided and verified. Furthermore, we discover that the SPSD of atmospheric aerosols undergoing coagulation is only determined using a shape factor variable Ω, which is composed of the first three moments at an initial stage. This study has critical implications for developing tropospheric atmospheric aerosol or small cloud droplet dynamics models and further verifies the SPSD theory from the viewpoint of theoretical analysis.

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R. Rotunno, Y. Chen, W. Wang, C. Davis, J. Dudhia, and G. J. Holland
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