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  • Author or Editor: Yao Yao x
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C. S. Yao

Abstract

Statistical methods of dichotomous variables are suggested in order to analyze the historical climatic records in ancient writings. From historical descriptive records of floods and droughts, we calculate the variability, persistence and interchangeability, cyclic period and period, and index of floods and droughts.

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Augustine Y. M. Yao

Abstract

The beta distribution is the model for frequency distributions of relative humidity observations. The standard chi-square (χ2) test measures the goodness of fit of the beta distribution model to the observed data base. Ninety distributions of daily, mean 5-, 10- and 15-day, and mean monthly relative humidity data sets from 19 U. S. stations form the basis for this report. At the 0.05 level of significance the tests reject only 5% of the mean monthly and 3% of the daily and the mean 5-, 10- and 15-day distributions. The hypothesis that relative humidity follows a beta distribution is not rejected.

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Yao Zhou and Corene J. Matyas

Abstract

The western Gulf Coast and Caribbean coast are regions that are highly vulnerable to precipitation associated with tropical cyclones (TCs). Defining the spatial dimensions of TC rain fields helps determine the timing and duration of rainfall for a given location. Therefore, this study measured the area, dispersion, and displacement of light and moderate rain fields associated with 35 TCs making landfalls in this region and explored conditions contributing to their spatial variability. The spatial patterns of satellite-estimated rain rates are determined through hot spot analysis. Rainfall coverage is largest as TCs approach the western Caribbean coast, and smaller as TCs move over the Gulf of Mexico (GM) after making landfall over the Yucatan Peninsula. The rain fields are displaced eastward and northward over the western and central Caribbean Sea and the central GM. Rainfall fields have more displacement toward the west and south, which is over land, when TCs move over the southern GM, possibly as a result of the influence of Central American gyres. The area and dispersion of rainfall are significantly correlated with storm intensity and total precipitable water. The displacement of rainfall is significantly correlated with vertical wind shear. Over the Bay of Campeche, TC precipitation extends westward, which may be related to the convergence of moisture above the boundary layer from the Pacific Ocean and near-surface convergence enhanced by land. Additionally, half of the storms produce rainfall over land about 48 h before landfall. TCs may produce light rainfall over land for more than 72 h in this region.

Open access
Zhigang Yao, Jun Li, Jinlong Li, and Hong Zhang

Abstract

An accurate land surface emissivity (LSE) is critical for the retrieval of atmospheric temperature and moisture profiles along with land surface temperature from hyperspectral infrared (IR) sounder radiances; it is also critical to assimilating IR radiances in numerical weather prediction models over land. To investigate the impact of different LSE datasets on Atmospheric Infrared Sounder (AIRS) sounding retrievals, experiments are conducted by using a one-dimensional variational (1DVAR) retrieval algorithm. Sounding retrievals using constant LSE, the LSE dataset from the Infrared Atmospheric Sounding Interferometer (IASI), and the baseline fit dataset from the Moderate Resolution Imaging Spectroradiometer (MODIS) are performed. AIRS observations over northern Africa on 1–7 January and 1–7 July 2007 are used in the experiments. From the limited regional comparisons presented here, it is revealed that the LSE from the IASI obtained the best agreement between the retrieval results and the ECMWF reanalysis, whereas the constant LSE gets the worst results when the emissivities are fixed in the retrieval process. The results also confirm that the simultaneous retrieval of atmospheric profile and surface parameters could reduce the dependence of soundings on the LSE choice and finally improve sounding accuracy when the emissivities are adjusted in the iterative retrieval. In addition, emissivity angle dependence is investigated with AIRS radiance measurements. The retrieved emissivity spectra from AIRS over the ocean reveal weak angle dependence, which is consistent with that from an ocean emissivity model. This result demonstrates the reliability of the 1DVAR simultaneous algorithm for emissivity retrieval from hyperspectral IR radiance measurements.

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Yunjun Yao, Shunlin Liang, Qiming Qin, and Kaicun Wang

Abstract

Monitoring land surface drought using remote sensing data is a challenge, although a few methods are available. Evapotranspiration (ET) is a valuable indicator linked to land drought status and plays an important role in surface drought detection at continental and global scales. In this study, the evaporative drought index (EDI), based on the estimated actual ET and potential ET (PET), is described to characterize the surface drought conditions. Daily actual ET at 4-km resolution for April–September 2003–05 across the continental United States is estimated using a simple improved ET model with input solar radiation acquired by Moderate-Resolution Imaging Spectroradiometer (MODIS) at a spatial resolution of 4 km and input meteorological parameters from NCEP Reanalysis-2 data at a spatial resolution of 32 km. The PET is also calculated using some of these data. The estimated actual ET has been rigorously validated with ground-measured ET at six Enhanced Facility sites in the Southern Great Plains (SGP) of the Atmosphere Radiation Measurement Program (ARM) and four AmeriFlux sites. The validation results show that the bias varies from −11.35 to 27.62 W m−2 and the correlation coefficient varies from 0.65 to 0.86. The monthly composites of EDI at 4-km resolution during April–September 2003–05 are found to be in good agreement with the Palmer Z index anomalies, but the advantage of EDI is its finer spatial resolution. The EDI described in this paper incorporates information about energy fluxes in response to soil moisture stress without requiring too many meteorological input parameters, and performs well in assessing drought at continental scales.

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Xiuping Yao, Jiali Ma, Da-Lin Zhang, and Lizhu Yan

Abstract

A 33-yr climatology of shear lines occurring over the Yangtze–Huai River basin (YHSLs) of eastern China during the mei-yu season (i.e., June and July) of 1981–2013 is examined using the daily ERA-Interim reanalysis data and daily rain gauge observations. Results show that (i) nearly 75% of the heavy-rainfall days (i.e., >50 mm day−1) are accompanied by YHSLs, (ii) about 66% of YHSLs can produce heavy rainfall over the Yangtze–Huai River basin, and (iii) YHSL-related heavy rainfall occurs frequently in the south-central basin. The statistical properties of YHSLs are investigated by classifying them into warm, cold, quasi-stationary, and vortex types based on their distinct flow and thermal patterns as well as orientations and movements. Although the warm-type rainfall intensity is the weakest among the four, it has the highest number of heavy-rainfall days, making it the largest contributor (33%) to the total mei-yu rainfall amounts associated with YHSLs. By comparison, the quasi-stationary type has the smallest number of heavy-rainfall days, contributing about 19% to the total rainfall, whereas the vortex type is the more frequent extreme-rain producer (i.e., >100 mm day−1). The four types of YHSLs are closely related to various synoptic-scale low-to-midtropospheric disturbances—such as the southwest vortex, low-level jets, and midlatitude traveling perturbations that interact with mei-yu fronts over the basin and a subtropical high to the south—that provide favorable lifting and the needed moisture supply for heavy-rainfall production. The results have important implications for the operational rainfall forecasts associated with YHSLs through analog pattern recognition.

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Dong-Peng Guo, Ren-Tai Yao, and Dan Fan

Abstract

This paper introduces a wind tunnel experiment to study the effect of the cooling tower of a nuclear power plant on the flow and the characteristics of visible plume regions. The relevant characteristics of the flow field near the cooling tower, such as the plume rise and the visible plume region, are compared with the results of previous experimental data from Électricité de France (EDF) and the Briggs formulas. The results show that the wind tunnel experiment can simulate the top backflow of the cooling tower and the rear cavity regions among others. In the near-wake region, including the recirculation cavity, mean velocity decreases and turbulence intensity increases significantly. The maximum turbulence intensity observed is 0.5. In addition, the disturbed flow extent of the cooling tower top reaches 1.5 times the cooling tower height. Analysis of the visible plume region shows that the wind tunnel experiment can simulate the variation of a visible plume region. The results are consistent with the wind tunnel experiment of EDF. Moreover, the plume rise analysis shows that the wind tunnel experiment data are in agreement with the Briggs formulas for 50–200 m. As a whole, the proposed wind tunnel experiment can simulate the flow field variation of the visible plume region and the plume rise around the buildings with reasonable accuracy.

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Meilin Zhu, Tandong Yao, Wei Yang, Baiqing Xu, and Xiaojun Wang

Abstract

Accurate evaluations of incoming longwave radiation (L in) parameterization have practical implications for glacier and river runoff changes in high-mountain regions of the Tibetan Plateau (TP). To identify potential means of accurately predicting spatiotemporal variations in L in, 13 clear-sky parameterizations combined with 10 cloud corrections for all-sky atmospheric emissivity were evaluated at five sites in high-mountain regions of the TP through temporal and spatial parameter transfer tests. Most locally calibrated parameterizations for clear-sky and all-sky conditions performed well when applied to the calibration site. The best parameterization at five sites is Dilley and O’Brien’s A model combined with Sicart et al.’s A for cloud-correction-incorporated relative humidity. The performance of parameter transferability in time is better than that in space for the same all-sky parameterizations. The performance of parameter transferability in space presents spatial discrepancies. In addition, all all-sky parameterizations show a decrease in performance with increasing altitude regardless of whether the parameters of all-sky parameterizations were recalibrated by local conditions or transferred from other study sites. This may be attributable to the difference between screen-level air temperature and the effective atmospheric boundary layer temperature and to different cloud-base heights. Nevertheless, such worse performance at higher altitudes is likely to change because of terrain, underlying surfaces, and wind systems, among other factors. The study also describes possible spatial characteristics of L in and its driving factors by reviewing the few studies about L in for the mountain regions of the TP.

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Zhanyu Yao, Wanbiao Li, Yuanjing Zhu, Bolin Zhao, and Yong Chen

Abstract

The Tibetan Plateau is a unique location for studying the global climate and China's severe weather. The precipitation on the Tibetan Plateau can be studied conveniently with the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). It is shown that the TMI brightness temperature at 85 GHz in the vertical polarization (TB85V) is negatively correlated to the surface rain rate, but a very low value of TB85V does not correspond to very intense surface rain rates on the Tibetan Plateau, a result that is different from what is observed in other areas of the world. For surface precipitation retrieval on the Tibetan Plateau from TMI, the effect from snow cover on precipitation retrieval is removed before analysis of precipitation. Using the dynamic cluster K-mean method, five categories of surface types and rain areas are identified on the Tibetan Plateau: dry soil, wet soil, water area, stratiform rain area, and convective rain area. The precipitation areas are screened by classification before the precipitation retrieval. Two datasets of rain-free areas and precipitation areas are formed after surface classification. Based on the dataset of rain-free areas, the value of TB85V can be simulated well by TB10V, TB19V, and TB21V when it is not raining. By means of the dataset of precipitation areas, it is revealed that the scattering index over land (SIL) is positively correlated and the polarization-corrected brightness temperature at 85 GHz (PCT85) is negatively correlated with the surface rain rate. With SIL, PCT85, and their combinations as retrieval algorithms, three precipitation retrieval formulas are proposed in which the SIL algorithm is most suitable for small rain retrieval, the PCT85 algorithm is most suitable for moderate rain retrieval, and the combined SIL and PCT85 algorithm is most suitable for relatively large rain retrieval on the Tibetan Plateau. By means of two thresholds, 265 and 245 K, for TB85V, the combination of the three formulas is applied to precipitation retrieval on the Tibetan Plateau during the Tibetan Plateau Experiment Intensive Observing Period of 1998, resulting in acceptable and encouraging surface rain-rate retrievals. Intercomparison among the TMI algorithms and the 17 Special Sensor Microwave Imager algorithms from the second Precipitation Intercomparison Project demonstrates that the comprehensive application of the TMI algorithms has good precision and error index and is suitable for precipitation retrieval on the Tibetan Plateau.

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Dong-Peng Guo, Peng Zhao, Ran Wan, Ren-Tai Yao, and Ji-Min Hu

Abstract

This paper applied a commercial computational fluid dynamics code, STAR-CD, with the renormalization group k–ε turbulence model to simulate the flow and dispersion of contaminants released from a source on the windward side of a hill under different thermal stratifications. In the wake region, the influence of atmospheric stratification on the flow field is inconspicuous under neutral and unstable conditions because of the effect of mechanical disturbance. However, this influence becomes slightly conspicuous under stable conditions. When atmospheric stratification is stable, in the range of z/H < 1.0 (where z is height above the surface and H is height of the hill), the velocity deficits are smaller than those under neutral and unstable conditions. The maximum turbulence kinetic energy (TKE) appears in the wake regions, and the variation in TKE is significantly lower than that under neutral and unstable conditions. When atmospheric stratification is unstable, the vertical and horizontal spread of the plume is slightly greater than that under neutral and stable conditions and the maximum concentration is less than that under neutral conditions. When the Froude number is large (~11; Brunt–Väisälä frequency = 0.52), atmospheric stratification is slightly stable, the structure of flow around the hill is generally similar to that under neutral conditions, and the high-concentration regions are large on the windward side of the hill. Smaller high-concentration regions just appear on the windward side of the hill under unstable conditions. The pollutant concentrations in the wake region of the hill increase as a result of the effect of thermal stability, and the vertical spreading range of the plume along the downwind axis (x axis) is larger than that under neutral and stable conditions.

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