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Liu Y.,Numerical Weather Prediction Center | Liu Y.,National Meteorological Center | Tang N.,Nanjing University of Information Science and Technology
Atmospheric Measurement Techniques | Year: 2014

The problem of abnormally dry bias induced by radiosonde humidity sensor failure in the low and mid-troposphere is studied based on the global operational radiosonde relative humidity observations from December 2008 to November 2009. The concurrent humidity retrievals from the FORMOSAT-3/COSMIC radio occultation mission are also used to assess the quality of the radiosonde humidity observations. It is found that extremely dry relative humidity are common in the low and mid-troposphere, with an annual globally averaged occurrence of 4.2%. These low-humidity observations usually exist between 20 and 40° latitude in both the Northern Hemisphere and Southern Hemisphere, and from heights of 700 to 450 hPa. Winter and spring are the favored seasons for their occurrence, with a maximum fraction of 9.53 % in the Northern Hemisphere and 16.82% in the Southern Hemisphere. The phenomenon does not result from natural atmospheric variability, but rather humidity sensor failure. If the performance of humidity sensors is not good, low-humidity observations occur easily, particularly when the radiosonde ascends through stratiform clouds with high moisture content. The humidity sensor cannot adapt to the huge change of the atmospheric environment inside and outside stratiform clouds, resulting in sensor failure and no response to atmospheric change. These extremely dry relative humidity observations are erroneous. However, they have been archived as formal data and applied in many research studies. This may seriously undermine the reliability of numerical weather prediction and the analysis of weather and climate if quality control is not applied before using these data. © Author(s) 2014.

Wannawong W.,Numerical Weather Prediction Center | Humphries U.W.,King Mongkut's University of Technology Thonburi | Wongwises P.,King Mongkut's University of Technology Thonburi | Vongvisessomjai S.,Regional Environmental Management Center
International Journal of Computational and Mathematical Sciences | Year: 2011

The three steps of the standard one-way nested grid for a regional scale of the third generation WAve Model Cycle 4 (WAMC4) is scrutinized. The model application is enabled to solve the energy balance equation on a coarse resolution grid in order to produce boundary conditions for a smaller area by the nested grid technique. In the present study, the model takes a full advantage of the fine resolution of wind fields in space and time produced by the available U.S. Navy Global Atmospheric Prediction System (NOGAPS) model with 1 degree resolution. The nested grid application of the model is developed in order to gradually increase the resolution from the open ocean towards the South China Sea (SCS) and the Gulf of Thailand (GoT) respectively. The model results were compared with buoy observations at Ko Chang, Rayong and Huahin locations which were obtained from the Seawatch project. In addition, the results were also compared with Satun based weather station which was provided from Department of Meteorology, Thailand. The data collected from this station presented the significant wave height (Hs) reached 12.85 m. The results indicated that the tendency of the Hs from the model in the spherical coordinate propagation with deep water condition in the fine grid domain agreed well with the Hs from the observations.

Hong S.-Y.,Yonsei University | Kim H.M.,Yonsei University | Kim J.-E.,Yonsei University | Hwang S.-O.,Yonsei University | Park H.,Numerical Weather Prediction Center
Terrestrial, Atmospheric and Oceanic Sciences | Year: 2011

The impact of model uncertainties on analyzed data is investigated using a global data assimilation system. This issue is explored in a 3D-Var system based on the National Centers for Environmental Prediction (NCEP)/Department of Energy (DOE) system using two convective parameterization schemes, the Simplified Arakawa scheme and the Community Climate Model (CCM) scheme. Two sets of six-hourly analysis data are generated for the summer of 2004. The difference between the resulting analyses using different convective parameterization schemes is found to be significantly greater than that between two well-known analyzed data sets, the NCEP/National Center for Atmospheric Research (NCAR) reanalysis (RAl) and the NCEP/DOE reanalysis (RA2). This dependency is more pronounced in data-sparse areas like the East Asian region than in data-rich areas like the North American region. Our study indicates that predictabilities for short- to medium-range forecasts in the global forecast system are indirectly influenced by forecast model accuracy via the quality of the initial conditions.

Li X.,Numerical Weather Prediction Center | Chen C.,Xi'an Jiaotong University | Xiao F.,Tokyo Institute of Technology | Shen X.,Numerical Weather Prediction Center
Quarterly Journal of the Royal Meteorological Society | Year: 2015

A high-order global shallow-water model on a Yin-Yang grid has been developed by using the multi-moment constrained finite-volume (MCV) method. Unlike the traditional finite-volume method, more degrees of freedom (DOFs)-which are the values at the solution points within each mesh element-are defined and updated in time. The time evolution equations for these point values (PVs) are derived from a set of constraint conditions in terms of the so-called multi-moment quantities, such as the PV, the volume-integrated average (VIA) and derivative. Different moments use different forms of equations which are all consistent with the shallow-water equations, among which the VIA moment is computed from a finite-volume formulation of flux form that guarantees rigorous numerical conservation. A fourth-order formulation is devised with the third-order reconstruction built over each element using the DOFs locally available. A simple and orthogonal overset grid, the Yin-Yang grid, is used to represent the spherical geometry with quasi-uniform grid spacing. The resulting global shallow-water model is attractive in algorithmic simplicity and computational efficiency. The model has been validated by widely used benchmark tests. The numerical results of the present model are competitive with most existing advanced models. © 2015 Royal Meteorological Society.

Li J.,National Meteorological Center | Li J.,Numerical Weather Prediction Center | Liu G.,National Meteorological Center | Liu G.,Numerical Weather Prediction Center
Atmospheric Measurement Techniques | Year: 2016

FengYun-3C (FY-3C) is an operational polar-orbiting satellite carrying the new-generation microwave sounding instruments in China. This paper describes the assimilation of the FY-3C Microwave Temperature Sounder-2 (MWTS-2) radiances in the Global and Regional Assimilation and PrEdiction System (GRAPES) of China Meteorological Administration. A quality control (QC) procedure for the assimilation of MWTS-2 radiance is proposed. Extensive monitoring before assimilation shows that MWTS-2 observations exhibit a clear striping pattern. A technique combining principal component analysis (PCA) and ensemble empirical mode decomposition (EEMD) is applied to the observations to remove the striping noise. Cloudy field-of-views (FOVs) are identified by applying the Visible and InfrarRed Radiometer (VIRR) cloud fraction threshold of 76ĝ€%. Other QC steps are conducted in the follow order: (i) coastal FOVs are removed, (ii) eight outmost FOVs are not used, (iii) channel 5 data over sea ice and land are not used, (iv) channel 6 observations are not used if the terrain altitudes are higher than 500ĝ€m, and (v) outliers with large differences between observations and model simulations are removed. Approximately 83, 75, 40, and 40ĝ€% of the observations are removed by the proposed QC for channels 5-8, respectively. After QC, the global biases and standard deviations are reduced significantly. The assimilation of the MWTS-2 radiances shows a positive impact when the control experiment assimilates only conventional observations. The experiments also show that the analysis and forecast errors are slightly reduced when the striping noise is removed from the observations. The quality control scheme of extracting the striping noise may contribute to the analysis and forecast accuracy. The impact of MWTS-2 is neutral when the conventional data and other satellite data are all assimilated. © Author(s) 2016.

In this paper, we discuss the applications of random balance design Fourier amplitude sensitivity test (RBD-FAST) and extended Fourier amplitude sensitivity test (EFAST) in the parameter sensitivity analysis of land surface process model. We use the common land model and data of Tongyu station, which is a reference site of CEOP in the semi-arid regions, use five model outputs (sensible heat flux, latent heat flux, surface temperature, temperature of air at 2 m over surface, moisture of air at 2 m over surface) as focus output, and use 11 model parameter (soil depth, the soil proportion of 1-5 layers of soil, the porosity of soil, the max dew depth, the roughness of the air between surface and the canopy, and the drag coefficient under the canopy) as the parameters to be analyzed. After the 10 RBD-FAST experiments, we obtain the first-order sensitivity results, and we gain not only first-order sensitivity but also the total sensitivity after the EFAST experiment. The first-order results of two methods show their consistency. The RBD-FAST takes less computing time and is easy to implemente, while the EFAST also has a more comprehensive and reasonable total sensitivity result. All results above illustrate the applications of both RBD-FAST and EFAST in the parameter sensitivity analysis of land surface model. Researchers can choose the suitable one to solve the different problems. © 2015 Chinese Physical Society.

Liu Y.,Numerical Weather Prediction Center | Xu T.,PLA University of Science and Technology | Liu J.,Guangxi University
Advances in Space Research | Year: 2014

Using the Global Navigation Satellite System (GNSS) radio occultation observations from Formosa Satellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) from 2007 to 2012, the climatological characteristics of the global tropopause was studied, with the following features identified. The overall results generally agree with previous studies. The tropopause has an obvious zonal structure, with more zonal characteristics in the Southern Hemisphere than the Northern Hemisphere. The vertical shape of the tropopause is sharp in the tropics and broad in the sub-tropical latitudes, with the sharpest latitudinal gradient in the mid-latitudes of both hemispheres. The global tropopause exists in a large range between 8 km and 17 km (or between 100 hPa and 340 hPa). The highest tropopause is over the South Asian monsoon regions for the entire year. The spatial structure of the tropopause in the polar region is of concentric structure, with an altitude between 7.5 km and 10 km. It is more symmetric in the Antarctic than the Arctic. Differing from other places, the height of the tropopause in the Antarctic is higher in winter as opposed to summer. The tropopause has distinct seasonal variability, especially in polar regions. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

Liu Y.,Numerical Weather Prediction Center | Liu Y.,National Meteorological Center | Xue J.,Chinese Academy of Meteorological Sciences
Atmospheric Measurement Techniques | Year: 2014

This paper reviews the development of the global navigation satellite system (GNSS) radio occultation (RO) observations assimilation in the Global/Regional Assimilation and PrEdiction System (GRAPES) of China Meteorological Administration, including the choice of data to assimilate, the data quality control, the observation operator, the tuning of observation error, and the results of the observation impact experiments. The results indicate that RO data have a significantly positive effect on analysis and forecast at all ranges in GRAPES, not only in the Southern Hemisphere where conventional observations are lacking but also in the Northern Hemisphere where data are rich. It is noted that a relatively simple assimilation and forecast system in which only the conventional and RO observation are assimilated still has analysis and forecast skill even after nine months integration, and the analysis difference between both hemispheres is gradually reduced with height when compared with NCEP (National Centers for Environmental Prediction) analyses. Finally, as a result of the new on-board payload of the Chinese FengYun-3 (FY-3) satellites, the research status of the RO of FY-3 satellites is also presented. © Author(s) 2014.

Wang X.C.,CAS Institute of Atmospheric Physics | Wang X.C.,University of Chinese Academy of Sciences | Wang X.C.,Numerical Weather Prediction Center | Bao Q.,CAS Institute of Atmospheric Physics | And 3 more authors.
Science China Earth Sciences | Year: 2011

Using the latest version of SAMIL (Spectral Atmosphere Model of IAP LASG) developed by LASG/IAP, we evaluate the model performance by analyzing rainfall, latent heating structure and other basic fields with two different convective parameterization schemes: Manabe Scheme and Tiedtke Scheme. Results show that convective precipitation is excessively overestimated while stratiform precipitation is underestimated by Tiedtke scheme, thus causing less stratiform rainfall proportion compared with TRMM observation. In contrast, for Manabe scheme stratiform rainfall belt is well simulated, although precipitation center near Bay of Bengal (BOB) spreads eastward and northward associated with unrealistic strong rainfall downstream of the Tibet Plateau. The simulated latent heating structure indicates that Tiedtke scheme has an advantage over Manabe scheme, as the maximum convective latent heating near middle of troposphere is well reproduced. Moreover, the stratiform latent heating structure is also well simulated by Tiedtke scheme with warming above freezing level and cooling beneath freezing level. As for Manabe scheme, the simulated maximum convective latent heating lies near 700 hPa, lower than the observation. Additionally, the warming due to stratiform latent heating extends to the whole vertical levels, which is unreasonable compared with observation. Taylor diagram further indicates that Tiedtke scheme is superior to Manabe scheme as higher correlation between model output and observation data is achieved when Tiedtke scheme is employed, especially for the temperature near 200 hPa. Finally, a possible explanation is addressed for the unrealistic stratiform rainfall by Tiedtke scheme, which is due to the neglect of detrained cloud water and cloud ice during convective process. The speculation is verified through an established sensitivity experiment. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

Liu J.,Guangxi University | Liu Y.,Numerical Weather Prediction Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Using the Constellation Observation System of Meteorology, Ionosphere and Climate (COSMIC) radio occultation (RO) data from December 2008 to November 2009, and the contemporaneous high vertical resolution radiosonde data, the accuracy of COSMIC RO data in the Qinghai-Tibet Plateau is evaluated. Results show that there is a good consistency between COSMIC refractivity and those calculated from the radiosondes between 5 and 30km altitude both in day and at night. Their annual mean fractional refractivity difference is -0.474%, and standard deviation is 1.056%. It illustrates that the RO data is reliable and may be effectively applied in the Qinghai-Tibet Plateau for the weather and climate research, or as a reference data to evaluate other observations and the model' simulations. © 2014 SPIE.

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