Title: The climate version of the Eta regional forecast model. 1. Evaluation of consistency between the Eta model and HadAM3P global model
ArXiv ID: 0709.2110
Date: 2007-11-27
Authors: ** - (논문에 명시된 저자 목록을 여기 삽입) **
📝 Abstract
The regional climate model prepared from Eta WS forecast model has been integrated over South America with the horizontal resolution of 40 km for the period of 1960-1990. The model was forced at its lateral boundaries by the outputs of HadAM3P. The data of HadAM3P represent simulation of modern climate with the resolution about 150 km. In order to prepare climate regional model from the Eta forecast model multiple modifications and corrections were made in the original model. The run of climate Eta model was made on the supercomputer SX-6. The detailed analysis of the results of dynamical downscaling experiment includes an investigation of a consistency between the regional and AGCM models as well as of ability of the regional model to resolve important features of climate fields on the finer scale than that resolved by AGCM. In this work the results of the investigation of a consistency between the output fields of the Eta model and HadAM3P are presented. The geopotential, temperature and wind fields of both models were analysed. For the evaluation of the likeness of these two models outputs,there were used Fourier analysis of time series, consistency index, constituted from linear regression coefficients, time mean and space mean models' arithmetic difference and root mean square difference, dispersion analysis,and some others characteristics. This investigation demonstrates that there are not significant differences in behaviour and spatial arragement of large-scale structures of the two models. Also, the regional model characteristics do not have considerable positive or negative trend during integration time in relation to the global model characteristics. From the total analysis we can affirm that in the description of large-scale climate structures these two models are in consistency.
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The time averaged large-scale meteorological fields ( >500 km) are actively studied in the works on climate theory and climate change analysis. Needs of agriculture, industrial and energy development planning require the knowledge of detailed, regional and local scale (100km -10 km) climatic information. As the modern net of climate observation stations can supply data only suited for large-scale climate field investigations, the dynamical downscaling using high-resolution regional climate model (RCM) is the most powerful instrument for obtaining the smaller-scaled climate information. For the study of regional climate change in the future the dynamical downscaling is the only way to obtain necessary information. The dynamical downscaling approach involves RCM forced at the lateral and bottom boundaries by an atmospheric general circulation model (AGCM) or reanalysis data (e.g., Dickinson et al. 1989;Giorgi and Bates 1989). The finer regional-scale features of RCM can be attributed to detailed topography and land surface features, more comprehensive parameterization of unresolved physical processes in the model equations, and explicit simulation of large mesoscale processes.
Atmosphere-ocean general circulation models (AOGCM) with the horizontal resolution of a few hundred kilometers are currently used for the simulation of large-scale response of the climate system to increasing of greenhouse gases and aerosol concentrations in the future. The running of RCM with the horizontal resolution of a few tens of kilometers over an area of interest with boundary conditions of AOGCM for the periods of 10-30 years in the present and in the future can give additional information about the regional-scale climate and climatechange effects in this area. Such downscaling studies related to climate change have been made already for various parts of Europe, North America, Australia, and Africa; see for example the references cited by Jones et al. (1997), Laprise et al. (2003), Giorgi et al. (2004), Duffy et al. (2006). Currently some large projects such as (PRUDENCE (Christensen et al. 2002) and NARCCAP (http://www.narccap.ucar.edu
)), launched to investigate uncertainties in the RCM climate-change simulations over Europe and North America, are underway. Multiple regional climate model ensembles are used in these studies in order to minimize uncertainties obtained in simulations with each model.
The downscaling studies related to climate change over South America are just started.
The project “Climate change scenarios using PRECIS” (Jones et al. 2004) was launched by Hadley Center for Climate Prediction and Research to develop user-friendly RCM which can be easily running on personal computer for any area of the globe. The South American countries including Brazil are participated in this project running PRECIS over various parts of South America. The data of the atmospheric global model HadAM3P were provided by Hadley Center for using them as boundary conditions in these simulations. The first regional climatology for South America is presented by Seth et al. (2007) for the period from 1982 to 2003. It was obtained by using the RegCM3 model (Pal et al. 2006) which was forced both by the reanalysis data (Kanamitsu et al. 2002) and by the European-Hamburg (ECHAM) AGCM (Roeckner et al. 1996) global model.
The aim of this study is to propose one more regional climate model for use in the climate downscaling research over South America. For this aim we prepared the climate version from the NCEP Eta regional forecast model (Black 1994). The Eta Model was chosen because it was intensively used for weather forecast as well as for seasonal predictability and processes studies over South America during last decade (Figueroa et al. 1995;Tanajura 1996;Chou et al. 2000;Chou et al. 2002;Vernekar et al. 2003;Tarasova et al. 2006). Analysis of the integration results in most cases demonstrates better agreement with observations of meteorological fields simulated by the Eta model as compared with AGCM. Nevertheless, the longest integrations with the Eta model were limited to the continuous integrations for 3-5 months because of the limitations in the codes of the Eta model which was developed for the forecast studies. The climate versions of the Eta model which permit integrations for the period of any duration were developed at the Brazilian Instituto Nacional de Pesquisas Espaciais/ Centro de Previsao de Tempo e Estudos Cimaticos (INPE/CPTEC) during last years (Pisnichenko et al. 2006;Fernandez et al. 2006;Tarasova et al. 2006).
In order to be considered as a valid tool for dynamical downscaling of low-resolution GCM fields a regional climate model has to satisfy some requirements (e.g., Wang et al. 2004;Castro et al. 2005;Laprise, 2006). Firstly, it is needed to show that RCM is able to reproduce the principal features of the large-scale fields of GCM which data is used as driving boundary conditions and its main statistics. It is